FMR1 and fragile X-associated tremor/ataxia syndrome: Fragile X-associated tremor/ataxia syndrome (FXTAS) is one of these repeat expansion disorders characterized by a CGG or GGC repeat expansion (55–200 repeats) in the 5′ UTR of the Fragile X Mental Retardation 1 (FMR1) gene (Hagerman et al., 2001).