This site is intended for healthcare professionals

Go to /sign-in page

You can view 5 more pages before signing in

Fragile X syndrome

Last reviewed dd mmm yyyy. Last edited dd mmm yyyy

Authoring team

The fragile X syndrome is said to be the most common heritable cause of mental retardation after Down's syndrome. It is caused by a dominant X-linked gene with a penetrance of only 50% in females.

The gene which is most commonly responsible is FMR-1 (familial mental retardation 1). The disease occurs when the expression of FMR-1 is disrupted by:

  • a large number, more than 230, of trinucleotide repeats
  • a deletion (rare)

It seems that loss of fmr-1 results in the fragile X syndrome.


Related pages

Create an account to add page annotations

Add information to this page that would be handy to have on hand during a consultation, such as a web address or phone number. This information will always be displayed when you visit this page