FMR1 and fragile X syndrome: We only detected a main effect of sex for FXS mice (day: F(1,18) = 17.48; p < 0.001; night: F(1,18) = 4.835; p < 0.05) and an interaction between sex and genotype for DS mice at night (F(1,18) = 5.758; p < 0.05) and a slight, albeit significant, difference was found between Fmr1−/− males and their WT counterparts at night (Fig. 2F).