16q12.2q21 deletion: A newly recognized cause of dystonia related to GNAO1 haploinsufficiency

Personalized allele-specific antisense oligonucleotides for GNAO1-neurodevelopmental disorder

GNAO1-associated disorders are ultra-rare autosomal dominant conditions, which can manifest, depending on the exact pathogenic variant in GNAO1, as a spectrum of neurological phenotypes, including epileptic encephalopathy, developmental delay with movement disorders, or late-onset dystonia. There are currently no effective treatments available, apart from symptomatic options. In this work, we suggest harnessing personalized RNA therapy to treat GNAO1 patients and focus specifically on a recurrent pathogenic variant (E246K). We systemically screened allele-specific antisense oligonucleotides (ASOs) targeting the mutated allele to identify a potent and specific sequence using both reporter-based platforms and a patient-derived cellular model. We show that reduction of mutated GNAO1 in vitro by knockout or by ASO has a beneficial functional outcome, which can be measured by cAMP accumulation and gene expression changes. We established a Gnao1-E246K mouse model that shows a neurological phenotype, which partially recapitulates the human condition. Due to sequence similarity, the mouse can be treated with the selected ASO to test treatment efficacy in animal models, as shown in vitro using murine neural progenitor cells. Our results demonstrate a beneficial effect for the reduction of mutated GNAO1 by ASO in patient-derived models, demonstrating its feasibility as a therapeutic approach.

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.

CRISPR/Cas9-generated mouse model with humanizing single-base substitution in the Gnao1 for safety studies of RNA therapeutics

The development of personalized medicine for genetic diseases requires preclinical testing in the appropriate animal models. GNAO1 encephalopathy is a severe neurodevelopmental disorder caused by heterozygous de novo mutations in the GNAO1 gene. GNAO1 c.607 G>A is one of the most common pathogenic variants, and the mutant protein Gαo-G203R likely adversely affects neuronal signaling. As an innovative approach, sequence-specific RNA-based therapeutics such as antisense oligonucleotides or effectors of RNA interference are potentially applicable for selective suppression of the mutant GNAO1 transcript. While in vitro validation can be performed in patient-derived cells, a humanized mouse model to rule out the safety of RNA therapeutics is currently lacking. In the present work, we employed CRISPR/Cas9 technology to introduce a single-base substitution into exon 6 of the Gnao1 to replace the murine Gly203-coding triplet (GGG) with the codon used in the human gene (GGA). We verified that genome-editing did not interfere with the Gnao1 mRNA or Gαo protein synthesis and did not alter localization of the protein in the brain structures. The analysis of blastocysts revealed the off-target activity of the CRISPR/Cas9 complexes; however, no modifications of the predicted off-target sites were detected in the founder mouse. Histological staining confirmed the absence of abnormal changes in the brain of genome-edited mice. The created mouse model with the “humanized” fragment of the endogenous Gnao1 is suitable to rule out unintended targeting of the wild-type allele by RNA therapeutics directed at lowering GNAO1 c.607 G>A transcripts.