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FEN004 V1 QSTR 1 


Quantitative fluorescent–polymerase chain reaction (QF-PCR) has been shown to be a reliable and efficient methodology for the rapid diagnosis of the common autosomal and sex chromosome aneuploidies during pregnancy1. Using this approach, chromosomes are ‘counted’ by way of assessment of height ratios or peak area for informative short tandem repeat (STR) markers. Where an STR marker is the same size from both the paternal and maternal contribution, i.e. a homozygous result generating a single peak, this would be considered uninformative. More specifically, loci are tested and chromosome number is inferred from the aggregate result. A trisomy is detected either by the presence of three equal peak ratios (1:1:1), or two peaks with a skewed ratio (2:1). 

Most laboratories would consider a result to be accurate and reportable providing at least two markers are informative for the given chromosome. In cases where fewer than two markers are informative for a given chromosome laboratories are required to undertake further testing. Many options may be considered, for example karyotyping or array CGH. However, it is commonplace to perform so called ‘reflex’ QF-PCR to examine additional STR markers for the chromosome in question. Irrespective of the analysis method chosen this extra evaluation step will increase costs and turnaround times. 

Several commercially available QF-PCR options exist to undertake testing, including the Yourgene Health QST*Rplusv2 kit. Yourgene Health also offer a suite of single chromosome ‘reflex kits’ for laboratories to use in the event of an uninformative result. These kits contain additional chromosome specific markers in order to obtain the necessary number of informative results. A laboratory considering several commercial kits prior to purchase will likely consider the rate of required reflex testing as part of performance evaluation, due to the potential impact on turnaround times and cost. The rate of reflex testing is closely related to the original choice of STR markers for inclusion in the kit, as well as the patient population being tested. 

The Molecular Laboratory within the University of Alberta Department of Medical Genetics, Canada, offers a comprehensive diagnostic and clinical service as well as an exceptional cross-functional translational research effort. In an effort to reduce turnaround times and costs associated with delivering a high-throughput rapid prenatal aneuploidy service, the department evaluated the performance of the AneufastTM v2 (MolgentixSL) QF-PCR assay alongside the QST*Rplusv2 kit1. Yourgene Health have also been made aware of an assessment of reflex testing rates using the kit by the Genomics Laboratory at the Royal University Hospital of Saskatoon, Canada. The laboratory is a major centre for reproductive and prenatal genetic testing, and the findings of their performance evaluation are also discussed below.

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