Testing of this invasive sample to give a diagnostic result was traditionally undertaken using standard cytogenetic techniques. These techniques, involving tissue culture and microscopic analysis, can take up to 14 days to provide a diagnosis. In particular, fluorescent in situ Hybridisation (FISH) using interphase cells is expensive, time consuming and unsuitable for high throughput use.

Yourgene’s range of QST*R kits take advantage of the QF-PCR (Quantitative Fluorescence-Polymerase Chain Reaction) technique. Using PCR amplification, fluorescent dye labelled primers target highly polymorphic regions of DNA sequence, short tandem repeats (STRs), located on the chromosomes of interest.

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.

Individual results can be obtained within a few hours of receipt of samples. In routine use, turnaround reporting times of less than 24 hours from sample receipt are easily achievable. QF-PCR does not require cell culture, resulting in reduced failure rates and cost savings.

The Yourgene® QST*R range is compatible with most commonly employed DNA extraction protocols, thermal cyclers and capillary electrophoresis instruments. This flexibility in approach is complemented by simple and easy to use analysis software for reporting.

Results can be analysed through either Life Technologies GeneMapper™ or SoftGenetics GeneMarker® software. GeneMarker’s® operation now includes a customised Trisomy Analysis function.

By selecting BPG (Best Practice Guidelines) settings within the Trisomy Analysis function users can quickly and accurately measure allele ratios to obtain a full patient sample report within minutes.