Method for amplifying a genomic sample
Provided herein is method for, among other things, estimating the number of sequence variations in a sample of DNA. In some embodiments, the method can be used to estimate the mutational load of a sample. In some embodiments, the method makes use of a set of primers that have 3′ ends that specifically hybridizes to a sequence that is repeated multiple times in the genome. Thermocycling a reaction mix containing the primers may produce a reaction product comprising at least 50 amplicons having a total length of at least 100 kb. This product can be sequenced to provide an estimate of the number of sequence variations in the sample, and thus the mutational load of the sample.
1. A method for amplifying a sample, comprising:
(a) combining a sample of cfDNA from the blood of a human with a thermostable polymerase, dNTPs and a set of at least 10 primers to produce a reaction mix, wherein:
(i) the 3′ end of each primer specifically hybridizes to a sequence that is repeated at least 20 times in the human genome,
(ii) the binding sites for the primers on opposite strands of the human genome have a median interval in the range of 50-114 nucleotides; and
(iii) collectively, the set of primers amplifies at least 50 regions having a total length of at least 100 kb, in a polymerase chain reaction using the human genome as a template; and
(b) subjecting the reaction mix to thermocycling to produce a reaction product comprising at least 50 amplicons having a total length of at least 100 kb.
2. The method of claim 1 , further comprising:
(c) sequencing the amplicons of step (b) or amplification products thereof to produce sequence reads; and
(d) analysing the sequence reads to identify sequence variations in the regions of the human genome amplified in step (b).
3. The method of claim 2 , further comprising (e) determining the number of sequence variations in the regions amplified in step (b).
4. The method of claim 2 , wherein the sequence variations are mutations.
5. The method of claim 2 , wherein the sequence variations are polymorphisms.
6. The method of claim 1 , further comprising:
(c) sequencing the amplicons of step (b) or amplification products thereof to produce sequence reads; and
(d) analysing the sequence reads to identify copy number variations in the regions of the human genome amplified in step (b).
7. The method of claim 1 , wherein the sample of DNA is a sample of cfDNA from maternal blood.
8. The method of claim 7 , wherein the method comprises:
(c) sequencing the amplicons of step (b) or amplification products thereof to produce sequence reads; and
(d) analysing the sequence reads to detect a foetal aneuploidy.
9. The method of claim 8 , wherein the method is done by detecting an increase in copy number of the amplicons amplified from chromosomes 21, 18 and/or 13, relative to a reference region.
10. The method of claim 1 , wherein the human is an organ transplant recipient.
11. The method of claim 10 , wherein the method comprises detecting a change in copy number of amplicons amplified from cfDNA from the transplanted organ.
12. The method of claim 1 , wherein the 3′ terminal 12 nucleotides of each primer are repeated at least 50 times in the human genome.
13. A set of at least 10 primers, wherein:
the 3′ end of each primer specifically hybridizes to a sequence that is repeated at least 20 times in the human genome,
the binding sites for the primers on opposite strands of the human genome have a median interval in the range of 50-114 nucleotides; and
collectively, the set of primers amplifies at least 50 regions having a total length of at least 100 kb, in a polymerase chain reaction using the human a genome as a template,
wherein some but not all of the primers comprise a first 5′ tail and the reminder of the primers comprise a second 5′ tail.
14. The set of primers of claim 13 , wherein the 3′ terminal 12 nucleotides of each primer are repeated at least 50 times in the human genome.
15. The set of primers of claim 13 , wherein the primers are in a mixture.