All in one vectors for the treatment of facioscapulohumeral muscular dystrophy

Abstract

The disclosure relates to optimized therapeutic cassettes useful for inhibiting the expression of the DUX4 gene in skeletal muscle as a treatment for facioscapulohumeral muscular dystrophy (FSHD) in subjects in need thereof. In some aspects, the disclosure includes methods and compositions comprising said therapeutic cassettes.

Description

[0001] ALL IN ONE VECTORS FOR THE TREATMENT OF FACIOSCAPULOHUMERAL MUSCULAR DYSTROPHY The present application claims the benefit of U.S. provisional application no.63 / 527,698 filed July 19, 2023, which is incorporated by reference herein in its entirety. BACKGROUND Facioscapulohumeral muscular dystrophy (FSHD) is the third most common muscular dystrophy in humans, characterized by progressive weakness and atrophy of specific muscle groups. FSHD is caused by incomplete epigenetic silencing of the disease locus, leading to pathogenic misexpression of the DUX4 retrogene in skeletal muscle. FSHDl, the most common form of the disease, is linked to dysregulation of the D4Z4 macrosatellite repeat array at chromosome 4q35 with large deletions of chromatin at this locus. The other form of FSHD, FSHD2, is caused by mutations in proteins that maintain epigenetic silencing. Both conditions lead to a similar relaxation of D4Z4 chromatin, resulting in the aberrant expression of DUX4 in skeletal muscle. While DUX4 resides in every D4Z4 repeat unit in the macrosatellite array, only the full-length DUX4 mRNA (DUX4-fl) encoded by the distal-most repeat is stably expressed, due to the presence of a polyadenylation signal in disease-permissive alleles. The DUX4-FL protein, in turn, activates a host of genes normally expressed in early development, which cause pathology when misexpressed in adult skeletal muscle. A CRISPR inhibition strategy using several epigenetic regulators successfully targets and represses DUX4 in FSHD myocytes (Himeda et al 2021 Mol Ther Methods and Clin Dev.20: p. 298-311.), making it well-suited to a gene therapy approach for FSHD. Since the heart is not affected in FSHD, an AAV-mediated gene therapy for this disease requires a regulatory cassette that provides high-level, skeletal muscle-specific activity. However, for translatability, AAV- mediated gene therapies must include all components within a single vector that expresses at therapeutic levels in all target tissues. This is a challenge for gene therapies utilizing a CRISPR platform for epigenetic modulation, since dCas9 fused to an epigenetic effector takes up most of the available space in an AAV vector. SUMMARY There is a clear need in the art for treatment strategies that correct the epigenetic dysregulation in FSHD by minimizing the size of therapeutic cassettes and optimizing regulatory cassettes for high skeletal muscle-specific activity. The present disclosure addresses this need. Accordingly, in one aspect, a polynucleotide encoding a muscle-specific therapeutic cassette is provided, the polynucleotide comprising a regulatory portion comprising one or more modified enhancer sequences upstream and operably linked to a promoter which is operably linked to a payload portion comprising a first payload and a U6 promoter which is operably linked to a second payload, wherein the one or more modified enhancer sequences comprise a Trex sequence, an AT-rich sequence, a left E-box sequence, a right E-box sequence, and a MEF2 sequence, wherein the promoter is a -80 to +50 promoter containing a consensus Inr sequence, wherein the first payload is a catalytically inactive Cas9 fused to an epigenetic repressor, and wherein the second payload is a single guide RNA (sgRNA) and scaffold. In certain embodiments, the sgRNA targets the Double Homeobox Protein 4 (DUX4) locus. In certain embodiments, the sgRNA comprises a nucleotide sequence comprising SEQ ID NOs: 6-8, or complementary sequences thereof. In certain embodiments, the catalytically inactive Cas9 is dSaCas9. In certain embodiments, the epigenetic repressor is selected from the group consisting of HPlα, HPlγ, the chromo shadow domain and C-terminal extension region of HPlα or HPlγ, and MeCP2 transcription repression domain (TRD). In certain embodiments, the cassette has high expression activity in skeletal muscle tissue compared to other tissues. In certain embodiments, the cassette has low expression activity in cardiac muscle tissue compared to skeletal muscle tissue. In certain embodiments, the regulatory portion of the therapeutic cassette is encoded by a nucleic acid comprising at least 80%, at least 85%, at least 90%, at least 95%, at least 98%, and at least 99% sequence identity to the sequence set forth in SEQ ID NO: 2 or complementary sequences thereof. In certain embodiments, the regulatory portion of the therapeutic cassette is encoded by a nucleic acid comprising the sequence set forth in SEQ ID NO: 2 or complementary sequences thereof. In certain embodiments, the therapeutic cassette comprises a nucleic acid sequence set forth in any one of SEQ ID NOs: 3-5 or complementary sequences thereof. In certain aspects, the polynucleotide comprises a regulatory portion comprising 1, 2 or 3 modified enhancer sequences upstream and operably linked to the promoter. In another aspect, an AAV vector comprises a muscle-specific therapeutic cassette comprising a polynucleotide embodied herein. In certain embodiments, the AAV capsid comprises AAV1, AAV2, AAV3, AAV3B, AAV4, AAV5, AAV6, AAV7, AAV8, AAV9, AAV12, AAV-B1, AAV-DJ, AAV-Retro, AAVrh8, AAVrh10, AAVrh25, Anc80L65, LK03, AAVrh18, rAAVrh74, AAVrh32.33, AAVrh39, AAVrh43, MyoAAV2, Oligo001, PHP-B, LICA1 or Spark100. In certain embodiments, the capsid is an rAAVrh74. In certain embodiments, the capsid is an AAV9. In certain embodiments, the capsid is a MyoAAV2. In certain embodiments, the capsid is a LICA1. In certain embodiments, the AAV vector has a specificity for muscle tissue. In a further aspect, a polynucleotide encoding a muscle-specific therapeutic cassette is provided and comprises a regulatory portion comprising one or more modified Muscle Creatine Kinase (CKM) enhancer sequences upstream and operably linked to a modified CKM promoter which is operably linked to a payload portion comprising a first payload and a promoter which is operably linked to a second payload, wherein the first payload is a catalytically inactive Cas9 (dCas9) fused to an epigenetic repressor, and wherein the second payload is a single guide RNA (sgRNA) and scaffold. In certain embodiments, the sgRNA targets the DUX4 locus. In certain embodiments, the sgRNA comprises a nucleotide sequence comprising SEQ ID NOs: 6-8, or complementary sequences thereof. In certain embodiments, the catalytically inactive Cas9 is dSaCas9. In certain embodiments, the epigenetic repressor is selected from the group consisting of HPlα, HPlγ, the chromo shadow domain and C-terminal extension region of HPlα or HPlγ, and MeCP2 transcription repression domain (TRD). In certain embodiments, the cassette has high expression activity in skeletal muscle tissue compared to other tissues. In certain embodiments, the cassette has low expression activity in cardiac muscle tissue compared to skeletal muscle tissue. In certain embodiments, the regulatory portion of the therapeutic cassette is encoded by a nucleic acid comprising the sequence set forth in SEQ ID NO: 2 or complementary sequences thereof. In certain embodiments, the regulatory portion of the therapeutic cassette is encoded by a nucleic acid comprising at least 80%, at least 85%, at least 90%, at least 95%, at least 98%, or at least 99% sequence identity to the sequence set forth in SEQ ID NO: 2 or complementary sequences thereof. In certain embodiments, the therapeutic cassette comprises a nucleic acid sequence set forth in any one of SEQ ID NOs: 3-5 or complementary sequences thereof. In certain aspects, the polynucleotide encoding a muscle-specific therapeutic cassette is comprises a regulatory portion comprising 1, 2 or 3 modified Muscle Creatine Kinase (CKM) enhancer sequences upstream and operably linked to the promoter. In certain embodiments, the polynucleotide encoding a muscle-specific therapeutic cassette comprises a promoter operably linked to the second payload, which is a U6 promoter. In certain embodiments, the polynucleotide encoding a muscle-specific therapeutic cassette comprises one or more modified CKM enhancer sequences, which comprise a Trex sequence, an AT-rich sequence, a left E-box sequence, a right E-box sequence, and a MEF2 sequence. In certain embodiments, the polynucleotide encoding a muscle-specific therapeutic cassette comprises the promoter operably linked to the first payload, which is a -80 to +50 CKM promoter containing a consensus Inr sequence. In certain embodiments, the first payload is a catalytically inactive Cas9 fused to an epigenetic repressor. In another aspect, a composition comprises AAV vector particles comprising the polynucleotide embodied herein and a pharmaceutically acceptable carrier or excipient. In another aspect, a method of treating facioscapulohumeral muscular dystrophy (FSHD) in a subject in need thereof, comprises administering to the subject an effective amount of an AAV vector comprising a muscle-specific therapeutic cassette comprising a regulatory portion comprising one or more modified enhancer sequences upstream and operably linked to a promoter which is operably linked to a payload portion comprising a first payload and a U6 promoter which is operably linked to a second payload, wherein the one or more modified enhancer sequences comprise a Trex sequence, an AT-rich sequence, a left E- box sequence, a right E-box sequence, and a MEF2 sequence, wherein the promoter is a -80 to +50 promoter containing a consensus Inr sequence, wherein the first payload is a catalytically inactive Cas9 fused to an epigenetic repressor, and wherein the second payload is a single guide RNA (sgRNA) and scaffold. In a further aspect, a method of treating facioscapulohumeral muscular dystrophy (FSHD) in a subject in need thereof, comprises administering to the subject an effective amount of an AAV vector comprising a polynucleotide encoding a muscle-specific therapeutic cassette is provided and comprises a regulatory portion comprising one or more modified Muscle Creatine Kinase (CKM) enhancer sequences upstream and operably linked to a modified CKM promoter which is operably linked to a payload portion comprising a first payload and a promoter which is operably linked to a second payload, wherein the first payload is a catalytically inactive Cas9 (dCas9) fused to an epigenetic repressor, and wherein the second payload is a single guide RNA (sgRNA) and scaffold. In certain embodiments of these methods, the sgRNA targets the DUX4 locus. In certain embodiments, the sgRNA comprises a nucleotide sequence selected from the group consisting of SEQ ID NOs: 6-8. In certain embodiments of these methods, the catalytically inactive Cas9 is dSaCas9. In certain embodiments of these methods, the epigenetic repressor is selected from the group consisting of HPlα, HPlγ, the chromo shadow domain and C-terminal extension region of HPlα or HPlγ, and MeCP2 transcription repression domain (TRD). In certain embodiments of these methods, the therapeutic cassette comprises a nucleic acid sequence set forth in SEQ ID NOs: 3-5. In certain embodiments of these methods, the AAV vector comprises an AAV capsid that comprises AAV1, AAV2, AAV3, AAV3B, AAV4, AAV5, AAV6, AAV7, AAV8, AAV9, AAV12, AAV-B1, AAV-DJ, AAV-Retro, AAVrh8, AAVrh10, AAVrh25, Anc80L65, LK03, AAVrh18, rAAVrh74, AAVrh32.33, AAVrh39, AAVrh43, MyoAAV2, Oligo001, PHP-B, LICA1 or Spark100. In certain embodiments, the capsid is an rAAVrh74. In certain embodiments, the capsid is an AAV9. In certain embodiments, the capsid is a MyoAAV2. In certain embodiments, the capsid is a LICA1. In certain embodiments, the AAV vector has a specificity for muscle tissue. In another aspect, a method of introducing a transgene into a target cell, comprises contacting the cell with a polynucleotide encoding a muscle-specific therapeutic cassette comprising a regulatory portion comprising one or more modified enhancer sequences upstream and operably linked to a promoter which is operably linked to a payload portion comprising a first payload and a U6 promoter which is operably linked to a second payload, wherein the one or more modified enhancer sequences comprise a Trex sequence, an AT-rich sequence, a left E- box sequence, a right E-box sequence, and a MEF2 sequence, wherein the promoter is a -80 to +50 promoter containing a consensus Inr sequence, wherein the first payload is a catalytically inactive Cas9 fused to an epigenetic repressor, and wherein the second payload is a single guide RNA (sgRNA) and scaffold. In another aspect, a method of introducing a transgene into a target cell, comprises contacting the cell with a polynucleotide encoding a muscle-specific therapeutic cassette comprising a regulatory portion comprising one or more modified Muscle Creatine Kinase (CKM) enhancer sequences upstream and operably linked to a modified CKM promoter which is operably linked to a payload portion comprising a first payload and a promoter which is operably linked to a second payload, wherein the first payload is a catalytically inactive Cas9 (dCas9) fused to an epigenetic repressor, and wherein the second payload is a single guide RNA (sgRNA) and scaffold. In certain embodiments, the cassette has high expression activity in skeletal muscle tissue compared to other tissues. In certain embodiments, the sgRNA targets the DUX4 locus. In certain embodiments, an sgRNA comprises a nucleotide sequence comprising SEQ ID NOs: 6, 7, 8 or complementary sequences thereof. In certain embodiments, the therapeutic cassette comprises a nucleic acid sequence set forth in SEQ ID NOs: 3-5 or complementary sequences thereof. In another aspect, a regulatory cassette comprises one or more modified enhancer sequences derived from the Muscle Creatine Kinase (CKM) gene and a modified promoter sequence derived from CKM (e.g., NH, HLH) (Himeda et al, Hum Gene Ther.2024 Jul 6. doi: 10.1089 / hum.2024.041. Online ahead of print.PMID: 38970421) driving a dCas protein (e.g., dCas9, dCas6, dCpf1, dCas12a, dCas13a, dCasX, dCasY) in frame with a transcriptional repressor or repression domain (TRD) (e.g., MeCP2 TRD, HP1 ^, HP1 ^, SUV39H1, KRAB) which is operably linked to a nuclear localization signal (NLS) (e.g., SV40, nucleoplasmin) and a polyadenylation signal (PAS) (e.g., SV40, bGH) and an RNA Polymerase III promoter (e.g., U6 promoter, M11 hybrid promoter, 7SK promoter, H1 promoter) driving a single guide RNA (sgRNA) comprising a spacer portion targeting the DUX4 gene and a scaffold portion. In another aspect, a method of treating a subject comprises administering the polynucleotides embodied herein in combination with one or more secondary therapeutics, e.g., use of modulators of specific signaling pathways including Src, PRKDC (also known as DNA- PK), Tie, Abl, Fit, Trk, Yes. FAK kinase families to modulate DUX4 activity in muscle cells (e.g., by inhibiting or repressing its transcriptional activity, inhibiting or repressing its expression, increasing the degradation of DUX4, mRNA or protein, or any other mechanism that results in reduced DUX4 activity). Other examples of secondary therapeutics include epigenetic modulators or epigenetic signaling machinery molecules, including, but not limited to: epigenetic writers (e.g., DNA methyltransferases, histone acetyltransferases, histone methyltransferases, and serine / threonine kinases); epigenetic readers (e.g., MeCP2, MBD1, MBD2, MBD3, BRD2, BRD3, BRD4, Bdf, Brg), chromodomain proteins (e.g., HP-1 like, polycomb-like, CHD-like), Tudor domain proteins (e.g., SMN), PHD finger proteins (e.g., CBD, ING2, DNMT3L, PHF6), 14-3-3 proteins; epigenetic erasers (e.g., MBD, TET, HDAC Classes I-V, lysine demethylases, protein phosphatases, PARP, HIF, Pim, Aurora kinases), or combinations thereof. Other aspects are disclosed below. BRIEF DESCRIPTION OF THE DRAWINGS The following detailed description of preferred embodiments of the disclosure will be better understood when read in conjunction with the appended drawings. For the purpose of illustrating the disclosure, there are shown in the drawings embodiments which are presently preferred. It should be understood, however, that the disclosure is not limited to the precise arrangements and instrumentalities of the embodiments shown in the drawings. FIG.1 depicts the evolution of the regulatory cassette platform. Illustrated is a schematic of tMCK and CK8 (original Ckm-based muscle regulatory cassettes) and the two new cassettes based on the CK8 design disclosed herein. The seven known transcriptional regulatory elements within the Ckm enhancer are labeled. For CK8, changes from the endogenous sequence and / or previous Ckm-based cassettes include: 1) deletion of 63 bp between the Right E-box and the MEF2 site; 2) 3 tandem copies of the modified enhancer; 3) mutation of sequence overlapping +1 to a consensus Initiator element (Inr); and 4) inclusion of +50 sequence downstream of the transcription start site. The NH cassette contains the following modifications from CK8: 1) CArG and AP2 sites removed; 2) sequence between regulatory elements minimized; 3) Left E- box mutated to a Right E-box; and 4) -80 basal promoter sequence used. The HLH cassette contains the following modification from the NH cassette: additional Right E-box replaced with the original Left E-box. FIGs.2A-2C depict the HLH cassette displaying higher activity than the NH cassette in skeletal muscle over time. The mCherry reporter under control of either the NH or HLH regulatory cassette was delivered in rAAVrh74 at 2.6x1014GC / kg by retro-orbital injection to wild-type mice (n=3 per virus). The epi-fluorescent signal, measured as (FIG.2A) total flux or (FIG.2B) maximum radiance, in abdominal and pectoral muscles was (FIG.2C) visualized at various times post-injection. Peak of Total flux and Max radiance of NH-mCherry signals are indicated with dashed line in FIG.2A (1.27x1011) and FIG.2B (4.68x109). FIGs.3A-3E depict the HLH cassette displaying higher activity than the NH cassette in all striated muscles. All mice from FIG.2 were sacrificed at 12 weeks post-injection, individual tissues were dissected, and the epi-fluorescent signals were quantified as FIG.3A) total flux or FIG.3B) maximum radiance. FIG.3B) Maximum radiance in each tissue was normalized to that in abdominal muscle from the same animal; for HLH-injected mice, signals from each tissue were further normalized to the average abdominal signal from NH-injected mice (set to 1). Representative images of isolated tissues are shown from FIG.3C) uninjected mouse, FIG.3D) NH-injected mouse, and FIG.3E) HLH-injected mouse. Tissues in C and D are arranged as labeled in panel E. Abbreviations: tibialis anterior (TA), extensor digitorum longus (EDL), soleus (SOL), gastrocnemius (GA), quadriceps (QUA), abdominal muscles (Ab). Xs (panels A and B) indicate no signal above background detected. FIGs.4A-4F depict the HLH cassette displaying higher activity than the NH cassette in all striated muscles. Fluorescent signals in the isolated tissues from FIG.3 were visualized with a 0.2-second exposure time. FIGs.4A-4D, 4F) Expression of mCherry regulated by NH (left) and HLH (right) is compared to uninjected (CTL) tissues (middle). FIG.4E) mCherry expression is compared between NH (left) and HLH (right). FIG.4F) mCherry expression in soleus (three muscles in left sub-panel) and EDL (three muscles in right sub-panel). Abbreviations: tibialis anterior (TA), gastrocnemius (GA), quadriceps (QUA), soleus (SOL), extensor digitorum longus (EDL). Bar = 2mm. FIGs.5A-5B depict tissue transduction for rAAVrh74. The mCherry reporter under control of either FIG.5A) NH or FIG.5B) HLH was delivered systemically by retro-orbital injection to wild- type mice using rAAVrh74 virions at 2.6x1014GC / kg. The rAAV genomes present in various tissues were assessed by qPCR using primers specific for the bGH PAS in the cargo genome and normalized to the single copy endogenous murine Rosa26 locus. This data confirms that tissues such as kidney and liver, which did not express any detectable mCherry signal by IVIS imaging, were still highly transduced by the virus, supporting the tissue specificity of the regulatory cassettes. Light grey bars indicate muscles with high mCherry expression; dark grey bars indicate muscles with low mCherry expression; black bars indicate muscles with undetectable mCherry expression. Abbreviations: tibialis anterior (TA), extensor digitorum longus (EDL), soleus (SOL), gastrocnemius (GA), quadriceps (QUA), abdominal muscle (Ab), diaphragm (Diaph). FIGs.6A-6L depict the NH cassette displaying high activity in most fast-twitch muscles and virtually no activity in EDL, soleus, diaphragm, and heart. The mCherry reporter under control of the NH regulatory cassette was delivered systemically by retro-orbital injection to wild-type mice using rAAVrh74 virions at 2.6x1014GC / kg. The fluorescent signal was visualized at 12 weeks post-injection with the same exposure time of 1 second (1 s), except where indicated. Tissues dissected from rAAV-injected mice are indicated by asterisks and compared with tissues from uninjected mice. For two-tissue panels (FIGs.6A-6B and 6D-6H), tissues from uninjected mice are shown on the left. For the four-tissue panel (FIG.6C), uninjected tissues for soleus and EDL are on the left of each sub-panel. For single-tissue panels (FIG.6I-6L), panels J- L are rAAV- injected, while panel I is uninjected. Abbreviations: tibialis anterior (TA), gastrocnemius (GA), quadriceps (QUA), soleus (SOL), extensor digitorum longus (EDL). FIGs.7A-7J depict the NH cassette having no detectable activity in non-muscle tissues. Non-muscle tissues from the rAAV-transduced mice assayed in FIG.6 were similarly imaged for mCherry expression (3-second exposure, except where indicated). rAAV- injected tissues are indicated by asterisks. For two-tissue panels (FIGs.7B-7E and 7G-7J), tissues from uninjected mice are shown on the left. Single-tissue panels (FIGs.7A and 7F) show only the tissues from rAAV-injected mice. FIG.7A) The skeletal muscle from a hindlimb, including the posterior biceps femoris, quadriceps, and gastrocnemius, express mCherry, while the sciatic nerve, indicated by a black arrow, has no detectable mCherry expression. FIG.7F) The dorsal view of a dissected abdomen, including liver and the large and small intestines, which do not express detectable levels of mCherry, compared with the mCherry expressing abdominal muscle in view at the left of the frame. FIGs.8A-8L depict the HLH cassette displaying extremely high activity in most fast- twitch muscles, moderate activity in EDL, soleus, and diaphragm, and low activity in heart. The mCherry reporter under control of HLH was delivered systemically by retro-orbital injection to wild-type mice using rAAVrh74 virions at 2.6x1014GC / kg. The fluorescent signal was visualized at 12 weeks post-injection with an exposure time of 1 second (1 s). rAAV-injected tissues are indicated by asterisks. For two-tissue panels FIGs.8A-8B and 8D-8H, tissues from uninjected mice are shown on the left. For four-tissue panel FIG.8C, uninjected tissues for soleus and EDL are on the left of each sub-panel. Single-tissue panels FIGs.8J-8L show rAAV- injected; FIG.8I shows uninjected. Abbreviations: tibialis anterior (TA), gastrocnemius (GA), quadriceps (QUA), soleus (SOL), extensor digitorum longus (EDL). FIGs.9A-9J depict the HLH cassette having no detectable activity in non-muscle tissues. Non-muscle tissues from the rAAVrh74-injected wild-type mice assayed in FIG.8 were similarly assayed for mCherry expression and imaged at 0.5-second exposure. FIGs.9A-9J show tissues from rAAV-injected mice. FIG.9A. Hindlimb skeletal muscles, including the posterior biceps femoris, quadriceps, and gastrocnemius, express mCherry, while the sciatic nerve, indicated by a black arrow, has no detectable mCherry expression. FIG.9F. The dorsal view of a dissected abdomen, including liver and the large and small intestines, which do not express detectable levels of mCherry, compared with the mCherry expressing abdominal muscle in view at the left of the frame. FIGs.10A-10C depict the evolution of the CRISPRi platform for epigenetic repression of DUX4. FIG.10A) Original two-vector system: 1) dSpCas9 fused to the KRAB TRD under control of the CK8 regulatory cassette and 2) a DUX4-targeting sgRNA with dSpCas9- compatible scaffold under control of the U6 promoter. FIG.10B) Optimized two-vector system: 1) the NH minimized skeletal muscle regulatory cassette driving the smaller dSaCas9 ortholog fused to one of four epigenetic repressors (MeCP2 TRD, HP1α, HP1γ, or the SUV39H1 pre- SET, SET, and post-SET domains), and 2) the U6 promoter driving a DUX4-targeting sgRNA with dSaCas9-compatible scaffold incorporating modifications that remove a putative Pol III terminator and improve assembly with dCas9 (Ran et al 2015 Nature.520, p.186–191). FIG. 10C) AIO single-vector system: five independent therapeutic cassettes, each containing: 1) the HLH regulatory cassette (NH cassette modified to replace the additional Right E-box with the original Left E-box from the CKM enhancer) driving dSaCas9 fused to one of five minimal repressors, and 2) sgRNA components as in (FIG.10B). A variation of the AIO system using the NH regulatory cassette is also shown. Repressor domains: MeCP2 TRD, HP1α or HP1γ chromo shadow domain and C-terminal extension, SUV39H1 SET domain, or KRAB TRD. Size of components is not to scale. Abbreviations: inverted terminal repeat (ITR), nuclear localization signal (NLS), hemagglutinin (HA), bovine growth hormone (bGH), polyadenylation signal (PAS), central polypurine tract (cPPT) with central termination sequence (CTS), additional Right E-box (REB), Left E-box (LEB). FIGs.11A-11E illustrate that AIO CRISPRi vectors using minimized epigenetic repressors suppress DUX4-fl in FSHD1 myocytes. FSHD1 myocytes were transduced with AIO vectors containing each minimized repressor targeted to DUX4 (described in FIG.10) or the equivalent control vector containing a non-targeting (NT) sgRNA (TRD, FIG.11A; HP1α, FIG. 11B; HP1γ, FIG.11C; KRAB, FIG.11D; SET, FIG.11E). Expression levels of DUX4-fl, DUX4- FL target genes MBD3L2 and TRIM43, and the differentiation marker MYH1 were assessed by qRT-PCR. (TRD: MeCP2 TRD; HP1α / HP1γ: respective chromo shadow domain and C-terminal extension; SET: SET domain; KRAB: KRAB TRD). Data are plotted as the mean + / - SEM from at least four independent experiments, with average expression from cells infected with each control vector set to 1. *p<0.05, **p<0.01, ***p<0.001 are from comparing to NT. FIG.12 illustrates that two-vector and single-vector CRISPRi systems repress DUX4-fl in FSHD2 myocytes. FSHD2 myocytes were transduced with either the CRISPRi two-vector or AIO vector system (described in FIG.10) using the MeCP2 TRD as the effector. Expression levels of DUX4-fl, DUX4-FL target genes MBD3L2, TRIM43, ZSCAN4, and the differentiation marker MYH1 were assessed by qRT-PCR. Data are plotted as the mean + / - SEM from three independent experiments, with average expression from mock infected cells set to 1. *p<0.05, **p<0.01 are from comparing to NT. FIGs.13A-13B depict an AIO CRISPRi system repressing DUX4-fl in an FSHD xenograft mouse model. Immortalized FSHD1 myoblasts were injected into the TA muscle compartment of immunodeficient NRG mice. At 4 weeks post-engraftment, the AIO CRISPRi system was injected: 1) intramuscularly (IM) into xenografts in rAAVrh74 vectors (rAAVrh74.TRD-DUX4 or rAAVrh74.TRD-NT) at 1x1013GC / kg, or 2) systemically, via retro- orbital injection (ROI), in MyoAAV2A vectors (MyoAAV2A.TRD-DUX4 or MyoAAV2A.TRD- NT) at 5x1013GC / kg. Four weeks post-injection, engrafted TAs were dissected for analysis. Expression of DUX4-fl and DUX4-FL downstream targets MBD3L2 and TRIM43 from IM (FIG. 13A) and ROI (FIG.13B) injected TAs were assessed by qRT-PCR and normalized to levels of RPL13A. Data are plotted as the mean + / - SEM from at least six independent experiments. **p<0.01 is from comparing to NT. DETAILED DESCRIPTION Definitions Unless defined otherwise, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which the disclosure pertains. Although any methods and materials similar or equivalent to those described herein can be used in the practice for testing of the present disclosure, the preferred materials and methods are described herein. In describing and claiming the present disclosure, the following terminology will be used. It is also to be understood that the terminology used herein is for the purpose of describing particular embodiments only, and is not intended to be limiting. The articles “a” and “an” are used herein to refer to one or to more than one (i.e., to at least one) of the grammatical object of the article. By way of example, “an element” means one element or more than one element. “About” as used herein when referring to a measurable value such as an amount, a temporal duration, and the like, is meant to encompass variations of ±20% or ±10%, more preferably ±5%, even more preferably ±1%, and still more preferably ±0.1% from the specified value, as such variations are appropriate to perform the disclosed methods. The term “AAV vector” as used herein refers to a polynucleotide vector comprising one or more genes of interest (or transgenes) that are flanked by AAV terminal repeat sequences (ITRs). AAV vectors can be produced and packaged into infectious viral particles when present in a host cell that has been transfected with one or more helper plasmids encoding and expressing rep and cap proteins and one or more proteins from adenovirus open reading frame E4orf6. The AAV vectors may be operably linked to promoter and enhancer sequences that can regulate the expression of the protein encoded by the AAV vector. The terms “AAV virion” or “AAV viral particle” or “AAV vector particle” as used herein refers to a viral particle composed of capsid proteins from at least one AAV serotype surrounding a polynucleotide AAV vector. If the particle comprises a heterologous polynucleotide (i.e. a polynucleotide other than a wild-type AAV genome such as a transgene to be delivered to a mammalian cell), it is typically referred to as an “AAV vector particle” or simply an “AAV vector”. Thus, production of AAV vector particle necessarily includes production of AAV vector, as such a vector is contained within an AAV vector particle. The term “Packaging” as used herein refers to intracellular process by which viral virions or particles (e.g. AAV virions or particles), especially viral vector particles or virions are assembled in a host cell. “Packaging” cells comprise the polynucleotide (e.g. helper plasmids) and protein components necessary to assemble functional viral virions. By “agent” is meant any nucleic acid molecule, small molecule chemical compound, antibody, or polypeptide, or fragments thereof. By “alteration” or “change” is meant an increase or decrease. An alteration may be by as little as 1%, 2%, 3%, 4%, 5%, 10%, 20%, 30%, or by 40%, 50%, 60%, or even by as much as 70%, 75%, 80%, 90%, or 100%. As used herein, the term “autologous” is meant to refer to any material derived from the same individual to which it is later to be re-introduced into the individual. “Allogeneic” refers to a graft derived from a different animal of the same species. “Xenogeneic” refers to a graft derived from an animal of a different species. By “biologic sample” is meant any tissue, cell, fluid, or other material derived from an organism. As used herein, the term “cassette” or “expression cassette” or “regulatory cassette” refer to distinct nucleic acid vectors consisting of a payload sequence (e.g. encoding a transgene or RNA) and regulatory sequences (i.e. promoter, enhancers, terminators, and the like) which control its expression. Upon successful insertion into a host cell, the regulatory sequences allow for the transcription and translation of the payload transgene. As used herein, the term “therapeutic cassette” refers to the combination of therapeutic cargo sequences along with all regulatory and expression sequences within a cassette vector. In certain embodiments, a therapeutic cassette can comprise a muscle-specific regulatory cassette, one or more promoters driving expression of one or more sgRNAs, and encode a dCas9 protein fused to an effector. The term “combination therapy”, as used herein, refers to those situations in which two or more different pharmaceutical agents are administered in overlapping regimens so that the subject is simultaneously exposed to both agents. When used in combination therapy, two or more different agents may be administered simultaneously or separately. This administration in combination can include simultaneous administration of the two or more agents in the same dosage form, simultaneous administration in separate dosage forms, and separate administration. That is, two or more agents can be formulated together in the same dosage form and administered simultaneously. Alternatively, two or more agents can be simultaneously administered, wherein the agents are present in separate formulations. In another alternative, a first agent can be administered just followed by one or more additional agents. In the separate administration protocol, two or more agents may be administered a few minutes apart, or a few hours apart, or a few days apart. As used herein, the term “conservative sequence modifications” is intended to refer to amino acid modifications that do not significantly affect or alter the binding characteristics of the antibody containing the amino acid sequence. Such conservative modifications include amino acid substitutions, additions and deletions. Modifications can be introduced into an antibody of the disclosure by standard techniques known in the art, such as site-directed mutagenesis and PCR-mediated mutagenesis. Conservative amino acid substitutions are ones in which the amino acid residue is replaced with an amino acid residue having a similar side chain. Families of amino acid residues having similar side chains have been defined in the art. These families include amino acids with basic side chains (e.g., lysine, arginine, histidine), acidic side chains (e.g., aspartic acid, glutamic acid), uncharged polar side chains (e.g., glycine, asparagine, glutamine, serine, threonine, tyrosine, cysteine, tryptophan), nonpolar side chains (e.g., alanine, valine, leucine, isoleucine, proline, phenylalanine, methionine), beta-branched side chains (e.g., threonine, valine, isoleucine) and aromatic side chains (e.g., tyrosine, phenylalanine, tryptophan, histidine). Thus, one or more amino acid residues within the CDR regions of an antibody can be replaced with other amino acid residues from the same side chain family and the altered antibody can be tested for the ability to bind antigens using the functional assays described herein. A “disease” is a state of health of an animal wherein the animal cannot maintain homeostasis, and wherein if the disease is not ameliorated then the animal’s health continues to deteriorate. In contrast, a “disorder” in an animal is a state of health in which the animal is able to maintain homeostasis, but in which the animal’s state of health is less favorable than it would be in the absence of the disorder. Left untreated, a disorder does not necessarily cause a further decrease in the animal’s state of health. “Effective amount” or “therapeutically effective amount” are used interchangeably herein, and refer to an amount of a compound, formulation, material, or composition, as described herein effective to achieve a particular biological result or provides a therapeutic or prophylactic benefit. Such results may include, but are not limited to, anti-tumor activity as determined by any means suitable in the art. “Encoding” refers to the inherent property of specific sequences of nucleotides in a polynucleotide, such as a gene, a cDNA, or an mRNA, to serve as templates for synthesis of other polymers and macromolecules in biological processes having either a defined sequence of nucleotides (i.e., rRNA, tRNA and mRNA) or a defined sequence of amino acids and the biological properties resulting therefrom. Thus, a gene encodes a protein if transcription and translation of mRNA corresponding to that gene produces the protein in a cell or other biological system. Both the coding strand, the nucleotide sequence of which is identical to the mRNA sequence and is usually provided in sequence listings, and the non-coding strand, used as the template for transcription of a gene or cDNA, can be referred to as encoding the protein or other product of that gene or cDNA. As used herein “endogenous” refers to any material from or produced inside an organism, cell, tissue or system. As used herein, the term “exogenous” refers to any material introduced from or produced outside an organism, cell, tissue or system. The term “expression” as used herein is defined as the transcription and / or translation of a particular nucleotide sequence driven by its promoter. “Expression vector” refers to a vector comprising a recombinant polynucleotide comprising expression control sequences operatively linked to a nucleotide sequence to be expressed. An expression vector comprises sufficient cis-acting elements for expression; other elements for expression can be supplied by the host cell or in an in vitro expression system. Expression vectors include all those known in the art, such as cosmids, plasmids (e.g., naked or contained in liposomes) and viruses (e.g., Sendai viruses, lentiviruses, retroviruses, adenoviruses, and adeno-associated viruses) that incorporate the recombinant polynucleotide. “Homologous” as used herein, refers to the subunit sequence identity between two polymeric molecules, e.g., between two nucleic acid molecules, such as, two DNA molecules or two RNA molecules, or between two polypeptide molecules. When a subunit position in both of the two molecules is occupied by the same monomeric subunit; e.g., if a position in each of two DNA molecules is occupied by adenine, then they are homologous at that position. The homology between two sequences is a direct function of the number of matching or homologous positions; e.g., if half (e.g., five positions in a polymer ten subunits in length) of the positions in two sequences are homologous, the two sequences are 50% homologous; if 90% of the positions (e.g., 9 of 10), are matched or homologous, the two sequences are 90% homologous. “Identity” as used herein refers to the subunit sequence identity between two polymeric molecules particularly between two amino acid molecules, such as, between two polypeptide molecules. When two amino acid sequences have the same residues at the same positions; e.g., if a position in each of two polypeptide molecules is occupied by an Arginine, then they are identical at that position. The identity or extent to which two amino acid sequences have the same residues at the same positions in an alignment is often expressed as a percentage. The identity between two amino acid sequences is a direct function of the number of matching or identical positions; e.g., if half (e.g., five positions in a polymer ten amino acids in length) of the positions in two sequences are identical, the two sequences are 50% identical; if 90% of the positions (e.g., 9 of 10), are matched or identical, the two amino acids sequences are 90% identical. As used herein, an “instructional material” includes a publication, a recording, a diagram, or any other medium of expression which can be used to communicate the usefulness of the compositions and methods of the disclosure. The instructional material of the kit of the disclosure may, for example, be affixed to a container which contains the nucleic acid, peptide, and / or composition of the disclosure or be shipped together with a container which contains the nucleic acid, peptide, and / or composition. Alternatively, the instructional material may be shipped separately from the container with the intention that the instructional material and the compound be used cooperatively by the recipient. “Isolated” means altered or removed from the natural state. For example, a nucleic acid or a peptide naturally present in a living animal is not “isolated,” but the same nucleic acid or peptide partially or completely separated from the coexisting materials of its natural state is “isolated.” An isolated nucleic acid or protein can exist in substantially purified form, or can exist in a non-native environment such as, for example, a host cell. By the term “modified” as used herein, is meant a changed state or structure of a molecule or cell of the disclosure. Molecules may be modified in many ways, including chemically, structurally, and functionally. Cells may be modified through the introduction of nucleic acids. By the term “modulating,” as used herein, is meant mediating a detectable increase or decrease in the level of a response in a subject compared with the level of a response in the subject in the absence of a treatment or compound, and / or compared with the level of a response in an otherwise identical but untreated subject. The term encompasses perturbing and / or affecting a native signal or response thereby mediating a beneficial therapeutic response in a subject, preferably, a human. In the context of the present disclosure, the following abbreviations for the commonly occurring nucleic acid bases are used. “A” refers to adenosine, “C” refers to cytosine, “G” refers to guanosine, “T” refers to thymidine, and “U” refers to uridine. Unless otherwise specified, a “nucleotide sequence encoding an amino acid sequence” includes all nucleotide sequences that are degenerate versions of each other and that encode the same amino acid sequence. The phrase nucleotide sequence that encodes a protein or an RNA may also include introns to the extent that the nucleotide sequence encoding the protein may in some version contain an intron(s). The term “operably linked” refers to functional linkage between a regulatory sequence and a heterologous nucleic acid sequence resulting in expression of the latter. For example, a first nucleic acid sequence is operably linked with a second nucleic acid sequence when the first nucleic acid sequence is placed in a functional relationship with the second nucleic acid sequence. For instance, a promoter is operably linked to a coding sequence if the promoter affects the transcription or expression of the coding sequence. Generally, operably linked DNA sequences are contiguous and, where necessary to join two protein coding regions, in the same reading frame. “Parenteral” administration of an immunogenic composition includes, e.g., subcutaneous (s.c.), intravenous (i.v.), intramuscular (i.m.), or intrasternal injection, or infusion techniques. The term “polynucleotide” as used herein is defined as a chain of nucleotides. Furthermore, nucleic acids are polymers of nucleotides. Thus, nucleic acids and polynucleotides as used herein are interchangeable. One skilled in the art has the general knowledge that nucleic acids are polynucleotides, which can be hydrolyzed into the monomeric “nucleotides.” The monomeric nucleotides can be hydrolyzed into nucleosides. As used herein polynucleotides include, but are not limited to, all nucleic acid sequences which are obtained by any means available in the art, including, without limitation, recombinant means, i.e., the cloning of nucleic acid sequences from a recombinant library or a cell genome, using ordinary cloning technology and PCR™, and the like, and by synthetic means. As used herein, the terms “peptide,” “polypeptide,” and “protein” are used interchangeably, and refer to a compound comprised of amino acid residues covalently linked by peptide bonds. A protein or peptide must contain at least two amino acids, and no limitation is placed on the maximum number of amino acids that can comprise a protein’s or peptide’s sequence. Polypeptides include any peptide or protein comprising two or more amino acids joined to each other by peptide bonds. As used herein, the term refers to both short chains, which also commonly are referred to in the art as peptides, oligopeptides and oligomers, for example, and to longer chains, which generally are referred to in the art as proteins, of which there are many types. “Polypeptides” include, for example, biologically active fragments, substantially homologous polypeptides, oligopeptides, homodimers, heterodimers, variants of polypeptides, modified polypeptides, derivatives, analogs, fusion proteins, among others. The polypeptides include natural peptides, recombinant peptides, synthetic peptides, or a combination thereof. The term “promoter” as used herein is defined as a DNA sequence recognized by the synthetic machinery of the cell, or introduced synthetic machinery, required to initiate the specific transcription of a polynucleotide sequence. As used herein, the term “promoter / regulatory sequence” means a nucleic acid sequence which is required for expression of a gene product operably linked to the promoter / regulatory sequence. In some instances, this sequence may be the core promoter sequence and in other instances, this sequence may also include an enhancer sequence and other regulatory elements which are required for expression of the gene product. The promoter / regulatory sequence may, for example, be one which expresses the gene product in a tissue specific manner. A “constitutive” promoter is a nucleotide sequence which, when operably linked with a polynucleotide which encodes or specifies a gene product, causes the gene product to be produced in a cell under most or all physiological conditions of the cell. An “inducible” promoter is a nucleotide sequence which, when operably linked with a polynucleotide which encodes or specifies a gene product, causes the gene product to be produced in a cell substantially only when an inducer which corresponds to the promoter is present in the cell. A “tissue-specific” promoter is a nucleotide sequence which, when operably linked with a polynucleotide encodes or specified by a gene, causes the gene product to be produced in a cell substantially only if the cell is a cell of the tissue type corresponding to the promoter. The term “epigenetic” as used herein refers to heritable influences on gene expression that do not involve alterations in DNA nucleotide sequence. Epigenetic regulation can enhance or inhibit expression of affected genes, and can involve chemical modifications of the deoxyribose backbone of the DNA or the association of DNA / histone protein complexes or both. The term “epigenetic regulator” as used herein refers to factors, enzymes, compounds, or compositions that act to alter the epigenetic status of a specific DNA locus. Epigenetic regulators can induce or catalyze the modification of DNA-associated proteins or the chemical structure of the DNA itself. The terms “epigenetic tag” or “epigenetic marker” or “epigenetic mark” as used interchangeably herein, describe the specific chemical modifications made to DNA and DNA- associated proteins that result in epigenetic regulation of gene expression. Examples of epigenetic marks or tags can include but are not limited to the addition or removal of methyl or acetyl groups from CpG dinucleotides and histone proteins. The number and density of epigenetic tags or marks may correlate with the degree of epigenetic regulation a particular DNA locus is subject to. A “signal transduction pathway” refers to the biochemical relationship between a variety of signal transduction molecules that play a role in the transmission of a signal from one portion of a cell to another portion of a cell. The phrase “cell surface receptor” includes molecules and complexes of molecules capable of receiving a signal and transmitting signal across the plasma membrane of a cell. By the term “specifically binds,” as used herein with respect to an antibody, is meant an antibody which recognizes a specific antigen, but does not substantially recognize or bind other molecules in a sample. For example, an antibody that specifically binds to an antigen from one species may also bind to that antigen from one or more species. But such cross-species reactivity does not itself alter the classification of an antibody as specific. In another example, an antibody that specifically binds to an antigen may also bind to different allelic forms of the antigen. However, such cross reactivity does not itself alter the classification of an antibody as specific. In some instances, the terms “specific binding” or “specifically binding,” can be used in reference to the interaction of an antibody, a protein, or a peptide with a second chemical species, to mean that the interaction is dependent upon the presence of a particular structure (e.g., an antigenic determinant or epitope) on the chemical species; for example, an antibody recognizes and binds to a specific protein structure rather than to proteins generally. If an antibody is specific for epitope “A”, the presence of a molecule containing epitope A (or free, unlabeled A), in a reaction containing labeled “A” and the antibody, will reduce the amount of labeled A bound to the antibody. The term “subject” is intended to include living organisms in which an immune response can be elicited (e.g., mammals). A “subject” or “patient,” as used therein, may be a human or non-human mammal. Non-human mammals include, for example, livestock and pets, such as ovine, bovine, porcine, canine, feline and murine mammals. Preferably, the subject is human. A “target site” or “target sequence” refers to a genomic nucleic acid sequence that defines a portion of a nucleic acid to which a binding molecule may specifically bind under conditions sufficient for binding to occur. The term “therapeutic” as used herein means a treatment and / or prophylaxis. A therapeutic effect is obtained by suppression, remission, or eradication of a disease state. The term “transfected” or “transformed” or “transduced” as used herein refers to a process by which exogenous nucleic acid is transferred or introduced into the host cell. A “transfected” or “transformed” or “transduced” cell is one which has been transfected, transformed or transduced with exogenous nucleic acid. The cell includes the primary subject cell and its progeny. The term “transgene” refers to the genetic material that has been or is about to be artificially inserted into the genome of an animal, particularly a mammal and more particularly a mammalian cell of a living animal. The term “transgenic animal” refers to a non-human animal, usually a mammal, having a non-endogenous (i.e., heterologous) nucleic acid sequence present as an extrachromosomal element in a portion of its cells or stably integrated into its germ line DNA (i.e., in the genomic sequence of most or all of its cells), for example a transgenic mouse. A heterologous nucleic acid is introduced into the germ line of such transgenic animals by genetic manipulation of, for example, embryos or embryonic stem cells of the host animal. The term “knockout mouse” refers to a mouse that has had an existing gene inactivated (i.e. “knocked out”). In some embodiments, the gene is inactivated by homologous recombination. In some embodiments, the gene is inactivated by replacement or disruption with an artificial nucleic acid sequence. To “treat” a disease as the term is used herein, means to reduce the frequency or severity of at least one sign or symptom of a disease or disorder experienced by a subject. The term “tropism”, as used herein, refers to the cell types or tissue types that can be productively infected by a particular virus or virus-based vector (e.g. an AAV vector). Though not necessarily exclusive, tropism is often expressed as a “preference” or “specificity” of a virus or viral vector for a particular cell or tissue type. Being parasitic entities, cellular or tissue tropism is one of the major characteristics of specific viruses, which often require insertion into particular cell types in order to maintain a successful infectious cycle in target cells. When referring to viral vectors (e.g. AAV vectors), tissue or cellular tropism or specificity or preference can be used to direct therapeutic payloads to specific tissue or cell types. The phrase “under transcriptional control” or “operatively linked” as used herein means that the promoter is in the correct location and orientation in relation to a polynucleotide to control the initiation of transcription by RNA polymerase and expression of the polynucleotide. A “vector” is a composition of matter which comprises an isolated nucleic acid and which can be used to deliver the isolated nucleic acid to the interior of a cell. Numerous vectors are known in the art including, but not limited to, linear polynucleotides, polynucleotides associated with ionic or amphiphilic compounds, plasmids, and viruses. Thus, the term “vector” includes an autonomously replicating plasmid or a virus. The term should also be construed to include non- plasmid and non-viral compounds which facilitate transfer of nucleic acid into cells, such as, for example, polylysine compounds, liposomes, and the like. Examples of viral vectors include, but are not limited to, Sendai viral vectors, adenoviral vectors, adeno-associated virus vectors, retroviral vectors, lentiviral vectors, and the like. Ranges: throughout this disclosure, various aspects of the disclosure can be presented in a range format. It should be understood that the description in range format is merely for convenience and brevity and should not be construed as an inflexible limitation on the scope of the disclosure. Accordingly, the description of a range should be considered to have specifically disclosed all the possible subranges as well as individual numerical values within that range. For example, description of a range such as from 1 to 6 should be considered to have specifically disclosed subranges such as from 1 to 3, from 1 to 4, from 1 to 5, from 2 to 4, from 2 to 6, from 3 to 6 etc., as well as individual numbers within that range, for example, 1, 2, 2.7, 3, 4, 5, 5.3, and 6. This applies regardless of the breadth of the range. Description The disclosure relates to methods and compositions useful for the treatment of facioscapulohumeral muscular dystrophy (FSHD) comprising therapeutic cassettes containing optimized, muscle-specific regulatory cassettes. FSHD results from the incomplete epigenetic silencing of the Double Homeobox Protein 4 (DUX4) gene locus, leading to the inappropriate and pathogenic expression of the DUX4 gene in skeletal muscle. Accession numbers for the gene and protein sequences of DUX4 include: HGNC: 50800; NCBI Gene: 100288687; Ensembl: ENSG00000260596; OMIM®: 606009, RefSeq NM_001293798; UniProtKB / Swiss-Prot: Q9UBX2. In some embodiments, expression of DUX4 can be inhibited via the use of epigenetic modulators that alter the chromatin structure of the DUX4 locus, resulting in repressed transcription. In some embodiments, a CRISPR inhibitory (CRISPRi) system is used to direct the epigenetic modulators to the DUX4 locus through the use of specific single guide RNAs (sgRNAs). In some embodiments of the disclosure, epigenetic modulator proteins are coupled to catalytically-dead Cas9 (dCas9) proteins, which when combined with sequence- specific sgRNAs and controlled by tissue-specific promoters, ensure expression and function of the epigenetic modulators only in skeletal muscle cells. The present disclosure provides methods and compositions for the treatment of FSHD in a subject in need thereof comprising therapeutic cassettes that contain muscle-specific regulatory cassettes encoding epigenetic modulators coupled to dCas9 and a cassette for sgRNA expression. This CRISPRi system targets the DUX4 locus specifically in muscle cells. In some embodiments, the method involves administering to the subject a therapeutically effective amount of a vector comprising the muscle-specific cassettes. In some embodiments, the muscle- specific regulatory cassettes have been uniquely modified for size so that they may be packaged within an adeno- associated viral (AAV) vector as a single polynucleotide, thus allowing for in vivo use in a clinical setting. The regulatory cassettes of the present disclosure have also been minimized with respect to size, such that they are smaller than other muscle-specific regulatory cassettes known in the art. In this way, these cassettes maximize the size of the payload gene which can be packaged into cell-transduction systems, such as AAV vector systems and the like. As such, in certain embodiments, the regulatory cassettes of the disclosure can be comprised within AAV vector systems, which efficiently transfer the regulatory cassette and its associated transgene payload (e.g. a CRISPRi system that targets DUX4) into mammalian muscle cells and tissues. Gene Therapy of Muscle Tissues Gene therapy approaches in preclinical models of muscle disease can result in cardiotoxicity caused by cardiac expression of the transgene. While this toxicity can be prevented with the use of muscle-specific regulatory cassettes in conjunction with miRNA detargeting sequences, together these elements add considerable size to therapeutic cassettes already limited by the stringent packaging capacity of recombinant AAV (rAAV) vectors. Of even greater concern are the severe adverse events reported in recent gene therapy trials for two muscle diseases. Deaths in the ASPIRO X-linked myotubular myopathy (XLMTM) clinical trial were due to liver failure, but several patients had laboratory findings indicative of myocarditis, and in a Pfizer trial for Duchenne Muscular Dystrophy (DMD), two instances of myocarditis were reported. Thus, there is a great need for highly minimized regulatory cassettes with high activity in skeletal muscle, but low or no activity in heart. Previous studies have found that the regulatory regions of the muscle creatine kinase (MCK) gene, which mediate transcription, are useful for directing highly tissue-specific expression in skeletal and cardiac muscle tissues (Salva et al. (2007) Mol Ther, 2007.15(2): p. 320-9.). Regulatory cassettes comprising sequences derived from these regions have been demonstrated to drive robust, tissue-specific, transgene expression. In certain embodiments, the present disclosure includes Muscle creatine kinase (CKM)- based regulatory cassettes which have undergone multiple modifications in order to increase and narrow their tissue specificities beyond currently-available cassette systems: 1) No Heart (NH), a cassette that is highly active in fast-twitch skeletal muscles, but essentially inactive in soleus (slow-twitch muscle) and heart; and 2) Have a Little Heart (HLH), a cassette that has high activity in fast-twitch muscles, with moderate activity in soleus and diaphragm, and low activity in heart. Thus, the NH cassette is useful for skeletal muscle indications where no cardiac expression is needed or can be tolerated, whereas the HLH cassette is useful for providing transgene expression in all striated muscles while avoiding cardiotoxicity. Together, these cassettes are applicable to diverse gene therapy strategies targeting a broad range of myopathies. AAV Vectors AAV are relatively small, non-enveloped viruses with a ~4 kb genome that is flanked by inverted terminal repeats (ITRs). The genome contains two open reading frames, one of which provides proteins necessary for replication and the other provides components required for construction of the viral capsid. Wild-type AAV is typically found in the presence of adenovirus as the adenoviruses provide helper proteins that are essential for packaging of the AAV genome into virions. Therefore, AAV production piggy-backs on co-infection with adenovirus and relies on three key elements: the ITR-flanked genome, the open-reading frames, and adeno-helper genes. Due to their non-pathogenic ability to readily infect human cells, AAV is well-studied as a vector for gene delivery. AAV may be readily obtained and their use as vectors for gene delivery has been described in, for example, Muzyczka, 1992; U.S. Patent No.4,797,368, and PCT Publication WO 91 / 18088. Construction of AAV vectors is described in a number of publications, including Lebkowski et al., 1988; Tratschin et al., 1985; Hermonat and Muzyczka, 1984. AAV-based vector systems typically separate the viral AAV genes, Adenovirus-derived helper genes, and the transgene payload onto two or three separate plasmids. Three plasmid systems consist of an AAV helper plasmid comprising the rep (replication) and cap (capsid) genes, an adenoviral helper plasmid comprising at least the E2a gene, E4 gene, and VA (viral associated) RNA, and a payload plasmid comprising the transgene and associated promoters and enhancers flanked by ITR sequences. The helper plasmid or plasmids do not comprise ITRs in order to prevent packaging of a functional, infectious viral genome. Two plasmid systems combine the AAV rep and cap genes and adenoviral helper genes onto a single plasmid and simplify viral vector production by reducing the number of transfected plasmids. Often, a dedicated packaging cell line is used which is engineered to express AAV / helper genes prior to introduction of the payload plasmid. Successful gene therapies require efficient infection of target tissues and establishment of long term gene expression, and previous studies have demonstrated that AAV vectors can successfully infect and transduce a broad variety of cell and tissue types, such as brain, liver, and muscle, among others, and have the ability to infect both dividing and quiescent cells. Additionally, AAV-mediated transduction of tissues has been demonstrated to result in long term transgene expression greater than 1.5 years in animal models including canine, murine and hamster. The tissue tropism of AAV vector particles is influenced by the serotype of the capsid protein, though the receptors and co-receptors that the capsid proteins bind to are often poorly understood and can be expressed by multiple tissue types. For example, AAV2, one of the most well-studied serotypes, has a binding affinity largely for heparan sulfate proteoglycan (HSPG) and as such has a tropism in humans for eye, brain, lung, liver, muscle, and joint tissues. Likewise, AAVs 1, 4, 5, and 6 have a binding affinity largely for sialic acid and a tropism for neuronal tissues while AAVs 5 and 8 share a tropism for skeletal muscle. In this way, the serotype of the AAV capsid protein can be selected to target the payload nucleic acid (e.g. a regulatory cassette) of the AAV vector to a specific tissue or cell type. Alteration or modification of capsid protein structure can also alter the tissue or cellular tropism and affinity of the resulting AAV vector particles. In certain preferred embodiments, the current disclosure comprises AAV vectors comprising a capsid protein derived from AAV9 and variants thereof. AAV9 and capsid proteins based on AAV9 transduce muscle, liver, and lung tissues about 100-fold more efficiently than AAV2, while also being able to cross the blood brain barrier. In certain preferred embodiments, the current disclosure comprises AAV vectors comprising a capsid protein derived from rAAVrh74 and variants thereof. rAAVrh74 and capsid proteins based on rAAVrh74 have a tropism for skeletal and cardiac muscle and are useful for delivering therapeutic nucleic acids to those tissues. In certain preferred embodiments, the current disclosure comprises AAV vectors comprising a capsid protein derived from a MyoAAV capsid and variants thereof. MyoAAV are a family of capsid proteins which share a common arginine-glycine-aspartic acid (RGD) motif and were generated via directed evolution to select for high specificity and expression in muscle tissues, especially as compared to AAV9. Among the MyoAAV capsids that are known in the art include, but are not limited to MyoAAV 1A, the so-called second generation capsid MyoAAV 2 or 2A, MyoAAV 3A, MyoAAV 4A, MyoAAV 4C, and MyoAAV4E. Given the tissue specificities of MyoAAV family capsids for muscle tissues, it is contemplated that any MyoAAV capsid could be used with the therapeutic cassettes, vectors, compositions, and methods of the current disclosure. In certain preferred embodiments, the AAV vectors of the current disclosure comprise capsid proteins derived from MyoAAV2 or variants thereof. It is contemplated that the therapeutic cassettes of the disclosure can be used with any naturally occurring, modified, hybrid, or engineered AAV capsid protein that provides the desired tissue tropism including, but not limited to AAV1, AAV2, AAV3, AAV3B, AAV4, AAV5, AAV6, AAV7, AAV8, AAV9, AAV12, AAV-B1, AAV-DJ, AAV-Retro, AAVrh8, AAVrh10, AAVrh25, Anc80L65, LK03, AAVrh18, rAAVrh74, AAVrh32.33, AAVrh39, AAVrh43, MyoAAV2, Oligo001, PHP-B, LICA1 or Spark100 among others as well as variants thereof. In certain embodiments, the capsid is a LICA1.The skilled artisan would be able to select an appropriate capsid protein for use with the disclosure based on the desired target tissue or cell type. Alternative Delivery Vehicles Other delivery vehicles as used herein, include any types of molecules for delivery of the compositions embodied herein, both for in vitro or in vivo delivery. Examples, include, without limitation: expression vectors, nanoparticles, colloidal compositions, lipids, liposomes, nanosomes, carbohydrates, organic or inorganic compositions and the like. In some embodiments, a delivery vehicle is an expression vector, wherein the expression vector comprises an isolated nucleic acid sequence encoding polynucleotides embodied herein. It will be appreciated that a number of nucleic acids can encode a polypeptide having a particular amino acid sequence. The degeneracy of the genetic code is well known in the art. For many amino acids, there is more than one nucleotide triplet that serves as the codon for the amino acid. For example, codons in the coding sequence for Cas9 can be modified such that optimal expression in a particular organism is obtained, using appropriate codon bias tables for that organism. Vectors containing nucleic acids such as those described herein also are provided. A “vector” is a replicon, such as a plasmid, phage, or cosmid, into which another DNA segment may be inserted so as to bring about the replication of the inserted segment. Generally, a vector is capable of replication when associated with the proper control elements. Suitable vector backbones include, for example, those routinely used in the art such as plasmids, viruses, artificial chromosomes, BACs, YACs, or PACs. The term “vector” includes cloning and expression vectors, as well as viral vectors and integrating vectors. An “expression vector” is a vector that includes a regulatory region. A wide variety of host / expression vector combinations may be used to express the nucleic acid sequences described herein. Suitable expression vectors include, without limitation, plasmids and viral vectors derived from, for example, bacteriophage, baculoviruses, and retroviruses. Numerous vectors and expression systems are commercially available from such corporations as Novagen (Madison, Wis.), Clontech (Palo Alto, Calif.), Stratagene (La Jolla, Calif.), and Invitrogen / Life Technologies (Carlsbad, Calif.). The vectors provided herein also can include, for example, origins of replication, scaffold attachment regions (SARs), and / or markers. A marker gene can confer a selectable phenotype on a host cell. For example, a marker can confer biocide resistance, such as resistance to an antibiotic (e.g., kanamycin, G418, bleomycin, or hygromycin). As noted above, an expression vector can include a tag sequence designed to facilitate manipulation or detection (e.g., purification or localization) of the expressed polypeptide. Tag sequences, such as green fluorescent protein (GFP), glutathione S-transferase (GST), polyhistidine, c-myc, hemagglutinin, or Flag™ tag (Kodak, New Haven, Conn.) sequences typically are expressed as a fusion with the encoded polypeptide. Such tags can be inserted anywhere within the polypeptide, including at either the carboxyl or amino terminus. Additional expression vectors also can include, for example, segments of chromosomal, non-chromosomal and synthetic DNA sequences. Suitable vectors include derivatives of SV40 and known bacterial plasmids, e.g., E. coli plasmids col E1, pCR1, pBR322, pMal-C2, pET, pGEX, pMB9 and their derivatives, plasmids such as RP4; phage DNAs, e.g., the numerous derivatives of phage 1, e.g., NM989, and other phage DNA, e.g., M13 and filamentous single stranded phage DNA; yeast plasmids such as the 2μ plasmid or derivatives thereof, vectors useful in eukaryotic cells, such as vectors useful in insect or mammalian cells; vectors derived from combinations of plasmids and phage DNAs, such as plasmids that have been modified to employ phage DNA or other expression control sequences. Yeast expression systems can also be used. For example, the non-fusion pYES2 vector (XbaI, SphI, ShoI, NotI, GstXI, EcoRI, BstXI, BamH1, SacI, Kpn1, and HindIII cloning sites; Invitrogen) or the fusion pYESHisA, B, C (XbaI, SphI, ShoI, NotI, BstXI, EcoRI, BamH1, SacI, KpnI, and HindIII cloning sites, N-terminal peptide purified with ProBond resin and cleaved with enterokinase; Invitrogen), to mention just two, can be employed according to the invention. A yeast two-hybrid expression system can also be prepared in accordance with the invention. The vector can also include a regulatory region. The term “regulatory region” refers to nucleotide sequences that influence transcription or translation initiation and rate, and stability and / or mobility of a transcription or translation product. Regulatory regions include, without limitation, promoter sequences, enhancer sequences, response elements, protein recognition sites, inducible elements, protein binding sequences, 5′ and 3′ untranslated regions (UTRs), transcriptional start sites, termination sequences, polyadenylation sequences, nuclear localization signals, and introns. For example, to bring a coding sequence under the control of a promoter, the translation initiation site of the translational reading frame of the polypeptide is typically positioned between one and about fifty nucleotides downstream of the promoter. A promoter can, however, be positioned as much as about 5,000 nucleotides upstream of the translation initiation site or about 2,000 nucleotides upstream of the transcription start site. A promoter typically comprises at least a core (basal) promoter. A promoter also may include at least one control element, such as an enhancer sequence, an upstream element or an upstream activation region (UAR). The choice of promoters to be included depends upon several factors, including, but not limited to, efficiency, selectability, inducibility, desired expression level, and cell- or tissue-preferential expression. It is a routine matter for one of skill in the art to modulate the expression of a coding sequence by appropriately selecting and positioning promoters and other regulatory regions relative to the coding sequence. In certain embodiments, the muscle-specific therapeutic cassettes disclosed herein further comprise a Polymerase II promoter. The promoter can be any Polymerase II promoter capable of driving the transcription of a DNA coding sequence into mRNA. In some aspects, the Polymerase II promoter is a constitutive promoter, a regulatable promoter, an ubiquitous promoter, or a tissue-specific promoter. In some aspects, the Polymerase II promoter is a constitutive promoter. Non-limiting examples of constitutive Polymerase II promoters are a CBA promoter, a CMV promoter, an EF1α promoter, a CAG promoter, an UbC promoter, and CBh promoter. In some aspects, the Polymerase II promoter is a muscle tissue-specific Polymerase II promoter. Non-limiting examples of muscle tissue-specific Polymerase II promoters are a MHCK7 promoter, a CK8 promoter, a CK8e promoter, a CKM promoter, a dMCK promoter, a tMCK promoter, a DES promoter, a HSA promoter, a SPc5-12 promoter, a SP-301 promoter, a MHC promoter, a Sk-CRM promoter, a Sk-CRM4 promoter, or a functional fragment thereof. In some aspects, the muscle tissue-specific promoter is a CKM promoter or a functional fragment thereof. In certain embodiments, the muscle-specific therapeutic cassettes disclosed herein further comprise a Polymerase III promoter or a functional fragment thereof. The promoter can be any Polymerase III promoter or a functional fragment thereof capable of driving the transcription of a DNA coding sequence into a non-coding RNA. Non-limiting examples of Polymerase III promoters are 7SK, U6, M11 (e.g., M11 hybrid promoter), H1, and functional fragments thereof. In some embodiments, the Polymerase III promoter is a U6 promoter. In some embodiments, the Polymerase III promoter is a M11 hybrid promoter. Other examples of promoters include but are not limited to promoters from Simian Virus 40 (SV40, Mouse Mammary Tumor Virus (MMTV) promoter, Human Immunodeficiency Virus (HIV) such as the HIV Long Terminal Repeat (LTR) promoter, Moloney virus, ALV, Cytomegalovirus (CMV) such as the CMV immediate early promoter, Epstein Barr Virus (EBV), Rous Sarcoma Virus (RSV) as well as promoters from human genes such as human Actin, human Myosin, human Hemoglobin, human muscle creatine and human metalothionein. Vectors include, for example, viral vectors (such as adenoviruses (“Ad”), adeno- associated viruses (AAV), and vesicular stomatitis virus (VSV) and retroviruses), liposomes and other lipid-containing complexes, and other macromolecular complexes capable of mediating delivery of a polynucleotide to a host cell. Replication-defective recombinant adenoviral vectors, can be produced in accordance with known techniques. See, Quantin, et al., Proc. Natl. Acad. Sci. USA, 89:2581-2584 (1992); Stratford-Perricadet, et al., J. Clin. Invest., 90:626-630 (1992); and Rosenfeld, et al., Cell, 68:143-155 (1992). Vectors can also comprise other components or functionalities that further modulate gene delivery and / or gene expression, or that otherwise provide beneficial properties to the targeted cells. As described and illustrated in more detail below, such other components include, for example, components that influence binding or targeting to cells (including components that mediate cell-type or tissue-specific binding); components that influence uptake of the vector nucleic acid by the cell; components that influence localization of the polynucleotide within the cell after uptake (such as agents mediating nuclear localization); and components that influence expression of the polynucleotide. Such components also might include markers, such as detectable and / or selectable markers that can be used to detect or select for cells that have taken up and are expressing the nucleic acid delivered by the vector. Such components can be provided as a natural feature of the vector (such as the use of certain viral vectors which have components or functionalities mediating binding and uptake), or vectors can be modified to provide such functionalities. Other vectors include those described by Chen et al; Bio Techniques, 34: 167-171 (2003). A large variety of such vectors are known in the art and are generally available. If desired, the polynucleotides of the disclosure may also be used with a microdelivery vehicle such as cationic liposomes and adenoviral vectors. For a review of the procedures for liposome preparation, targeting and delivery of contents, see Mannino and Gould- Fogerite, BioTechniques, 6:682 (1988). See also, Feigner and Holm, Bethesda Res. Lab. Focus, 11(2):21 (1989) and Maurer, R. A., Bethesda Res. Lab. Focus, 11(2):25 (1989). Another delivery method is to use single stranded DNA producing vectors which can produce the expressed products intracellularly. See for example, Chen et al, Bio Techniques, 34: 167-171 (2003), which is incorporated herein, by reference, in its entirety. Another delivery method is to use single stranded DNA producing vectors which can produce the expressed products intracellularly. See for example, Chen et al, BioTechniques, 34: 167-171 (2003), which is incorporated herein, by reference, in its entirety. The nucleic acid sequences of the disclosure can be delivered to an appropriate cell of a subject. This can be achieved by, for example, the use of a polymeric, biodegradable microparticle or microcapsule delivery vehicle, sized to optimize phagocytosis by phagocytic cells such as macrophages. For example, PLGA (poly-lacto-co-glycolide) microparticles approximately 1-10 µm in diameter can be used. The polynucleotide is encapsulated in these microparticles, which are taken up by macrophages and gradually biodegraded within the cell, thereby releasing the polynucleotide. Once released, the DNA is expressed within the cell. A second type of microparticle is intended not to be taken up directly by cells, but rather to serve primarily as a slow-release reservoir of nucleic acid that is taken up by cells only upon release from the micro-particle through biodegradation. These polymeric particles should therefore be large enough to preclude phagocytosis (i.e., larger than 5 µm and preferably larger than 20 µm). Another way to achieve uptake of the nucleic acid is using liposomes, prepared by standard methods. The nucleic acids can be incorporated alone into these delivery vehicles or co- incorporated with tissue-specific antibodies. Alternatively, one can prepare a molecular complex composed of a plasmid or other vector attached to poly-L-lysine by electrostatic or covalent forces. Poly-L-lysine binds to a ligand that can bind to a receptor on target cells. Delivery of “naked DNA” (i.e., without a delivery vehicle) to an intramuscular, intradermal, or subcutaneous site, is another means to achieve in vivo expression. In some embodiments, the compositions can be formulated as a nanoparticle, for example, nanoparticles comprised of a core of high molecular weight linear polyethylenimine (LPEI) complexed with DNA and surrounded by a shell of polyethyleneglycol modified (PEGylated) low molecular weight LPEI. In some embodiments, the compositions can be formulated as a nanoparticle encapsulating the compositions embodied herein. Regardless of whether compositions are administered as nucleic acids or polypeptides, they are formulated in such a way as to promote uptake by the mammalian cell. Useful vector systems and formulations are described above. In some embodiments the vector can deliver the compositions to a specific cell type. The disclosure is not so limited however, and other methods of DNA delivery such as chemical transfection, using, for example calcium phosphate, DEAE dextran, liposomes, lipoplexes, surfactants, and perfluoro chemical liquids are also contemplated, as are physical delivery methods, such as electroporation, micro injection, ballistic particles, and “gene gun” systems. In other embodiments, the compositions comprise a cell which has been transformed or transfected with one or more AIO vectors. In some embodiments, the methods of the invention can be applied ex vivo. That is, a subject's cells can be removed from the body and treated with the compositions and the treated cells returned to the subject's body. The cell can be the subject's cells or they can be haplotype matched or a cell line. The cells can be irradiated to prevent replication. In some embodiments, the cells are human leukocyte antigen (HLA)-matched, autologous, cell lines, or combinations thereof. In other embodiments the cells can be a stem cell. For example, an embryonic stem cell or an artificial pluripotent stem cell (induced pluripotent stem cell (iPS cell)). Embryonic stem cells (ES cells) and artificial pluripotent stem cells (induced pluripotent stem cell, iPS cells) have been established from many animal species, including humans. These types of pluripotent stem cells would be the most useful source of cells for regenerative medicine because these cells are capable of differentiation into almost all of the organs by appropriate induction of their differentiation, with retaining their ability of actively dividing while maintaining their pluripotency. iPS cells, in particular, can be established from self-derived somatic cells, and therefore are not likely to cause ethical and social issues, in comparison with ES cells which are produced by destruction of embryos. Further, iPS cells, which are self-derived cell, make it possible to avoid rejection reactions, which are the biggest obstacle to regenerative medicine or transplantation therapy. Transduced cells are prepared for reinfusion according to established methods. After a period of about 2-4 weeks in culture, the cells may number between 1×106and 1×1010. In this regard, the growth characteristics of cells vary from patient to patient and from cell type to cell type. About 72 hours prior to reinfusion of the transduced cells, an aliquot is taken for analysis of phenotype, and percentage of cells expressing the therapeutic agent. For administration, cells of the present invention can be administered at a rate determined by the LD50 of the cell type, and the side effects of the cell type at various concentrations, as applied to the mass and overall health of the patient. Administration can be accomplished via single or divided doses. Adult stem cells may also be mobilized using exogenously administered factors that stimulate their production and egress from tissues or spaces that may include, but are not restricted to, bone marrow or adipose tissues. CRISPR / Cas9-Based Systems “Clustered Regularly Interspaced Short Palindromic Repeats” and “CRISPR”, as used herein are terms that refer to a microbial nuclease system that evolved as a defense against invading phages and plasmids and provides a form of acquired immunity for prokaryotic cells. CRISPR loci are flanked by segments of “spacer DNA”, which are short sequences derived from viral genomic material. In the Type II CRISPR system, spacer DNA hybridizes to transactivating RNA (tracrRNA) and is processed into CRISPR-RNA (crRNA), which then associates with CRISPR-associated (Cas) nucleases to form complexes that recognize and degrade foreign DNA. In an embodiment of the disclosure, CRISPR system utilizes a Cas9 endonuclease. Other endonucleases may also be used, including but not limited to, T7, Cas3, Cas8a, Cas8b, Casl0d, Csel, Csyl, Csn2, Cas4, Casl0, Csm2, Cmr5, Fokl, or other nucleases known in the art, and any combination thereof. Examples of CRISPR nucleases include, but are not limited to, Cas9 dCas9, Cas6, Cpfl, Casl2a, Casl3a, CasX, CasY, and natural and synthetic variants thereof. In certain embodiments, the CRISPR / Cas-like protein can be a wild type CRISPR / Cas protein, a modified CRISPR / Cas protein, or a fragment of a wild type or modified CRISPR / Cas protein. The CRISPR / Cas-like protein can be modified to increase nucleic acid binding affinity and / or specificity, alter an enzymatic activity, and / or change another property of the protein. For example, nuclease (i.e., DNase, RNase) domains of the CRISPR / Cas-like protein can be modified, deleted, or inactivated. Alternatively, the CRISPR / Cas-like protein can be truncated to remove domains that are not essential for the function of the fusion protein. The CRISPR / Cas- like protein can also be truncated or modified to optimize the activity of the effector domain of the fusion protein. As used herein, the term “Cas” is meant to include all Cas molecules comprising variants, mutants, orthologues, homologues, high-fidelity variants and the like. Three classes of CRISPR systems (Types I, II and III effector systems) are known. The Type II effector system carries out targeted DNA double-strand break in four sequential steps, using a single Cas nuclease, Cas9, to cleave dsDNA. Compared to the Type I and Type III effector systems, which require multiple distinct effectors acting as a complex, the relative simplicity of the Type II system enables its use in other cell types, such as eukaryotic cells. In some embodiments, the CRISPR / Cas system used herein can be a type I, a type II, or a type III system. Non-limiting examples of suitable CRISPR / Cas proteins include Cas3, Cas4, Cas5, Cas5e (or CasD), Cas6, Cas6e, Cas6f, Cas7, Cas8a1, Cas8a2, Cas8b, Cas8c, Cas9, Cas10, Cas10d, CasF, CasG, CasH, CasX, CasΦ, Csy1, Csy2, Csy3, Cse1 (or CasA), Cse2 (or CasB), Cse3 (or CasE), Cse4 (or CasC), Csc1, Csc2, Csa5, Csn2, Csm2, Csm3, Csm4, Csm5, Csm6, Cmr1, Cmr3, Cmr4, Cmr5, Cmr6, Csb1, Csb2, Csb3, Csx17, Csx14, Csx10, Csx16, CsaX, Csx3, Csz1, Csx15, Csf1, Csf2, Csf3, Csf4, and Cu1966. By way of further example, in some embodiments, the CRISPR-Cas protein is a Cas1, Cas1B, Cas2, Cas3, Cas4, Cas5, Cash, Cas7, Cas8, Cas10, Csy1, Csy2, Csy3, Cse1, Cse2, Csc1, Csc2, Csa5, Csn2, Csm2, Csm3, Csm4, Csm5, Csm6, Cmr1, Cmr3, Cmr4, Cmr5, Cmr6, Csb1, Csb2, Csb3, Csx17, Csx14, Csx16, CsaX, Csx3, Csx1, Csx15, Csf1, Csf2, Csf3, Csf4, Cas9, Cas12 (e.g., Cas12a, Cas12b, Cas12c, Cas12d, Cas12k, Cas12j / CasΦ, Cas12L etc.), Cas13 (e.g., Cas13a, Cas13b (such as Cas13b-t1, Cas13b- t2, Cas13b-t3), Cas13c, Cas13d, etc.), Cas14, CasX, CasY, or an engineered form of the Cas protein. In some embodiments, the CRISPR / Cas protein or endonuclease is Cas9. In some embodiments, the CRISPR / Cas protein or endonuclease is Cas12. In certain embodiments, the Cas12 polypeptide is Cas12a, Cas12b, Cas12c, Cas12d, Cas12e, Cas12g, Cas12h, Cas12i, Cas12L or Cas12J.   CRISPR target recognition occurs upon detection of complementary pairing between a “protospacer” sequence in the target DNA and the spacer sequence in the crRNA. The Cas9 nuclease then cleaves the target DNA if a matched protospacer-adjacent motif (PAM) is also present at the 3' end of the protospacer. Different Type II systems have differing PAM sequence requirements. In some embodiments, the S. pyogenes CRISPR system may have the PAM sequence for this Cas9 (SpCas9) as 5'-NRG-3', where R is either A or G, and confers the specificity of this system to human cells. A unique capability of the CRISPR / Cas9 system is the straightforward ability to simultaneously target multiple distinct genomic loci by co-expressing a single Cas9 protein with two or more sgRNAs. For example, the Streptococcus pyogenes (S. pyogenes) Type II system naturally prefers to use an “NGG” sequence, where “N” can be any nucleotide, but also accepts other PAM sequences, such as “NAG” in engineered systems (Hsu et al, (2013) Nature Biotechnology, 10: 1038). Similarly, the Cas9 derived from Neisseria meningitidis (NmCas9) normally has a native PAM of NNNNGATT (SEQ ID NO: 8), but is able to recognize a variety of PAM sequences. The wild type Streptococcus pyogenes Cas9 sequence can be modified. The Cas9 nuclease sequence can be, for example, the sequence contained within a commercially available vector such as PX330 or PX260 from Addgene (Cambridge, MA). In some embodiments, the Cas9 endonuclease can have an amino acid sequence that is a variant or a fragment of any of the Cas9 endonuclease sequences of Genbank accession numbers KM099231.1 GI:669193757; KM099232.1 GI:669193761; or KM099233.1 GI:669193765 or Cas9 amino acid sequence of PX330 or PX260 (Addgene, Cambridge, MA). The Cas9 nucleotide sequence can be modified to encode biologically active variants of Cas9, and these variants can have or can include, for example, an amino acid sequence that differs from a wild type Cas9 by virtue of containing one or more mutations (e.g., an addition, deletion, or substitution mutation or a combination of such mutations). One or more of the substitution mutations can be a substitution (e.g., a conservative amino acid substitution). For example, a biologically active variant of a Cas9 polypeptide can have an amino acid sequence with at least or about 50% sequence identity (e.g., at least or about 50%, 55%, 60%, 65%, 70%, 75%, 80%, 85%, 90%, 95%, 97%, 98%, or 99% sequence identity) to a wild type Cas9 polypeptide. Conservative amino acid substitutions typically include substitutions within the following groups: glycine and alanine; valine, isoleucine, and leucine; aspartic acid and glutamic acid; asparagine, glutamine, serine and threonine; lysine, histidine and arginine; and phenylalanine and tyrosine. The amino acid residues in the Cas9 amino acid sequence can be non-naturally occurring amino acid residues. Naturally occurring amino acid residues include those naturally encoded by the genetic code as well as non-standard amino acids (e.g., amino acids having the D-configuration instead of the L-configuration). The present peptides can also include amino acid residues that are modified versions of standard residues (e.g. pyrrolysine can be used in place of lysine and selenocysteine can be used in place of cysteine). Non-naturally occurring amino acid residues are those that have not been found in nature, but that conform to the basic formula of an amino acid and can be incorporated into a peptide. These include D-alloisoleucine(2R,3S)-2-amino-3- methylpentanoic acid and L-cyclopentyl glycine (S)-2-amino-2-cyclopentyl acetic acid. For other examples, one can consult textbooks or the worldwide web (a site currently maintained by the California Institute of Technology displays structures of non-natural amino acids that have been successfully incorporated into functional proteins). The Cas9 nuclease sequence can be a mutated sequence. For example, the Cas9 nuclease can be mutated in the conserved HNH and RuvC domains, which are involved in strand specific cleavage. For example, an aspartate-to-alanine (D10A) mutation in the RuvC catalytic domain allows the Cas9 nickase mutant (Cas9n) to nick rather than cleave DNA to yield single-stranded breaks, and the subsequent preferential repair through HDR can potentially decrease the frequency of unwanted indel mutations from off-target double-stranded breaks. The Cas9 nucleotide sequence can be modified to encode biologically active variants of Cas9, and these variants can have or can include, for example, an amino acid sequence that differs from a wild type Cas9 by virtue of containing one or more mutations (e.g. , an addition, deletion, or substitution mutation or a combination of such mutations). One or more of the substitution mutations can be a substitution (e.g., a conservative amino acid substitution). The Cas9 can be an orthologous. Six smaller Cas9 orthologues have been used and reports have shown that Cas9 from Staphylococcus aureus (SaCas9) can edit the genome with efficiencies similar to those of SpCas9, while being more than 1 kilobase shorter. In addition to the wild type and variant Cas9 endonucleases described, embodiments of the disclosure also encompass CRISPR systems including newly developed “enhanced- specificity” S. pyogenes Cas9 variants (eSpCas9), which dramatically reduce off target cleavage. These variants are engineered with alanine substitutions to neutralize positively charged sites in a groove that interacts with the non-target strand of DNA. This aim of this modification is to reduce interaction of Cas9 with the non-target strand, thereby encouraging re-hybridization between target and non-target strands. The effect of this modification is a requirement for more stringent Watson-Crick pairing between the gRNA and the target DNA strand, which limits off-target cleavage (Slaymaker, I.M. et al. (2015) DOI:10.1126 / science.aad5227). The present disclosure also includes another type of enhanced specificity Cas9 variant, “high fidelity” spCas9 variants (HF-Cas9) (Kleinstiver, B. P. et al., 2016, Nature. DOI: 10.1038 / nature16526) and high-fidelity SaCas9 (SaCas9-HF) variants, e.g. enhanced-fidelity SaCas9 (efSaCas9) (variant Mut268 harboring the single mutation of N260D) (Xie H, et al. (2020) High-fidelity SaCas9 identified by directional screening in human cells. PLOS Biology 18(7): e3000747. doi.org / 10.1371 / journal.pbio.3000747). Examples of high fidelity variants include SpCas9-HF1 (N497A / R661A / Q695A / Q926A), SpCas9-HF2 (N497A / R661A / Q695A / Q926A / D1135E), SpCas9-HF3 (N497A / R661A / Q695A / Q926A / L169A), SpCas9-HF4 (N497A / R661A / Q695A / Q926A / Y450A). Also included are all SpCas9 variants bearing all possible single, double, triple and quadruple combinations of N497A, R661A, Q695A, Q926A or any other substitutions (Kleinstiver, B. P. et al., 2016, Nature. DOI: 10.1038 / nature16526). Three variants found to have the best cleavage efficiency and fewest off-target effects: SpCas9(K855A), SpCas9(K810A / K1003A / R1060A) (a.k.a. eSpCas91.0), and SpCas9(K848A / K1003A / R1060A) (a.k.a. eSPCas91.1) are employed in the compositions. The invention is by no means limited to these variants, and also encompasses all Cas9 variants (Slaymaker, I.M. et al. (2015)). In some embodiments, SpCas9 variants comprise one or more point mutations, including, but not limited to R780A, K810A, K848A, K855A, H982A, K1003A, and R1060A (Slaymaker et al., 2016, Science, 351(6268): 84-88). In some embodiments, SpCas9 variants comprise D1135E point mutation (Kleinstiver et al., 2015, Nature, 523(7561): 481-485). In some embodiments, SpCas9 variants comprise one or more point mutations, including, but not limited to N497A, R661A, Q695A, Q926A, D1135E, L169A, and Y450A (Kleinstiver et al., 2016, Nature, doi:10.1038 / nature16526). In some embodiments, SpCas9 variants comprise one or more point mutations, including but not limited to M495A, M694A, and M698A. Y450 is involved with hydrophobic base pair stacking. N497, R661, Q695, Q926 are involved with residue to base hydrogen bonding contributing to off-target effects. N497 hydrogen bonding through peptide backbone. L169A is involved with hydrophobic base pair stacking. M495A, M694A, and H698A are involved with hydrophobic base pair stacking. In some embodiments, SpCas9 variants comprise one or more point mutations at one or more of the following residues: R780, K810, K848, K855, H982, K1003, R1060, D1135, N497, R661, Q695, Q926, L169, Y450, M495, M694, and M698. In some embodiments, SpCas9 variants comprise one or more point mutations selected from the group of: R780A, K810A, K848A, K855A, H982A, K1003A, R1060A, D1135E, N497A, R661A, Q695A, Q926A, L169A, Y450A, M495A, M694A, and M698A. In some embodiments, the SpCas9 variant comprises the point mutations, relative to wildtype SpCas9, of N497A, R661A, Q695A, and Q926A. In some embodiments, the SpCas9 variant comprises the point mutations, relative to wildtype SpCas9, of N497A, R661A, Q695A, Q926A, and D1135E. In some embodiments, the SpCas9 variant comprises the point mutations, relative to wildtype SpCas9, of N497A, R661A, Q695A, Q926A, and L169A. In some embodiments, the SpCas9 variant comprises the point mutations, relative to wildtype SpCas9, of N497A, R661A, Q695A, Q926A, and Y450A. In some embodiments, the SpCas9 variant comprises the point mutations, relative to wildtype SpCas9, of N497A, R661A, Q695A, Q926A, and M495A. In some embodiments, the SpCas9 variant comprises the point mutations, relative to wildtype SpCas9, of N497A, R661A, Q695A, Q926A, and M694A. In some embodiments, the SpCas9 variant comprises the point mutations, relative to wildtype SpCas9, of N497A, R661A, Q695A, Q926A, and H698A. In some embodiments, the SpCas9 variant comprises the point mutations, relative to wildtype SpCas9, of N497A, R661A, Q695A, Q926A, D1135E, and L169A. In some embodiments, the SpCas9 variant comprises the point mutations, relative to wildtype SpCas9, of N497A, R661A, Q695A, Q926A, D1135E, and Y450A. In some embodiments, the SpCas9 variant comprises the point mutations, relative to wildtype SpCas9, of N497A, R661A, Q695A, Q926A, D1135E, and M495A. In some embodiments, the SpCas9 variant comprises the point mutations, relative to wildtype SpCas9, of N497A, R661A, Q695A, Q926A, D1135E, and M694A. In some embodiments, the SpCas9 variant comprises the point mutations, relative to wildtype SpCas9, of N497A, R661A, Q695A, Q926A, D1135E, and M698A. In some embodiments, the SpCas9 variant comprises the point mutations, relative to wildtype SpCas9, of R661A, Q695A, and Q926A. In some embodiments, the SpCas9 variant comprises the point mutations, relative to wildtype SpCas9, of R661A, Q695A, Q926A, and D1135E. In some embodiments, the SpCas9 variant comprises the point mutations, relative to wildtype SpCas9, of R661A, Q695A, Q926A, and L169A. In some embodiments, the SpCas9 variant comprises the point mutations, relative to wildtype SpCas9, of R661A, Q695A, Q926A, and Y450A. In some embodiments, the SpCas9 variant comprises the point mutations, relative to wildtype SpCas9, of R661A, Q695A, Q926A, and M495A. In some embodiments, the SpCas9 variant comprises the point mutations, relative to wildtype SpCas9, of R661A, Q695A, Q926A, and M694A. In some embodiments, the SpCas9 variant comprises the point mutations, relative to wildtype SpCas9, of R661A, Q695A, Q926A, and H698A. In some embodiments, the SpCas9 variant comprises the point mutations, relative to wildtype SpCas9, of R661A, Q695A, Q926A, D1135E, and L169A. In some embodiments, the SpCas9 variant comprises the point mutations, relative to wildtype SpCas9, of R661A, Q695A, Q926A, D1135E, and Y450A. In some embodiments, the SpCas9 variant comprises the point mutations, relative to wildtype SpCas9, of R661A, Q695A, Q926A, D1135E, and M495A. In some embodiments, the SpCas9 variant comprises the point mutations, relative to wildtype SpCas9, of R661A, Q695A, Q926A, D1135E, and M694A. In some embodiments, the SpCas9 variant comprises the point mutations, relative to wildtype SpCas9, of R661A, Q695A, Q926A, D1135E, and M698A. In some embodiments, the mutant Cas9 comprises one or more mutations that alter PAM specificity (Kleinstiver et al., 2015, Nature, 523(7561):481-485; Kleinstiver et al., 2015, Nat Biotechnol, 33(12): 1293-1298). In some embodiments, the mutant Cas9 comprises one or more mutations that alter the catalytic activity of Cas9, including but not limited to D10A in RuvC and H840A in HNH (Cong et al., 2013; Science 339 : 919-823, Gasiubas et al., 2012;PNAS 109:E2579-2586 Jinek et al ; 2012; Science 337: 816-821). In certain embodiments, a Cas9 variant comprises a human-optimized Cas9; a nickase mutant Cas9; saCas9; enhanced-fidelity SaCas9 (efSaCas9); SpCas9(K855a); SpCas9(K810A / K1003A / r1060A); SpCas9(K848A / K1003A / R1060A); SpCas9 N497A, R661A, Q695A, Q926A; SpCas9 N497A, R661A, Q695A, Q926A, D1135E; SpCas9 N497A, R661A, Q695A, Q926A L169A; SpCas9 N497A, R661A, Q695A, Q926A Y450A; SpCas9 N497A, R661A, Q695A, Q926A M495A; SpCas9 N497A, R661A, Q695A, Q926A M694A; SpCas9 N497A, R661A, Q695A, Q926A H698A; SpCas9 N497A, R661A, Q695A, Q926A, D1135E, L169A; SpCas9 N497A, R661A, Q695A, Q926A, D1135E, Y450A; SpCas9 N497A, R661A, Q695A, Q926A, D1135E, M495A; SpCas9 N497A, R661A, Q695A, Q926A, D1135E, M694A; SpCas9 N497A, R661A, Q695A, Q926A, D1135E, M698A; SpCas9 R661A, Q695A, Q926A; SpCas9 R661A, Q695A, Q926A, D1135E; SpCas9 R661A, Q695A, Q926A, L169A; SpCas9 R661A, Q695A, Q926A Y450A; SpCas9 R661A, Q695A, Q926A M495A; SpCas9 R661A, Q695A, Q926A M694A; SpCas9 R661A, Q695A, Q926A H698A; SpCas9 R661A, Q695A, Q926A D1135E L169A; SpCas9 R661A, Q695A, Q926A D1135E Y450A; SpCas9 R661A, Q695A, Q926A D1135E M495A; or SpCas9 R661A, Q695A, Q926A, D1135E or M694A. The disclosure should also be construed to include any form of a peptide having substantial homology to a Cas peptide (e.g., Cas9) disclosed herein. Preferably, a peptide which is “substantially homologous” is about 50% homologous, about 70% homologous, about 80% homologous, about 90% homologous, about 95% homologous, or about 99% homologous to amino acid sequence of a Cas peptide disclosed herein. The single guide RNA (sgRNA) can include, for example, a nucleotide sequence that comprises an at least 12-20 nucleotide sequence that is complementary to the target DNA sequence and can include a common scaffold RNA sequence at its 3' end which resembles the tracrRNA sequence or any RNA sequences that function as a tracrRNA. A sgRNA sequence can be determined, for example, by identifying a sgRNA binding site by locating a PAM sequence in the target DNA, and then choosing about 12 to 20 or more nucleotides immediately upstream of the PAM site. The spacer sequence (gap size) between the two sgRNA binding sites on a target DNA can depend on the target DNA sequence and can be determined by those skilled in the art. In one embodiment of the present disclosure, introducing the CRISPR system comprises introducing an inducible CRISPR system. The CRISPR system may be induced by exposing the cell comprising the CRISPR vector to an agent that activates an inducible promoter in the CRISPR system, such as the Cas expression vector. In such an embodiment, the Cas expression vector includes an inducible promoter, such as one that is inducible by exposure to an antibiotic (e.g., by tetracycline or a derivative of tetracycline, for example doxycycline). However, it should be appreciated that other inducible promoters can be used. The inducing agent can be a selective condition (e.g., exposure to an agent, for example an antibiotic) that results in induction of the inducible promoter. In another embodiment, the CRISPR system may be induced by a tissue-specific promoter. In this case, the promoter from a gene whose expression is largely limited to the cell or tissue type of interest is used to drive expression of the CRISPR vector. Thus, expression of the CRISPR system is restricted to only certain cell types. In one embodiment of the disclosure, the CRISPR system is under control of a regulatory cassette based on the Creatine Kinase, M-type (CKM) enhancer and promoter, which limits its expression to skeletal muscle cells. Inactivated dCas9 CRISPR Systems CRISPR / Cas9-based systems used in the disclosure may include a Cas9 protein or a fragment thereof, a Cas9 fusion protein, a nucleic acid encoding a Cas9 protein or a fragment thereof, or a nucleic acid encoding a Cas9 fusion protein. Cas9 protein is an endonuclease that cleaves nucleic acid and is encoded by the CRISPR loci and is involved in the Type II CRISPR system. The Cas9 protein may be from any bacterial or archaea species, such as Streptococcus pyogenes. Cas9 sequences and structures from different species are known in the art, see, e.g., Ferretti et al., Proc Natl Acad Sci USA. (2001); 98(8): 4658-63; Deltcheva et al., Nature.2011 Mar.31; 471(7340):602-7; and Jinek et al., Science. (2012); 337(6096):816-21, incorporated herein by reference in their entirety. S. pyogenes Cas9 is perhaps the most widely-used Cas9 molecule. Notably, S. pyogenes Cas9 is quite large (the gene itself is over 4.1 Kb), making it a challenge to be packed into certain delivery vectors. For example, Adeno-associated virus (AAV) vector has a packaging limit of 4.5 or 4.75 Kb. This means that Cas9 as well as regulatory elements such as a promoter and a transcription terminator all have to fit into the same viral vector. Constructs larger than 4.5 or 4. 75 Kb will lead to significantly reduced virus production. One possibility is to use a functional fragment of S. pyogenes Cas9. Another possibility is to split Cas9 into its sub-portions (e.g., the N-terminal lobe and the C-terminal lobe of Cas9). Each sub-portion is expressed by a separate vector, and these sub-portions associate to form a functional Cas9. See, e.g., Chew et al., Nat Methods.2016; 13 :868-74; Truong et al., Nucleic Acids Res.2015; 43: 6450-6458; and Fine et al., Sci Rep.2015; 5: 10777, incorporated by reference herein in their entirety. Alternatively, shorter Cas9 molecules from other species can be used in the compositions and methods disclosed herein, e.g., Cas9 molecules from Staphylococcus aureus, Campylobacter jejuni, Corynebacterium diphtheria, Eubacterium ventriosum, Streptococcus pasteuriamus, Lactobacillus farciminis, Sphaerochaeta globus, Azospirillum (strain B510), Gluconacetobacter diazotrophicus, Neisseria cinerea, Roseburia intestinalis, Parvibaculum lavamentivorans, Nitratifractor salsuginis (strain DSM 16511), Campylobacter Zari (strain CF89-12), or Streptococcus thermophilus (strain LMD-9). In one embodiment of the present disclosure, the present disclosure is directed to a chimeric fusion protein including a DNA modifying domain fused to a catalytically inactive Cas protein. One who is skilled in the art would recognize that inactivated Cas nucleases are referred to interchangeably as “dead” Cas, iCas, or dCas proteins. In this way, the dCas9 protein lacks normal nuclease activity but retains the sgRNA-binding and DNA-targeting activity of the wildtype protein. dCas9 proteins derived from S. pyogenes (dSpCas9), paired with specific sgRNAs can be targeted to genes in bacteria, yeast, and human cells in order to silence gene expression either through steric hindrance or by fusion with other gene expression-modifying proteins. Such CRISPR systems that reduce or interfere with transcription of the target gene are known as CRISPR interference or CRISPRi or sgRNA / CRISPRi systems. Suitable dCas molecules for the CRISPRi system of certain embodiments of the disclosure can be derived from a wild type Cas molecules, and can be from a type I, type II, or type III CRISPR-Cas systems. In some embodiments, suitable dCas molecules can be derived from a Casl, Cas2, Cas3, Cas4, Cas5, Cash, Cas7, Cas8, Cas9, or Casl0 molecule. In some embodiments of the disclosure, the dCas molecule is derived from a Cas9 molecule. The dCas9 molecule can be obtained, for example, by introducing point mutations (e.g., substitutions, deletions, or additions) in the Cas9 molecule at the DNA-cleavage domain, e.g., the nuclease domain, e.g., the RuvC and / or HNH domain. See, e.g., Jinek et al., Science (2012) 337:816-21. Similar mutations can also apply to any other Cas9 proteins from any other nature sources and from any artificially mutated Cas9 proteins from any other species such as, for example, Staphylococcus aureus, Streptococcus thermophiles, Streptococcus salivarius, Streptococcus pasteurianus, Streptococcus mutans, Streptococcus mitis, Streptococcus infantarius, Streptococcus intermedius, Streptococcus equ, Streptococcus agalactiae, Streptococcus anginosus, Bacillus thuringiensis. Finitimus, Streptococcus dysgalactiae, Streptococcus gallolyticus, Streptococcus macedonicus, Streptococcus gordonii, Streptococcus suis, Streptococcus iniae, Neisseria meningitides, Lactobacillus casei, Lactobacillus salivarius, Listeria innocua, Listeria monocytogenes, Lactobacillus buchneri, Lactobacillus paracasei, Lactobacillus sanfranciscensis, Lactobacillus fermentum, Listeria innocua serovar, Lactobacillus rhamnosus, Lactobacillus casei, Lactobacillus sanfranciscensis, Haemophilus sputorum, Geobacillus, Enterococcus hirae, Enterococcus faecalis, Bacillus cereus, Treponema socranskii, Finegoldia magna and others. Similar catalytically inactive mutations can also apply to any other Cas9 proteins from any other natural sources, from any artificially mutated Cas9 proteins, and / or from any artificially created protein fragments that comprise a dCas9 like sgRNA binding domain. dCas9 Fusion Proteins In one embodiment of the disclosure, the CRISPR / dCas9-based system may include a fusion protein. The fusion protein may comprise a catalytically inactive Cas (dCas) protein conjugated to a second polypeptide via a short linker polypeptide sequence. In some embodiments of the disclosure, the second polypeptide comprises a DNA modifying domain derived from any DNA modification enzyme known to those skilled in the art. The DNA modifying domain of the fusion protein can be a full-length DNA modifying enzyme or a domain obtained from the full-length DNA modifying enzyme in which the domain retains the DNA modifying activity of the full-length DNA modifying enzyme. In some embodiments of the disclosure, the second polypeptide is an enzyme or a functional domain from an enzyme having an activity selected from the group consisting of, but not limited to, transcription activation, transcription repression, transcription release factor activity, histone modification activity, epigenetic transcriptional repression activity, nuclease activity, nucleic acid association activity, methylase activity, and demethylase activity among others. In one embodiment of the disclosure, the second polypeptide domain may have an epigenetic repressor activity. The epigenetic repressor activity can include a number of mechanisms affect transcriptional gene activity by inducing structural changes of the chromatin. Examples of such mechanisms include, but are not limited to, DNA methylation and demethylation as well as histone modifications including deacetylation, acetylation, methylation, and demethylation. In some embodiments of the disclosure, the dCas9 fusion protein comprises an epigenetic repressor derived from the SUV39Hl pre-SET, SET, and post-SET domains. SUV39Hl is a histone methyltransferase that trimethylates lysine 9 of histone H3, a repressive mark that recruits other repressive factors such as HPl and results in transcriptional silencing. All three SET domains are necessary for methyltransferase activity. In some embodiments of the disclosure, the dCas9 protein is fused an epigenetic regulator derived from an HPl family protein. HPl or heterochromatin protein 1 proteins bind to methylated histone H3 and help form heterochromatin complexes that repress transcriptional activity. In some embodiments of the disclosure, the HPl protein is HPlα, which normally localizes to heterochromatin. In some embodiments of the disclosure, the HPl protein is HPIγ, which similarly localizes to heterochromatin and mediates transcriptional silencing. In some embodiments of the disclosure, the dCas9 protein is fused to the chromo shadow domain and C-terminal extension regions of HPlα or HPlγ. HPlγ is particularly enriched in the normal D4Z4 macrosatellite array that serves to silence the DUX4 gene in healthy skeletal muscle cells and HP1γ binding is lost in FSHD. In some embodiments of the disclosure, the dCas9 fusion protein comprises a transcriptional repressor domain (TRD) derived from MeCP2. This domain specifically binds repressive histone marks and forms co-repressor complexes with other regulatory proteins to enforce transcriptional silencing. Nucleic Acids and Vectors The present disclosure provides an isolated polynucleic acid encoding a muscle-specific therapeutic cassette. In certain embodiments, the muscle-specific therapeutic cassette comprises a regulatory portion comprising one or more modified enhancer sequences upstream and operably linked to a promoter which is operably linked to a payload portion comprising a first payload and a U6 promoter which is operably linked to second payload, wherein the three modified enhancer sequences comprise a Trex sequence, an AT-rich sequence, a right E-box sequence, and a MEF2 sequence, wherein the right E-box sequence is repeated at least once, wherein the promoter is a -80 to +50 promoter containing a consensus Inr sequence, wherein the first payload is a catalytically inactive Cas9 fused to an epigenetic repressor, and wherein the second payload is a single guide RNA (sgRNA) and scaffold. In certain embodiments, the muscle-specific regulatory portion of the therapeutic cassette is encoded by a nucleic acid comprising a polynucleotide sequence having at least 80%, 85%, 90%, 95%, 96%, 96%, 97%, 98%, 99% identity to SEQ ID NO: 1. In certain embodiments, the muscle-specific regulatory portion of the therapeutic cassette is encoded by a nucleic acid comprising the polynucleotide sequence set forth in SEQ ID NO: 1. In certain embodiments, the muscle-specific regulatory portion of the therapeutic cassette is encoded by a nucleic acid consisting of the polynucleotide sequence set forth in SEQ ID NO: 1. In certain embodiments, the muscle-specific therapeutic cassette comprises a regulatory portion comprising one or more modified enhancer sequences upstream and operably linked to a promoter which is operably linked to a payload portion comprising a first payload and a U6 promoter which is operably linked to a second payload, wherein the one or more modified enhancer sequences comprise a Trex sequence, an AT-rich sequence, a left E-box sequence, a right E-box sequence, and a MEF2 sequence, wherein the promoter is a -80 to +50 promoter containing a consensus Inr sequence, wherein the first payload is a catalytically inactive Cas9 fused to an epigenetic repressor, and wherein the second payload is a single guide RNA (sgRNA) and scaffold. In certain embodiments, the muscle-specific regulatory portion of the therapeutic cassette is encoded by a nucleic acid comprising a polynucleotide sequence having at least 80%, 85%, 90%, 95%, 96%, 96%, 97%, 98%, 99% identity to SEQ ID NOs: 2. In certain embodiments, the muscle-specific regulatory portion of the therapeutic cassette is encoded by a nucleic acid comprising the polynucleotide sequence set forth in SEQ ID NOs: 2. In certain embodiments, the muscle-specific regulatory portion of the therapeutic cassette is encoded by a nucleic acid consisting of the polynucleotide sequence set forth in SEQ ID NOs: 2. In certain embodiments, the muscle-specific therapeutic cassette comprises a nucleic acid sequence encoding an HP1α-DUX4 cassette. In certain embodiments, the HP1α-DUX4 cassette comprises a nucleic acid sequence having at least 80%, 85%, 90%, 95%, 96%, 96%, 97%, 98%, 99% identity to SEQ ID NOs: 3 In certain embodiments, the HP1α-DUX4 cassette is encoded by a nucleic acid comprising the polynucleotide sequence set forth in SEQ ID NOs: 3. In certain embodiments, the HP1α -DUX4 cassette is encoded by a nucleic acid consisting of the polynucleotide sequence set forth in SEQ ID NOs: 3. In certain embodiments, the muscle-specific therapeutic cassette comprises a nucleic acid sequence encoding an HP1γ-DUX4 cassette. In certain embodiments, the HP1γ-DUX4 cassette comprises a nucleic acid sequence having at least 80%, 85%, 90%, 95%, 96%, 96%, 97%, 98%, 99% identity to SEQ ID NOs: 4 In certain embodiments, the HP1γ -DUX4 cassette is encoded by a nucleic acid comprising the polynucleotide sequence set forth in SEQ ID NOs: 4. In certain embodiments, the HP1γ -DUX4 cassette is encoded by a nucleic acid consisting of the polynucleotide sequence set forth in SEQ ID NOs: 4. In certain embodiments, the muscle-specific therapeutic cassette comprises a nucleic acid sequence encoding an TRD-DUX4 cassette. In certain embodiments, the TRD-DUX4 cassette comprises a nucleic acid sequence having at least 80%, 85%, 90%, 95%, 96%, 96%, 97%, 98%, 99% identity to SEQ ID NOs: 5 In certain embodiments, the TRD-DUX4 cassette is encoded by a nucleic acid comprising the polynucleotide sequence set forth in SEQ ID NOs: 5. In certain embodiments, the TRD-DUX4 cassette is encoded by a nucleic acid consisting of the polynucleotide sequence set forth in SEQ ID NOs: 5. In certain embodiments, the sgRNA comprises a nucleic acid sequence set forth in SEQ ID NOs: 6-8. In certain embodiments, the sgRNA comprises a nucleic acid sequence having at least 80%, 85%, 90%, 95%, 96%, 96%, 97%, 98%, 99% identity to SEQ ID NOs: 6-8. Guide RNAs In certain embodiments, the guide RNA sequences can be configured as a single sequence or as a combination of one or more different sequences, e.g., a multiplex configuration. Multiplex configurations can include combinations of two, three, four, five, six, seven, eight, nine, ten, or more different guide RNAs. In some embodiments, the RNA molecules e.g. crRNA, tracrRNA, gRNA are engineered to comprise one or more modified nucleobases. For example, known modifications of RNA molecules can be found, for example, in Genes VI, Chapter 9 (“Interpreting the Genetic Code”), Lewis, ed. (1997, Oxford University Press, New York), and Modification and Editing of RNA, Grosjean and Benne, eds. (1998, ASM Press, Washington D.C.). Modified RNA components include the following: 2′-O-methylcytidine; N4-methylcytidine; N4-2′-O-dimethylcytidine; N4- acetylcytidine; 5-methylcytidine; 5,2′-O-di methylcytidine; 5-hydroxymethylcytidine; 5- formylcytidine; 2′-O-methyl-5-formaylcytidine; 3-methylcytidine; 2-thiocytidine; lysidine; 2′-O- methyluridine; 2-thiouridine; 2-thio-2′-O-methyluridine; 3,2′-O-dimethyluridine; 3-(3-amino-3- carboxypropyl)uridine; 4-thiouridine; ribosylthymine; 5,2′-O-dimethyluridine; 5-methyl-2- thiouridine; 5-hydroxyuridine; 5-methoxyuridine; uridine 5-oxyacetic acid; uridine 5-oxyacetic acid methyl ester; 5-carboxymethyluridine; 5-methoxycarbonylmethyluridine; 5- methoxycarbonylmethyl-2′-O-methyluridine; 5-methoxycarbonylmethyl-2′-thiouridine; 5- carbamoylmethyluridine; 5-carbamoylmethyl-2′-O-methyluridine; 5- (carboxyhydroxymethyl)uridine; 5-(carboxyhydroxymethyl) uridinemethyl ester; 5- aminomethyl-2-thiouridine; 5-methylaminomethyluridine; 5-methylaminomethyl-2-thiouridine; 5-methylaminomethyl-2-selenouridine; 5-carboxymethylaminomethyluridine; 5- carboxymethylaminomethyl-2′-O-methyl-uridine; 5-carboxymethylaminomethyl-2-thiouridine; dihydrouridine; dihydroribosylthymine; 2′-methyladenosine; 2-methyladenosine; N6N- methyladenosine; N6,N6-dimethyladenosine; N6,2′-O-trimethyladenosine; 2-methylthio-N6N- isopentenyladenosine; N6-(cis-hydroxyisopentenyl)-adenosine; 2-methylthio-N6-(cis- hydroxyisopentenyl)-adenosine; N6-glycinylcarbamoyl)adenosine; N6-threonylcarbamoyl adenosine; N6-methyl-N6-threonylcarbamoyl adenosine; 2-methylthio-N6-methyl-N6- threonylcarbamoyl adenosine; N6-hydroxynorvalylcarbamoyl adenosine; 2-methylthio-N6- hydroxnorvalylcarbamoyl adenosine; 2′-O-ribosyladenosine (phosphate); inosine; 2′O-methyl inosine; 1-methyl inosine; 1;2′-O-dimethyl inosine; 2′-O-methyl guanosine; 1-methyl guanosine; N2-methyl guanosine; N2,N2-dimethyl guanosine; N2,2′-O-dimethyl guanosine; N2,N2,2′-O- trimethyl guanosine; 2′-O-ribosyl guanosine (phosphate); 7-methyl guanosine; N2;7-dimethyl guanosine; N2; N2;7-trimethyl guanosine; wyosine; methylwyosine; under-modified hydroxywybutosine; wybutosine; hydroxywybutosine; peroxywybutosine; queuosine; epoxyqueuosine; galactosyl-queuosine; mannosyl-queuosine; 7-cyano-7-deazaguanosine; arachaeosine [also called 7-formamido-7-deazaguanosine]; and 7-aminomethyl-7- deazaguanosine. In some embodiments, the gRNA is a synthetic oligonucleotide. In some embodiments, the synthetic nucleotide comprises a modified nucleotide. Modification of the inter-nucleoside linker (i.e. backbone) can be utilized to increase stability or pharmacodynamic properties. For example, inter-nucleoside linker modifications prevent or reduce degradation by cellular nucleases, thus increasing the pharmacokinetics and bioavailability of the gRNA. Generally, a modified inter-nucleoside linker includes any linker other than other than phosphodiester (PO) liners, that covalently couples two nucleosides together. In some embodiments, the modified inter-nucleoside linker increases the nuclease resistance of the gRNA compared to a phosphodiester linker. For naturally occurring oligonucleotides, the inter-nucleoside linker includes phosphate groups creating a phosphodiester bond between adjacent nucleosides. In some embodiments, the gRNA comprises one or more inter-nucleoside linkers modified from the natural phosphodiester. In some embodiments all of the inter-nucleoside linkers of the gRNA, or contiguous nucleotide sequence thereof, are modified. For example, in some embodiments the inter-nucleoside linkage comprises sulfur (S), such as a phosphorothioate inter-nucleoside linkage. Modifications to the ribose sugar or nucleobase can also be utilized herein. Generally, a modified nucleoside includes the introduction of one or more modifications of the sugar moiety or the nucleobase moiety. In some embodiments, the gRNAs, as described, comprise one or more nucleosides comprising a modified sugar moiety, wherein the modified sugar moiety is a modification of the sugar moiety when compared to the ribose sugar moiety found in deoxyribose nucleic acid (DNA) and RNA. Numerous nucleosides with modification of the ribose sugar moiety can be utilized, primarily with the aim of improving certain properties of oligonucleotides, such as affinity and / or stability. Such modifications include those where the ribose ring structure is modified. These modifications include replacement with a hexose ring (HNA), a bicyclic ring having a biradical bridge between the C2 and C4 carbons on the ribose ring (e.g. locked nucleic acids (LNA)), or an unlinked ribose ring which typically lacks a bond between the C2 and C3 carbons (e.g. UNA). Other sugar modified nucleosides include, for example, bicyclohexose nucleic acids or tricyclic nucleic acids. Modified nucleosides also include nucleosides where the sugar moiety is replaced with a non-sugar moiety, for example in the case of peptide nucleic acids (PNA), or morpholino nucleic acids. Sugar modifications also include modifications made by altering the substituent groups on the ribose ring to groups other than hydrogen, or the 2′-OH group naturally found in DNA and RNA nucleosides. Substituents may, for example be introduced at the 2′, 3′, 4′ or 5′ positions. Nucleosides with modified sugar moieties also include 2′ modified nucleosides, such as 2′ substituted nucleosides. Indeed, much focus has been spent on developing 2′ substituted nucleosides, and numerous 2′ substituted nucleosides have been found to have beneficial properties when incorporated into oligonucleotides, such as enhanced nucleoside resistance and enhanced affinity. A 2′ sugar modified nucleoside is a nucleoside that has a substituent other than H or -OH at the 2′ position (2′ substituted nucleoside) or comprises a 2′ linked biradicle, and includes 2′ substituted nucleosides and LNA (2′-4′ biradicle bridged) nucleosides. Examples of 2′ substituted modified nucleosides are 2′-O-alkyl-RNA, 2′-O-methyl-RNA, 2′-alkoxy-RNA, 2′-O- methoxyethyl-RNA (MOE), 2′-amino-DNA, 2′-Fluoro-RNA, and 2′-F-ANA nucleoside. By way of further example, in some embodiments, the modification in the ribose group comprises a modification at the 2′ position of the ribose group. In some embodiments, the modification at the 2′ position of the ribose group is selected from the group consisting of 2′-O-methyl, 2′-fluoro, 2′- deoxy, and 2′-O-(2-methoxyethyl). In some embodiments, the gRNA comprises one or more modified sugars. In some embodiments, the gRNA comprises only modified sugars. In certain embodiments, the gRNA comprises greater than 10%, 25%, 50%, 75%, or 90% modified sugars. In some embodiments, the modified sugar is a bicyclic sugar. In some embodiments, the modified sugar comprises a 2′- O-methoxyethyl group. In some embodiments, the gRNA comprises both inter-nucleoside linker modifications and nucleoside modifications. Target specificity can be used in reference to a guide RNA, or a crRNA specific to a target polynucleotide sequence or region (e.g., DUX4 or fragments thereof) and further includes a sequence of nucleotides capable of selectively annealing / hybridizing to a target (sequence or region) of a target polynucleotide (e.g. corresponding to a target), e.g., a target DNA. In some embodiments, a crRNA or the derivative thereof contains a target-specific nucleotide region complementary to a region of the target DNA sequence. In some embodiments, a crRNA or the derivative thereof contains other nucleotide sequences besides a target-specific nucleotide region. In some embodiments, the other nucleotide sequences are from a tracrRNA sequence. gRNAs are generally supported by a scaffold, wherein a scaffold refers to the portions of gRNA or crRNA molecules comprising sequences which are substantially identical or are highly conserved across natural biological species (e.g. not conferring target specificity). Scaffolds include the tracrRNA segment and the portion of the crRNA segment other than the polynucleotide-targeting guide sequence at or near the 5′ end of the crRNA segment, excluding any unnatural portions comprising sequences not conserved in native crRNAs and tracrRNAs. In some embodiments, the crRNA or tracrRNA comprises a modified sequence. In certain embodiments, the crRNA or tracrRNA comprises at least 1, 2, 3, 4, 5, 10, or 15 modified bases (e.g. a modified native base sequence). “Complementary”, as used herein, generally refers to a polynucleotide that includes a nucleotide sequence capable of selectively annealing to an identifying region of a target polynucleotide under certain conditions. As used herein, the term “substantially complementary” and grammatical equivalents is intended to mean a polynucleotide that includes a nucleotide sequence capable of specifically annealing to an identifying region of a target polynucleotide under certain conditions. Annealing refers to the nucleotide base-pairing interaction of one nucleic acid with another nucleic acid that results in the formation of a duplex, triplex, or other higher-ordered structure. The primary interaction is typically nucleotide base specific, e.g., A:T, A:U, and G:C, by Watson-Crick and Hoogsteen-type hydrogen bonding. In some embodiments, base-stacking and hydrophobic interactions can also contribute to duplex stability. Conditions under which a polynucleotide anneals to complementary or substantially complementary regions of target nucleic acids are well known in the art, e.g., as described in Nucleic Acid Hybridization, A Practical Approach, Hames and Higgins, eds., IRL Press, Washington, D.C. (1985) and Wetmur and Davidson, Mol. Biol.31:349 (1968). Annealing conditions will depend upon the particular application and can be routinely determined by persons skilled in the art, without undue experimentation. Hybridization generally refers to process in which two single- stranded polynucleotides bind non-covalently to form a stable double-stranded polynucleotide. A resulting double-stranded polynucleotide is a “hybrid” or “duplex.” In certain instances, 100% sequence identity is not required for hybridization and, in certain embodiments, hybridization occurs at about greater than 70%, 75%, 80%, 85%, 90%, or 95% sequence identity. In certain embodiments, sequence identity includes in addition to non-identical nucleobases, sequences comprising insertions and / or deletions. The nucleic acid of the disclosure, including the RNA (e.g., crRNA, tracrRNA, gRNA) or nucleic acids encoding the RNA, may be produced by standard techniques. For example, polymerase chain reaction (PCR) techniques can be used to obtain an isolated nucleic acid containing a nucleotide sequence described herein, including nucleotide sequences encoding a polypeptide described herein. PCR can be used to amplify specific sequences from DNA as well as RNA, including sequences from total genomic DNA or total cellular RNA. Various PCR methods are described in, for example, PCR Primer: A Laboratory Manual, 2ndedition, Dieffenbach and Dveksler, eds., Cold Spring Harbor Laboratory Press, 2003. Generally, sequence information from the ends of the region of interest or beyond is employed to design oligonucleotide primers that are identical or similar in sequence to opposite strands of the template to be amplified. Various PCR strategies also are available by which site-specific nucleotide sequence modifications can be introduced into a template nucleic acid. The isolated nucleic acids also can be chemically synthesized, either as a single nucleic acid (e.g., using automated DNA synthesis in the 3’ to 5’ direction using phosphoramidite technology) or as a series of oligonucleotides. Isolated nucleic acids of the disclosure also can be obtained by mutagenesis of, e.g., a naturally occurring portion crRNA, tracrRNA, RNA- encoding DNA, or of a Cas9 -encoding DNA In certain embodiments, the isolated RNAs are synthesized from an expression vector encoding the RNA molecule, as described in detail elsewhere herein. Gene Transfer Systems and Adeno-Associated Virus (AAV) Gene transfer systems, such as those described in the present disclosure, depend upon a vector or vector system to shuttle the genetic constructs into target cells. Methods of introducing a nucleic acid into the hematopoietic stem or progenitor cell include physical, biological and chemical methods. Physical methods for introducing a polynucleotide, such as RNA, into a host cell include calcium phosphate precipitation, lipofection, particle bombardment, microinjection, electroporation, and the like. RNA can be introduced into target cells using commercially available methods which include electroporation (Amaxa Nucleofector-II (Amaxa Biosystems, Cologne, Germany)), (ECM 830 (BTX) (Harvard Instruments, Boston, Mass.) or the Gene Pulser II (BioRad, Denver, Colo.), Multiporator (Eppendort, Hamburg Germany). RNA can also be introduced into cells using cationic liposome mediated transfection using lipofection, using polymer encapsulation, using peptide mediated transfection, or using biolistic particle delivery systems such as “gene guns” (see, for example, Nishikawa, et al. Hum Gene Ther., 12(8):861-70 (2001). Chemical means for introducing a polynucleotide into a host cell include colloidal dispersion systems, such as macromolecule complexes, nanocapsules, microspheres, beads, and lipid-based systems including oil-in-water emulsions, micelles, mixed micelles, and liposomes. An exemplary colloidal system for use as a delivery vehicle in vitro and in vivo is a liposome (e.g., an artificial membrane vesicle). Lipids suitable for use can be obtained from commercial sources. For example, dimyristyl phosphatidylcholine (“DMPC”) can be obtained from Sigma, St. Louis, MO; dicetyl phosphate (“DCP”) can be obtained from K & K Laboratories (Plainview, NY); cholesterol (“Choi”) can be obtained from Calbiochem-Behring; dimyristyl phosphatidylglycerol (“DMPG”) and other lipids may be obtained from Avanti Polar Lipids, Inc. (Birmingham, AL). Stock solutions of lipids in chloroform or chloroform / methanol can be stored at about -20ºC. Chloroform is used as the only solvent since it is more readily evaporated than methanol. “Liposome” is a generic term encompassing a variety of single and multilamellar lipid vehicles formed by the generation of enclosed lipid bilayers or aggregates. Liposomes can be characterized as having vesicular structures with a phospholipid bilayer membrane and an inner aqueous medium. Multilamellar liposomes have multiple lipid layers separated by aqueous medium. They form spontaneously when phospholipids are suspended in an excess of aqueous solution. The lipid components undergo self-rearrangement before the formation of closed structures and entrap water and dissolved solutes between the lipid bilayers (Ghosh et al., (1991) Glycobiology 5: 505-10). However, compositions that have different structures in solution than the normal vesicular structure are also encompassed. For example, the lipids may assume a micellar structure or merely exist as nonuniform aggregates of lipid molecules. Also contemplated are lipofectamine- nucleic acid complexes. Biological methods for introducing a polynucleotide of interest into a host cell include the use of DNA and RNA vectors. Viral vectors, and especially retroviral vectors, have become the most widely used method for inserting genes into mammalian, e.g., human cells. Other viral vectors can be derived from lentivirus, poxviruses, herpes simplex virus I, adenoviruses and adeno-associated viruses, and the like. See, for example, U.S. Pat. Nos.5,350,674 and 5,585,362. Currently, the most efficient and effective way to accomplish the transfer of genetic constructs into living cells is through the use of vector systems based on viruses that have been made replication-defective. Some of the most effective vectors known in the art are those based on adeno-associated viruses (AAVs). AAVs are small viruses of the parvoviridae family that make attractive vectors for gene transfer in that they are replication defective, not known to cause any human disease, cause only a very mild immune response, can infect both actively dividing and quiescent cells, and stably persist in an extrachromosomal state without integrating into the target cell’s genome. In certain embodiments, the present disclosure provides an AAV vector comprising the dCas9-based CRISPRi system of the disclosure. Regardless of the method used to introduce the nucleic acid into the cell, a variety of assays may be performed to confirm the presence of the nucleic acid in the cell. Such assays include, for example, “molecular biological” assays well known to those of skill in the art, such as Southern and Northern blotting, RT-PCR and PCR; “biochemical” assays, such as detecting the presence or absence of a particular peptide, e.g., by immunological means (ELISAs and Western blots) or by assays described herein to identify agents falling within the scope of the disclosure. Methods of Treatment and Use In certain embodiments, the present disclosure includes a method of treating a genetic disease or disorder in a subject in need thereof, comprising administering to the subject an effective amount of an AAV vector comprising a therapeutic cassette comprising a regulatory portion comprising one or more modified enhancer sequences upstream and operably linked to a promoter which is operably linked to a payload portion comprising a first payload and a U6 promoter which is operably linked to second payload, wherein the three modified enhancer sequences comprise a Trex sequence, an AT-rich sequence, a right E-box sequence, and a MEF2 sequence, wherein the right E-box sequence is repeated at least once, wherein the promoter is a - 80 to +50 promoter containing a consensus Inr sequence, wherein the first payload is a catalytically inactive Cas9 fused to an epigenetic repressor, and wherein the second payload is a single guide RNA (sgRNA) and scaffold. As such, in certain embodiments, the AAV vector has a specificity for muscle tissue. In certain embodiments, the regulatory cassette is highly active in fast-twitch skeletal muscles with relatively low expression activity in the soleus and diaphragm muscles and no expression activity in cardiac tissues. In certain embodiments, the genetic disease is facioscapulohumeral muscular dystrophy (FSHD). In certain embodiments, the therapeutic cassette further comprises a single guide RNA (sgRNA) and encodes a catalytically inactive Cas9 fused to an epigenetic repressor. In certain embodiments, the sgRNA targets the DUX4 locus. In certain embodiments, the catalytically inactive Cas9 is dSaCas9. In certain embodiments, the epigenetic repressor is selected from the group consisting of HPlα, HPlγ, the chromo shadow domain and C-terminal extension region of HPlα or HPlγ, MeCP2 transcription repression domain (TRD), and SUV39Hl pre-SET, SET, and post-SET domains. In certain embodiments, the AAV vector comprises an AAV capsid comprising AAV1, AAV2, AAV3, AAV3B, AAV4, AAV5, AAV6, AAV7, AAV8, AAV9, AAV12, AAV-B1, AAV-DJ, AAV- Retro, AAVrh8, AAVrh10, AAVrh25, Anc80L65, LK03, AAVrh18, rAAVrh74, AAVrh32.33, AAVrh39, AAVrh43, MyoAAV2, Oligo001, PHP-B, LICA1 or Spark100. In certain embodiments, the capsid is an rAAVrh74. In certain embodiments, the capsid is an AAV9 serotype. In certain embodiments, the capsid is a MyoAAV2. In certain embodiments, the capsid is a LICA1. In certain embodiments, the disclosure of the present disclosure includes a method of treating a genetic disease or disorder in a subject in need thereof, comprising administering to the subject an effective amount of an AAV vector comprising a therapeutic cassette comprising a regulatory portion comprising one or more modified enhancer sequences upstream and operably linked to a promoter which is operably linked to a payload portion comprising a first payload and a U6 promoter which is operably linked to a second payload, wherein the one or more modified enhancer sequences comprise a Trex sequence, an AT-rich sequence, a left E-box sequence, a right E-box sequence, and a MEF2 sequence, wherein the promoter is a -80 to +50 promoter containing a consensus Inr sequence, wherein the first payload is a catalytically inactive Cas9 fused to an epigenetic repressor, and wherein the second payload is a single guide RNA (sgRNA) and scaffold. As such, in certain embodiments, the AAV vector has a specificity for muscle tissue. In certain embodiments, the regulatory cassette exhibits moderate to high activity in all skeletal muscles and low expression activity in cardiac tissue. In this way, these cassettes provide moderate to high-level expression across all skeletal muscles in conjunction with low-level expression in heart, making them well-suited to the treatment of genetic diseases or disorders that affect all striated muscles, but where high expression of the therapeutic transgene is toxic in cardiac muscle. In certain embodiments, the genetic disease is facioscapulohumeral muscular dystrophy (FSHD). In certain embodiments, the therapeutic cassette further comprises a single guide RNA (sgRNA) and encodes a catalytically inactive Cas9 fused to an epigenetic repressor. In certain embodiments, the sgRNA targets the DUX4 locus. In certain embodiments, the catalytically inactive Cas9 is dSaCas9. In certain embodiments, the epigenetic repressor is selected from the group consisting of HPlα, HPlγ, the chromo shadow domain and C-terminal extension region of HPlα or HPlγ, MeCP2 transcription repression domain (TRD), and SUV39Hl pre-SET, SET, and post-SET domains. In certain embodiments, the AAV vector comprises an AAV capsid comprising AAV1, AAV2, AAV3, AAV3B, AAV4, AAV5, AAV6, AAV7, AAV8, AAV9, AAV12, AAV-B1, AAV-DJ, AAV- Retro, AAVrh8, AAVrh10, AAVrh25, Anc80L65, LK03, AAVrh18, rAAVrh74, AAVrh32.33, AAVrh39, AAVrh43, MyoAAV2, Oligo001, PHP-B, LICA1 or Spark100. In certain embodiments, the capsid is an rAAVrh74. In certain embodiments, the capsid is an AAV9 serotype. In certain embodiments, the capsid is a MyoAAV2. In certain embodiments, the capsid is a LICA1. In certain embodiments, the genetic disease or disorder which is treated by way of the methods of the current disclosure is a muscle-related genetic disease or disorder. Non-limiting examples of muscle-related genetic diseases or disorders which could be treated by the methods of the disclosure include, but are not limited to facioscapulohumeral muscular dystrophy (FSHD), X-linked myotubular myopathy (XLMTM), central core myopathy, inclusion body myositis, nemaline myopathy, distal myopathy, centronuclear myopathy, oculopharyngeal muscular dystrophy, a dysferlinopathy, a limb-girdle muscular dystrophy (LGMD), and Duchenne muscular dystrophy (DMD). In certain embodiments, the disclosure includes a method of introducing a transgene into a target cell, comprising contacting the cell with a polynucleotide encoding a muscle-specific therapeutic cassette comprising a regulatory portion comprising one or more modified enhancer sequences upstream and operably linked to a promoter which is operably linked to a payload portion comprising a first payload and a U6 promoter which is operably linked to a second payload, wherein the one or more modified enhancer sequences comprise a Trex sequence, an AT-rich sequence, a right E-box sequence, and a MEF2 sequence, wherein the right E-box sequence is repeated at least once, wherein the promoter is a -80 to +50 promoter containing a consensus Inr sequence, wherein the first payload is a catalytically inactive Cas9 fused to an epigenetic repressor, and wherein the second payload is a single guide RNA (sgRNA) and scaffold. In certain embodiments, the target cell is a mammalian muscle cell. In certain embodiments, the cassette has high expression activity in skeletal muscle cells. In certain preferred embodiments, the skeletal muscle tissue is fast-twitch muscle tissue. As used herein, the term “fast-twitch muscle tissue” refers to type II muscle tissues which are specialized for short, powerful contractions, as opposed to “slow-twitch” or type I muscle tissues which can sustain contractions for an extended period of time. In certain embodiments, the cassette has very low expression in cardiac tissue as compared to skeletal muscle tissue. In certain embodiments, the disclosure includes a method of introducing a transgene into a target cell, comprising contacting the cell with a polynucleotide encoding a muscle-specific therapeutic cassette comprising a regulatory portion comprising one or more modified enhancer sequences upstream and operably linked to a promoter which is operably linked to a payload portion comprising a first payload and a U6 promoter which is operably linked to a second payload, wherein the one or more modified enhancer sequences comprise a Trex sequence, an AT-rich sequence, a left E-box sequence, a right E-box sequence, and a MEF2 sequence, wherein the promoter is a -80 to +50 promoter containing a consensus Inr sequence, wherein the first payload is a catalytically inactive Cas9 fused to an epigenetic repressor, and wherein the second payload is a single guide RNA (sgRNA) and scaffold. In certain embodiments, the target cell is a mammalian muscle cell. In certain embodiments, the cassette has high expression activity in skeletal muscle tissue accompanied by low-level, but still present, expression in cardiac tissues. In certain embodiments, the disclosure includes a method of introducing a transgene into a target cell, comprising contacting the cell with a polynucleotide encoding any of the muscle- specific therapeutic cassettes disclosed herein. In certain embodiments, the therapeutic cassette further comprises a single guide RNA (sgRNA) and encodes a catalytically inactive Cas9 fused to an epigenetic repressor. In certain embodiments, the sgRNA targets the DUX4 locus. In certain embodiments, the catalytically inactive Cas9 is dSaCas9. In certain embodiments, the epigenetic repressor is selected from the group consisting of HPlα, HPlγ, the chromo shadow domain and C-terminal extension region of HPlα or HPlγ, pre-SET, SET, and post-SET domains, and MeCP2 transcription repression domain (TRD). In certain embodiments, the AAV vector comprises an AAV capsid comprising AAV1, AAV2, AAV3, AAV3B, AAV4, AAV5, AAV6, AAV7, AAV8, AAV9, AAV12, AAV-B1, AAV-DJ, AAV-Retro, AAVrh8, AAVrh10, AAVrh25, Anc80L65, LK03, AAVrh18, rAAVrh74, AAVrh32.33, AAVrh39, AAVrh43, MyoAAV2, Oligo001, PHP-B, LICA or Spark100. In certain embodiments, the capsid is an rAAVrh74. In certain embodiments, the capsid is an AAV9 serotype. In certain embodiments, the capsid is a MyoAAV2. Pharmaceutical Compositions Pharmaceutical compositions of the present disclosure may comprise as described herein, in combination with one or more pharmaceutically or physiologically acceptable carriers, diluents, adjuvants or excipients. Such compositions may comprise buffers such as neutral buffered saline, phosphate buffered saline and the like; carbohydrates such as glucose, mannose, sucrose or dextrans, mannitol; proteins; polypeptides or amino acids such as glycine; antioxidants; chelating agents such as EDTA or glutathione; adjuvants (e.g., aluminum hydroxide); and preservatives. Compositions of the present disclosure are preferably formulated for intravenous administration. Pharmaceutical compositions of the present disclosure may comprise the AAV vector particles as described herein, in combination with one or more pharmaceutically or physiologically acceptable carriers, diluents or excipients. Such compositions may comprise buffers such as neutral buffered saline, phosphate-buffered saline (PBS) and the like; carbohydrates such as glucose, mannose, sucrose or dextran, mannitol; proteins; polypeptides or amino acids such as glycine; antioxidants; chelating agents such as EDTA or glutathione; adjuvants (e.g., aluminum hydroxide); and preservatives. Compositions of the present disclosure are preferably formulated for a number of administration routes including oral, inhalation, nasal, nebulization, intravenous injection, intramuscular injection, intrathecal injection, intrapleural injection, intracisternal magna injection, subcutaneous injection, and / or transdermal injection. Pharmaceutical compositions of the present disclosure may be administered in a manner appropriate to the disease to be treated (or prevented). The quantity and frequency of administration will be determined by such factors as the condition of the patient, the type and severity of the patient’s disease, and the type and functional nature of the patient’s immune response to the phage particles, although appropriate dosages may be determined by clinical trials. The AAV vector particles of the disclosure can be administered in dosages and routes and at times to be determined in appropriate pre-clinical and clinical experimentation and trials. Administration of the AAV vector particles of the disclosure may be combined with other methods useful to treat the desired disease or condition as determined by those of skill in the art. In certain embodiments, the effective dose range is measured in units known to a person of skill in the art to be suitable for the description of AAV vector particle doses. In some embodiments, the effective dose range for a vaccine or therapeutic compound of the disclosure is measured by transducing units (TU) / kg / dose or genome copies(GC) / kg / dose or particles / kg / dose. In some embodiments, the dosage provided to a patient is between about 106– 1014TU / kg. In some embodiments, the dosage provided to a patient is between about 106– 1014GC / kg. In some embodiments, the effective dose range is measured by colony forming units (CFU), 50% tissue culture infectious dose (TCID50), and combinations thereof. Actual dosage levels of the active ingredients in the pharmaceutical compositions of this disclosure can be varied so as to obtain an amount of the active ingredient that is effective to achieve the desired therapeutic response for a particular patient, composition, and mode of administration, without being toxic to the patient. The therapeutically effective amount or dose of a compound of the present disclosure depends on the age, sex and weight of the patient, the current medical condition of the patient and the progression of a disease or disorder contemplated in the disclosure. A medical doctor, e.g., physician or veterinarian, having ordinary skill in the art can readily determine and prescribe the effective amount of the pharmaceutical composition required. For example, the physician or veterinarian could start doses of the compounds of the disclosure employed in the pharmaceutical composition at levels lower than that required in order to achieve the desired therapeutic effect and gradually increase the dosage until the desired effect is achieved. In certain embodiments, the compositions of the disclosure are administered to the patient in dosages that range from one to five times per day or more. In other embodiments, the compositions of the disclosure are administered to the patient in range of dosages that include, but are not limited to, once every day, every two, days, every three days to once a week, and once every two weeks. It is readily apparent to one skilled in the art that the frequency of administration of the various combination compositions of the disclosure varies from individual to individual depending on many factors including, but not limited to, age, disease or disorder to be treated, gender, overall health, and other factors. Thus, the disclosure should not be construed to be limited to any particular dosage regime and the precise dosage and composition to be administered to any patient is determined by the attending physical taking all other factors about the patient into account. Dosage size can be adjusted according to the weight, age, and stage of the disease of the subject being treated. AAV vector particles may also be administered multiple times at these dosages. The AAV vector particles can be administered by using infusion techniques that are commonly known in the art of immunotherapy or vaccinology. The optimal dosage and treatment regime for a particular patient can readily be determined by one skilled in the art of medicine by monitoring the patient for signs of disease and adjusting the treatment accordingly. The administration of the AAV vector particle compositions of the disclosure may be carried out in any convenient manner known to those of skill in the art. The AAV vector particles of the present disclosure may be administered to a subject by aerosol inhalation, injection, ingestion, transfusion, implantation or transplantation. The compositions described herein may be administered to a subject or patient trans-arterially, subcutaneously, intranasally, intradermally, intratumorally, intranodally, intramedullary, intramuscularly, intravenously, or intraperitoneally. In other instances, the AAV vector particles of the disclosure are injected directly into a site of inflammation in the subject, a local disease site in the subject, a LN, an organ, a tumor, and the like. It should be understood that the method and compositions that would be useful in the present disclosure are not limited to the particular formulations set forth in the examples. In certain embodiments, the compositions of the disclosure are formulated using one or more pharmaceutically acceptable excipients or carriers. In certain embodiments, the pharmaceutical compositions of the disclosure comprise a therapeutically effective amount of a compound of the disclosure and a pharmaceutically acceptable carrier. The carrier can be a solvent or dispersion medium containing, for example, saline, buffered saline, water, ethanol, polyol (for example, glycerol, propylene glycol, and liquid polyethylene glycol, and the like), suitable mixtures thereof, and vegetable oils. The proper fluidity can be maintained, for example, by the use of a coating such as lecithin, by the maintenance of the required particle size in the case of dispersion and by the use of surfactants. Prevention of the action of microorganisms can be achieved by various antibacterial and antifungal agents, for example, parabens, chlorobutanol, phenol, ascorbic acid, thimerosal and the like. In many cases, it is advisable to include isotonic agents, for example, sugars, sodium chloride, or polyalcohols such as mannitol and sorbitol, in the composition. Formulations can be employed in admixtures with conventional excipients, i.e., pharmaceutically acceptable organic or inorganic carrier substances suitable for any suitable mode of administration, known to the art. The pharmaceutical preparations can be sterilized and if desired mixed with auxiliary agents, e.g., lubricants, preservatives, stabilizers, wetting agents, emulsifiers, salts for influencing osmotic pressure buffers, coloring, flavoring and / or aromatic substances and the like. They can also be combined where desired with other active agents, e.g., analgesic agents. The practice of the present disclosure employs, unless otherwise indicated, conventional techniques of molecular biology (including recombinant techniques), microbiology, cell biology, biochemistry, and immunology, which are well within the purview of the skilled artisan. Such techniques are explained fully in the literature, such as, “Molecular Cloning: A Laboratory Manual”, fourth edition (Sambrook, 2012); 30 “Oligonucleotide Synthesis” (Gait, 1984); “Culture of Animal Cells” (Freshney, 2010); “Methods in Enzymology” “Handbook of Experimental Immunology” (Weir, 1997); “Gene Transfer Vectors for Mammalian Cells” (Miller and Calos, 1987); “Short Protocols in Molecular Biology” (Ausubel, 2002); “Polymerase Chain Reaction: Principles, Applications and Troubleshooting”, (Babar, 2011); “Current Protocols in Immunology” (Coligan, 2002). These techniques are applicable to the production of the polynucleotides and AAV particles of the disclosure, and, as such, may be considered in making and practicing the disclosure. Attention is also directed to C. Himeda, Hum Gene Ther.2024 Jul 6 doi: 10.1089 / hum.2024.041, which is incorporated herein by reference in its entirety. It should be understood that the method and compositions that would be useful in the present disclosure are not limited to the particular formulations set forth in the examples. The following examples are put forth so as to provide those of ordinary skill in the art with a complete disclosure and description of how to make and use the cells, expansion and culture methods, and therapeutic methods of the disclosure, and are not intended to limit the scope of what the inventors regard as their disclosure. EXPERIMENTAL EXAMPLES The disclosure is further described in detail by reference to the following experimental examples. These examples are provided for purposes of illustration only, and are not intended to be limiting unless otherwise specified. Thus, the disclosure should in no way be construed as being limited to the following examples, but rather, should be construed to encompass any and all variations which become evident as a result of the teaching provided herein. Without further description, it is believed that one of ordinary skill in the art can, using the preceding description and the following illustrative examples, make and utilize the compounds of the present disclosure and practice the claimed methods. The following working examples, therefore, specifically point out the preferred embodiments of the present disclosure and are not to be construed as limiting in any way the remainder of the disclosure. The materials and methods are now described. Study Design. The goal of this study was to re-engineer and validate the CRISPRi platform for ultimate rAAV-mediated therapeutic delivery and high-level expression in all skeletal muscles. This involved: 1) modifying the FSHD-specific regulatory cassette to increase its activity in soleus and diaphragm, 2) re-engineering the CRISPRi platform into AIO vectors, and 3) testing the new single-vector system in FSHD myocytes in culture and in an FSHD xenograft mouse model. Two experimental systems were used: 1) primary FSHD1 and FSHD2 myocytes, and 2) FSHD1 xenografted mice. Therapeutic cassettes were delivered in LV for transduction of primary myocytes in culture, or in AAV vectors for efficient delivery to skeletal muscles in vivo. All experiments (biological replicates) in primary cells were performed at least four times for gene expression analysis by qRT-PCR. AAV transductions of AIO vectors utilized 6-9 mice for each treatment. Plasmids. dSaCas9 constructs were designed with the HLH regulatory cassette, which is the FSHD-specific regulatory cassette disclosed elsewhere herein with the following modification: the additional Right E-box was replaced with the original Left E-box from the CKM enhancer. The HLH cassette was designed upstream of the SV40 bipartite nuclear localization signal flanking dSaCas9, which was fused in-frame to one of five repressor domains (the MeCP2 TRD, the HP1α or HP1γ CS domain and CTE, the SUV39H1 SET domain, or the KRAB TRD) and HA tag, followed by the SV40 late pA signal. This was followed immediately by the U6 promoter driving an sgRNA targeted to the DUX4 promoter / exon 1, the SaCas9- optimized scaffold, and cPPT / CTS. Constructs were synthesized in pUC57 and sequenced by GenScript Biotech, then cloned into a pRRLSIN LV vector for transduction of primary FSHD myocytes. pRRLSIN.cPPT.PGK-GFP.WPRE was a gift from Didier Trono (Addgene plasmid # 12252). MyoAAV2A and rAArh74 vectors were produced by GENEWIZ, LLC (South Plainfield, NJ). Cell culture, transient transfection, and LV transduction. Myogenic cells derived from biceps muscle of an FSHD1 patient (17Abic) were obtained from the Sen Paul D. Wellstone Cooperative Research Center FSHD cell repository and grown as described. For xenograft transplantation, immortalized myoblasts derived from biceps muscle of an FSHD1 patient (15Abic) were similarly obtained from the Wellstone FSHD cell repository and expanded in culture prior to injection. FSHD2 myoblasts (18MB051) were a gift from the University of Rochester and grown as described. LV particles were generated using 293T packaging cells, as described. At ~70-80% confluency, myoblasts were subjected to four serial infections, as described, and allowed to self-differentiate. FSHD1 myocytes were harvested at 7 days and FSHD2 myocytes at 9 days following the last round of infection. Quantitative reverse transcriptase PCR (qRT-PCR). Total RNAs were extracted using TRIzol (Invitrogen) and purified using the RNeasy Mini kit (Qiagen) after on-column DNase I digestion. From cultured myocytes, total RNA (2 μg) was used for cDNA synthesis using oligo dT and Superscript III Reverse Transcriptase (Invitrogen); DUX4-fl was amplified by qPCR using 200 ng of cDNA, and other genes were amplified using 10-20 ng of cDNA, as described. Oligonucleotide primer sequences are as reported. AAV transduction of AIO CRISPRi system in human xenografted mice. All animal experiments were approved by the Institutional Animal Care and Use Committee of the University of Nevada, Reno. All mice were anesthetized prior to injection. Human xenografted mice were created essentially as described (Mueller et al 2019 Exp Neurol; Sakellariou et al 2016 Skelet Muscle). Briefly, the hindlimbs of 8-week-old immunodeficient NRG mice were X- irradiated to prevent regeneration of murine muscle. Five days later, the irradiated TAs were injected with BaCl2 to eliminate the majority of mouse muscle tissue. The following day, 2x106immortalized FSHD1 myoblasts (15Abic) were injected into the TA compartments. Over the next 4 weeks, intermittent neuromuscular electrical stimulation (iNMES) of the peroneal nerve was performed to induce repeated maximal contractions of the engrafted TA muscles. At 4 weeks post-engraftment, the AIO CRISPRi system was: 1) injected intramuscularly into xenografts in rAAVrh74 vectors (rAAVrh74.TRD- DUX4 or rAAVrh74.TRD-NT) at 1x1013GC / kg (~2.5- 3x1011GC / TA) or 2) injected systemically, via ROI, in MyoAAV2A vectors (MyoAAV2A.TRD- DUX4 or MyoAAV2A.TRD- NT) at 5x1013GC / kg. Four weeks post- injection, engrafted TAs were dissected for analysis of DUX4-fl and target gene expression. Statistical Analysis. Experiments in primary cells were performed using at least four biological replicates, and in vivo experiments were performed using at least six mice for each treatment. All data was analyzed on Prism using an unpaired, two-tailed Student’s t-test (p values: *p<0.05, **p<0.01, ***p<0.001).

[0002] Table 1. Gene expression regulatory cassettes, vectors and DUX4-targeting sgRNAs

[0003] Example 1: High activity, muscle-specific regulatory cassettes with no or low expression in cardiac muscle. The goal of the studies of the present disclosure was to design a highly minimized skeletal muscle-specific regulatory cassette for use in a CRISPR inhibition approach to Facioscapulohumeral muscular dystrophy (FSHD). To accommodate all therapeutic CRISPR components within a single rAAV vector required minimizing current regulatory cassettes. Building on previous work (Salva, M.Z., et al., Mol Ther, 2007.15(2): p.320-9. and Himeda, C.L., et al., Methods Mol Biol, 2011.709: p.3-19) and taking into account that cardiac muscle is not involved in FSHD, a minimized skeletal muscle regulatory cassette was designed to drive the expression of larger therapeutic components. Several muscle-specific regulatory cassettes optimized for expression in striated muscles have been developed (PCT application no: WO2022216988A2) and are being actively used in both academic and clinical settings. However, inconsistent nomenclature among users is a serious issue, with researchers often referring to different cassettes by the same name (e.g., the “tMCK” cassette in Addgene plasmid #105556 uses three copies of the wild-type Ckm enhancer, while “tMCK” in Addgene plasmid #149410 uses three copies of a modified Ckm enhancer). Although the significance of these differences is unclear, they can certainly complicate comparisons of efficacy and specificity between studies. Starting with the well-established and widely used CK8 cassette, which is a modified version of three CKM enhancers upstream of the CKM promoter, additional sequences between elements were removed, and the CarG and AP2 sites, which are dispensable for expression in skeletal muscle, were deleted (FIG.1). The Left E-box sequence was also mutated to create an additional Right E-box, a change that was reported to increase activity in skeletal myocytes (Nguyen et al., (2003) J Biol Chem.278(47): p46494-505 and Hauser et al. (2000) Mol Ther. 2(1): p16-25), and the promoter was reduced to the 80-bp basal sequence (Donoviel et al., (1996) Mol Cell Biol.16(4): p1649-58). This cassette was highly active in all skeletal muscles tested except for soleus, extensor digitorum longus (EDL), and diaphragm; it was virtually inactive in heart and in non-muscle tissues (Himeda et al. (2021) Mol Ther Methods Clin Dev.20: p298- 311). Thus, we named this regulatory cassette No Heart (NH). Importantly, NH is active in most skeletal muscles, the critical target tissue for FSHD and a host of other skeletal myopathies, and the absence of heart expression is inconsequential for FSHD since heart is not pathologically affected (Galetta et al. (2005) Neuromuscul Disord.15(6): p403-8; van Dijk et al. (2014) Funct Neurol.29(3): p159-65; Ducharme-Smith et al. (2021) Front Neurol.12: p668180). While NH is highly active in most fast-twitch muscles, one weakness is the extremely low activity in soleus, EDL, and diaphragm (Himeda et al. (2021) Mol Ther Methods Clin Dev. 20: p298-311). To address this, we redesigned NH to replace the additional Right E-box with the original Left E-box from the Ckm enhancer (Himeda, C.L., et al., Methods Mol Biol, 2011.709: p.3-19) (FIG.1). Following the analysis described below, this cassette was named Have a Little Heart (HLH). In vivo activities of the two cassettes were compared directly using systemic rAAVrh74-mediated transgene delivery to wild-type mice. Viral particles were delivered by retro-orbital injection (2.6x1014genome copy [GC] / kg body weight), and mCherry reporter activity (assessed as epi-fluorescence in abdominal and pectoral muscles) was monitored over time. Over ten weeks of monitoring, HLH showed much higher skeletal muscle activity than NH at every time point (FIG.2). Most notably, HLH rapidly achieved high expression; within just two weeks of delivery, total flux of HLH (ave.1.21 x 1011) was already 95% of peak total flux of NH observed after 8 weeks of delivery (ave.1.27 x 1011), reaching 485% at 3 weeks (ave.6.16 x 1011) (FIG.2A). The total flux is the epi-fluorescence signal (radiance) summed over the area where signal was detected, and may vary between animals; however, even by the maximum radiance measurement (the higest radiance for a pixel in the field), HLH outperformed NH (FIG. 2B); HLH showed 81% of peak NH maximum radiance by the first week (ave.3.74 x 109vs 4.64 x 109 of NH at 6 weeks), increased to 165% at 2 weeks (ave.7.63 x 109), and reached 606% at 3 weeks (ave.2.81 x 1010) post ROI. Overall, HLH displayed 5-6X higher activity than NH in abdominal / pectoral muscles. To further evaluate both cassettes in other muscles and tissues, mice were sacrificed at 12 weeks post-injection for in vitro epi-fluorescence quantification and fluorescence imaging. As previously reported (Pozsgai et al. (2017) Mol Ther.25(4): p855-869; Potter et al. (2021) Hum Gene Ther.32(7-8): p375-389), quantitative PCR (qPCR) for viral genomes present across tissues showed that rAAVrh74 strongly transduced liver, with moderate transduction of heart, kidney, and skeletal muscles (FIG.5). Nonetheless, both cassettes maintained high activity across striated muscles, with HLH exhibiting 7.4-36.5X higher activity than NH, and no activity in non-muscle tissues (FIGs.2-4, 6-9). Mice injected with NH-mCherry in rAAVrh74 showed strong expression in tibialis anterior (TA), gastrocnemius (GA), and quadriceps (QUA), as well as pectoral, abdominal, back, and facial muscles (FIGs.3-4, 6). Expression was virtually undetectable in soleus (SOL), EDL, diaphragm, and heart (FIGs.3-4), even at a higher exposure (FIG.6), and in non-muscle tissues (FIG.7). This recapitulates the expression pattern we observed with this cassette delivered in AAV9 virions (Himeda et al. (2021) Mol Ther Methods Clin Dev.20: p298-311), confirming that low activity in certain skeletal muscles and virtually undetectable activity in the heart is intrinsic to NH and not due to differences in vector transducibility. Restoration of the left E-box in HLH (FIG.1) dramatically improved reporter expression in all fast-twitch muscles, provided low expression in the heart, and most importantly allowed for moderate expression in SOL, EDL, and diaphragm (FIGs.3-4, 8). The total flux measurement showed 8.6, 12.3, 20, and 36.5X higher mCherry expression with HLH vs NH in QUA, GA, TA, and EDL muscles (FIG.3A), and their high expression turned muscles pink even under visible light (FIG.4). By contrast, low mCherry signals in the heart despite its size and higher AAV transducibility than skeletal muscles indicate that this cassette has low activity in the heart. To eliminate the influence of tissue size on signal measurement, we used max radiance data from the in vitro optical imaging analysis to compare mCherry signals in skeletal muscles and heart (FIG. 3B), and identified high to low HLH activity as follows: TA = GA = QUA (high: ~2.5X) > EDL = abdomen (moderate: 1X) > heart = SOL (low: ~0.3X). Since max radiance of the HLH mCherry signal in abdominal muscle was 2.5x1011and 5.12X more than NH (4.96x1010), comparative HLH activities over NH (abdominal activity = 1) are TA = GA = QUA (high: ~12.8X) > EDL = abdomen (moderate: 5.1X) > heart = SOL (low: ~1.5X). We conclude that HLH displays extremely high activity in most skeletal muscles, with no detectable expression in non-muscle tissues (FIG.9). Example 2: All-in-one vectors for epigenetic CRISPR inhibition of DUX4-fl in facioscapulohumeral muscular dystrophy Facioscapulohumeral muscular dystrophy (FSHD) (MIM 158900 and 158901) is the third most common muscular dystrophy, and one for which no cures or ameliorative treatments exist. All forms of the disease are caused by epigenetic dysregulation of the D4Z4 macrosatellite repeat array at chromosome 4q35, which is normally silenced in adult somatic cells. FSHD1, the most common form of the disease, is linked to contractions at this array, resulting in chromatin relaxation. FSHD2 is caused by mutations in proteins that maintain epigenetic silencing of the D4Z4 array, leading to a similar chromatin relaxation. In both forms of the disease, loss of epigenetic repression leads to aberrant expression of the DUX4 retrogene in skeletal muscle. DUX4, a cleavage-stage pioneer transcription factor, activates an early embryonic program, which causes pathology when misexpressed in adult skeletal muscle. Although an intact DUX4 open reading frame resides in every D4Z4 repeat unit in the macrosatellite array, only the full- length DUX4 mRNA (DUX4-fl) encoded by the distal-most repeat is stably expressed and translated due to the polyadenylation signal (PAS) residing in an exon distal to the array in disease-permissive alleles. Thus, FSHD is a toxic gain-of-function disease. While DUX4 and its downstream pathways offer numerous potential therapeutic targets, correcting the fundamental epigenetic dysregulation in FSHD may prove to be the most effective and economical avenue of therapy. CRISPR technology provides a means for modifying specific regions of the human genome, and thus, the ability to target the root cause of a disease. While others have attempted CRISPR editing to remove the DUX4 PAS, we have focused on developing a CRISPR inhibition (CRISPRi) approach as the safer alternative and one which is ideally suited to FSHD. Our goal is to use CRISPRi to correct the epigenetic dysregulation in FSHD and therapeutically reduce pathogenic DUX4 expression. The development of a CRISPRi platform for FSHD disclosed herein is an evolution from previously disclosed systems using small transcriptional inhibitors (e.g. WO2018 / 057863) to more powerful epigenetic repressors. However, for clinical use, gene therapies utilizing recombinant adeno-associated viral (rAAV) vectors should use therapeutic cassettes contained within single vectors. Eliminating the need for two or more vectors is critical for increasing the efficiency of delivery, lowering the high cost of therapy, and reducing the immunotoxicity associated with high viral doses. Thus, the therapeutic cassettes disclosed herein have been re- engineered to accommodate all CRISPRi components within all-in-one (AIO) vectors. Additionally, these regulatory cassettes are optimized for high activity in FSHD-affected tissues with low to no activity in unaffected tissues, which further increases the potential gene therapy safety profile. The studies herein demonstrate that the CRISPRi platform of the present disclosure is effective in a single-vector system, and that the smallest and most specific effector represses DUX4-fl in both FSHD1 and FSHD2 myocytes, as well as in a human xenograft mouse model of the disease. The goal of the studies of the present disclosure was to re-engineer a CRISPRi platform for ultimate rAAV-mediated therapeutic delivery and high-level expression in all skeletal muscles. Disclosed previously, an FSHD-optimized regulatory cassette that is highly active in most fast-twitch muscles with no detectable activity in the heart was developed (Himeda et al 2021 Mol Ther Methods and Clin Dev.20: p.298-311.). Due to the lack of activity in cardiac muscle, this skeletal muscle regulatory cassette was renamed No Heart (NH). However, one weakness in NH is the lack of activity in soleus and diaphragm. To address this, the regulatory cassette was redesigned (FIG.10) to replace the additional Right E-box with the original Left E- box from the CKM enhancer (Himeda et al 2011 Methods Mol Biol.709: p.3-19.), a change that increases activity in all skeletal muscles, while providing low activity in cardiac muscle and no detectable activity in non-muscle tissue. While expression in the heart is not necessary for an FSHD-specific therapeutic cassette, targeting CRISPRi components to DUX4 in a tissue where the locus is already repressed (such as cardiac muscle) shouldn't cause any negative effects. Due to its low activity in cardiac muscle, this new regulatory cassette was named Have a Little Heart (HLH). CRISPRi platforms for human gene therapy are limited by the large size of Cas9 targeting proteins, which take up most of the available space in rAAV vectors. While this is not a stumbling block for editing approaches that rely only on expression of Cas9 and sgRNAs, engineering therapeutic cassettes that fit within the AAV packaging limit is extremely challenging for approaches that utilize dCas9 fused to effector proteins. In a second-generation CRISPRi platform (Himeda et al 2021 Mol Ther Methods and Clin Dev.20: p.298-311.), a two- vector system was used containing: 1) a minimized skeletal muscle-specific regulatory cassette driving dSaCas9 fused to one of several small epigenetic repressors, and 2) a DUX4-targeting sgRNA (FIG.10B). To accommodate these components within single rAAV vectors required further minimization of the therapeutic cassettes. A plethora of Cas orthologs has been described in recent years. While some of these, such as CjCas9, are smaller than SaCas9, none are as well-characterized or have proven more effective when fused to an effector, and some (including CjCas9) have the disadvantage of a more stringent PAM requirement which severely limits DUX4 targeting. Thus, the decision was made to retain dSaCas9 in the therapeutic cassettes and attention was turned to minimizing the epigenetic effectors. Specifically, HP1a and HP1y were trimmed to their essential chromo shadow (CS) domain and C-terminal extension (CTE) sequences, and the pre- and post-SET domains were eliminated from the SUV39H1 cassette. Each AIO therapeutic cassette contains: 1) the HLH regulatory cassette driving dSaCas9 fused to one of five minimal repressors: the MeCP2 transcriptional repression domain (TRD), the HP1a or HP1y CS domain and CTE, the SUV39H1 SET domain, or the KRAB TRD, and 2) the U6 promoter driving an sgRNA targeting the DUX4 promoter / exon 1 or a non-targeting control sgRNA (FIG.10C). For each repressor, the targeting sgRNA was used that proved most effective previously (Himeda et al 2021 Mol Ther Methods and Clin Dev.20: p.298-311.). While the size of each therapeutic cassette was restricted to ~4.4kb for efficient full-length packaging into AAV vectors (Table 2), all cassettes were initially engineered in lentiviral (LV) vectors for transduction of cultured myocytes. Next, the AIO CRISPRi vectors were tested in FSHD1 myocytes as previously described (Himeda et al 2021 Mol Ther Methods and Clin Dev.20: p.298-311.) in order to validate the functionality of both the single-vector system and effectors that were minimized. Targeting either the MeCP2 TRD or the KRAB TRD to DUX4 (TRD-DUX4 or KRAB-DUX4) yielded a ~50% reduction in DUX4-fl levels (FIG.11). This is equivalent to the level of repression achieved with these effectors in the two-vector system. Similarly, targeting the CS domain and CTE of either HP1aor HP1yto DUX4 (HP1a-DUX4 or HP1y- DUX4) also repressed DUX4-fl by ~50% (FIG. 11). Importantly, this is equivalent to the levels of repression achieved with the full-length effector proteins in the two-vector system. By contrast, targeting the SUV39H1 SET domain to DUX4 (SET-DUX4) yielded no change in DUX4-fl levels (FIG.11), indicating that even in the context of fusion to dSaCas9 and direct targeting, the pre- and post-SET domains are indispensable for repression by the enzymatic SET domain. As levels of DUX4-FL protein are low and difficult to assess in FSHD myocytes, DUX4- FL target gene expression is routinely assessed as the more reliable assay and relevant functional readout of DUX4 activity. As expected, levels of DUX4-FL targets MBD3L2 and TRIM43 were reduced by ~40-50% in cells treated with each effector (FIG.11), similar to the levels of repression achieved in the two-vector system (Himeda et al 2021 Mol Ther Methods and Clin Dev.20: p.298-311.). In order to rule out any nonspecific effects on muscle differentiation, levels of Myosin heavy chain 1 (MYH1) were assessed in the treated cells. Interestingly, MYH1 levels were slightly reduced in cells treated with HP1a-DUX4, HP1y-DUX4, or SET-DUX4 (FIG.11). By contrast, MYH1 expression was unaffected in cells treated with TRD-DUX4 or KRAB-DUX4 (FIG.11), indicating that lower levels of DUX4-fl in these cells are not due to impairment of differentiation. In previously disclosed studies employing the two-vector system, the effects on the muscle transcriptome of targeting each epigenetic regulator to DUX4 with the most effective sgRNAs were determined. The MeCP2 TRD and HP1a proved the most specific, yielding 0 significant off-target effects that could not be attributed to viral transduction, compared to 8 for HP1y and 37 for KRAB (Himeda et al 2021 Mol Ther Methods and Clin Dev.20: p.298-311.). While the minimized versions of HP1a and HP1y remained as effective as the full-length proteins in mediating repression of DUX4-fl and DUX4-FL targets, the slight (~20-25%) but significant repression of MYH1 suggests that in both cases, the CSD and CTE alone are less specific than the full-length proteins. Thus, the most effective and specific repressor (TRD- DUX4) was selected for testing in FSHD2 myocytes in culture. Comparing the two-vector and single-vector systems in FSHD2 myocytes, it was found that the AIO system was equally effective at reducing DUX4-fl levels (FIG.12). The kinetics of target reduction appear to be slightly enhanced using the single-vector system, as DUX4-FL targets were reduced by ~80-85% (vs. a ~60-70% reduction with the two-vector system) (FIG. 12). Additionally, compared to the 50% reduction of DUX4 targets achieved by TRD-DUX4 in FSHD1 myocytes (FIG.11), CRISPRi mediated by the MeCP2 TRD appears to be even more effective in FSHD2 myocytes. Even ZSCAN4, a DUX4 target that is typically not repressed within the timeframe that FSHD myocytes are viable in culture, was reduced as effectively as the other targets in FSHD2 cells (FIG.12). To test the effectiveness of the CRISPRi platform in vivo, a human xenograft mouse model was utilized containing mature FSHD myofibers (Mueller et al 2019 Exp Neurol; Sakellariou et al 2016 Skelet Muscle.20: p.298-311.). As these mice contain a pathogenic D4Z4 array from an FSHD patient which maintains the endogenous nuclear context of the human FSHD locus, they are the best available in vivo model for assessing the effects of epigenetic repressors targeted to the disease locus. Immortalized FSHD1 myoblasts were injected into the TA muscle compartment of immunodeficient NRG mice. At 4 weeks post-engraftment, the AIO CRISPRi system was: 1) injected intramuscularly into xenografts in rAAVrh74 vectors (rAAVrh74.TRD- DUX4 or rAAVrh74.TRD-NT) at 1x1013GC / kg, or 2) injected systemically, via retro-orbital injection (ROI), in MyoAAV2A vectors (MyoAAV2A.TRD-DUX4 or MyoAAV2A.TRD-NT) at 5x1013GC / kg. Four weeks post-injection, expression of DUX4-fl and the mouse homologs of two direct DUX4-FL target genes were assessed by qRT-PCR in the injected xenografts. A confounding factor in determining the efficacy of any DUX4-targeted treatment is the high variability in DUX4-fl levels across samples and over time. This has been well-documented in primary FSHD myocytes and in xenograft studies using cells and tissue from multiple sources (immortalized FSHD1 and FSHD2 myoblasts, and muscle from biopsy and autopsy). Thus, extreme variability in the expression of DUX4-fl in control-treated xenografts was expected. In TRD-DUX4-treated xenografts, consistent clustering of DUX4-fl levels at the low end of this range would be considered successful inhibition. Indeed, despite the expected high variability in levels of DUX4-fl in control-treated xenografts, treatment with rAAVrh74.TRD-DUX4 yielded a ~54% reduction in levels of DUX4- fl in xenografts from IM-injected mice, although levels of two DUX4 targets, TRIM43 and MBD3L2, were not decreased at 4 weeks post-treatment (FIG.13A). Strikingly, treatment with MyoAAV2A.TRD-DUX4 reduced DUX4-fl levels by ~80% in xenografts from systemically injected mice, and levels of MBD3L2 were reduced by ~52% (FIG.13B). Over the past few years, several groups have attempted CRISPR editing of the FSHD locus. Recently, the Dumonceaux lab demonstrated that editing the DUX4 exon 3 PAS (by Cas9 or TALENs) is highly inefficient (Joubert, R., et al. (2020). J Pers Med.11). In edited clones, pathogenic DUX4 levels are reduced, but not silenced, likely due to compensation by a cryptic PAS; the authors concluded that this is not a viable therapeutic strategy for FSHD. Another group attempting a similar approach reported that CRISPR editing to delete the exon 3 PAS successfully reduced D4Z4 transcripts and expression of DUX4 target genes in immortalized FSHD1 myoblasts; however, this was also very inefficient (Das, et al. (2021) Sci Rep 11, 12598. 10.). A different editing approach, RNA-programmable base editing targeting the DUX4 PAS, reduced DUX4 and its target genes within edited clones of both FSHD1 and FSHD2 myoblasts (Sikrova et al 2021 Mol Ther.25, p.342-354.). Although the efficiency was only 18%, a cursory assessment of specificity was encouraging. Finally, Cas9-mediated correction of an SMCHD1 intronic variant restored SMCHD1 expression to healthy levels and reduced DUX4 expression in a single FSHD2 patient cell line (Goossens et al 2019 J Med Genet.10.1136 / jmedgenet-2019- 106402.). While these proof-of-concept studies confirmed that FSHD1 and FSHD2 are amenable to CRISPR editing strategies in vitro, they also confirm that these techniques lack the efficiency needed to be clinically viable even under the ideal conditions used in the lab for delivery and selection. In addition, the global genome specificity for these editing approaches has yet to be addressed. Off-target genomic editing, which would result in permanent heritable mutations, could be catastrophic in vivo even at very low efficiencies. In contrast, the studies presented herein have taken a CRISPRi approach to FSHD to mitigate the concerns related to genome editing, and because it is ideally suited to a disease caused by the pathogenic misexpression of a powerful transcription factor. Here, the CRISPRi platform has been re-engineered to a single-vector system in which all therapeutic components can be packaged into rAAV vectors for gene therapy. Of the effectors tested, the MeCP2 TRD has proven to be the smallest and most specific repressor, causing no significant adverse effects on the muscle transcriptome. In both FSHD1 and FSHD2 myocytes, TRD-DUX4 is equally effective in a single-vector vs. a two-vector system. In FSHD1 xenografts, our single-vector TRD-DUX4 platform in either rAAVrh74 or MyoAAV2A effectively reduces levels of DUX4-fl. Importantly, the most therapeutically relevant system (systemic delivery using the highly transducible MyoAAV2 vector) yielded a striking ~80% reduction of DUX4-fl. While DUX4-FL targets were mostly unaffected in xenografts at 4 weeks post-treatment, the kinetics of target gene expression are uncharacterized in FSHD xenografts, which (unlike patient biopsies) are composed of newly regenerated muscle fibers in an immune-compromised environment. Many investigators rely exclusively on a limited panel of DUX4-FL target mRNAs as convenient surrogates for DUX4-fl expression; however, this is problematic for several reasons: 1) it is unknown which targets, if any, are responsible for FSHD pathology; 2) the kinetics of target gene expression are complicated and may vary among patients; and 3) many targets are regulated in a DUX4-independent fashion, changing expression during normal muscle differentiation even in healthy cells. The data disclosed herein strongly supports that when testing DUX4-targeted therapeutics in human xenograft models of FSHD, levels of DUX4-fl must be assessed. While therapeutic levels of DUX4 inhibition are unknown, data from clinically affected and asymptomatic or non-manifesting FSHD subjects support the idea that any reduction in DUX4 expression will have therapeutic benefit. Ideally, the CRISPRi approach of the present disclosure provides stable repression of DUX4 that does not rely on continuous, lifelong expression of the transgene. This may be achieved through the recruitment of DNA methyltransferases (DNMTs) to the CRISPRi repressed locus; however, the most direct way to achieve stable silencing might be targeting DNMTs to DUX4. While DNMTs are too large to be used in conjunction with any full-length Cas ortholog in AAV, the catalytic domains of DNMT3A / B and the interacting domain of DNMT3L are small enough to be used with the newly described mini versions of dSaCas9. Additionally, the full-length versions of HP1α or HP1γ, used in conjunction with a mini-Cas9, might provide an alternative means of achieving stable repression, without the loss of specificity observed using truncated versions of these repressors. Studies exploring the utility of such constructs as well as the long-term persistence of the CRISPRi platform in xenografted mice are underway. Determining the stability of DUX4 repression mediated by CRISPRi is a critical goal, since current rAAV vectors for gene therapy can only be administered once. Whether the transduced vector will eventually be diluted past the point of therapeutic efficacy is unknown, but rAAV episomes have shown remarkable persistence in skeletal muscle, a largely quiescent tissue, assembling into active chromatin and mediating transgene expression for several years in the muscles of non-human primates. Overall, the present disclosure demonstrates further improvements in vector and cassette design that allow all CRISPRi therapeutic components to be included in single rAAV vectors, a critical preclinical milestone in the development of gene therapy for FSHD. Table 2. AIO CRISPRi vectors using minimized epigenetic repressors. Shown are the epigenetic repressors / domains used in the original two-vector CRISPRi system targeting DUX4 and their minimized versions used in the AIO single-vector system. All minimized therapeutic cassettes fit within the 4.4-kb packaging capacity of rAAV vectors. Abbreviations: transcription repression domain (TRD), chromo shadow domain (CSD), C- terminal extension (CTE). Enumerated Embodiments The following enumerated embodiments are provided, the numbering of which is not to be construed as designating levels of importance. Embodiment 1 provides a polynucleotide encoding a muscle-specific therapeutic cassette comprising a regulatory portion comprising one or more modified enhancer sequences upstream and operably linked to a promoter which is operably linked to a payload portion comprising a first payload and a U6 promoter which is operably linked to a second payload, wherein the one or more modified enhancer sequences comprise a Trex sequence, an AT-rich sequence, a left E- box sequence, a right E-box sequence, and a MEF2 sequence, wherein the promoter is a -80 to +50 promoter containing a consensus Inr sequence, wherein the first payload is a catalytically inactive Cas9 fused to an epigenetic repressor, and wherein the second payload is a single guide RNA (sgRNA) and scaffold. Embodiment 2 provides the polynucleotide of embodiment 1, wherein the sgRNA targets the DUX4 locus. Embodiment 3 provides the polynucleotide of embodiment 1, wherein the sgRNA comprises a nucleotide sequence selected from the group consisting of SEQ ID NOs: 6-8. Embodiment 4 provides the polynucleotide of embodiment 1, wherein the catalytically inactive Cas9 is dSaCas9. Embodiment 5 provides the polynucleotide of embodiment 1, wherein the epigenetic repressor is selected from the group consisting of HPlα, HPlγ, the chromo shadow domain and C-terminal extension region of HPlα or HPlγ, and MeCP2 transcription repression domain (TRD). Embodiment 6 provides the polynucleotide of embodiment 1, wherein the cassette has high expression activity in skeletal muscle tissue. Embodiment 7 provides the polynucleotide of embodiment 1, wherein the cassette has low expression activity in cardiac muscle tissue compared to skeletal muscle tissue. Embodiment 8 provides the polynucleotide of embodiment 1, wherein the regulatory portion of the therapeutic cassette is encoded by a nucleic acid comprising the sequence set forth in SEQ ID NO: 2. Embodiment 9 provides the polynucleotide of embodiment 1, wherein the regulatory portion of the therapeutic cassette is encoded by a nucleic acid comprising at least 80%, at least 85%, at least 90%, at least 95%, at least 98%, and at least 99% sequence identity to the sequence set forth in SEQ ID NO: 2. Embodiment 10 provides the polynucleotide of embodiment 1, wherein the therapeutic cassette comprises a nucleic acid sequence set forth in any one of SEQ ID NOs: 3-5. Embodiment 11 provides an AAV vector comprising a muscle-specific therapeutic cassette comprising the polynucleotide of any one of embodiments 1-9. Embodiment 12 provides the AAV vector of embodiment 11, comprising an AAV capsid that is a serotype selected from the group consisting of AAV1, AAV2, AAV3, AAV3B, AAV4, AAV5, AAV6, AAV7, AAV8, AAV9, AAV12, AAV-B1, AAV-DJ, AAV-Retro, AAVrh8, AAVrh10, AAVrh25, Anc80L65, LK03, AAVrh18, rAAVrh74, AAVrh32.33, AAVrh39, AAVrh43, MyoAAV2, Oligo001, PHP-B, LICA1 or Spark100. Embodiment 13 provides the AAV vector of embodiment 12, wherein the capsid is an rAAVrh74. Embodiment 14 provides the AAV vector of embodiment 12, wherein the capsid is an AAV9. Embodiment 15 provides the AAV vector of embodiment 12, wherein the capsid is a MyoAAV2. Embodiment 16 provides the AAV vector of embodiment 12, wherein the capsid is a LICA1. Embodiment 17 provides the AAV vector of any one of embodiments 11-15, wherein the capsid has a specificity for muscle tissue. Embodiment 18 provides a composition comprising AAV vector particles comprising the polynucleotide of any one of embodiments 1-10 and a pharmaceutically acceptable carrier or excipient. Embodiment 19 provides a method of treating facioscapulohumeral muscular dystrophy (FSHD) in a subject in need thereof, comprising administering to the subject an effective amount of an AAV vector comprising a muscle-specific therapeutic cassette comprising a regulatory portion comprising one or more modified enhancer sequences upstream and operably linked to a promoter which is operably linked to a payload portion comprising a first payload and a U6 promoter which is operably linked to a second payload, wherein the one or more modified enhancer sequences comprise a Trex sequence, an AT-rich sequence, a left E-box sequence, a right E-box sequence, and a MEF2 sequence, wherein the promoter is a -80 to +50 promoter containing a consensus Inr sequence, wherein the first payload is a catalytically inactive Cas9 fused to an epigenetic repressor, and wherein the second payload is a single guide RNA (sgRNA) and scaffold. Embodiment 20 provides the method of embodiment 18, wherein the sgRNA targets the DUX4 locus. Embodiment 21 provides the method of embodiment 18, wherein the sgRNA comprises a nucleotide sequence selected from the group consisting of SEQ ID NOs: 6-8. Embodiment 22 provides the method of embodiment 18, wherein the catalytically inactive Cas9 is dSaCas9. Embodiment 23 provides the method of embodiment 18, wherein the epigenetic repressor is selected from the group consisting of HPlα, HPlγ, the chromo shadow domain and C-terminal extension region of HPlα or HPlγ, and MeCP2 transcription repression domain (TRD). Embodiment 24 provides the method of embodiment 18, wherein the therapeutic cassette comprises a nucleic acid sequence set forth in SEQ ID NOs: 3-5. Embodiment 25 provides the method of embodiment 18, wherein the AAV vector comprises an AAV capsid that is a serotype selected from the group consisting of AAV1, AAV2, AAV3, AAV3B, AAV4, AAV5, AAV6, AAV7, AAV8, AAV9, AAV12, AAV-B1, AAV-DJ, AAV- Retro, AAVrh8, AAVrh10, AAVrh25, Anc80L65, LK03, AAVrh18, rAAVrh74, AAVrh32.33, AAVrh39, AAVrh43, MyoAAV2, Oligo001, PHP-B, LICA1 or Spark100. Embodiment 26 provides the method of embodiment 24, wherein the capsid is an rAAVrh74. Embodiment 27 provides the method of embodiment 24, wherein the capsid is an AAV9 serotype. Embodiment 28 provides the method of embodiment 24, wherein the capsid is a MyoAAV2 serotype. Embodiment 29 provides the AAV vector of embodiment 12, wherein the capsid is a LICA1. Embodiment 30 provides the method of any one of embodiments 19-29, wherein the AAV vector has a specificity for muscle tissue. Embodiment 31 provides a method of introducing a transgene into a target cell, comprising contacting the cell with a polynucleotide encoding a muscle-specific therapeutic cassette comprising a regulatory portion comprising one or more modified enhancer sequences upstream and operably linked to a promoter which is operably linked to a payload portion comprising a first payload and a U6 promoter which is operably linked to a second payload, wherein the one or more modified enhancer sequences comprise a Trex sequence, an AT-rich sequence, a left E-box sequence, a right E-box sequence, and a MEF2 sequence, wherein the promoter is a -80 to +50 promoter containing a consensus Inr sequence, wherein the first payload is a catalytically inactive Cas9 fused to an epigenetic repressor, and wherein the second payload is a single guide RNA (sgRNA) and scaffold. Embodiment 32 provides the method of embodiment 29, wherein the cassette has high expression activity in skeletal muscle tissue. Embodiment 33 provides the method of embodiment 29, wherein the sgRNA targets the DUX4 locus. Embodiment 34 provides the method of embodiment 29, wherein the sgRNA comprises a nucleotide sequence selected from the group consisting of SEQ ID NOs: 6-8. Embodiment 35 provides the method of embodiment 29, wherein the therapeutic cassette comprises a nucleic acid sequence set forth in SEQ ID NOs: 3-5. Embodiment 36 provides a polynucleotide encoding a muscle-specific therapeutic cassette comprising a regulatory portion comprising one or more modified Muscle Creatine Kinase (CKM) enhancer sequences upstream and operably linked to a modified CKM promoter which is operably linked to a payload portion comprising a first payload and a promoter which is operably linked to a second payload, wherein the first payload is a catalytically inactive Cas9 (dCas9) fused to an epigenetic repressor, and wherein the second payload is a single guide RNA (sgRNA) and scaffold. Embodiment 37 provides the polynucleotide of embodiment 36, wherein the sgRNA targets the DUX4 locus. Embodiment 38 provides the polynucleotide of embodiment 36, wherein the sgRNA comprises a nucleotide sequence comprising SEQ ID NOs: 6-8, or complementary sequences thereof. Embodiment 39 provides the polynucleotide of embodiment 36, wherein the catalytically inactive Cas9 is dSaCas9. Embodiment 40 provides the polynucleotide of embodiment 36, wherein the epigenetic repressor is selected from the group consisting of HPlα, HPlγ, the chromo shadow domain and C-terminal extension region of HPlα or HPlγ, and MeCP2 transcription repression domain (TRD). Embodiment 41 provides the polynucleotide of embodiment 36, wherein the cassette has high expression activity in skeletal muscle tissue compared to other tissues. Embodiment 42 provides the polynucleotide of embodiment 36, wherein the cassette has low expression activity in cardiac muscle tissue compared to skeletal muscle tissue. Embodiment 43 provides the polynucleotide of embodiment 36, wherein the regulatory portion of the therapeutic cassette is encoded by a nucleic acid comprising the sequence set forth in SEQ ID NO: 2 or complementary sequences thereof. Embodiment 44 provides the polynucleotide of embodiment 36, wherein the regulatory portion of the therapeutic cassette is encoded by a nucleic acid comprising at least 80%, at least 85%, at least 90%, at least 95%, at least 98%, and at least 99% sequence identity to the sequence set forth in SEQ ID NO: 2 or complementary sequences thereof. Embodiment 45 provides the polynucleotide of embodiment 36, wherein the therapeutic cassette comprises a nucleic acid sequence set forth in any one of SEQ ID NOs: 3-5 or complementary sequences thereof. Embodiment 46 provides the polynucleotide of embodiment 36, wherein the promoter operably linked to the second payload is a U6 promoter. Embodiment 47 provides the polynucleotide of embodiment 36, wherein the one or more modified CKM enhancer sequences comprise a Trex sequence, an AT-rich sequence, a left E-box sequence, a right E-box sequence, and a MEF2 sequence. Embodiment 48 provides the polynucleotide of embodiment 36, wherein the promoter operably linked to the first payload is a -80 to +50 CKM promoter containing a consensus Inr sequence. Embodiment 49 provides the polynucleotide of embodiment 36, wherein the first payload is a catalytically inactive Cas9 fused to an epigenetic repressor. Embodiment 50 provides an AAV vector comprising the polynucleotide of embodiment 36. Other Embodiments The recitation of a listing of elements in any definition of a variable herein includes definitions of that variable as any single element or combination (or subcombination) of listed elements. The recitation of an embodiment herein includes that embodiment as any single embodiment or in combination with any other embodiment or portions thereof. The disclosures of each and every patent, patent application, and publication cited herein are hereby incorporated herein by reference in their entirety. While this disclosure has been disclosed with reference to specific embodiments, it is apparent that other embodiments and variations of this disclosure may be devised by others skilled in the art without departing from the true spirit and scope of the disclosure. The appended claims are intended to be construed to include all such embodiments and equivalent variations.

Claims

CLAIMS What is claimed is:

1. A polynucleotide encoding a muscle-specific therapeutic cassette comprising a regulatory portion comprising one or more modified Muscle Creatine Kinase (CKM) enhancer sequences upstream and operably linked to a modified CKM promoter which is operably linked to a payload portion comprising a first payload and a promoter which is operably linked to a second payload, wherein the first payload is a catalytically inactive Cas9 (dCas9) fused to an epigenetic repressor, and wherein the second payload is a single guide RNA (sgRNA) and scaffold.

2. The polynucleotide of claim 1, wherein the sgRNA targets the DUX4 locus.

3. The polynucleotide of claim 1, wherein the sgRNA comprises a nucleotide sequence comprising SEQ ID NOs: 6-8, or complementary sequences thereof.

4. The polynucleotide of any one of claims 1 to 3, wherein the catalytically inactive Cas9 is dSaCas9.

5. The polynucleotide of any one of claims 1 to 4, wherein the epigenetic repressor is selected from the group consisting of HPlα, HPlγ, the chromo shadow domain and C- terminal extension region of HPlα or HPlγ, and MeCP2 transcription repression domain (TRD).

6. The polynucleotide of any one of claims 1 to 5, wherein the cassette has high expression activity in skeletal muscle tissue compared to other tissues.

7. The polynucleotide of any one of claims 1 to 6, wherein the cassette has low expression activity in cardiac muscle tissue compared to skeletal muscle tissue.

8. The polynucleotide of any one of claims 1 to 7, wherein the regulatory portion of the therapeutic cassette is encoded by a nucleic acid comprising the sequence set forth in SEQ ID NO: 2 or complementary sequences thereof.

9. The polynucleotide of any one of claims 1 to 8, wherein the regulatory portion of the therapeutic cassette is encoded by a nucleic acid comprising at least 80%, at least 85%, at least 90%, at least 95%, at least 98%, or at least 99% sequence identity to the sequence set forth in SEQ ID NO: 2 or complementary sequences thereof.

10. The polynucleotide of any one of claims 1 to 9, wherein the therapeutic cassette comprises a nucleic acid sequence set forth in any one of SEQ ID NOs: 3-5 or complementary sequences thereof.

11. The polynucleotide of any one of claims 1 to 10, wherein the promoter operably linked to the second payload is a U6 promoter.

12. The polynucleotide of any one of claims 1 to 11, wherein the one or more modified CKM enhancer sequences comprise a Trex sequence, an AT-rich sequence, a left E-box sequence, a right E-box sequence, and a MEF2 sequence.

13. The polynucleotide of any one of claims 1 to 12, wherein the promoter operably linked to the first payload is a -80 to +50 CKM promoter containing a consensus Inr sequence.

14. The polynucleotide of any one of claims 1 to 13, wherein the first payload is a catalytically inactive Cas9 fused to an epigenetic repressor.

15. A polynucleotide of any one of claims 1 to 14 wherein the regulatory portion comprises 1, 2 or 3 modified Muscle Creatine Kinase (CKM) enhancer sequences upstream and operably linked to a modified CKM promoter.

16. An AAV vector comprising a muscle-specific therapeutic cassette comprising the polynucleotide of any one of claims 1-15.

17. The AAV vector of claim 16, comprising an AAV capsid that is a serotype comprising AAV1, AAV2, AAV3, AAV3B, AAV4, AAV5, AAV6, AAV7, AAV8, AAV9, AAV12, AAV-B1, AAV-DJ, AAV-Retro, AAVrh8, AAVrh10, AAVrh25, Anc80L65, LK03, AAVrh18, rAAVrh74, AAVrh32.33, AAVrh39, AAVrh43, MyoAAV2, Oligo001, PHP-B, LICA1 or Spark100.

18. The AAV vector of claim 16, wherein the capsid is an rAAVrh74.

19. The AAV vector of claim 16, wherein the capsid is an AAV9.

20. The AAV vector of claim 16, wherein the capsid is a MyoAAV2.

21. The AAV vector of claim 16, wherein the capsid is LICA1.

22. The AAV vector of any one of claims 16-21, wherein the AAV vector has a specificity for muscle tissue.

23. A composition comprising AAV vector particles comprising the polynucleotide of any one of claims 1-22 and a pharmaceutically acceptable carrier or excipient.

24. A method of treating facioscapulohumeral muscular dystrophy (FSHD) in a subject in need thereof, comprising administering to the subject an effective amount of an AAV vector comprising a muscle-specific therapeutic cassette comprising a regulatory portion comprising one or more modified Muscle Creatine Kinase (CKM) enhancer sequences upstream and operably linked to a CKM promoter which is operably linked to a payload portion comprising a first payload and a U6 promoter which is operably linked to a second payload, wherein the first payload is a catalytically inactive Cas9 (dCas9) fused to an epigenetic repressor, and wherein the second payload is a single guide RNA (sgRNA) and scaffold.

25. The method of claim 24, wherein the sgRNA targets the DUX4 locus.

26. The method of claim 24, wherein the sgRNA comprises a nucleotide sequence selected from the group consisting of SEQ ID NOs: 6-8.

27. The method of any one of claims 24 to 26, wherein the catalytically inactive Cas9 is dSaCas9.

28. The method of any one of claims 24 to 27, wherein the epigenetic repressor is selected from the group consisting of HPlα, HPlγ, the chromo shadow domain and C-terminal extension region of HPlα or HPlγ, and MeCP2 transcription repression domain (TRD).

29. The method of any one of claims 24 to 28, wherein the therapeutic cassette comprises a nucleic acid sequence set forth in SEQ ID NOs: 3-5.

30. The method of any one of claims 24 to 29, wherein the AAV vector comprises an AAV capsid that is a comprising AAV1, AAV2, AAV3, AAV3B, AAV4, AAV5, AAV6, AAV7, AAV8, AAV9, AAV12, AAV-B1, AAV-DJ, AAV-Retro, AAVrh8, AAVrh10, AAVrh25, Anc80L65, LK03, AAVrh18, rAAVrh74, AAVrh32.33, AAVrh39, AAVrh43, MyoAAV2, Oligo001, PHP-B, LICA1 or Spark100.

31. The method of claim 30, wherein the capsid is an rAAVrh74.

32. The method of claim 30, wherein the capsid is an AAV9.

33. The method of claim 30, wherein the capsid is a MyoAAV2.

34. The method of claim 30, wherein the capsid is LICA1.

35. The method of any one of claims 24-34, wherein the AAV vector has a specificity for muscle tissue.

36. A method of introducing a transgene into a target cell, comprising contacting the cell with a polynucleotide encoding a muscle-specific therapeutic cassette comprising a regulatory portion comprising one or more modified Muscle Creatine Kinase (CKM) enhancer sequences upstream and operably linked to a CKM promoter which is operably linked to a payload portion comprising a first payload and a U6 promoter which is operably linked to a second payload, wherein the first payload is a catalytically inactive Cas9 (dCas9) fused to an epigenetic repressor, and wherein the second payload is a single guide RNA (sgRNA) and scaffold.

37. The method of claim 36, wherein the cassette has high expression activity in skeletal muscle tissue compared to other tissues.

38. The method of claim 36 or 37, wherein the cassette has low expression activity in cardiac muscle tissue compared to skeletal muscle tissue.

39. The method of any one of claims 36 to 38, wherein the sgRNA targets the DUX4 locus.

40. The method of any one of claims 36 to 39, wherein the sgRNA comprises a nucleotide sequence selected from the group consisting of SEQ ID NOs: 6-8.

41. The method of any one of claims 36 to 40, wherein the therapeutic cassette comprises a nucleic acid sequence set forth in SEQ ID NOs: 3-5.

42. A polynucleotide encoding a muscle-specific therapeutic cassette comprising a regulatory portion comprising one or more modified enhancer sequences upstream and operably linked to a promoter which is operably linked to a payload portion comprising a first payload and a U6 promoter which is operably linked to a second payload, wherein the one or more modified enhancer sequences comprise a Trex sequence, an AT-rich sequence, a left E-box sequence, a right E-box sequence, and a MEF2 sequence, wherein the promoter is a -80 to +50 promoter containing a consensus Inr sequence, wherein the first payload is a catalytically inactive Cas9 fused to an epigenetic repressor, and wherein the second payload is a single guide RNA (sgRNA) and scaffold.

43. The polynucleotide of claim 42, wherein the sgRNA targets the DUX4 locus.

44. The polynucleotide of claim 42, wherein the sgRNA comprises a nucleotide sequence comprising SEQ ID NOs: 6-8, or complementary sequences thereof.

45. The polynucleotide of any one of claims 42 to 44, wherein the catalytically inactive Cas9 is dSaCas9.

46. The polynucleotide of any one of claims 42 to 45, wherein the epigenetic repressor is selected from the group consisting of HPlα, HPlγ, the chromo shadow domain and C- terminal extension region of HPlα or HPlγ, and MeCP2 transcription repression domain (TRD).

47. The polynucleotide of any one of claims 42 to 46, wherein the cassette has high expression activity in skeletal muscle tissue compared to other tissues.

48. The polynucleotide of any one of claims 42 to 47, wherein the cassette has low expression activity in cardiac muscle tissue compared to skeletal muscle tissue.

49. The polynucleotide of any one of claims 42 to 48, wherein the regulatory portion of the therapeutic cassette is encoded by a nucleic acid comprising the sequence set forth in SEQ ID NO: 2 or complementary sequences thereof.

50. The polynucleotide of any one of claims 42 to 49, wherein the regulatory portion of the therapeutic cassette is encoded by a nucleic acid comprising at least 80%, at least 85%, at least 90%, at least 95%, at least 98%, or at least 99% sequence identity to the sequence set forth in SEQ ID NO: 2 or complementary sequences thereof.

51. The polynucleotide of any one of claims 42 to 50, wherein the therapeutic cassette comprises a nucleic acid sequence set forth in any one of SEQ ID NOs: 3-5 or complementary sequences thereof.

52. The polynucleotide of any one of claims 42 to 51, wherein the promoter operably linked to the second payload is a U6 promoter.

53. The polynucleotide of any one of claims 42 to 52, wherein the one or more modified CKM enhancer sequences comprise a Trex sequence, an AT-rich sequence, a left E-box sequence, a right E-box sequence, and a MEF2 sequence.

54. The polynucleotide of any one of claims 42 to 53, wherein the promoter operably linked to the first payload is a -80 to +50 CKM promoter containing a consensus Inr sequence.

55. The polynucleotide of any one of claims 42 to 54, wherein the first payload is a catalytically inactive Cas9 fused to an epigenetic repressor.

56. The polynucleotide of any one of claims 42 to 54, wherein the first payload is a catalytically inactive Cas9 fused to an epigenetic repressor57. The polynucleotide of any one of claims 42 to 56 wherein the regulatory portion comprises 1, 2 or 3 modified enhancer sequences upstream and operably linked to a promoter.

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