FMR1 and fragile X syndrome: Indeed, although Patient 2 tested negative for expanded fragile X ribonucleoprotein 1 (FMR1) CGG repeats, the usual cause of FXS (Sherman et al., 2005), the patient proved to have a unique de novo FMR1 missense mutation (I304N; Zang et al., 2009), with isoleucine replacing asparagine in the second KH-type RNA-binding domain of the fragile X ribonucleoprotein 1 (FMRP) translational regulator (Zang et al., 2009; Feng et al., 1997).