GOF consistent with neuronal hyperexcitability has been observed for SCN2A/NaV1.2 pathogenic variants identified in mild benign neonatal/infantile epilepsy (Scalmani et al., 2006) and neonatal/early infantile DEE (Wolff et al., 2017), whereas LOF consistent with hypoexcitability has been observed for pathogenic variants identified in infantile/childhood epileptic encephalopathy or neurodevelopmental disorders (e.g., autism and intellectual disability) without seizures (Wolff et al., 2017). This evidence concerns the gene SCN2A and Intellectual disability.