The Fmr1 knockout (KO) mouse model, which lacks the Fragile X (FMRP) protein, results in a feature profile that closely resembles the behavioral and physiological clinical presentation of FXS patients (i.e. cognitive deficits, repetitive behaviors, altered social behaviors, structural changes in dendritic spines, and atypical neurotransmission). Here, FMR1 is linked to fragile X syndrome.