Fragile X mental retardation protein (FMRP), the protein absent in FXS, regulates neuron function via multiple mechanisms, including protein–protein interactions, translational control, and protein trafficking (Hagerman et al., 2005; Bhakar et al., 2012; Santoro et al., 2012; Brager and Johnston, 2014). The gene discussed is FMR1; the disease is fragile X syndrome.