cfDNA Methylation Signatures for Tissue-of-Origin Detection
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Solution Overview
Problem
Existing methods for determining the tissue or cell origin of DNA, particularly in cell-free DNA (cfDNA), face challenges in sensitivity and specificity, especially when using clusters of adjacent CpG sites, which are limited to four or more CpGs, restricting the number of informative loci and leading to potential false signals from other cell types.
Innovation Solution
The method involves analyzing the methylation status of two or three methylation sites on a continuous DNA sequence of no more than 167 nucleotides, utilizing methylation-dependent oligonucleotides and next-generation sequencing to identify distinct methylation patterns that uniquely identify a cell or tissue of interest, minimizing noise from other cells.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If clusters of four or more adjacent CpG sites are used for tissue-specific detection, then specificity is enhanced, but the number of informative loci is limited and sensitivity is reduced
Solution Approach 1:
The invention changes the parameter of methylation site quantity from the conventional requirement of 4 or more CpGs to just 2 or 3 CpG sites. This parameter change is achieved by selecting specific genomic loci where 2-3 CpG sites exhibit highly differentiated methylation patterns between tissue types, thereby maintaining high specificity while increasing the number of available informative loci across the genome.
2Measurement precision
If clusters of four or more adjacent CpG sites are used, then tissue-specific signal is enhanced, but false signals from other cell types increase
Solution Approach 1:
The invention applies local quality by selecting specific genomic loci where 2-3 CpG sites display unique and highly differentiated methylation characteristics for each tissue type. Rather than requiring uniform clusters of 4+ CpGs everywhere, the method identifies localized regions with optimal discriminatory power, thereby enhancing tissue-specific signal while minimizing cross-reactivity and false signals from other cell types.
3Measurement precision
If longer DNA sequences are analyzed for methylation status, then more CpG sites can be included, but the method becomes less applicable to cfDNA which has size limitations
Solution Approach 1:
The invention segments the genomic DNA into specific loci containing only 2-3 CpG sites each, which can be individually analyzed within the size constraints of cfDNA fragments. This segmentation approach allows comprehensive tissue-of-origin analysis across multiple distributed loci rather than requiring analysis of long continuous sequences, making the method highly suitable for cfDNA while maintaining accurate methylation status determination.
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 approach enhances the specificity and sensitivity of tissue or cell origin identification, allowing for accurate differentiation between different cell types, even when cfDNA is present in low concentrations, and is applicable to various bodily fluids.
Implementation Method 1
The methylation status of some cytosines adjacent to guanosines in the genome (CpG sites) is typical of specific cell types. Some sites are unmethylated in a specific cell type and methylated elsewhere
Data Source
AI summary
Methods of detecting death of a cell type or tissue in a subject comprising determining the origin of cfDNA by ascertaining the methylation status of two or three methylation sites on a cfDNA molecule of no more than 167 nucleotides is provided. Methods of identifying regions of genomic DNA comprising no more than 167 nucleotides whose methylation signature distinguishes the origin of the region are also provided. Kits for use in performing the methods of the invention are also provided.