Tremor/ataxia syndrome and fragile X premutation: diagnostic caveats.

The fragile X-associated tremor/ataxia syndrome (FXTAS) is a newly discovered late-onset neurodegenerative disorder caused by a premutation in the FMR1 X-linked gene. We present examples of a discrepancy between obvious brain changes observed on MRI, and minimal clinical neurological manifestations in three older carriers of this premutation. This discrepancy occurred in three of nine carriers ascertained in an unbiased manner. If the systematic follow-up studies of adult carriers confirm this trend, this will have an impact on early diagnosis of neurological involvement and possible prevention. If MRI changes precede clinical manifestation of FXTAS this may explain the low detection rate of fragile X carriers among patients with neurological syndromes associated with tremor/ataxia.