SCN2A mutations in patients with the severe end of epilepsies such as early-infantile epileptic encephalopathy, Ohtahara syndrome and West syndrome are almost exclusively missense, while nonsense, frameshift and splice site mutations are dominant in patients with ASD and intellectual disability associated with milder, later-onset epilepsy or without epilepsy (reviewed in Yamakawa22). Here, SCN2A is linked to early-infantile DEE.