GRM5 and fragile X syndrome: Considering the functional relevance of mGlu5 to SUMO homeostasis (Loriol et al., 2014; Schorova et al., 2019), the analysis of brain sumoylome in animal models of PMS and FXS is of primary importance and might uncover pivotal roles of sumoylation in the molecular pathogenesis of these neurodevelopmental disorders.