Fragile X-associated tremor/ataxia syndrome

Fragile X-associated tremor/ataxia syndrome (FXTAS) is a late-onset neurodegenerative disorder most frequently seen in male premutation carriers of Fragile X syndrome (FXS) over the age of 50. The main clinical features of FXTAS include problems of movement with cerebellar gait ataxia and action tremor. Associated features include parkinsonism, cognitive decline, and dysfunction of the autonomic nervous system. FXTAS is found in Fragile X "premutation" carriers, which is defined as a trinucleotide repeat expansion of 55-200 CGG repeats in the Fragile X mental retardation-1 (FMR1) gene. 4-40 CGG repeats in this gene is considered normal, while individual with >200 repeats have full Fragile X Syndrome.

In contrast to FXS full mutation, which is diagnosed early in childhood, symptoms of FXTAS manifest in individuals over the age of 50. Like FXS, FXTAS is most common and most severe in males due to the mutation's X-linked inheritance pattern. FXTAS has an incidence of 30-40% (male) and 8-15% (female) among FXS premutation carriers over the age of 50.

FMR1 mRNA is found to be elevated in patients with FXTAS in contrast to FXS, where the FMR1 gene is transcriptionally silenced via DNA methylation. In both diseases the FMR1 gene product, Fragile X mental retardation protein (FMRP) is diminished, but in FXTAS this is believed to be mediated by RNA toxicity, while in FXS, FMRP is absent due to transcriptional silencing.

There is no cure for FXTAS, but several of the symptoms can be managed with medication.