Mouse models of FXS have provided critical insights into the role of FMRP in cortical circuit development and function, with loss of Fmr1 inducing abnormal neuronal excitability, synaptic plasticity, and long-range connectivity (Hays et al., 2011; Haberl et al., 2015; Gibson et al., 2008; Pfeiffer and Huber, 2007; Martin et al., 2016). The gene discussed is FMR1; the disease is fragile X syndrome.