In contrast, FXS patient-derived hiPSCs exhibit silencing of the FMR1 gene in both the pluripotent and the differentiated states (Urbach et al., 2010) indicating that FXS patient-derived iPSCs cannot recapitulate the developmentally dependent silencing of FMR1. Premature gene silencing brings into question the validity of FXS hiPSC cell lines in recapitulating the effect of FMRP loss during neural development. Here, FMR1 is linked to fragile X syndrome.