SCN2A and Intellectual disability: Mutations in STXBP1, which encodes Munc18-1, a presynaptic protein essential for neurotransmitter release, and SCN2A, which encodes Nav1.2, a voltage-gated sodium channel alpha II subunit, are common in patients with a wide spectrum of neurological disorders, including epilepsy, intellectual disability, autism, and schizophrenia1–7.