ARX and movement disorder: Severe hyperkinetic (dystonia, choreoathetosis, myoclonus) movements have been described in a range of genetic encephalopathies caused by SCN2A, SCN8A, FOXG1, STXBP1, GNAO1, ARX, and DNM1, among others.12,15, –, 17 Distinguishing a movement disorder from seizures may affect therapeutic approaches in terms of when to introduce antiepileptic therapy or other treatment modalities.