HDAC9 and fragile X syndrome: Recent reports investigating the TNR disorder fragile X syndrome (FXS), have shown promising results using the DNMT inhibitor, 5-aza-CdR, either alone or in combination with HDAC inhibitors (Chiurazzi et al., 1999) or with HMTase inhibitors (Kumari and Usdin, 2016) to effectively reduce the FMR1 promoter hypermethylation and reinstating mRNA and protein levels to normal in FXS patient cells.