Drosophila FMRP also limits two heparan sulfate proteoglycan (HSPG) co-receptors that modulate trans-synaptic signaling, and genetic reduction of these HSPGs suppresses synaptic structure/function defects in the Drosophila FXS model (Friedman et al., 2013). This evidence concerns the gene FMR1 and fragile X syndrome.