Pathogenic de novo mutations in the SYNGAP1 gene, resulting in SYNGAP1 haploinsufficiency, are a cause of intellectual disability, childhood epilepsy and autism. Currently there are no effective treatment options for SYNGAP1 haploinsufficiency; gene replacement therapy is now being discussed as a valid treatment option. SYNGAP1is a complex gene that gives rise to multiple N- and C-terminal isoforms that contain functional protein domains, some of which are isoform-specific. My project aims to determine isoform-specific roles of SynGAP in brain development and plasticity, and to determine which SynGAP isoform is most effective at rescuing phenotypes of SYNGAP1 haploinsufficiency.