In support of a genetically modulated phenotypic spectrum are the findings that individuals with FXS or the premutation (with or without FXTAS) share symptoms of executive function impairments [21-23] that are modulated by CGG repeat length [18,19,24-26], FMR1 mRNA [27], and FMRP [28-32]. This evidence concerns the gene FMR1 and fragile X-associated tremor/ataxia syndrome.