FMR1 and fragile X syndrome: Hyperactivity is a salient feature of human FXS (Bailey et al., 2008; Wheeler et al., 2014; Hagerman et al., 2017) and has been reliably reproduced in the previously characterized Dutch-Belgian Fmr1 KO mouse (Olmos-Serrano et al., 2010; Kazdoba et al., 2014).