SMC1A and Familial paroxysmal ataxia: Infantile onset is described for paroxysmal non-epileptic events and athetosis in ATP1A3, excessive startle, focal dystonia and reduced spontaneous movements in GNAO1, and dystonia and opistotonic posturing in SYNJ1. Between 1 and 3 years, hypokinesia and oculogyric crises develop in GRIA2, and stereotypies in SMC1A and STXBP1, while episodic ataxia develops in SCN2A-positive patients with previous benign familial infantile seizures (BFIS).