Using Fmr1 knockout (Fmr1 KO) mice, we and others have demonstrated that the cognitive impairments in FXS may be linked to a disruption in N-methyl-D-aspartate receptor (NMDAR)-dependent synaptic plasticity in the hippocampal dentate gyrus (DG) (Yun and Trommer, 2011; Eadie et al., 2012; Franklin et al., 2014; Bostrom et al., 2015, 2016). The gene discussed is FMR1; the disease is fragile X syndrome.