Microsatellite Instability Detection Using Sequencing-Based Variant Allele Frequency Analysis
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Solution Overview
Problem
Current methods for evaluating microsatellite instability (MSI) in patient samples are limited by their sensitivity to germline variation, susceptibility to noisy or artifactual signals, and the need for matched normal tissue samples.
Innovation Solution
The methods involve nucleic acid sequencing data analysis to determine variant allele frequencies at multiple microsatellite loci, applying filters to exclude noise and germline alleles, and calculating an MSI score to classify samples as MSI-H, MSI-E, or MSS without the need for a matched normal sample.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If PCR-based methods are used to evaluate MSI status, then the assay can be performed with matched normal tissue samples, but the number of microsatellite loci that can be interrogated simultaneously is limited and the method requires matched normal samples for every specimen
Solution Approach 1:
The patent replaces the mechanical/chemical PCR amplification system with a sequencing-based system. Instead of using PCR to amplify and size-determine microsatellite loci, the method uses next-generation sequencing to directly sequence microsatellite regions and analyze variant allele frequencies, thereby eliminating the need for matched normal tissue samples while maintaining detection accuracy
Solution Approach 2:
The patent segments the analysis by evaluating multiple microsatellite loci independently through sequencing, allowing each locus to be analyzed for variant allele frequency. This segmentation enables the simultaneous interrogation of many more loci than traditional multiplexed PCR methods while maintaining the ability to distinguish somatic mutations from germline variants
2Quantity of substance
If existing sequencing-based approaches are used to determine MSI status, then the number of loci can be increased, but the methods are sensitive to germline variation and susceptible to noisy or artifactual signals
Solution Approach 1:
The patent implements feedback through iterative filtering and validation of sequencing data. The method applies multiple filters to exclude candidate alleles that are likely to be noise, sequencing errors, or germline alleles, and uses variant allele frequency thresholds to validate true somatic mutations, thereby improving signal reliability while maintaining high locus coverage
Solution Approach 2:
The patent changes the analytical parameter from amplicon size determination (PCR-based) to variant allele frequency measurement (sequencing-based). By measuring the frequency of variant alleles at each microsatellite locus and applying minimum allele frequency requirements, the method can reliably distinguish true somatic mutations from germline variation and sequencing noise
3Measurement precision
If matched normal tissue samples are required for every specimen, then germline polymorphisms can be distinguished from somatic mutations, but the cost and complexity of the assay increases
Solution Approach 1:
The patent enables the tumor sample itself to serve as its own control by analyzing variant allele frequencies within the tumor DNA. The method uses the tumor sample's own sequencing data to identify somatic mutations through elevated variant allele frequencies, eliminating the need for separate matched normal tissue samples and reducing assay complexity and cost
Data Source
AI summary
Methods for detecting a deficient DNA repair mechanism and/or evaluating microsatellite instability in a sample from a subject are described. The disclosed methods comprise analyzing nucleic acid sequence data for a plurality of microsatellite loci to calculate a microsatellite instability (MSI) score for the sample from a ratio of the number of microsatellite loci that exhibit variant alleles to the total number of microsatellite loci that meet, e.g., a minimum sequencing coverage requirement. The MSI score is compared a first threshold and, m some cases, to a second threshold to assign a status of high microsatellite instability′(MSI-H), microsatellite stable (MSS), or equivocal microsatellite instability (MSI-E) for the sample.