Potential pathogenic mechanisms underlying Fragile X Tremor Ataxia Syndrome: RAN translation and/or RNA gain-of-function?

Fragile X-associated tremor/ataxia syndrome (FXTAS) is an inherited neurodegenerative disease caused by an expansion of 55-200 CGG repeats located in the FMR1 gene. The main clinical and neuropathological features of FXTAS are progressive intention tremor and gait ataxia associated with brain atrophy, neuronal cell loss and presence of ubiquitin-positive intranuclear inclusions in both neurons and astrocytes. At the molecular level, FXTAS is characterized by increased expression of FMR1 sense and antisense RNA containing expanded CGG or GGC repeats, respectively. Here, we discuss the putative molecular mechanisms underlying FXTAS and notably recent reports that expanded CGG and GGC repeats may be pathogenic through RAN translation into toxic proteins.