Fragile X premutation

The fragile X premutation is an intermediate-sized expansion in the FMR1 gene, smaller than the full expansion that causes fragile X syndrome. People carrying a premutation are usually unaffected by fragile X syndrome themselves, but women with a premutation have a higher chance of developing premature ovarian insufficiency (sometimes called fragile X-associated primary ovarian insufficiency), affecting fertility and the timing of family planning. A fragile X premutation can also expand further when passed to the next generation, particularly through a mother, meaning a child could inherit a full expansion associated with fragile X syndrome, a condition linked to intellectual and developmental differences. Fragile X testing may be considered for women with unexplained premature ovarian insufficiency or a relevant family history, and results are best interpreted with genetic counselling given the implications for both a woman's own fertility and future children.

Also known as: FMR1 premutation, fragile X syndrome carrier, FXPOI

Last reviewed: 9 September 2026. Written by the Antega Editorial Team. General information only — always follow the advice of your own clinic, doctor or pharmacist.