Fragile X syndrome is caused by loss of function of the fragile X mental retardation protein (FMRP; Pieretti et al., 1991; Verkerk et al., 1991), which acts as a translational repressor of specific mRNAs (Corbin et al., 1997; Feng et al., 1997; Ascano et al., 2012). The gene discussed is FMR1; the disease is fragile X syndrome.