Methods for non-invasive assessment of fetal genetic variations that factor experimental conditions
Provided herein are methods, processes and apparatuses for non-invasive assessment of genetic variations.
1. A method for sequencing circulating cell-free nucleic acid and adjusting nucleotide sequence read counts comprising:
(a) providing a group of circulating cell-free nucleic acid test samples, wherein each test sample of the group of circulating cell-free nucleic acid test samples is obtained from the blood of a pregnant female to determine the presence or absence of a genetic variation;
(b) sequencing the group of circulating cell-free nucleic acid test samples by a massively parallel sequencer, wherein the group of circulating cell-free nucleic acid test samples is sequenced on a single flow cell, and wherein the group of circulating cell-free nucleic acid test samples is sequenced on the same single flow cell;
(c) generating thousands to millions of nucleotide sequence reads for each test sample of the group of circulating cell-free nucleic acid test samples sequenced on the single flow cell;
(d) mapping the thousands to millions of nucleotide sequence reads for each test sample of the group of circulating cell-free nucleic acid test samples sequenced on the single flow cell to reference genome sections;
(e) counting the thousands to millions of nucleotide sequence reads for each test sample of the group of circulating cell-free nucleic acid test samples sequenced on the single flow cell mapped to the reference genome sections, wherein the reference genome sections are euploid, thereby obtaining counts of the thousands to millions of nucleotide sequence reads mapped to the reference genome sections for each test sample of the group of circulating cell-free nucleic acid test samples sequenced on the single flow cell;
(f) normalizing the counts of the thousands to millions of nucleotide sequence reads for a chromosome for each test sample of the group of circulating cell-free nucleic acid test samples sequenced on the single flow cell according to guanine and cytosine (GC) content, thereby generating a GC-normalized count for the chromosome for each test sample of the group of circulating cell-free nucleic acid test samples sequenced on the single flow cell;
(g) determining an expected count for the chromosome based on the GC-normalized counts obtained in (f), wherein the expected count is a median GC-normalized count for the chromosome for the group of circulating cell-free nucleic acid test samples sequenced on the single flow cell; and
(h) adjusting the GC-normalized count for the chromosome for each test sample of the group of circulating cell-free nucleic acid test samples sequenced on the single flow cell according to (1) the GC-normalized count generated in (f), (2) the expected count determined in (g), and (3) a median absolute deviation (MAD) of the expected count, thereby generating an adjusted GC-normalized count for the chromosome, wherein the presence of a genetic variation is determined based on detection of a numerical gain or a numerical loss between the adjusted GC-normalized count for genome sections of the chromosome and the expected count obtained for the reference genome sections of the same chromosome.
2. The method of claim 1 , wherein the adjusted GC-normalized count for the chromosome is a z-score or a robust z-score.
3. The method of claim 1 , wherein the chromosome is chromosome 21.
4. The method of claim 1 , wherein the chromosome is chromosome 18.
5. The method of claim 1 , wherein the chromosome is chromosome 13.