Recently,Khayachi et al.[1] showed that fragile X mental retardation protein (FMRP) is an active substrate of the small ubiquitin-like modifier (SUMO) pathway in neurons.FMRP SUMOylation is induced by the activation of metabotropic glutamate receptors (mGlu5Rs).FMRP SUMOylation is required for dissociating FMRP from dendritic RNA granules and controlling spine density and proper maturation.