Copy number variation determination, methods and systems
The present invention methods and systems for determining copy number variation of a target polynucleotide in a genome of a subject including amplification based techniques. Methods can include pre-amplification of the sample followed by distribution of sample and a plurality of reaction volumes, quantitative detection of a target polynucleotide and a reference polynucleotide, and analysis so as to determine the relative copy number of the target polynucleotide sequence in the genome of the subject.
1. A method for determining the relative copy number of a target polynucleotide sequence in a genome of a subject, comprising:
pre-amplifying a target gene sequence and a reference gene sequence in a sample containing genomic DNA of the subject such that multiple copies of said target gene sequence that are linked together in the genome will be amplified separately;
assaying the target gene sequence and the reference gene sequence of the preamplified sample by digital PCR; and
determining a ratio of (a) to (b), where (a) is the number of amplified polynucleotide molecules containing the target gene sequence and (b) is the number of amplified polynucleotide molecules containing the reference gene sequence.
2. The method of claim 1 wherein the sample is from a human.
3. The method of claim 1 wherein the ratio of (a) to (b) is about 0.5 and there is a deletion of (a) on one chromosome.
4. The method of claim 1 wherein the ratio of (a) to (b) is about 1.5 and there is a duplication of (a) on one chromosome.
5. The method of claim 1 , wherein: the reference gene sequence has a predetermined genomic copy number N;
determining the number of amplified polynucleotide molecules containing the target gene sequence comprises determining the number of reaction volumes in which the target gene sequence or subsequence thereof is present (a);
determining the number of amplified polynucleotide molecules containing the reference polynucleotide sequence comprises determining the number of reaction volumes in which the reference gene sequence or subsequence thereof is present (b); and
the relative copy number of the target polynucleotide in the genome is approximately equal to the product of N multiplied by the ratio (a)/(b).
6. The method of claim 5 , wherein pre-amplifying a target gene sequence and a reference gene sequence comprises combining the sample with a composition comprising primers specific for the target gene sequence and primers specific for reference gene sequence, and conducting a polymerase chain reaction (PCR) assay so as to separately amplify target gene sequences and reference gene sequences in substantially equal proportion.
7. The method of claim 6 wherein pre-amplifying a target gene sequence and a reference gene sequence comprises from 4 to 15 cycles.
8. The method of claim 5 , wherein the reaction volumes are disposed in a microfluidic device, and the first polynucleotide amplification is conducted in a reaction volume separate from the microfluidic device.
9. The method of claim 5 , wherein prior to assaying the target polynucleotide sequence and the reference polynucleotide sequence of the
pre-amplified sample by digital PCR, all or a portion of the amplified sample is combined with reagents selected for quantitative amplification of target gene sequence and reference gene sequence.
10. The method of claim 9 wherein the primers used in the pre-amplification step to amplify the reference gene sequence are the same as those used in assaying the reference gene sequence of the pre-amplified sample by digital PCR.
11. The method of claim 10 wherein the primers used in the pre-amplification step to amplify the target gene sequence are the same as those used in assaying the target gene sequence of the pre-amplified sample by digital PCR.
12. The method of claim 9 , wherein the reagents comprise a first probe that selectively hybridizes to a target gene sequence and a second probe that selectively hybridizes to a reference gene sequence under conditions suitable for polynucleotide amplification.
13. The method of claim 12 , wherein the first and second probes comprise different detectable labels, and wherein binding of the first or second probe or degradation of the first or second probe upon polymerase chain reaction (PCR) based polymerization results in a change in detectable fluorescence of the respective detectable label.
14. The method of claim 1 , wherein the reference gene sequence comprises a polynucleotide sequence at least partially encoding an RNase P enzyme, beta-actin or GAPDH.
15. The method of claim 1 , wherein a ratio of target gene sequence to reference gene sequence substantially deviating from a value of 1 indicates an abnormal target gene sequence copy number in the genome of the subject.
16. The method of claim 1 , wherein determining the relative copy number of the target gene sequence comprises detecting a loss of heterozygosity in the genome of the subject.
17. The method of claim 1 , wherein a ratio of target gene sequence to reference gene sequence with a value substantially greater than or less than 1 indicates a loss of heterozygosity in the genome of the subject.
18. The method of claim 1 wherein the pre-amplifying comprises conducting 4 to 15 cycles of a polymerase chain reaction (PCR) so as to amplify the target gene sequence and reference gene sequence in substantially equal proportion.