The numerous presynaptic and postsynaptic defects in the FXS disease state, which have often been first characterized in the Drosophila FXS model (Zhang et al., 2001; Pan et al., 2004; Pan and Broadie, 2007; Tessier and Broadie, 2012), have established clear roles for FMRP on both sides of the synaptic cleft. The gene discussed is FMR1; the disease is fragile X syndrome.