FMR1 and Cognitive impairment: 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).