Cas9-Mediated Sequencing for Myotonic Dystrophy Diagnosis
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Solution Overview
Problem
Current diagnostic methods for myopathies, particularly myotonic dystrophy types 1 and 2, face challenges in accurately determining large microsatellite expansions due to limitations in sequencing fully expanded alleles, lack of single-nucleotide resolution, and difficulties in detecting minor alleles and somatic mosaicism, which are crucial for understanding disease phenotype and severity.
Innovation Solution
A PCR-free Cas9-mediated sequencing method using guideRNAs for targeted DNA enrichment and long-read DNA sequencing, allowing for the precise characterization of repeat expansions in the DMPK and CNBP genes, enabling the diagnosis of myotonic dystrophy types 1 and 2 from a single biological sample with high-molecular-weight DNA.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If PCR-based approaches (SR-PCR, LR-PCR, QP-PCR) are used for DM1 and DM2 genetic testing, then detection rate reaches around 99%, but exact length of large expanded alleles cannot be defined and single-nucleotide resolution is completely lacking
Solution Approach 1:
The patent segments the diagnostic process into two distinct parts: (1) PCR-based detection to identify the presence of expanded alleles with high sensitivity, and (2) long-read sequencing to precisely characterize the repeat length and structure at single-nucleotide resolution. This segmentation allows each method to excel at its specific function without compromise
Solution Approach 2:
The patent uses long-read sequencing technology as an intermediary method that bridges the gap between PCR detection and exact repeat length determination. The sequencing reads serve as a mediator that captures both the presence and precise characteristics of expanded alleles, combining the advantages of both detection sensitivity and measurement precision
2Measurement precision
If Southern blot is used to determine exact length of large expanded alleles, then sensitivity reaches about 80%, but the procedure is time-consuming, requires large amount of DNA, and is not included in routine workflow
Solution Approach 1:
The patent replaces the mechanical Southern blot procedure with a molecular sequencing approach. Instead of using restriction enzymes, gel electrophoresis, and hybridization probes, the patent employs long-read sequencing technology that directly reads the DNA sequence, eliminating the need for complex mechanical steps while maintaining or improving measurement precision
Solution Approach 2:
The patent changes the fundamental parameter of measurement from indirect size estimation via gel migration (Southern blot) to direct sequence reading (long-read sequencing). This parameter change enables precise repeat length determination without the time-consuming and DNA-intensive Southern blot procedure, making the method suitable for routine diagnostic workflows
3Reliability
If current methods are used for molecular diagnosis, then DM1 or DM2 diagnosis can be enabled, but severe limitations exist in detecting the presence of minor alleles and the level of somatic mosaicism
Solution Approach 1:
The patent employs long-read sequencing as an intermediary technology that captures all alleles present in the sample, including minor alleles and mosaic variants. The sequencing reads serve as a comprehensive record that reveals the presence and proportion of different alleles, enabling detection of somatic mosaicism that is invisible to conventional PCR methods
Solution Approach 2:
The patent creates a comprehensive copy of the genomic region of interest through long-read sequencing. This digital copy preserves information about all alleles present in the original DNA sample, including minor variants and mosaic patterns, allowing for accurate quantification and characterization that is lost in PCR-based methods
Applied Scientific Principles
This section explains which scientific principles are used to turn an abstract innovation direction into a practical engineering solution.
Function Achieved in This Case
This method provides single-nucleotide resolution for repeat length and structure analysis, detects interruptions and mosaicism, and correlates genetic features with phenotypes, improving diagnostic accuracy and patient stratification for personalized therapies.
Implementation Method 1
A PCR-free Cas9-mediated sequencing method using guideRNAs for targeted DNA enrichment
Implementation Method 2
long-read DNA sequencing, allowing for the precise characterization of repeat expansions
Data Source
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AI summary
The present invention concerns the field of repeat expansion-linked disorder, and in particular to an in-vitro method for determining whether said subject is suffering from or has a genetic predisposition to develop such medical conditions. The invention further relates to uses of isolated oligonucleotides and a kit carrying out Cas9-mediated sequencing or PCR-free targeted long-read sequencing to be applied in translational research and in clinical settings, with ultimately strong benefits for the diagnostic workflow and genetic counselling in this class of diseases. Further described in the present invention is a method for the validation of the cut efficiency a guideRNA.