Late on Friday, the FDA authorised the marketing of the first genetic test for Fragile X syndrome (FXS): AmplideX, a Fragile X diagnostic and carrier screen kit from Asuragen. The press release can be found here

The assay is intended to be used alongside clinical evaluation and the patient’s family history and can also be used to test adults who may be carriers of FMR1 alterations, the gene associated with FXS.

FXS is caused by an excess of CGG trinucleotide repeats in the FMR1 gene. AmplideX uses triple repeat primed PCR (TP-PCR) to measure the number of CGG repeats in the FMR1 gene in a patient’s blood sample. Some repetition of the CGG repeat is considered normal, between 5 to 44, and the test can help to determine whether the repeat number is considered normal, intermediate, premutation, or full mutation.

Symptoms of FXS include developmental delays, learning difficulties, and social and behavioural issues. The condition is located on the X-chromosome and individuals with normal or intermediate repeats are currently thought to be asymptomatic.

As well as its diagnostic use in carrier testing, AmplideX can help to diagnose Fragile-X associated disorders, including a movement and cognitive disorder called Fragile X-associated ataxia syndrome. The FDA used its de novo classification program to review their data and evaluated data from three clinical trial sites to determine that the assay has a diagnostic accuracy of greater than 95%.

Currently, Asuragen only offers the AmplideX PCRCE FMR1 reagents in a for research-use-only capacity.