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 the presence or absence of a chromosomal abnormality in a fetus, the method comprising:
(a) performing a multiplex amplification for at least 70 loci in a single reaction, wherein the reaction comprises cell free DNA derived from maternal blood, and wherein the amplification comprises ligating oligonucleotides that hybridize to target sequences and amplifying the ligated oligonucleotides using PCR;
(b) performing microarray analysis to measure an amount of genetic material at the at least 70 loci on a chromosome or chromosome segment of interest in a sample comprising DNA derived from the fetus and from the mother of the fetus, wherein the amount of genetic material at a particular locus is determined irrespective of an identity of alleles at that locus;
(c) determining a probability of the presence and a probability of the absence of a chromosomal abnormality in the fetus by comparing the amount from step (b) to either (i) a threshold value or (ii) an expected amount for a particular copy number hypothesis;
(d) identifying the presence or absence of a chromosomal abnormality in the fetus by selecting the probability most likely to be true; and
(e) outputting the selected probability as an indication of whether the fetus has a chromosomal abnormality, thereby detecting the presence or absence of a chromosomal abnormality in the fetus.
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 the at least 70 loci are loci having alleles with 100% penetrance in the population.
4. 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, and wherein the chromosomal abnormality is selected from the group consisting of monosomy, uniparental disomy, trisomy, other aneuploidies, unbalanced translocations, insertions, deletions, and combinations thereof.
5. The method of claim 1 , wherein the method further comprises a PCR amplification using universal amplification sequences.
6. A method for detecting aneuploidy in a fetus, the method comprising:
(a) performing a multiplex amplification for at least 70 loci in a single reaction, wherein the reaction comprises cell free DNA derived from maternal blood, and wherein the amplification comprises ligating oligonucleotides that hybridize to target sequences and amplifying the ligated oligonucleotides using PCR;
(b) performing microarray analysis to measure an amount of genetic material at the at least 70 loci on a chromosome or chromosome segment of interest in a sample comprising DNA derived from the fetus and from the mother of the fetus, wherein the amount of genetic material at a particular locus is determined irrespective of an identity of alleles at that locus;
(c) computing, for a particular copy number hypothesis, a difference between the mean of the measured amount of genetic material at the at least 70 loci and a mean of an expected amount of genetic material at the at least 70 loci for a reference chromosome or chromosome segment that is present in two copies;
(d) determining a probability of a particular copy number hypothesis by comparing the difference for each particular copy number hypothesis; and
(e) selecting the particular copy number hypothesis with the probability most likely to be true, thereby detecting aneuploidy if the selected hypothesis is an aneuploidy hypothesis.
7. The method of claim 6 , wherein the method further comprises using data from a method that makes use of allele calls at a plurality of single nucleotide polymorphism (SNP) loci to determine the probability of a particular copy number hypothesis.
8. The method of claim 6 , wherein the at least 70 loci are loci having alleles with 100% penetrance in the population.
9. The method of claim 6 , wherein the aneuploidy is trisomy of chromosome 21.
10. A method for detecting aneuploidy in a fetus, the method comprising:
(a) performing a multiplex amplification for at least 70 loci in a single reaction, wherein the reaction comprises cell free DNA derived from maternal blood, and wherein the amplification comprises ligating oligonucleotides that hybridize to target sequences and amplifying the ligated oligonucleotides using PCR;
(b) performing microarray analysis to measure an amount of genetic material at the at least 70 loci on a chromosome or chromosome segment of interest in a sample comprising DNA derived from the fetus and from the mother of the fetus, wherein the at least 70 loci are loci having alleles with 100% penetrance in the population;
(c) determining a 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 the at least 70 loci for a reference chromosome or chromosome segment that is present in two copies; and
(d) selecting a particular copy number with a greatest probability, thereby detecting aneuploidy if the selected hypothesis is an aneuploidy hypothesis.
11. The method of claim 10 , wherein the aneuploidy is trisomy of chromosome 21.