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 of amplifying target loci in a cell-free nucleic acid sample, the method comprising:
performing in a single reaction volume multiplex polymerase chain reaction (PCR) on the cell-free nucleic acid sample comprising 200 to 2,000 target loci and either (i) 200 to 2,000 different target loci-specific PCR primer pairs, or (ii) 200 to 2,000 different target loci-specific PCR primers and a universal or tag-specific PCR primer, wherein the concentration of each PCR primer in the primer pairs or each target-specific PCR primer is from 5 nM to 20 nM and the length of the annealing step of the multiplex PCR amplification is from 10 minutes to 20 minutes, thereby producing amplified products comprising greater than 50% target amplicons that map to target loci.
2. The method of claim 1 , comprising simultaneously amplifying from 800 to 2000 distinct target loci in a single reaction volume.
3. The method of claim 1 , wherein the target loci are present in the human genome, or wherein the target loci comprise human single nucleotide polymorphisms.
4. The method of claim 1 , wherein the nucleic acid sample comprises DNA from a tumor.
5. The method of claim 1 , wherein the sample comprises DNA from an individual, and wherein the DNA comprises DNA from a cancer and DNA not from a cancer.
6. The method of claim 1 , wherein the nucleic acid sample comprises DNA from a transplant.
7. The method of claim 1 , wherein the length of the target amplicons is less than 100 nucleotides.
8. A method of amplifying target loci in a cell-free nucleic acid sample, the method comprising:
performing in a single reaction volume multiplex PCR on the cell-free nucleic acid sample comprising DNA molecules having an average length of less than 200 base pairs and including from 200 to 2,000 target loci and either (i) 200 to 2,000 different target loci-specific PCR primer pairs, or (ii) 200 to 2,000 different target loci-specific PCR primers and a universal or tag-specific PCR primer, wherein the concentration of each PCR primer in the primer pairs or each target-specific PCR primer is from 5 nM to 20 nM and the length of the annealing step of the multiplex PCR amplification is from 10 minutes to 20 minutes, thereby producing amplified products comprising greater than 50% target amplicons, wherein target amplicons are less than 100 nucleotides in length and map to target loci.
9. The method of claim 1 or 8 , wherein the nucleic acid sample comprises DNA molecules from a mixed origin.
10. The method of claim 9 , wherein the nucleic acid sample is from a cancer patient.
11. The method of claim 9 , wherein the nucleic acid sample is from an individual who has undergone transplantation.
12. The method of claim 1 , wherein the length of the target amplicons is 40-65 nucleotides.
13. The method of claim 1 , wherein the annealing step is performed at 60° C. to 65° C.