Fragile X (FraX A) is one of the most common requests for genetic testing. The Clinical Molecular Genetics Society (CMGS) audit for 2006/2007 records over 10,500 postnatal FraX A reports issued across UK labs. This comprises 13.6% of all postnatal molecular genetic testing reports, a number second only to cystic fibrosis. A significant proportion of these reports are only issued after carrying out Southern blot analysis as PCR analysis is inconclusive in homozygous normal female samples and large expansions cannot be detected by standard PCR methods. Abbott Molecular have recently released a PCR based analyte specific reagent (ASR) kit for Fragile X diagnosis. They stated that the kit can reduce the burden of Southern blot testing by reliably PCR amplifying repeat alleles much larger than those possible using ‘in house’ methods as well as distinguishing between female samples homozygous for repeat alleles in the normal range and those with a single allele and a large expansion. We have carried out a multi-centre technology assessment of the kit. 13 laboratories (10 UK and 3 EuroGentest) took part in the study. The aim of the study was to measure the performance of the kit using the following parameters:

• Accuracy of allele sizing
• Detection of homozygosity in females
• Detection of large expansions/full mutations
• Detection of mosaicism
• Ease of use in diagnostic setting
• Reproducibility

It was not possible to carry out a cost/benefit analysis due to the price of the kit being negotiable.

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