OBJECTIVE: SCN2A encodes the voltage-gated sodium (Na+) channel α subunit Na METHODS: Here, we identified seven de novo heterozygous variants in SCN2A in eight individuals with developmental and epileptic encephalopathy (DEE) accompanied by prominent malformation of cortical development (MCD). We characterized the electrophysiological properties of Na + currents in human embryonic kidney (HEK) cells transfected with the adult (A) or neonatal (N) isoform of wild-type (WT) and variant Na RESULTS: The neonatal isoforms of all SCN2A variants studied exhibit gain of function (GoF) with a large depolarized shift in steady-state inactivation, creating a markedly enhanced window current common across all four variants tested. Computational modeling demonstrated that expression of the Na SIGNIFICANCE: These results support expansion of the clinical spectrum of SCN2A-related disorders and the association of genetic variation in SCN2A with MCD, which suggests previously undescribed roles for SCN2A in fetal brain development.