Single nucleotide polymorphisms or SNPs are small differences in the genetic code that do not cause disease but allow the creation of a unique DNA fingerprint for every individual.
These same differences can now be used to tell if twins are identical (monozygotic) or fraternal (dizygotic). Identical twins have essentially identical DNA fingerprints. Dizygotic or fraternal twins share some of the same DNA but also have differences, just like siblings.
NIPTs use SNPs to evaluate the 1 percent of DNA that makes patients genetically different from one another.
Natera’s Panorama is the only commercially available NIPT that specifically analyzes SNPs to determine chromosome copy number, according to the US diagnostics firm. Validated at foetal fraction as low as 2.8%, this approach sequences cell-free DNA from maternal plasma to infer the foetal genotype.
The ability to differentiate between maternal and foetal placental DNA also enables SNP-based tests to identify the presence of a vanishing twin and to minimize false positives due to maternal abnormalities. It also able to pinpoint triploidy and complete molar pregnancies. The company’s validation data have shown a combined sensitivity of >99% and specificity of >99 for its NIPT.
Panorama targets 13,392 SNPs, covering chromosomes 21, 18, 13, X, and Y; additional sets of SNPs are targeted for identification of microdeletions. A patented algorithm is then used to determine the chance for foetal chromosome abnormalities and foetal sex (when requested), says Natera.