Phenotypic spectrum of GNAO1 variants: epileptic encephalopathy to involuntary movements with severe developmental delay

Abstract

De novo GNAO1 variants have been found in four patients including three patients with Ohtahara syndrome and one patient with childhood epilepsy. In addition, two patients showed involuntary movements, suggesting that GNAO1 variants can cause various neurological phenotypes. Here we report an additional four patients with de novo missense GNAO1 variants, one of which was identical to that of the previously reported. All the three novel variants were predicted to impair Gαo function by structural evaluation. Two patients showed early-onset epileptic encephalopathy, presenting with migrating or multifocal partial seizures in their clinical course, but the remaining two patients showed no or a few seizures. All the four patients showed severe intellectual disability, motor developmental delay, and involuntary movements. Progressive cerebral atrophy and thin corpus callosum were common features in brain images. Our study demonstrated that GNAO1 variants can cause involuntary movements and severe developmental delay with/without seizures, including various types of early-onset epileptic encephalopathy.

Figure 1

De novo GNAO1 variants in four patients. (a) Schematic representation of GNAO1 containing two transcript variants: variant 1 (GenBank accession number, NM_020988.2) and transcript variant 2 (NM_138736.2). The UTRs and coding regions are shown in white and dark blue rectangles, respectively. Previously reported three variants except for c.607G>A (red), which is recurrently identified in this study, are shown on the upper side. Five of seven variants occurred in common exons of two transcript variants. The c.736G>A and c.836 T>A substitutions affect specifically transcript variant 1 (exon 7; NM_020988.2). All the four variants in this study caused substitution at evolutionarily highly conserved amino acids. Homologous sequences were aligned using the CLUSTALW website. (b) Mapping of the variant sites on the crystal structures of Gα-containing complexes: the GDP-bound Gαiβγ heterotrimer (PDB code 1GG2), the nucleotide-free Gαsβγ heterotrimer in complex with an agonist-occupied monomeric β2AR (PDB code 3SN6), the transition-state GTP analog (GDP⁺AlF₄⁻)-bound Gαq in complex with its effector PLCβ (PDB code 3OHM), and the GTP analog (GTPγS)-bound Gαs in complex with the catalytic domains of AC (PDB code 1AZS), from left to right, respectively. Gα, β, and γ subunits are colored in green, yellow, and pink, respectively, and the switch I and II regions in the Gα subunit are in cyan. The β2AR, PLCβ, and AC molecules are colored in gray, slate, and light brown, respectively. Guanine nucleotides are depicted as orange sticks. The variant sites are shown in red with their amino-acid number corresponding to human Gαo1 and, in parentheses, rat Gαi1 (UniProtKB/Swiss-Prot P10824), bovine Gαs (UniProtKB/Swiss-Prot P04896), mouse Gαq (UniProtKB/Swiss-Prot P21279), or bovine Gαs (UniProtKB/Swiss-Prot P04896). Molecular structures except for guanine nucleotides are shown as the space-filling representation from PyMOL (www.pymol.org). The illustrations below each model show a part of the G-protein activation process. (c) Free-energy change upon the amino-acid substitutions in each complex, calculated by the FoldX software.

Figure 2

EEG and brain MRI features of patients with GNAO1 variants. (a) A monopolar recording of an ictal EEG of patient 2 at day 39 demonstrated the presence of sharp waves that initially emerged from the fronto-central region of the right hemisphere (left box), migrated into the contralateral side, and then evolved as an ictal pattern over the left hemisphere (right box). The scale bar at the bottom shows the duration (1 s) and the amplitude (50 μV). T1-weighted (b and g) and T2-weighted (c and d) axial images through the basal ganglia, and T1-weighted sagittal images (e, f). Cerebral atrophy in patient 1 (b), cerebral atrophy with delayed myelination in patient 2 (c), and almost normal findings in patient 3 (d) were observed. (e–g) Progressive cerebral and cerebellar atrophy, brainstem atrophy, and thin corpus callosum were observed in patient 4. m, months; y, years.