FMR1 and fragile X syndrome: Preliminary studies using clustered regularly interspaced short palindromic repeats (CRISPR)/Cas9-mediated gene editing approaches to (i) delete the expanded CGG repeats in FXS patient cells [39,40], (ii) induce DNA demethylation in the FMR1 promoter region [41], and (iii) target transcriptional activators to the FMR1 promoter in FXS cells [42] have all been successful in partially reactivating the FMR1 gene in cell models.