Clinical Cases and the Molecular Profiling of a Novel Childhood Encephalopathy-Causing GNAO1 Mutation P170R

Zinc for GNAO1 encephalopathy: Preclinical profiling and a clinical case

BACKGROUND

De novo pathogenic variants in GNAO1-the gene encoding the major neuronal G protein Gαo-cause pediatric encephalopathies and other neurological deficiencies largely refractory to available therapies. Zn2+ emerged to restore guanosine triphosphate hydrolysis and cellular interactions of pathogenic Gαo; dietary zinc salt supplementation improves lifespan and motoric function in a Drosophila disease model.

METHODS

Using biochemical, animal, and first-in-human studies, we provide support for the patient stratification and application of zinc acetate in GNAO1-associated disorders.

FINDINGS

We show that 16 different pathogenic missense variants cluster in three distinct groups in their responsiveness to Zn2+, and we provide the safety study in a mouse disease model. We further describe treatment of a 3-year-old patient with the common pathogenic GNAO1 variant c607G>A, p.Gly203Arg with oral 50 mg zinc (in the form of zinc acetate) daily, as applied in Wilson's disease. During 11 months of treatment, the patient shows cessation of daily dyskinetic crises, improved Burke-Fahn Marsden Dystonia Rating Scale movement score, reduction in epileptic seizures, and an excellent safety profile.

CONCLUSIONS

Our findings warrant a large-scale clinical trial and might set the new standard of care for GNAO1-related disorders.

FUNDING

This work was funded by the Russian Science Foundation (grant #21-15-00138) and GNAO1 España.

Clinical and Molecular Profiling in GNAO1 Permits Phenotype-Genotype Correlation

BACKGROUND

Defects in GNAO1, the gene encoding the major neuronal G-protein Gαo, are related to neurodevelopmental disorders, epilepsy, and movement disorders. Nevertheless, there is a poor understanding of how molecular mechanisms explain the different phenotypes.

OBJECTIVES

We aimed to analyze the clinical phenotype and the molecular characterization of GNAO1-related disorders.

METHODS

Patients were recruited in collaboration with the Spanish GNAO1 Association. For patient phenotyping, direct clinical evaluation, analysis of homemade-videos, and an online questionnaire completed by families were analyzed. We studied Gαo cellular expression, the interactions of the partner proteins, and binding to guanosine triphosphate (GTP) and G-protein-coupled receptors (GPCRs).

RESULTS

Eighteen patients with GNAO1 genetic defects had a complex neurodevelopmental disorder, epilepsy, central hypotonia, and movement disorders. Eleven patients showed neurological deterioration, recurrent hyperkinetic crisis with partial recovery, and secondary complications leading to death in three cases. Deep brain stimulation improved hyperkinetic crisis, but had inconsistent benefits in dystonia. The molecular defects caused by pathogenic Gαo were aberrant GTP binding and hydrolysis activities, an inability to interact with cellular binding partners, and reduced coupling to GPCRs. Decreased localization of Gαo in the plasma membrane was correlated with the phenotype of "developmental and epileptic encephalopathy 17." We observed a genotype-phenotype correlation, pathogenic variants in position 203 were related to developmental and epileptic encephalopathy, whereas those in position 209 were related to neurodevelopmental disorder with involuntary movements. Milder phenotypes were associated with other molecular defects such as del.16q12.2q21 and I344del.

CONCLUSION

We highlight the complexity of the motor phenotype, which is characterized by fluctuations throughout the day, and hyperkinetic crisis with a distinct post-hyperkinetic crisis state. We confirm a molecular-based genotype-phenotype correlation for specific variants. © 2024 The Author(s). Movement Disorders published by Wiley Periodicals LLC on behalf of International Parkinson and Movement Disorder Society.

GNAO1 Mutations Affecting the N-Terminal α-Helix of Gαo Lead to Parkinsonism

BACKGROUND

Patients carrying pathogenic variants in GNAO1 present a phenotypic spectrum ranging from severe early-onset epileptic encephalopathy and developmental delay to mild adolescent/adult-onset dystonia. Genotype-phenotype correlation and molecular mechanisms underlying the disease remain understudied.

METHODS

We analyzed the clinical course of a child carrying the novel GNAO1 mutation c.38T>C;p.Leu13Pro, and structural, biochemical, and cellular properties of the corresponding mutant Gαo-GNAO1-encoded protein-alongside the related mutation c.68T>C;p.Leu23Pro.

RESULTS

The main clinical feature was parkinsonism with bradykinesia and rigidity, unlike the hyperkinetic movement disorder commonly associated with GNAO1 mutations. The Leu ➔ Pro substitutions have no impact on enzymatic activity or overall folding of Gαo but uniquely destabilize the N-terminal α-helix, blocking formation of the heterotrimeric G-protein and disabling activation by G-protein-coupled receptors.

CONCLUSIONS

Our study defines a parkinsonism phenotype within the spectrum of GNAO1 disorders and suggests a genotype-phenotype correlation by GNAO1 mutations targeting the N-terminal α-helix of Gαo. © 2024 The Authors. Movement Disorders published by Wiley Periodicals LLC on behalf of International Parkinson and Movement Disorder Society.