The fragile-X premutation: a maturing perspective.

Carriers of premutation alleles (55-200 CGG repeats) of the fragile-X mental retardation 1 (FMR1) gene are often regarded as being clinically uninvolved. However, it is now apparent that such individuals can present with one (or more) of three distinct clinical disorders: mild cognitive and/or behavioral deficits on the fragile-X spectrum; premature ovarian failure; and a newly described, neurodegenerative disorder of older adult carriers, fragile-X-associated tremor/ataxia syndrome (FXTAS). Awareness of these clinical presentations is important for proper diagnosis and therapeutic intervention, not only among families with known cases of fragile-X syndrome but also more broadly for adults with tremor, gait ataxia, and parkinsonism who are seen in movement-disorders clinics.