Rare Variant Detection Using Unique Molecular Identifiers
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Solution Overview
Problem
Current sequencing methods are inadequate for detecting rare genetic variations, particularly those occurring at frequencies below 1%, as they often result in false positives due to experimental artifacts and are unsuitable for degraded nucleic acid samples like FFPE tissue.
Innovation Solution
The method involves splitting nucleic acid samples into pools, using molecular labeling and amplification with unique sequence tags to distinguish true variations from experimental errors, confirming variations on both strands of double-stranded molecules, and employing multiplexing and quality control measures to enhance detection fidelity.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If standard sequencing approaches are used to detect genetic variations, then sequencing capability is provided, but detection of rare variants below 1% frequency is insufficient due to limits of detection and false positives
Solution Approach 1:
The sample is divided into multiple independent amplification reactions, each targeting specific genomic loci. By segmenting the detection process into individual locus-specific reactions with unique molecular identifiers, the method achieves precise tracking of rare variants while eliminating false positives through statistical validation across multiple partitions.
Solution Approach 2:
Unique molecular identifiers (UMIs) and locus-specific tags are introduced as intermediary elements during sample preparation. These intermediaries label individual nucleic acid molecules before amplification, enabling distinction between true rare variants and amplification artifacts. The intermediaries serve as traceable markers throughout the sequencing process.
2Ease of operation
If standard sequencing is applied to degraded nucleic acid samples like FFPE tissue, then sample analysis is possible, but detection accuracy decreases due to reduced nucleic acid copies and degradation artifacts
Solution Approach 1:
Locus-specific tags and unique molecular identifiers are attached to nucleic acid molecules during the initial tagging step before any amplification or sequencing occurs. This preliminary labeling ensures that even degraded fragments retain their identity markers, enabling accurate reconstruction and validation of rare variants despite sample degradation.
Solution Approach 2:
The method incorporates validation mechanisms where detected variants are cross-checked against multiple independent signals including forward and reverse strand information, UMI consistency, and locus-specific tag matching. This feedback loop filters out degradation artifacts and confirms true variants through concordant evidence from multiple sources.
3Measurement precision
If amplification is performed to increase rare variant signals, then detection sensitivity improves, but experimental artifacts such as polymerase errors increase false positives
Solution Approach 1:
The method creates multiple copies of the original nucleic acid molecules through amplification, but each copy retains the original UMI and locus-specific tag from the template molecule. This copying approach allows reconstruction of the original molecule's identity, enabling distinction between true variants present in the original sample and errors introduced during amplification.
Solution Approach 2:
The method replaces reliance on amplification fidelity with molecular tagging and statistical validation. Instead of depending on perfect polymerase copying, the system uses UMI tracking and cross-validation across multiple amplification products to identify true variants, substituting mechanical copying accuracy with information-theoretic verification.
Data Source
AI summary
The invention generally relates to methods for distinguishing a rare genetic variation in a nucleic acid sequence.