FMR1 and fragile X syndrome: Microglia have emerged as potential critical contributors to FXS pathophysiology given that postmortem analyses of FXS patients and analyses of the Fmr1 knock-out (KO) mouse, the pre-clinical FXS mouse model, have revealed neurons with increased immature spines and spine density (Kazdoba et al., 2014; Galvez and Greenough, 2005; McKinney et al., 2005; Irwin et al., 2001).