FMR1 and fragile X syndrome: Many FXS phenotypes can be understood through the lens of neuronal hyperexcitability, with the prevalence of sensory hypersensitivity, hyperactive/aggressive behavior, epileptic seizures, and abnormal EEGs in FXS individuals and FMR1 KO animal models confirming neuronal network hyperexcitability as a characteristic defect owing to FMRP deficiency (Musumeci et al., 2000; Berry-Kravis, 2002; Lozano et al., 2014).