System and method for cleaning noisy genetic data from target individuals using genetic data from genetically related individuals
A system and method for determining the genetic data for one or a small set of cells, or from fragmentary DNA, where a limited quantity of genetic data is available, are disclosed. Genetic data for the target individual is acquired and amplified using known methods, and poorly measured base pairs, missing alleles and missing regions are reconstructed using expected similarities between the target genome and the genome of genetically related subjects. In accordance with one embodiment of the invention, incomplete genetic data is acquired from embryonic cells, fetal cells, or cell-free fetal DNA isolated from the mother's blood, and the incomplete genetic data is reconstructed using the more complete genetic data from a larger sample diploid cells from one or both parents, with or without genetic data from haploid cells from one or both parents, and/or genetic data taken from other related individuals.
1. A method for detecting aneuploidy in a fetus, the method comprising:
(a) measuring the amounts of genetic material at multiple loci on a chromosome or chromosome segment of interest in a sample comprising cell-free DNA derived from the fetus and from the mother of the fetus, wherein the measuring comprises amplifying at least 70 loci in a single reaction and using microarray or sequencing to detect amplified reaction products, and wherein the amount of genetic material at a particular locus is determined irrespective of the identity of the alleles at that locus;
(b) determining, on a computer, the probability of aneuploidy in the fetus by comparing the measured amounts of genetic material to an expected amount for a particular copy number; and
(c) outputting the selected probability as an indication of whether the fetus has aneuploidy.
2. The method of claim 1 , wherein the determining is performed by comparing the amount from step (a) to an expected amount, wherein the expected amount is a mean value of genetic material at multiple loci for a reference chromosome or chromosome segment that is present in two copies.
3. The method of claim 1 , wherein a microarray is used to measure the amount of genetic material at the multiple loci.
4. The method of claim 1 , wherein the amount of genetic material for at least 70 loci is measured by performing a multiplex amplification in a single reaction, and wherein a microarray is used to detect the amplified reaction products.
5. The method of claim 4 , wherein the method comprises a PCR amplification using universal amplification sequences, and wherein the multiplex amplification reaction and/or the PCR reaction comprise a ligation PCR reaction.
6. The method of claim 4 , wherein the multiple loci are loci having alleles with 100% penetrance in the population.
7. The method of claim 1 , wherein the sample comprises cell-free DNA isolated from blood from the mother of the fetus.
8. The method of claim 1 , wherein the chromosome of interest or the chromosome comprising the chromosome segment of interest is selected from the group consisting of chromosome 13, chromosome 18, chromosome 21, X chromosome, Y chromosome, and combinations thereof.
9. The method of claim 1 , wherein the amount of genetic material for at least 70 loci is measured by performing a multiplex amplification in a single reaction, wherein the method further comprises a PCR amplification using universal amplification sequences, wherein the multiplex amplification and PCR reaction comprise ligating oligonucleotides that hybridize to target sequences and amplifying the ligated oligonucleotides using PCR, and wherein a microarray is used to detect the amplified reaction products.
10. The method of claim 9 , wherein the multiplex amplification reaction and the ligation PCR reaction are performed in an Illumina Golden Gate assay.
11. The method of claim 1 , wherein the multiple loci on the chromosome or chromosome segment of interest comprise between 32 and 2002 loci.
12. The method of claim 8 , wherein the multiple loci on the chromosome or chromosome segment of interest comprise between 70 and 2002 loci.
13. A method for detecting aneuploidy in a fetus, the method comprising:
(a) measuring an amount of genetic material at multiple loci on a chromosome or chromosome segment of interest in a sample comprising cell-free DNA from the fetus and cell-free DNA from the mother of the fetus, wherein the measuring comprises amplifying at least 70 loci in a single reaction and using microarray or sequencing to detect amplified reaction products, and wherein the amount of genetic material at a particular locus is measured irrespective of the identity of the alleles at that locus;
(b) determining, on a computer, the probability of aneuploidy in the fetus by comparing the measured amounts of genetic material to an expected amount for a particular copy number hypothesis, wherein the expected amount is determined using a mean value of genetic material at multiple loci for a reference chromosome or chromosome segment that is present in two copies; and
(c) selecting a particular copy number with greatest probability, thereby detecting aneuploidy if present.
14. The method of claim 13 , wherein the method further comprises using data from a method that makes use of allele calls at a plurality of single nucleotide polymorphism loci to determine the probability of a particular copy number hypothesis.
15. The method of claim 13 , wherein a microarray is used to measure the amount of genetic material at the multiple loci and wherein the sample comprises cell-free DNA isolated from blood from the mother of the fetus.
16. The method of claim 13 , wherein the chromosome of interest or the chromosome comprising the chromosome segment of interest is selected from the group consisting of chromosome 13, chromosome 18, chromosome 21, X chromosome, Y chromosome, and combinations thereof.
17. The method of claim 13 , wherein the multiple loci on the chromosome or chromosome segment of interest comprise between 9 and 2002 loci.
18. The method of claim 13 , wherein the amount of genetic material is measured for alleles at each of the multiple loci that have 100% penetrance in the population.
19. The method of claim 18 , wherein the multiple loci on the chromosome or chromosome segment of interest comprise between 70 and 2002 loci.
20. The method of claim 13 , wherein the selecting comprises calculating an odds ratio using the probabilities for each copy number hypothesis.