De novo GNAO1 mutations were originally first reported in Ohtahara syndrome and EOEE in 4 children, associated with abnormal movements in 2.1 Since this initial description, 30 additional patients have been reported with an emerging phenotype characterized by neurodevelopmental delay with an early onset of a hyperkinetic movement disorder, inconsistently associated with epilepsy. The epilepsy phenotype of the 7 patients we studied ranged from EOEE to mild drug-sensitive epilepsy, whose onset could precede or follow that of the movement disorder, which was certainly a prominent feature. The occurrence of stereotypies (previously reported in 2 patients with EOEE)4,5 and characteristic paroxysmal exacerbations, associated often with clear triggers, may both be considered as 2 further important discerning clinical features of GNAO1 encephalopathy.
