Methods and systems for detecting genetic variants
Disclosed herein in are methods and systems for determining genetic variants (e.g., copy number variation) in a polynucleotide sample. A method for determining copy number variations includes tagging double-stranded polynucleotides with duplex tags, sequencing polynucleotides from the sample and estimating total number of polynucleotides mapping to selected genetic loci. The estimate of total number of polynucleotides can involve estimating the number of double-stranded polynucleotides in the original sample for which no sequence reads are generated. This number can be generated using the number of polynucleotides for which reads for both complementary strands are detected and reads for which only one of the two complementary strands is detected.
1. A method for estimating a number of non-uniquely tagged double-stranded cell-free deoxyribonucleic acid (cfDNA) molecules, comprising:
(a) non-uniquely tagging a plurality of cfDNA molecules from a sample of a subject with a set of duplex tags comprising molecular barcodes from a set of molecular barcodes to generate non-uniquely tagged parent polynucleotides, wherein the cfDNA molecules that map to a mappable base position of a reference sequence are tagged with a number of different molecular barcodes ranging from at least 2 to fewer than a number of the cfDNA molecules that map to the mappable base position;
(b) amplifying a plurality of the non-uniquely tagged parent polynucleotides to produce amplified progeny polynucleotides;
(c) sequencing a plurality of the amplified progeny polynucleotides to produce a set of sequencing reads;
(d) determining, from among a plurality of sequencing reads from the set of sequencing reads, a quantitative measure of individual cfDNA molecules for which both strands are detected;
(e) determining, from among a plurality of sequencing reads from the set of sequencing reads, a quantitative measure of individual cfDNA molecules for which only one strand is detected; and
(f) estimating a number of non-uniquely tagged double-stranded cfDNA molecules based on the quantitative measures determined in steps (d) and (e), wherein the number of non-uniquely tagged double-stranded cfDNA molecules comprises individual cfDNA molecules for which neither cfDNA strand is detected.
2. The method of claim 1 , wherein the sample is a bodily fluid.
3. The method of claim 1 , wherein the sample is blood, plasma, or serum.
4. The method of claim 1 , wherein the sample comprises from 1 nanogram (ng) to 100 ng of double-stranded cfDNA molecules.
5. The method of claim 1 , wherein the duplex tags comprising the molecular barcodes are ligated to the plurality of cfDNA molecules by blunt-end ligation or sticky-end ligation.
6. The method of claim 1 , wherein the molecular barcodes of the set of molecular barcodes have 2 to 10,000 different molecular barcode sequences.
7. The method of claim 1 , wherein the molecular barcodes of the set of molecular barcodes have 5 to 1,000 different molecular barcode sequences.
8. The method of claim 1 , wherein the molecular barcodes comprise pre-determined sequences.
9. The method of claim 1 , wherein the tagging comprises using more than a 10× molar excess of duplex tags comprising the molecular barcodes as compared to the cfDNA molecules.
10. The method of claim 1 , wherein the tagging comprises using more than a 80× molar excess of duplex tags comprising the molecular barcodes as compared to the cfDNA molecules.
11. The method of claim 9 , wherein at least 20% of the cfDNA molecules obtained from the sample are attached to duplex tags comprising the molecular barcodes.
12. The method of claim 9 , wherein at least 40% of the cfDNA molecules obtained from the sample are attached to duplex tags comprising the molecular barcodes.
13. The method of claim 1 , further comprising selectively enriching a subset of the amplified progeny polynucleotides for a plurality of genomic regions of interest prioruencing.
14. The method of claim 13 , wherein the plurality of genomic regions of interest comprises sequences from at least 5 genes selected from the group consisting of:
ALK, APC, BRAF, CDKN2A, EGFR, ERBB2, FBXW7, KRAS, MYC, NOTCH1, NRAS, PIK3CA, PTEN, RB1, TP53, MET, AR, ABL1, AKT1, ATM, CDH1, CSF1R, CTNNB1, ERBB4, EZH2, FGFR1, FGFR2, FGFR3, FLT3, GNA11, GNAQ, GNAS, HNF1A, HRAS, IDH1, IDH2, JAK2, JAK3, KDR, KIT, MLH1, MPL, NPM1, PDGFRA, PROC, PTPN11, RET, SMAD4, SMARCB1, SMO, SRC, STK11, VHL, TERT, CCND1, CDK4, CDKN2B, RAF1, BRCA1, CCND2, CDK6, NF1, TP53, ARID1A, BRCA2, CCNE1, ESR1, RIT1, GATA3, MAP2K1, RHEB, ROS1, ARAF, MAP2K2, NFE2L2, RHOA, and NTRK1.
15. The method of claim 13 , where selectively enriching the subset of the amplified progeny polynucleotides for the plurality of genomic regions of interest comprises using a set of probes that hybridize to the plurality of genomic regions of interest.
16. The method of claim 13 , further comprising amplifying a plurality of the enriched amplified progeny polynucleotides.
17. The method of claim 1 , further comprising, prior to steps (d) and (e), mapping a plurality of sequencing reads from the set of sequencing reads to a human reference sequence.
18. The method of claim 17 , further comprising, prior to steps (d) and (e), grouping a plurality of sequencing reads from the set of sequencing reads that map to the human reference sequence into families based on (1) sequence information from the molecular barcodes and (2) a start point of a given sequencing read from among the set of sequencing reads at which the given sequencing read is determined to start mapping to the human reference sequence, and a stop point of the given sequencing read at which the given sequencing read is determined to stop mapping to the human reference sequence.
19. The method of claim 1 , further comprising inferring, from said quantitative measures determined in steps (d) and (e), a quantitative measure of individual cfDNA molecules for which neither strand is detected.
20. The method of claim 1 , further comprising determining a normalized quantitative measure of one or more genetic loci to determine copy number variation in the sample.
21. The method of claim 18 , further comprising, for a plurality of the families, collapsing sequencing reads within a given family of the plurality of the families into a consensus sequence, and determining the quantitative measure of individual cfDNA molecules for which both strands are detected and the quantitative measure of individual cfDNA molecules for which only one strand is detected based at least in part on the consensus sequences.