Maternal Plasma Shotgun Sequencing for Fetal Aneuploidy Detection
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Solution Overview
Problem
Current methods for diagnosing fetal aneuploidy, such as karyotyping via invasive procedures or non-invasive screening using maternal serum markers and ultrasound, pose risks to the fetus and mother and have limited reliability, while existing non-invasive tests relying on allelic variation are limited to specific populations due to the need for genetic polymorphisms.
Innovation Solution
A method involving direct shotgun sequencing of maternal plasma DNA to enrich for fetal DNA based on its shorter fragment length, followed by mapping to specific chromosomes, allowing for the detection of aneuploidy without requiring sequence differentiation between maternal and fetal DNA, using massively parallel sequencing to count sequence tags and normalize for sequencing bias.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If invasive procedures such as chorionic villus sampling and amniocentesis are used for karyotyping, then diagnostic accuracy for fetal aneuploidy is improved, but the risk to the fetus and mother increases
Solution Approach 1:
The patent extracts fetal DNA from maternal plasma, separating the diagnostic target (fetal DNA) from the source material (maternal blood). This allows non-invasive diagnosis by analyzing cell-free fetal DNA that naturally circulates in maternal circulation, eliminating the need for invasive procedures while maintaining diagnostic capability for fetal aneuploidy
Solution Approach 2:
The patent uses maternal plasma as an intermediary medium to access fetal genetic information. Instead of directly sampling fetal cells through invasive procedures, the method analyzes fetal DNA that has been released into the maternal circulation, using maternal plasma as a safe intermediary that provides indirect access to fetal genetics without physical intrusion into the fetus
2Object-affected harmful factors
If non-invasive screening using maternal serum markers and ultrasound is used, then the risk to fetus and mother is reduced, but diagnostic reliability is limited
Solution Approach 1:
The patent replaces mechanical screening methods (ultrasound) and biochemical markers with direct molecular analysis of fetal DNA. Instead of indirect mechanical imaging or serum marker measurement, the method uses DNA sequencing and quantitative PCR to directly analyze fetal genetic material, substituting indirect mechanical/biochemical detection with direct molecular characterization for improved reliability
Solution Approach 2:
The patent changes the analytical parameter from indirect serum markers to direct fetal DNA sequences. By analyzing the actual genetic material rather than proxy markers, the method transforms the diagnostic parameter from indirect biochemical indicators to direct genetic information, significantly improving diagnostic reliability while maintaining non-invasive status
3Object-affected harmful factors
If allelic variation-based non-invasive tests are used, then non-invasive diagnosis is achieved, but applicability is limited to specific populations requiring genetic polymorphisms
Solution Approach 1:
The patent creates a universal diagnostic method that works across all populations by analyzing fetal DNA sequences rather than relying on population-specific polymorphisms. The method uses quantitative comparison of fetal to maternal DNA sequences, a approach that is applicable to all individuals regardless of their genetic background, making the test universally applicable rather than population-specific
Solution Approach 2:
The patent inverts the traditional approach by not searching for fetal-specific variants against a maternal background, but rather quantifying the proportion of fetal DNA sequences among total maternal-plasma DNA. This inversion allows detection of fetal aneuploidy through sequence quantity ratios rather than quality differences, eliminating the need for population-specific polymorphism databases
4Adaptability or versatility
If digital PCR or shotgun sequencing is used to quantify fetal DNA, then polymorphism-independent detection is achieved, but sequencing bias and background maternal DNA interfere with measurement precision
Solution Approach 1:
The patent uses feedback by comparing observed sequence tag distributions against expected distributions based on known genome composition and sequencing bias patterns. The method iteratively adjusts for systematic biases by referencing control data and statistical models, using feedback loops to correct measurement errors and improve quantification accuracy of fetal DNA in the presence of maternal background
Solution Approach 2:
The patent changes multiple parameters including sequencing depth, fragment size selection, and bioinformatic filtering thresholds to optimize fetal DNA detection. By adjusting these parameters and using normalized ratios of sequence tags from different chromosomal regions, the method compensates for sequencing biases and improves measurement precision despite the challenging background of maternal DNA
Data Source
AI summary
Disclosed is a method to achieve digital quantification of DNA (i.e., counting differences between identical sequences) using direct shotgun sequencing followed by mapping to the chromosome of origin and enumeration of fragments per chromosome. The preferred method uses massively parallel sequencing, which can produce tens of millions of short sequence tags in a single run and enabling a sampling that can be statistically evaluated. By counting the number of sequence tags mapped to a predefined window in each chromosome, the over- or under-representation of any chromosome in maternal plasma DNA contributed by an aneuploid fetus can be detected. This method does not require the differentiation of fetal versus maternal DNA. The median count of autosomal values is used as a normalization constant to account for differences in total number of sequence tags is used for comparison between samples and between chromosomes.