GNAO1 mutated in pediatric encephalopathies encodes the major neuronal G-protein Gαo. Of >80 pathogenic mutations, most are single amino acid substitutions spreading across Gαo sequence. We perform extensive characterization of Gαo mutants showing abnormal GTP uptake and hydrolysis, and deficiencies to bind Gβγ and RGS19. Plasma membrane localization of Gαo is decreased for a subset of mutations that leads to epilepsy; dominant interactions with GPCRs also emerge for the more severe mutants. Pathogenic mutants massively gain interaction with Ric8A and, surprisingly, Ric8B proteins, delocalizing them from cytoplasm to Golgi. Of these two mandatory Gα-subunit chaperones, Ric8A is normally responsible for the Gαi/o, Gαq, and Gα12/13 subfamilies, and Ric8B solely for Gαs/olf. Ric8A/B mediate the disease dominance when engaging in neomorphic interactions with pathogenic Gαo through disbalancing the neuronal G protein signaling networks. As the strength of Gαo-Ric8B interactions correlates with disease severity, our study further identifies an efficient biomarker and predictor for clinical manifestations in GNAO1 encephalopathies. Our work discovers the neomorphic molecular mechanism of mutations underlying pediatric encephalopathies and offers insights to other maladies caused by G protein misfunctioning and further genetic diseases.