Methods and materials for assessing allelic imbalance
Methods and systems for detecting allelic imbalance using nucleic acid sequencing are provided.
1. An in vitro method of detecting loss of heterozygosity (LOH) status in a plurality of single nucleotide polymorphism (SNP) genomic loci in a formalin-fixed paraffin-embedded tissue sample from a patient, comprising:
enriching a genomic DNA sample for DNA molecules each comprising a SNP locus of interest, wherein there is at least one SNP locus located on average every 5 Mb within each chromosome that is examined;
sequencing the DNA molecules to determine the genotype at each such SNP locus;
determining for each homozygous SNP locus whether it is homozygous due to LOH.
2. The method of claim 1 , wherein there is at least one SNP locus located on average every 1 Mb within each chromosome that is examined.
3. The method of claim 1 , wherein the plurality of genomic SNP loci comprises at least 5,000 more loci.
4. The method of claim 1 , wherein the plurality of genomic SNP loci comprises at least 10,000 more loci.
5. The method of claim 1 , wherein a SNP locus is determined to have allelic imbalance if the major copy proportion at the SNP locus is 0.51 or greater.
6. The method of claim 1 , wherein the SNP genomic loci are evenly spaced along the genome.
7. The method of claim 6 , wherein the percentage difference between the distance between any two of the plurality of SNP genomic loci and the distance between any other two of the plurality of SNP loci is less than or equal to 20%.
8. The method of claim 1 , wherein the sample is a tumor sample extracted from the patient.
9. The method of claim 8 , wherein the tumor sample comprises at least 5%, or more contamination with non-tumor cells.
10. The method of claim 1 , wherein there is at least one single nucleotide polymorphism locus located on average every 500 kb within each chromosome.
11. A system for determining LOH status in a plurality of SNP genomic loci in a formalin-fixed paraffin-embedded tissue sample, wherein the system comprises:
a sample analyzer configured to
enrich a genomic DNA sample for DNA molecules, each test DNA molecule comprising a SNP locus of interest and wherein there is at least one SNP locus located on average every 5 Mb within each chromosome that is examined;
sequencing the DNA molecules to produce a plurality of quantitative signals for each such SNP locus;
a computer program that is configured to analyze the plurality of quantitative signals to determine the genotype of each such SNP locus in the sample; and
a computer program that is configured to determine, for each homozygous SNP locus, whether the locus is homozygous due to LOH.
12. The system of claim 11 , wherein there is at least one SNP locus located on average every 1 Mb within each chromosome that is examined.
13. The system of claim 11 , wherein the plurality of genomic SNP loci comprises at least 5,000 more loci.
14. The system of claim 11 , wherein the plurality of genomic SNP loci comprises at least 10,000 more loci.
15. The system of claim 11 , wherein a SNP locus is determined to have allelic imbalance if the major copy proportion at the SNP locus is 0.51 or greater.
16. The system of claim 11 , wherein the SNP genomic loci are evenly spaced along the genome.
17. The system of claim 16 , wherein the percentage difference between the distance between any two of the plurality of SNP genomic loci and the distance between any other two of the plurality of SNP loci is less than or equal to 20%.
18. The system of claim 11 , wherein the sample is a tumor sample extracted from the patient.
19. The system of claim 18 , wherein the tumor sample comprises at least 5%, or more contamination with non-tumor cells.
20. The system of claim 11 , wherein there is at least one single nucleotide polymorphism locus located on average every 500 kb within each chromosome.