GNAO1 and neurodevelopmental disorder: ,5 Traditionally, GNAO1-related pathology is defined as one of two ultra-rare neurodevelopmental disorders, developmental and epileptic encephalopathy 17 (OMIM: 615473) or neurodevelopmental disorder with involuntary movements (OMIM: 617493), both stemming from heterozygote mutations in GNAO1. 6,7 Recently, a milder phenotype has been added to the spectrum of GNAO1-related disorders, with the identification of variants resulting in late-onset and mild dystonia.8