FMR1 and fragile X syndrome: With this in mind, Esanov and colleagues analyzed the levels of 5hmC at the FMR1 promoter in post-mortem brain samples, primary fibroblasts and immortalized lymphocytes from FXS and control subjects as well as in vitro differentiated neural progenitors (NPCs) from FXS iPSC and hESCs (WCMC-37) [50].