Direct molecular diagnosis of fetal aneuploidy
View Patent ↗Methods and materials for detection of aneuploidy and other chromosomal abnormalities using fetal tissue are disclosed. Results can be obtained rapidly, without cell culture. The method uses digital PCR for amplification and detection of single target sequences, allowing an accurate count of a specific chromosome or chromosomal region. Specific polynucleic acid primers and probes are disclosed for chromosomes 1, 13, 18, 21, X and Y. These polynucleic acid sequences are chosen to be essentially invariant between individuals, so the test is not dependent on sequence differences between fetus and mother.
1. A method for detecting a fetal chromosomal aneuploidy of a target chromosome, comprising the steps of:
(a) obtaining a fetal sample containing genomic DNA including a target chromosome sequence and a reference chromosome sequence, said fetal sample being at least one of amniotic fluid, uncultured amniocytes and chorionic villus tissue;
(b) distributing said fetal sample into a plurality of reaction areas, each reaction area containing on average not more than one target chromosome sequence and not more than one reference chromosome sequence;
(c) detecting whether said target chromosome sequence is present in said plurality of reaction areas, said detecting comprising the step of detecting an invariant sequence using primers that hybridize to ultraconserved elements in genomic DNA, to produce a target count;
(d) detecting whether said reference chromosome sequence is present in said plurality of reaction areas using primers comprising sequences according to SEQ ID NO: 1 and SEQ ID NO: 2 that hybridize to chromosome 1, said detecting comprising the step of detecting an invariant sequence, to produce a reference count;
(e) obtaining sufficient numbers in said target count and said reference count to achieve statistical significance; and
(f) comparing said target count to said reference count, whereby an abnormal difference between said target count and said reference count indicates fetal chromosomal aneuploidy in the target chromosome.
2. The method of claim 1 wherein said detecting step comprises amplification using one pair of primers and a detection probe for the target chromosome and another pair of primers and a detection probe for the reference chromosome.
3. The method of claim 1 wherein said target chromosome is one or more of chromosomes 13, 18, and 21, and said reference chromosome is chromosome 1.
4. The method of claim 1 wherein the step of comparing said target count to said reference count further includes the step of determining whether or not each count is within a confidence interval of at least 99% in order to determine statistical significance of said abnormal difference.
5. A method for detecting a chromosomal aneuploidy of a target chromosome, comprising the steps of:
(a) directly extracting genomic DNA from a sample, said DNA including target chromosome sequence and reference chromosome sequence, said sample being a fetal sample of at least one of amniotic fluid, uncultured amniocytes and chorionic villus tissue;
(b) distributing said fetal sample from step (a), concurrently into a plurality of reaction areas, each reaction area comprised in a microfluidic device and containing on average not more than one target chromosome sequence and not more than one reference chromosome sequence;
(c) adding amplification primers, where one amplification primer set comprises sequences according to SEQ ID NO: 1 and SEQ ID NO: 2 that hybridize to reference chromosome 1 and one amplification primer set hybridizes to the target chromosome and where said amplification primers hybridize to ultraconserved elements in a genome and carrying out a plurality of amplification reactions concurrently in the plurality of reaction areas;
(d) adding a label for detecting presence and absence of said target chromosome sequence and said reference chromosome sequence to produce a target count;
(e) detecting presence and absence of said reference chromosome sequence in said plurality of reaction areas to produce a reference count;
(f) obtaining sufficient numbers in said target count and said reference count to achieve a predetermined statistical significance in any difference between said target count and said reference count; and
(g) comparing said target count to said reference count, whereby an abnormal difference between said target count and said reference count indicates fetal chromosomal aneuploidy in the target chromosome.
6. The method of claim 5 wherein said amplification reactions comprise heating and denaturing primers in the presence of a DNA polymerase.
7. The method of claim 5 wherein said amplification primers amplify regions of similar size in both the target chromosome sequence and reference chromosome sequence.
8. The method of claim 5 wherein the detecting comprises contacting an amplified sequence with a fluorescent probe.
9. The method of claim 8 wherein a fluorescent probe having one label is used for detecting amplified target sequence and a fluorescent probe having another label is used for detecting amplified reference sequence.
10. The method of claim 9 wherein said amplification primers comprise multiple primers directed to a single chromosome.