[The neuropathological mechanism on guanine-rich repeat expansion diseases].

Repeat expansion diseases are caused by the aberrant repeat expansions within specific genes. RNAs derived from aberrant repeat sequences form non-canonical secondary structures, contributing to induce cell toxicity. In particular, RNA G-quadruplexes (G4RNAs) formed in guanine-rich repeat expanded RNAs trigger neurodegeneration. We have previously shown that the expanded CGG repeat-derived G4RNAs initiate aggregation of FMRpolyG, a neuropathogenic protein generated by repeat-associated non-AUG (RAN) translation in Fragile X-associated tremor/ataxia syndrome (FXTAS). In this review, we describe the neuropathological mechanism attributed to G4RNAs in guanine-rich repeat expansion diseases, including FXTAS.