FMR1 and fragile X-associated tremor/ataxia syndrome: The fragile X-associated tremor/ataxia syndrome (FXTAS) is a neurodegenerative disorder caused by the premutation (55–200 CGG repeats) in the fragile X messenger ribonucleoprotein-1 (FMR1) gene.1,2 The premutation is associated with elevation of the FMR1 mRNA.