FMR1 and fragile X syndrome: In a study of fragile X syndrome, TsangB et al. experimentally demonstrated that phosphorylation increased the local negative charge density of fragile X mental retardation protein (FMRP), suggesting that phosphorylation of the low-complexity disordered region at the C-terminus of FMRP may increase its phase separation by increasing the propensity for multivalent electrostatic interactions [73].