FMR1 and fragile X syndrome: The Drosophila model of FXS (dfmr1) has both abnormal sleep and circadian rhythm disruption, likely due to the fact that Drosophila not only lacks FMRP but also FXR2, a homolog of Fmr1 not found in Drosophila (Dockendorff et al., 2002; Bushey et al., 2009).