Each targeted STR marker is specific to the chromosome on which it is located, thus the copy number of the STR marker can be diagnostic of the copy number of the chromosome. In an individual unaffected by a trisomy, two alleles of a chromosome specific STR are determined by the QF-PCR technique as two peaks in a 1:1 ratio. The observation of an extra STR allele as either a three peak pattern in a 1:1:1 ratio or two peak pattern in a 2:1 or 1:2 peak ratio is diagnostic of the presence of an additional sequence, which in turn may represent an additional chromosome as in the case of a trisomy.
Yourgene® QST*R Base is a highly multiplexed, single tube assay containing a total of 22 markers. Autosomal markers are used to detect the three most common viable autosomal trisomies: trisomy 21 (Down's syndrome), trisomy 18 (Edwards’ syndrome) and trisomy 13 (Patau's syndrome). Additional markers on the sex chromosomes X and Y, including a specific marker for the quantification of the number of X chromosomes, are useful in the diagnosis of sex chromosome aneuploidies. The chosen markers are highly informative with results obtained in >99% of samples. Reflex kits containing additional markers are available for follow up analysis in the rare case of an uninformative result.