To determine whether CGG expansion is needed at all times to preserve aberrant methylation once silencing is achieved, researchers have taken advantage of XY FXS iPSCs with a heavily methylated expansion to eliminate (as opposed to shorten) the CGGs from FMR1 with the CRISPR/Cas9 system using gRNAs directed against the flanking sequences [71,72]. The gene discussed is FMR1; the disease is fragile X syndrome.