FMR1 and fragile X syndrome: It has been documented that a 50% reduction in mGluR5 expression in the Fmr1-knockout mouse rescued most FXS abnormalities, including altered ocular dominance plasticity, increased density of dendritic spines on cortical pyramidal neurons, increased basal protein synthesis in the hippocampus, exaggerated inhibitory avoidance extinction, audiogenic seizures and accelerated body growth.