FMR1 and fragile X syndrome: 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.