Size-based analysis of fetal or tumor DNA fraction in plasma

Patent metadata

Field	Value
Publication number	US-9892230-B2
Application number	US-201313789553-A
Country	US
Kind code	B2
Filing date	Mar 7, 2013
Priority date	Mar 8, 2012
Publication date	Feb 13, 2018
Grant date	Feb 13, 2018

Abstract

A fractional concentration of clinically-relevant DNA in a mixture of DNA from a biological sample is determined based on amounts of DNA fragments at multiple sizes. For example, the fractional concentration of fetal DNA in maternal plasma or tumor DNA in a patient's plasma can be determined. The size of DNA fragments in a sample is shown to be correlated with a proportion of fetal DNA and a proportion of tumor DNA, respectively. Calibration data points (e.g., as a calibration function) indicate a correspondence between values of a size parameter and the fractional concentration of the clinically-relevant DNA. For a given sample, a first value of a size parameter can be determined from the sizes of DNA fragments in a sample. A comparison of the first value to the calibration data points can provide the estimate of the fractional concentration of the clinically-relevant DNA.

First claim

What is claimed is:

1. A method of estimating a fractional concentration of fetal DNA in a biological sample from a female pregnant with a fetus, the biological sample including the cell-free fetal DNA and other DNA, the method comprising:
measuring an amount of DNA fragments from the biological sample corresponding to each of a plurality of sizes, the amount including the cell-free fetal DNA and the other DNA, thereby measuring amounts of DNA fragments at the plurality of sizes;
calculating, with a computer system, a first value of a first parameter based on the amounts of DNA fragments at the plurality of sizes, the first parameter providing a statistical measure of a size profile of DNA fragments in the biological sample;
obtaining one or more first calibration data points, wherein each of the one or more first calibration data points specifies a fractional concentration of fetal DNA corresponding to a calibration value of the first parameter, and wherein the one or more first calibration data points are determined from a plurality of calibration samples;
comparing the first value to a calibration value of at least one of the one or more first calibration data points; and
estimating the fractional concentration of the fetal DNA in the biological sample based on the comparison, thereby obtaining the fractional concentration using an assay that does not require a tissue-specific marker.

2. The method of claim 1 , wherein the DNA fragments correspond to one or more predetermined regions of a genome.

3. The method of claim 1 , wherein the first parameter represents an abundance of small DNA fragments relative to an abundance of large DNA fragments, and wherein the small DNA fragments have a smaller size than the large DNA fragments.

4. The method of claim 1 , further comprising
calculating one or more second values of one or more second parameters based on the amounts of DNA fragments at the plurality of sizes, the one or more second parameters providing different statistical measures of the size profile of DNA fragments in the biological sample;
obtaining one or more second calibration data points corresponding to the one or more second parameters;
comparing the one or more second values to corresponding second calibration values of the one or more second calibration data points; and
estimating the fractional concentration of the fetal DNA in the biological sample based on the comparisons involving the first value and the one or more second values.

5. The method of claim 4 , wherein the one or more first calibration data points and the one or more second calibration data points are points on a multidimensional curve and the comparisons involving the first value and the one or more second values include identifying a multidimensional point having coordinates corresponding to the first value and the one or more second values.

6. The method of claim 1 , wherein the one or more first calibration data points form a calibration curve.

7. The method of claim 1 , wherein each of the one or more first calibration data points is determined from a histogram corresponding to a different calibration sample, wherein the histogram provides amounts of DNA fragments at a plurality of sizes, and wherein at least a portion of the plurality of calibration samples have different fractional concentrations of fetal DNA.

8. The method of claim 1 , wherein measuring amounts of DNA fragments at the plurality of sizes includes:
for each of the DNA fragments from the biological sample:
measuring a size of the DNA fragment,

wherein measuring the size of the DNA fragment includes:
performing paired-end sequencing of the DNA fragment to obtain paired sequence reads;
aligning the paired sequence reads to locations in a reference genome; and
using the aligned locations to determine the size of the DNA fragment.

9. The method of claim 1 , wherein measuring amounts of DNA fragments at each of the plurality of sizes includes using electrophoresis.

10. The method of claim 1 , further comprising:
calculating the one or more first calibration data points by:
for each of the plurality of calibration samples:
measuring the fractional concentration of fetal DNA in the calibration sample;
measuring amounts of DNA fragments corresponding to the plurality of sizes; and
calculating the calibration value of the first parameter based on the amounts of DNA fragments at the plurality of sizes, the first calibration data point of the calibration sample including the calibration value and the measured fractional concentration of fetal DNA.

11. The method of claim 10 , wherein the one or more first calibration data points is a plurality of first calibration data points, the method further comprising:
determining a function that approximates the calibration values of the plurality of first calibration data points across a plurality of fractional concentrations.

12. The method of claim 11 , wherein the function is a linear function.

13. The method of claim 10 , wherein measuring the fractional concentration of fetal DNA in one of the plurality of calibration samples includes at least one of:
measuring a paternally-inherited sequence that is absent from a genome of the pregnant female; and
measuring fetal-specific epigenetic markers.

14. The method of claim 13 , wherein the fetal-specific epigenetic markers include DNA sequences that exhibit fetal or placental-specific DNA methylation patterns in maternal plasma or serum.

15. The method of claim 1 , wherein a size of the plurality of sizes is a length, a molecular mass, or a parameter that is proportional to the length.

16. The method of claim 1 , wherein at least one of the plurality of sizes corresponds to a range.

17. The method of claim 1 , wherein comparing the first value to the calibration value comprises determining if the first value is above or below the calibration value.

18. The method of claim 17 , wherein estimating the fractional concentration comprises:
determining that the fractional concentration of the fetal DNA in the biological sample is above a fractional concentration corresponding to the calibration value when the first value is above the calibration value, or
determining that the fractional concentration of the fetal DNA in the biological sample is below the fractional concentration corresponding to the calibration value when the first value is below the calibration value.

19. The method of claim 1 , wherein comparing the first value to the calibration value comprises inputting the first value into a calibration function.

20. The method of claim 19 , wherein the fractional concentration is an output value of the calibration function with the first value as an input.

21. The method of claim 1 , further comprising:
displaying, by the computer system, the estimated fractional concentration of the fetal DNA.

22. The method of claim 1 , further comprising:
comparing the fractional concentration to a threshold value,
when the fractional concentration is greater than the threshold value, performing an additional test on the biological sample, and
when the fractional concentration is not greater than the threshold value, not performing the additional test on the biological sample.

23. The method of claim 1 , wherein measuring amounts of DNA fragments at each of the plurality of sizes includes:
extracting plasma or serum from a blood sample to obtain the biological sample,
sequencing the DNA fragme

Assignees

• Univ Hong Kong Chinese

Inventors

• Lo Yuk Ming Dennis
• Chiu Wai Kwun Rossa
• Chan Kwan Chee
• Zheng Wenli
• Jiang Peiyong
• Liao Jiawei

Classifications

• C12Q1/6816

  characterised by the detection means (C12Q1/6804 takes precedence) · CPC title

• C12Q2600/112

  Disease subtyping, staging or classification · CPC title

• G16H50/20

  for computer-aided diagnosis, e.g. based on medical expert systems · CPC title

• G16B20/00

  ICT specially adapted for functional genomics or proteomics, e.g. genotype-phenotype associations · CPC title

• G16H50/30

  for calculating health indices; for individual health risk assessment · CPC title