FMR1 and fragile X-associated tremor/ataxia syndrome: FMR1 premutation carriers (55–200 CGG repeats) are at risk for developing fragile X-associated tremor/ataxia syndrome (FXTAS), a late-onset neurodegenerative disorder, and the salient central nervous system (CNS) diagnostic feature is white matter hyperintensity in the MCP in males [15].