Methods for non-invasive prenatal ploidy calling
The present disclosure provides methods for determining the ploidy status of a chromosome in a gestating fetus from genotypic data measured from a mixed sample of DNA comprising DNA from both the mother of the fetus and from the fetus, and optionally from genotypic data from the mother and father. The ploidy state is determined by using a joint distribution model to create a plurality of expected allele distributions for different possible fetal ploidy states given the parental genotypic data, and comparing the expected allelic distributions to the pattern of measured allelic distributions measured in the mixed sample, and choosing the ploidy state whose expected allelic distribution pattern most closely matches the observed allelic distribution pattern. The mixed sample of DNA may be preferentially enriched at a plurality of polymorphic loci in a way that minimizes the allelic bias, for example using massively multiplexed targeted PCR.
1. A method for measuring an amount of DNA from a first individual in a biological sample of a second individual, comprising:
extracting cell-free DNA of mixed origin from the biological sample, which comprises DNA from the first individual and DNA from the second individual;
performing a multiplex targeted amplification of at least 50 polymorphic loci from the cell-free DNA in a single reaction volume to obtain amplified DNA;
performing a barcoding PCR to add a sequencing tag and a sample index to obtain a barcoded sequencing library;
pooling a plurality of barcoded sequencing libraries carrying different sample indexes, wherein the plurality of barcoded sequencing libraries are obtained from a plurality of individuals, sequencing the pool of barcoded sequencing libraries together in one sequencing lane, and for each library measuring an amount of each allele at the polymorphic loci; and
determining the amount of the DNA from the first individual in the biological sample, wherein the second individual is an individual having a transplant, and the cell-free DNA of mixed origin comprises DNA from the transplant.
2. The method of claim 1 , wherein the biological sample is a blood, serum, plasma, or urine sample.
3. The method of claim 1 , wherein the multiplex targeted amplification is performed with a plurality of primer pairs each designed to amplify less than about 100 bp of DNA.
4. The method of claim 1 , wherein the multiplex targeted amplification is performed with a plurality of primer pairs each designed to amplify less than about 80 bp of DNA.
5. The method of claim 1 , wherein the multiplex targeted amplification is performed with a plurality of primer pairs each designed to amplify about 65-80 bp of DNA.
6. The method of claim 1 , wherein the multiplex targeted amplification comprises 10-30 PCR cycles.
7. The method of claim 1 , wherein the multiplex targeted amplification comprises 15 PCR cycles.
8. The method of claim 1 , wherein the multiplex targeted amplification comprises amplifying 50-5,000 polymorphic loci in a single reaction volume.
9. The method of claim 1 , wherein the multiplex targeted amplification comprises amplifying 50-500 polymorphic loci in a single reaction volume.
10. The method of claim 1 , wherein the multiplex targeted amplification comprises amplifying more than 100 polymorphic loci in a single reaction volume.
11. The method of claim 1 , wherein the multiplex targeted amplification comprises amplifying more than 200 polymorphic loci in a single reaction volume.
12. The method of claim 1 , wherein the polymorphic loci are SNP loci.
13. The method of claim 1 , wherein the sequencing is high-throughput sequencing.
14. The method of claim 1 , wherein the sequencing is sequencing-by-synthesis.
15. The method of claim 1 , wherein the method is performed without prior knowledge of genotypes of the first and second individuals.
16. The method of claim 1 , further comprising after performing the multiplex targeted amplification:
dividing the amplified DNA into a plurality of aliquots;
performing a second targeted amplification of the at least 50 polymorphic loci in the plurality of aliquots to generate a plurality of subpool amplification products, wherein subpools of the at least 50 polymorphic loci are amplified in each aliquot in a PCR reaction; and
pooling the plurality of subpool amplification products to generate pooled amplification products, wherein the barcoding PCR is either the second targeted amplification or is performed on the pooled amplification products.
17. The method of claim 16 , wherein at least one of the subpools is single-plex.
18. The method of claim 1 , wherein the multiplex targeted amplification is a PCR reaction performed with at least 100 different forward and reverse primer pairs.