FMR1 and fragile X-associated tremor/ataxia syndrome: To determine if the expression of FMR4 is affected by the CGG expansion in the 5′ UTR of FMR1 that occurs in FXS and/or FXTAS, we investigated the relative expression of FMR4 and FMR1 by RT-PCR in untransformed leukocytes from four control, four premutation and four FXS patients.