GNAO1 encephalopathy: further delineation of a severe neurodevelopmental syndrome affecting females

� 2016 Marc�-Grau et al. Background: De novo heterozygous mutations in the GNAO1 gene, encoding the Ga o subunit of G-proteins, are the cause of a severe neurodevelopmental disorder, featuring early infantile seizures, profound cognitive dysfunction and, occasionally, movement disorder (early infantile epileptic encephalopathy-17). Methods: We report a further case of this association in a 20 month-old Spanish girl with neonatal-onset refractory seizures, progressive microcephaly, oral-lingual dyskinesia and nearly absent psychomotor development. We performed whole-exome sequencing, a computational structural analysis of the novel gene variant identified and reviewed the previously reported cases. Results: Trio whole-exome-sequencing uncovered a de novo p.Leu199Pro GNAO1 mutation. Computational structura analysis indicates this novel variant adversely affects the stability of the G-protein heterotrimeric complex as a whole. Of note, our patient showed a sustained seizure reduction while on a ketogenic diet. Conclusions: With this observation, a total of twelve patients with GNAO1 encephalopathy have been reported. Oral-lingual dyskinesia and responsiveness of seizures to ketogenic diet are novel features. The distorted sex ratio (12/12 females) of the condition remains unexplained; a differential gender effect of the disruption of G-protein-mediated signal transduction on the developing brain can be hypothesized.