Possible population screening for FXS

An automated test could enable population screening to identify carriers of the genetic disease fragile X syndrome (FXS), the most common inherited form of mental retardation, reports a study in the April issue of Genetics in Medicine, published by the American College of Medical Genetics and Lippincott Williams & Wilkins, a part of Wolters Kluwer Health.

The study, by author Dr Charles Strom, claims this new assay has shown 100% sensitivity and at least 99.5% specificity for carrier detection of FXS. The automated test uses new "high-throughput' technology to rapidly screen for FXS-related gene mutations.

Affecting approximately 1 in 3600 boys, FXS causes mental retardation, behavioural problems such as attention deficit-hyperactivity disorder and certain physical abnormalities. The disease also occurs in 1 in 4000 to 6000 girls, causing less severe impairment.

Fragile X syndrome is caused by mutations of a gene called FMR1. The mutations are relatively common, with 1 in 70 to 259 women who are carriers of an abnormal gene. Currently, a PCR and a Southern blot analysis are required to determine whether or not FMR1 mutations are present. Population screening for FXS has previously been considered impractical because it would require many time-consuming tests each year.

The new technique uses an automated process to rapidly perform the tests, using a single blood sample but it is intended only as an initial screening test " women with positive results would require further genetic testing.

In a study of nearly 1000 women, the new automated process correctly identified all 13 women previously shown to have an FMR1 mutation. The test also detected all five affected males in a series of 557 tests, with a sensitivity and specificity of 100%.

The authors plan further studies evaluating the automated tests ability to detect FMR1 mutations in newborns.