Mutations in SCN2A were related to a spectrum of epilepsies and NDDs with phenotypic heterogeneity, including developmental and epileptic encephalopathy 11 (MIM #613721); episodic ataxia type 9 (MIM #618924); and benign familial infantile seizures 3 (MIM #607745). Here, SCN2A is linked to episodic ataxia, type 9.