FXTAS affects persons who have CGG expansions in the premutation range (that is, 55–200 CGG repeats), as opposed to fragile X syndrome (FXS), which is associated with the full mutation (over 200 CGG repeats) at FMR1. FXTAS and FXS have very different phenotypes, the latter involving an early childhood-onset intellectual development disorder, often with autistic features, while FXTAS affects persons who previously were cognitively normal, in the sixth or seventh decade of life. Here, FMR1 is linked to fragile X-associated tremor/ataxia syndrome.