Skip to main content

Genetic Testing for and Inheritance of Fragile X

FXS is the most common inherited cause of learning disability worldwide. FXS is inherited through a mutated gene on the X chromosome, which means that you only need one copy of the mutated gene in each cell to cause the condition (either from the mother or father). Female carriers can pass on the mutation to either their sons or daughters, whereas men can only pass the mutation to their daughters. FXS occurs in approximately 1 in 4,000 males and 1 in 6,000 females In addition, approximately 1 in 250 females and 1 in 600 males are carriers of the Fragile X pre-mutation . The small alteration to the gene makes it 'unstable’, meaning that it can change size and lead to FXS when it is passed to the next generation (from mothers).

In 2015, the UK National Screening Committee(NSC) did not recommend systematic population screening for FXS because:
• There are problems with the accuracy of the pre-natal genetic test, which does not give enough information about whether the baby would go on to develop Fragile X symptoms or not.
• The test is labour intensive and therefore unsuitable for a screening programme. There are alternatives, including specially designed kits, but the evidence for their efficacy is very limited.
• There is no good evidence that screening during pregnancy would mean that treating or managing the condition in the infant would improve compared to a diagnosis in childhood.
• There are no curative or preventative treatments that could be offered to those identified through screening.

There is also limited evidence on what families living with Fragile X think about screening. Our study will address this.

fxs dna