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. The gene discussed is FMR1-AS1; the disease is fragile X syndrome.