FXS and related syndromes, Fragile X Tremor Ataxia Syndrome (FXTAS) and Fragile X Premature Ovarian Failure (FXPOF), are X-linked disorders caused by expansion of a CGG triplet in the 5′ untranslated region (the promoter) of the FMR1 gene on the X chromosome. The gene discussed is FMR1; the disease is fragile X syndrome.