FMR1 and fragile X syndrome: The 5′ end of the FMR1 gene in FXS-derived patient cell lines is hypermethylated and associated with hypoacetylated histones (Chiurazzi et al., 1998, 1999; Coffee et al., 1999; Pietrobono et al., 2002, 2005; Biacsi et al., 2008).