The fragile X-associated tremor/ataxia syndrome (FXTAS) is an age-dependent neurodegenerative disorder caused by a 55–200 CGG repeat expansion (i.e. premutation) in the 5′ untranslated region of the fragile X mental retardation 1 (FMR1) gene, where the normal range is 5–40 CGG repeats. The gene discussed is FMR1; the disease is fragile X-associated tremor/ataxia syndrome.