FMR1 and fragile X syndrome: This has been shown in a Drosophila model for FXS, where reintroduction of the Drosophila homologue of FMRP (dFMRP) in the knock-out model rescues certain aspects of synaptic morphology only during a 2 day time-window, but not during earlier development or later in the adult (Gatto and Broadie, 2009).