Carriers of one FMR1 allele with a “premutation,” a modestly expanded trinucleotide repeat (55–200 repeats) at the FMR1 locus, are at risk for expression of “Fragile X-associated tremor/ataxia syndrome” (FXTAS), an aged-onset monogenic neurodegenerative disorder associated with decreased FMRP levels (Feng et al., 1995; Jacquemont et al., 2003; Sheridan et al., 2011; Cao et al., 2013). The gene discussed is FMR1; the disease is fragile X-associated tremor/ataxia syndrome.