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ContextPremutation expansions (55-200 CGG repeats) of the fragile X mental retardation 1 (FMR1) gene are frequent in the general population, with estimated prevalences of 1 per 259 females and 1 per 813 males. Several articles have recently described the presence of late-onset neurological symptoms in male carriers of premutation (FMR1) alleles. The main clinical features described in this newly identified syndrome are cerebellar ataxia and intention tremor. Additional documented symptoms include short-term memory loss, executive functional deficits, cognitive decline, parkinsonism, peripheral neuropathy, lower-limb proximal muscle weakness, and autonomic dysfunction.ObjectiveTo study the penetrance of the fragile X–associated tremor/ataxia syndrome (FXTAS) among premutation carriers.Design, Setting, and ParticipantsFamily-based study of 192 individuals (premutation carriers and controls) whose …