Movement disorder in GNAO1 encephalopathy associated with gain-of-function mutations

Exploring the Genetic Landscape of Chorea in Infancy and Early Childhood: Implications for Diagnosis and Treatment

Chorea is a hyperkinetic movement disorder frequently observed in the pediatric population, and, due to advancements in genetic techniques, an increasing number of genes have been associated with this disorder. In genetic conditions, chorea may be the primary feature of the disorder, or be part of a more complex phenotype characterized by epileptic encephalopathy or a multisystemic syndrome. Moreover, it can appear as a persistent disorder (chronic chorea) or have an episodic course (paroxysmal chorea). Managing chorea in childhood presents challenges due to its varied clinical presentation, often involving a spectrum of hyperkinetic movement disorders alongside neuropsychiatric and multisystemic manifestations. Furthermore, during infancy and early childhood, transient motor phenomena resembling chorea occurring due to the rapid nervous system development during this period can complicate the diagnosis. This review aims to provide an overview of the main genetic causes of pediatric chorea that may manifest during infancy and early childhood, focusing on peculiarities that can aid in differential diagnosis among different phenotypes and discussing possible treatment options.

Molecular Dynamic Simulations to Determine Individualized Therapy: Tetrabenazine for the GNAO1 Encephalopathy E246K Variant

INTRODUCTION

GNAO1 encephalopathy is characterized by severe hypotonia, psychomotor retardation, epilepsy, and movement disorders. Genetic variations in GNAO1 have been linked to neurological symptoms including movement disorders like dystonia. The correlation between the E246K mutation in the Gα subunit and aberrant signal transduction of G proteins has been established but no data are reported regarding the efficacy of medical treatment with tetrabenazine.

METHODS

Molecular modeling studies were performed to elucidate the molecular mechanisms underlying this mutation. We developed drug efficacy models using molecular dynamic simulations that replicated the behavior of wild-type and mutated proteins in the presence or absence of ligands.

RESULTS AND DISCUSSION

We demonstrated that the absence of the mutation leads to normal signal transduction upon receptor activation by the endogenous ligand, but not in the presence of tetrabenazine. In contrast, the presence of the mutation resulted in abnormal signal transduction in the presence of the endogenous ligand, which was corrected by the drug tetrabenazine. Tetrabenazine was identified as a promising therapeutic option for pediatric patients suffering from encephalopathy due to an E246K mutation in the GNAO1 gene validated through molecular dynamics. This is a potential first example of the use of this technique in a rare neurological pediatric disease.

RNA Interference Effectors Selectively Silence the Pathogenic Variant GNAO1 c.607 G > A In Vitro

RNA interference (RNAi)-based therapeutics hold the potential for dominant genetic disorders, enabling sequence-specific inhibition of pathogenic gene products. We aimed to direct RNAi for the selective suppression of the heterozygous GNAO1 c.607 G > A variant causing GNAO1 encephalopathy. By screening short interfering RNA (siRNA), we showed that GNAO1 c.607G>A is a druggable target for RNAi. The si1488 candidate achieved at least twofold allelic discrimination and downregulated mutant protein to 35%. We created vectorized RNAi by incorporating the si1488 sequence into the short hairpin RNA (shRNA) in the adeno-associated virus (AAV) vector. The shRNA stem and loop were modified to improve the transcription, processing, and guide strand selection. All tested shRNA constructs demonstrated selectivity toward mutant GNAO1, while tweaking hairpin structure only marginally affected the silencing efficiency. The selectivity of shRNA-mediated silencing was confirmed in the context of AAV vector transduction. To conclude, RNAi effectors ranging from siRNA to AAV-RNAi achieve suppression of the pathogenic GNAO1 c.607G>A and discriminate alleles by the single-nucleotide substitution. For gene therapy development, it is crucial to demonstrate the benefit of these RNAi effectors in patient-specific neurons and animal models of the GNAO1 encephalopathy.

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.

The Schwann cell-specific G-protein Gαo (Gnao1) is a cell-intrinsic controller contributing to the regulation of myelination in peripheral nerve system

Myelin sheath abnormality is the cause of various neurodegenerative diseases (NDDs). G-proteins and their coupled receptors (GPCRs) play the important roles in myelination. Gnao1, encoding the major Gα protein (Gαo) in mammalian nerve system, is required for normal motor function. Here, we show that Gnao1 restricted to Schwann cell (SCs) lineage, but not neurons, negatively regulate SC differentiation, myelination, as well as re-myelination in peripheral nervous system (PNS). Mice lacking Gnao1 expression in SCs exhibit faster re-myelination and motor function recovery after nerve injury. Conversely, mice with Gnao1 overexpression in SCs display the insufficient myelinating capacity and delayed re-myelination. In vitro, Gnao1 deletion in SCs promotes SC differentiation. We found that Gnao1 knockdown in SCs resulting in the elevation of cAMP content and the activation of PI3K/AKT pathway, both associated with SC differentiation. The analysis of RNA sequencing data further evidenced that Gnao1 deletion cause the increased expression of myelin-related molecules and activation of regulatory pathways. Taken together, our data indicate that Gnao1 negatively regulated SC differentiation by reducing cAMP level and inhibiting PI3K-AKT cascade activation, identifying a novel drug target for the treatment of demyelinating diseases.

Next-generation sequencing and bioinformatics in rare movement disorders

The ability to sequence entire exomes and genomes has revolutionized molecular testing in rare movement disorders, and genomic sequencing is becoming an integral part of routine diagnostic workflows for these heterogeneous conditions. However, interpretation of the extensive genomic variant information that is being generated presents substantial challenges. In this Perspective, we outline multidimensional strategies for genetic diagnosis in patients with rare movement disorders. We examine bioinformatics tools and computational metrics that have been developed to facilitate accurate prioritization of disease-causing variants. Additionally, we highlight community-driven data-sharing and case-matchmaking platforms, which are designed to foster the discovery of new genotype-phenotype relationships. Finally, we consider how multiomic data integration might optimize diagnostic success by combining genomic, epigenetic, transcriptomic and/or proteomic profiling to enable a more holistic evaluation of variant effects. Together, the approaches that we discuss offer pathways to the improved understanding of the genetic basis of rare movement disorders.

Molecular annotation of G protein variants in a neurological disorder

Heterotrimeric G proteins transduce extracellular chemical messages to generate appropriate intracellular responses. Point mutations in GNAO1, encoding the G protein αo subunit, have been implicated in a pathogenic condition characterized by seizures, movement disorders, intellectual disability, and developmental delay (GNAO1 disorder). However, the effects of these mutations on G protein structure and function are unclear. Here, we report the effects of 55 mutations on Gαo conformation, thermostability, nucleotide binding, and hydrolysis, as well as interaction with Gβγ subunits, receptors, and effectors. Our effort reveals four functionally distinct groups of mutants, including one group that sequesters receptors and another that sequesters Gβγ, both acting in a genetically dominant manner. These findings provide a more comprehensive understanding of disease-relevant mutations and reveal that GNAO1 disorder is likely composed of multiple mechanistically distinct disorders that will likely require multiple therapeutic strategies.

Severity of GNAO1-Related Disorder Correlates with Changes in G-Protein Function

OBJECTIVE

GNAO1-related disorders (OMIM #615473 and #617493), caused by variants in the GNAO1 gene, are characterized by developmental delay or intellectual disability, hypotonia, movement disorders, and epilepsy. Neither a genotype-phenotype correlation nor a clear severity score have been established for this disorder. The objective of this prospective and retrospective observational study was to develop a severity score for GNAO1-related disorders, and to delineate the correlation between the underlying molecular mechanisms and clinical severity.

METHODS

A total of 16 individuals with GNAO1-related disorders harboring 12 distinct missense variants, including four novel variants (p.K46R, p.T48I, p.R209P, and p.L235P), were examined with repeated clinical assessments, video-electroencephalogram monitoring, and brain magnetic resonance imaging. The molecular pathology of each variant was delineated using a molecular deconvoluting platform.

RESULTS

The patients displayed a wide variability in the severity of their symptoms. This heterogeneity was well represented in the GNAO1-related disorders severity score, with a broad range of results. Patients with the same variant had comparable severity scores, indicating that differences in disease profiles are not due to interpatient variability, but rather, to unique disease mechanisms. Moreover, we found a significant correlation between clinical severity scores and molecular mechanisms.

INTERPRETATION

The clinical score proposed here provides further insight into the correlation between pathophysiology and phenotypic severity in GNAO1-related disorders. We found that each variant has a unique profile of clinical phenotypes and pathological molecular mechanisms. These findings will contribute to better understanding GNAO1-related disorders. Additionally, the severity score will facilitate standardization of patients categorization and assessment of response to therapies in development. ANN NEUROL 2023;94:987-1004.

Genotype-phenotype correlation and treatment effects in young patients with GNAO1-associated disorders

BACKGROUND

Patients carrying pathogenic variants in GNAO1 often present with early-onset central hypotonia and global developmental delay, with or without epilepsy. As the disorder progresses, a complex hypertonic and hyperkinetic movement disorder is a common phenotype. A genotype-phenotype correlation has not yet been described and there are no evidence-based therapeutic recommendations.

METHODS

To improve understanding of the clinical course and pathophysiology of this ultra-rare disorder, we built up a registry for GNAO1 patients in Germany. In this retrospective, multicentre cohort study, we collected detailed clinical data, treatment effects and genetic data for 25 affected patients.

RESULTS

The main clinical features were symptom onset within the first months of life, with central hypotonia or seizures. Within the first year of life, nearly all patients developed a movement disorder comprising dystonia (84%) and choreoathetosis (52%). Twelve (48%) patients suffered life-threatening hyperkinetic crises. Fifteen (60%) patients had epilepsy with poor treatment response. Two patients showed an atypical phenotype and seven novel pathogenic variants in GNAO1 were identified. Nine (38%) patients were treated with bilateral deep brain stimulation of the globus pallidus internus. Deep brain stimulation reduced hyperkinetic symptoms and prevented further hyperkinetic crises. The in silico prediction programmes did not predict the phenotype by the genotype.

CONCLUSION

The broad clinical spectrum and genetic findings expand the phenotypical spectrum of GNAO1-associated disorder and therefore disprove the assumption that there are only two main phenotypes. No specific overall genotype-phenotype correlation was identified. We highlight deep brain stimulation as a useful treatment option in this disorder.

Phenotypes in children with GNAO1 encephalopathy in China

Background

The GNAO1 gene encodes the α-subunit (Gαo) of the heterotrimeric guanine nucleotide-binding protein (G protein). The aim of this study was to explore the clinical characteristics of patients with GNAO1 pathogenic variations.

Methods

Ten patients with pathogenic variations in GNAO1 were enrolled from the Shenzhen Children's Hospital. Clinical data from several cases previously reported from China were also included and analyzed.

Results

Twenty-seven patients with variations in GNAO1 were analyzed (10 patients from Shenzhen Children's Hospital, 17 patients from previously published studies) including 12 boys and 15 girls. The median age of onset was 3 months with moderate to severe global developmental delay. Nineteen different GNAO1 heterozygous variants were identified. Epilepsy was observed in 18 patients (67%, 18/27), movement disorder (MD) was observed in 22 patients (81%, 22/27), and both were seen in 13 patients (48%, 13/27). Seizures typically presented as focal seizures in all patients with epilepsy. MD typically presented as dystonia and chorea. Loss-of-function (LOF) or partial loss-of-function (PLOF) mutations were more frequent in patients with developmental and epileptic encephalopathy (p = 0.029). Interictal electroencephalograms showed multifocal or diffuse epileptiform discharges. The most common magnetic resonance imaging finding was widened extracerebral space. In contrast to MD, in which improvements were not common, seizures were easily controlled by anti-seizure medications. Severe dystonia in three patients was effectively treated by deep brain stimulation. Seven (26%, 7/27) patients died of respiratory complications, status dystonicus, choreoathetosis, or sudden unexpected death in epilepsy.

Conclusion

We analyzed clinical data of 27 cases of GNAO1-related encephalopathy in China. MD seemed to be the central feature and was most difficult to control. LOF or PLOF variants were significantly associated with developmental and epileptic encephalopathy. The active intervention of severe dystonia may prevent death due to status dystonicus. However, future studies with larger samples are needed to confirm these results.

Dystonia genes and their biological pathways

High-throughput sequencing has been instrumental in uncovering the spectrum of pathogenic genetic alterations that contribute to the etiology of dystonia. Despite the immense heterogeneity in monogenic causes, studies performed during the past few years have highlighted that many rare deleterious variants associated with dystonic presentations affect genes that have roles in certain conserved pathways in neural physiology. These various gene mutations that appear to converge towards the disruption of interconnected cellular networks were shown to produce a wide range of different dystonic disease phenotypes, including isolated and combined dystonias as well as numerous clinically complex, often neurodevelopmental disorder-related conditions that can manifest with dystonic features in the context of multisystem disturbances. In this chapter, we summarize the manifold dystonia-gene relationships based on their association with a discrete number of unifying pathophysiological mechanisms and molecular cascade abnormalities. The themes on which we focus comprise dopamine signaling, heavy metal accumulation and calcifications in the brain, nuclear envelope function and stress response, gene transcription control, energy homeostasis, lysosomal trafficking, calcium and ion channel-mediated signaling, synaptic transmission beyond dopamine pathways, extra- and intracellular structural organization, and protein synthesis and degradation. Enhancing knowledge about the concept of shared etiological pathways in the pathogenesis of dystonia will motivate clinicians and researchers to find more efficacious treatments that allow to reverse pathologies in patient-specific core molecular networks and connected multipathway loops.

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.

Dystonic Cerebral Palsy Phenotype Due to GNAO1 Variant Responsive to Levodopa

Background

Cerebral palsy (CP) should not be considered a diagnosis, but rather a syndrome related to several etiologies, including, but not limited to, neurological sequelae of a perinatal brain injury.

Case report

24-years-old man with dystonia and delayed motor and cognitive development had been previously diagnosed with CP. Molecular genetic testing identified a heterozygosity variant in GNAO 1 gene. A therapeutic trial with levodopa was started, with improvement of dystonia.

Discussion

GNAO1 gene variant disorders share similarities with other causes of CP syndrome, and thus investigation of this variant should be included in instances of CP syndrome without a clear history of previous perinatal brain injury. GNAO1 dystonic phenotype (DYT-GNAO1) should be considered as dopa-responsive dystonia in some cases.

Regulator of G-Protein Signalling 4 (RGS4) negatively modulates nociceptin/orphanin FQ opioid receptor signalling: Implication for l-Dopa-induced dyskinesia

BACKGROUND AND PURPOSE

Regulator of G-protein signalling 4 (RGS4) is a signal transduction protein that accelerates intrinsic GTPase activity of Gαi/o and Gαq subunits, suppressing GPCR signalling. Here, we investigate whether RGS4 modulates nociceptin/orphanin FQ (N/OFQ) opioid (NOP) receptor signalling and if this modulation has relevance for l-Dopa-induced dyskinesia.

EXPERIMENTAL APPROACH

HEK293T cells transfected with NOP, NOP/RGS4 or NOP/RGS19 were challenged with N/OFQ and the small-molecule NOP agonist AT-403, using D1-stimulated cAMP levels as a readout. Primary rat striatal neurons and adult mouse striatal slices were challenged with either N/OFQ or AT-403 in the presence of the experimental RGS4 chemical probe, CCG-203920, and D1-stimulated cAMP or phosphorylated extracellular signal regulated kinase 1/2 (pERK) responses were monitored. In vivo, CCG-203920 was co-administered with AT-403 and l-Dopa to 6-hydroxydopamine hemilesioned rats, and dyskinetic movements, striatal biochemical correlates of dyskinesia (pERK and pGluR1 levels) and striatal RGS4 levels were measured.

KEY RESULTS

RGS4 expression reduced NOFQ and AT-403 potency and efficacy in HEK293T cells. CCG-203920 increased N/OFQ potency in primary rat striatal neurons and potentiated AT-403 response in mouse striatal slices. CCG-203920 enhanced AT-403-mediated inhibition of dyskinesia and its biochemical correlates, without compromising its motor-improving effects. Unilateral dopamine depletion caused bilateral reduction of RGS4 levels, which was reversed by l-Dopa. l-Dopa acutely up-regulated RGS4 in the lesioned striatum.

CONCLUSIONS AND IMPLICATIONS

RGS4 physiologically inhibits NOP receptor signalling. CCG-203920 enhanced NOP responses and improved the antidyskinetic potential of NOP receptor agonists, mitigating the effects of striatal RGS4 up-regulation occurring during dyskinesia expression.

LINKED ARTICLES

This article is part of a themed issue on Advances in Opioid Pharmacology at the Time of the Opioid Epidemic. To view the other articles in this section visit http://onlinelibrary.wiley.com/doi/10.1111/bph.v180.7/issuetoc.

In-depth molecular profiling of an intronic GNAO1 mutant as the basis for personalized high-throughput drug screening

BACKGROUND

The GNAO1 gene, encoding the major neuronal G protein Gαo, is mutated in a subset of pediatric encephalopathies. Most such mutations consist of missense variants.

METHODS

In this study, we present a precision medicine workflow combining next-generation sequencing (NGS) diagnostics, molecular etiology analysis, and personalized drug discovery.

FINDINGS

We describe a patient carrying a de novo intronic mutation (NM_020988.3:c.724-8G>A), leading to epilepsy-negative encephalopathy with motor dysfunction from the second decade. Our data show that this mutation creates a novel splice acceptor site that in turn causes an in-frame insertion of two amino acid residues, Pro-Gln, within the regulatory switch III region of Gαo. This insertion misconfigures the switch III loop and creates novel interactions with the catalytic switch II region, resulting in increased GTP uptake, defective GTP hydrolysis, and aberrant interactions with effector proteins. In contrast, intracellular localization, Gβγ interactions, and G protein-coupled receptor (GPCR) coupling of the Gαo[insPQ] mutant protein remain unchanged.

CONCLUSIONS

This in-depth analysis characterizes the heterozygous c.724-8G>A mutation as partially dominant negative, providing clues to the molecular etiology of this specific pathology. Further, this analysis allows us to establish and validate a high-throughput screening platform aiming at identifying molecules that could correct the aberrant biochemical functions of the mutant Gαo.

FUNDING

This work was supported by the Joint Seed Money Funding scheme between the University of Geneva and the Hebrew University of Jerusalem.

Visual Function in Children with GNAO1-Related Encephalopathy

Background: GNAO1-related encephalopathies include a broad spectrum of developmental disorders caused by de novo heterozygous mutations in the GNAO1 gene, encoding the G (o) subunit α of G-proteins. These conditions are characterized by epilepsy, movement disorders and developmental impairment, in combination or as isolated features. Objective: This study aimed at describing the profile of neurovisual competences in children with GNAO1 deficiency to better characterize the phenotype of the disease spectrum. Methods: Four male and three female patients with confirmed genetic diagnosis underwent neurological examination, visual function assessment, and neurovisual and ophthalmological evaluation. Present clinical history of epilepsy and movement disorders, and neuroimaging findings were also evaluated. Results: The assessment revealed two trends in visual development. Some aspects of visual function, such as discrimination and perception of distance, depth and volume, appeared to be impaired at all ages, with no sign of improvement. Other aspects, reliant on temporal lobe competences (ventral stream) and more related to object–face exploration, recognition and environmental control, appeared to be preserved and improved with age. Significance: Visual function is often impaired, with patterns of visual impairment affecting the ventral stream less.

Clocking Epilepsies: A Chronomodulated Strategy-Based Therapy for Rhythmic Seizures

Epilepsy is a neurological disorder characterized by hypersynchronous recurrent neuronal activities and seizures, as well as loss of muscular control and sometimes awareness. Clinically, seizures have been reported to display daily variations. Conversely, circadian misalignment and circadian clock gene variants contribute to epileptic pathogenesis. Elucidation of the genetic bases of epilepsy is of great importance because the genetic variability of the patients affects the efficacies of antiepileptic drugs (AEDs). For this narrative review, we compiled 661 epilepsy-related genes from the PHGKB and OMIM databases and classified them into 3 groups: driver genes, passenger genes, and undetermined genes. We discuss the potential roles of some epilepsy driver genes based on GO and KEGG analyses, the circadian rhythmicity of human and animal epilepsies, and the mutual effects between epilepsy and sleep. We review the advantages and challenges of rodents and zebrafish as animal models for epileptic studies. Finally, we posit chronomodulated strategy-based chronotherapy for rhythmic epilepsies, integrating several lines of investigation for unraveling circadian mechanisms underpinning epileptogenesis, chronopharmacokinetic and chronopharmacodynamic examinations of AEDs, as well as mathematical/computational modeling to help develop time-of-day-specific AED dosing schedules for rhythmic epilepsy patients.

[Encephalopathy GNAO1]

OBJECTIVE

To study the clinical picture of all patients with GNAO1 encephalopathy detected in the Russian Federation. This publication is a multicenter study combining data from epileptological centers in Moscow, Novosibirsk, St. Petersburg, Nizhny Novgorod, Tyumen.

MATERIAL AND METHODS

Nine patients were included, aged 2 to 19 years, with 4 mutations. Male to female sex ratio = 5:4.

RESULTS

8 patients (5 with mutation c.607G>A (p.Gly203Arg), 1 - c.155A>G (Gln52Arg), 1 - c.485G>A (p.Arg162Gln)) had a variant of epileptic encephalopathy, developmental encephalopathy, 1 patient had torsion dystonia without epilepsy (mutation c.713A>G (p.Asp238Gly)). Epileptic seizures in 8 children with epileptic encephalopathy GNAO1 in 100% debuted at 1 month of life, becoming the earliest symptom of the disease. Motor development delayed in 100% of cases. Mental development was not affected only in the case of the dystonic variant. Hyperkinesis (dystonia, choreoathetosis, ballism) followed later, from 2 to 8 months. They were more severe than epilepsy. 4 patients with the c.607G>A (p.Gly203Arg) mutation developed repeated dystonic storms that were resistant to most drugs.

CONCLUSION

Epilepsy in GNAO1 is difficult to treat, but temporary or complete remission is possible. Effective drug strategies for the treatment of hyperkinesis have not yet been developed. Expansion of indications for surgical therapy (DBS) of hyperkinesis in this syndrome is desirable.

Phenotypic Assessment of Pathogenic Variants in GNAO1 and Response to Caffeine in C. elegans Models of the Disease

De novo mutations affecting the G protein α o subunit (Gαo)-encoding gene (GNAO1) cause childhood-onset developmental delay, hyperkinetic movement disorders, and epilepsy. Recently, we established Caenorhabditis elegans as an informative experimental model for deciphering pathogenic mechanisms associated with GNAO1 defects and identifying new therapies. In this study, we generated two additional gene-edited strains that harbor pathogenic variants which affect residues Glu246 and Arg209-two mutational hotspots in Gαo. In line with previous findings, biallelic changes displayed a variable hypomorphic effect on Gαo-mediated signaling that led to the excessive release of neurotransmitters by different classes of neurons, which, in turn, caused hyperactive egg laying and locomotion. Of note, heterozygous variants showed a cell-specific dominant-negative behavior, which was strictly dependent on the affected residue. As with previously generated mutants (S47G and A221D), caffeine was effective in attenuating the hyperkinetic behavior of R209H and E246K animals, indicating that its efficacy is mutation-independent. Conversely, istradefylline, a selective adenosine A2A receptor antagonist, was effective in R209H animals but not in E246K worms, suggesting that caffeine acts through both adenosine receptor-dependent and receptor-independent mechanisms. Overall, our findings provide new insights into disease mechanisms and further support the potential efficacy of caffeine in controlling dyskinesia associated with pathogenic GNAO1 mutations.

GNAO1-related neurodevelopmental disorder: Literature review and caregiver survey

Background

GNAO1-related neurodevelopmental disorder is a heterogeneous condition characterized by hypotonia, developmental delay, epilepsy, and movement disorder. This study aims to better understand the spectrum of epilepsy associated with GNAO1 variants and experience with anti-seizure medications, and to review published epilepsy phenotypes in GNAO1.

Methods

An online survey was distributed to caregivers of individuals diagnosed with GNAO1 pathogenic variants, and a literature review was conducted.

Results

Fifteen respondents completed the survey with the median age of 39 months, including a novel variant p.Q52P. Nine had epilepsy - six had onset in the first week of life, three in the first year of life - but two reported no ongoing seizures. Seizure types varied. Individuals were taking a median of 3 seizure medications without a single best treatment. Our cohort was compared to a literature review of epilepsy in GNAO1. In 86 cases, 38 discrete variants were described; epilepsy is reported in 53 % cases, and a developmental and epileptic encephalopathy in 36 %.

Conclusions

While GNAO1-related epilepsy is most often early-onset and severe, seizures may not always be drug resistant or lifelong. Experience with anti-seizure medications is varied. Certain variant "hotspots" may correlate with epilepsy phenotype though genotype-phenotype correlation is poorly understood.

Intestinal flora induces depression by mediating the dysregulation of cerebral cortex gene expression and regulating the metabolism of stroke patients

Post-stroke depression (PSD) is a common cerebrovascular complication characterized by complex pathogenesis and poor treatment effects. Here, we tested the influence of differentially expressed genes (DEGs), non-targeted metabolites, and intestinal microbes on the occurrence and development of PSD. We acquired gene expression profiles for stroke patients, depression patients, and healthy controls from the Gene Expression Omnibus database. After screening for DEGs using differential expression analysis, we identified common DEGs in stroke and depression patients that were considered to form the molecular basis of PSD. Functional enrichment analysis of DEGs also revealed that the majority of biological functions were closely related to metabolism, immunity, the nervous system, and microorganisms, and we also collected blood and stool samples from healthy controls, stroke patients, and PSD patients and performed 16S rDNA sequencing and untargeted metabolomics. After evaluating the quality of the sequencing data, we compared the diversity of the metabolites and intestinal flora within and between groups. Metabolic pathway enrichment analysis was used to identify metabolic pathways that were significantly involved in stroke and PSD, and a global metabolic network was constructed to explore the pathogenesis of PSD. Additionally, we constructed a global regulatory network based on 16S rDNA sequencing, non-targeted metabolomics, and transcriptomics to explore the pathogenesis of PSD through correlation analysis. Our results suggest that intestinal flora associates the dysregulation of cerebral cortex gene expression and could potentially promote the occurrence of depression by affecting the metabolism of stroke patients. Our findings may be helpful in identifying new targets for the prevention and treatment of PSD.

Restoration of the GTPase activity and cellular interactions of Gαo mutants by Zn2+ in GNAO1 encephalopathy models

De novo point mutations in GNAO1, gene encoding the major neuronal G protein Gα_o, have recently emerged in patients with pediatric encephalopathy having motor, developmental, and epileptic dysfunctions. Half of clinical cases affect codons Gly²⁰³, Arg²⁰⁹, or Glu²⁴⁶; we show that these mutations accelerate GTP uptake and inactivate GTP hydrolysis through displacement Gln²⁰⁵ critical for GTP hydrolysis, resulting in constitutive GTP binding by Gα_o. However, the mutants fail to adopt the activated conformation and display aberrant interactions with signaling partners. Through high-throughput screening of approved drugs, we identify zinc pyrithione and Zn²⁺ as agents restoring active conformation, GTPase activity, and cellular interactions of the encephalopathy mutants, with negligible effects on wild-type Gα_o. We describe a Drosophila model of GNAO1 encephalopathy where dietary zinc restores the motor function and longevity of the mutant flies. Zinc supplements are approved for diverse human neurological conditions. Our work provides insights into the molecular etiology of GNAO1 encephalopathy and defines a potential therapy for the patients.

The attenuation effect of potassium 2-(1-hydroxypentyl)-benzoate in a mouse model of diabetes-associated cognitive decline: The protein expression in the brain

Aims

dl‐PHPB (potassium 2‐(1‐hydroxypentyl)‐benzoate) has been shown to have neuroprotective effects against acute cerebral ischemia, vascular dementia, and Alzheimer's disease. The aim of this study was to investigate the effects of dl‐PHPB on memory deficits and preliminarily explore the underlying molecular mechanism.

Methods

Blood glucose and behavioral performance were evaluated in the KK‐A^y diabetic mouse model before and after dl‐PHPB administration. Two‐dimensional difference gel electrophoresis (2D‐DIGE)‐based proteomics was used to identify differentially expressed proteins in brain tissue. Western blotting was used to study the molecular mechanism of the related signaling pathways.

Results

Three‐month‐old KK‐A^y mice were given 150 mg/kg dl‐PHPB by oral gavage for 2 months, which produced no effect on the level of serum glucose. In the Morris water maze test, KK‐A^y mice treated with dl‐PHPB showed significant improvements in spatial learning and memory deficits compared with vehicle‐treated KK‐A^y mice. Additionally, we performed 2D‐DIGE to compare brain proteomes of 5‐month KK‐A^y mice treated with and without dl‐PHPB. We found 14 altered proteins in the cortex and 11 in the hippocampus; two of the 25 altered proteins and another four proteins that were identified in a previous study on KK‐A^y mice were then validated by western blot to further confirm whether dl‐PHPB can reverse the expression levels of these proteins. The phosphoinositide 3‐kinase/protein kinase B/glycogen synthase kinase‐3β (PI3K/Akt/GSK‐3β) signaling pathway was also changed in KK‐A^y mice and dl‐PHPB treatment could reverse it.

Conclusions

These results indicate that dl‐PHPB may play a potential role in diabetes‐associated cognitive impairment through PI3K/Akt/GSK‐3β signaling pathway and the differentially expressed proteins may become putative therapeutic targets.

Gonadal mosaicism in GNAO1 causing neurodevelopmental disorder with involuntary movements; two additional variants

Background

GNAO1 encodes an alpha subunit of the heterotrimeric guanine nucleotide-binding proteins (G proteins). Mutations in GNAO1 result in two clinical phenotypes: Early infantile epileptic encephalopathy 17 (EEIE17-OMIM #615473) and Neurodevelopmental disorder with involuntary movements (NEDIM-OMIM #617493). Both are inherited as autosomal dominant disorders and originate mainly as de novo. Only a few are reported as gonadal mosaicism.

Materials and methods

We recruited and retrospectively reviewed five patients from two families seen at King Faisal Specialist Hospital and Research Centre in Riyadh (KFSHRC).

Results

All patients presented with severe neurodevelopmental disorder, followed by progressive dystonia and hyperkinetic movements. In addition, none of the patients had seizures which was consistent with NEDIM phenotype. The specific diagnosis was not clinically entertained and was only found on whole exome sequencing (WES), which identified two variants (c.724-8G > A & c.709G > A). Both variants were previously reported as pathogenic de novo in patients with NEDIM, and one was reported as parental gonadal mosaicism.

Conclusion

We report these variants as additional variants in GNAO1 gene that may be inherited as parental gonadal mosaicism. Both variants resulted in NEDIM with no observed clinical differences in the severity than the reported cases. This noticeable reported association between GNAO1 gene associated disorders and gonadal mosaicism should be considered in reproductive genetic counselling of affected families. Furthermore, in view of these reports, more studies with prospective data collection to explore the association between GNAO1 and gonadal mosaicism and the underlying mechanisms will be necessary.

Both subthalamic and pallidal deep brain stimulation are effective for GNAO1-associated dystonia: three case reports and a literature review

Background

Mutations in the G-protein subunit alpha o1 (GNAO1) gene have recently been shown to be involved in the pathogenesis of early infantile epileptic encephalopathy and movement disorders. The clinical manifestations of GNAO1-associated movement disorders are highly heterogeneous. However, the genotype-phenotype correlations in this disease remain unclear, and the treatments for GNAO1-associated movement disorders are still limited.

Objective

The objective of this study was to explore diagnostic and therapeutic strategies for GNAO1-associated movement disorders.

Methods

This study describes the cases of three Chinese patients who had shown severe and progressive dystonia in the absence of epilepsy since early childhood. We performed genetic analyses in these patients. Patients 1 and 2 underwent globus pallidus internus (GPi) deep brain stimulation (DBS) implantation, and Patient 3 underwent subthalamic nucleus (STN) DBS implantation. In addition, on the basis of a literature review, we summarized and discussed the clinical characteristics and outcomes after DBS surgery for all reported patients with GNAO1-associated movement disorders.

Results

Whole-exome sequencing (WES) analysis revealed de novo variants in the GNAO1 gene for all three patients, including a splice-site variant (c.724-8G > A) in Patients 1 and 3 and a novel heterozygous missense variant (c.124G > A; p. Gly42Arg) in Patient 2. Both GPi and STN DBS were effective in improving the dystonia symptoms of all three patients.

Conclusion

DBS is effective in ameliorating motor symptoms in patients with GNAO1-associated movement disorders, and both STN DBS and GPi DBS should be considered promptly for patients with sustained refractory GNAO1-associated dystonia.

Efficacy of Caffeine in ADCY5-Related Dyskinesia: A Retrospective Study

BACKGROUND

ADCY5-related dyskinesia is characterized by early-onset movement disorders. There is currently no validated treatment, but anecdotal clinical reports and biological hypotheses suggest efficacy of caffeine.

OBJECTIVE

The aim is to obtain further insight into the efficacy and safety of caffeine in patients with ADCY5-related dyskinesia.

METHODS

A retrospective study was conducted worldwide in 30 patients with a proven ADCY5 mutation who had tried or were taking caffeine for dyskinesia. Disease characteristics and treatment responses were assessed through a questionnaire.

RESULTS

Caffeine was overall well tolerated, even in children, and 87% of patients reported a clear improvement. Caffeine reduced the frequency and duration of paroxysmal movement disorders but also improved baseline movement disorders and some other motor and nonmotor features, with consistent quality-of-life improvement. Three patients reported worsening.

CONCLUSION

Our findings suggest that caffeine should be considered as a first-line therapeutic option in ADCY5-related dyskinesia. © 2022 International Parkinson and Movement Disorder Society.

An intronic GNAO1 variant leading to in-frame insertion cause movement disorder controlled by deep brain stimulation

GNAO1 variants are associated with a wide range of neurodevelopmental disorders including epileptic encephalopathies and movement disorders. It has been reported that some GNAO1 variants are associated with movement disorders, and the 207-246 amino acid region was proposed as a mutational hotspot. Here, we report an intronic variant (NM_020988.3:c.724-8G>A) in GNAO1 in a Japanese girl who showed mild developmental delay and movement disorders including dystonia and myoclonus. Her movement disorders were improved by deep brain stimulation treatment as previously reported. This variant has been recurrently reported in four patients and was transmitted from her mother who possessed the variant as low-prevalent mosaicism. Using RNA extracted from lymphoblastoid cells derived from the patient, we demonstrated that the variant caused abnormal splicing of in-frame 6-bp intronic retention, leading to 2 amino acid insertion (p.Thr241_Asn242insProGln). Immunoblotting and immunostaining using WT and mutant GNAO1 vectors showed no significant differences in protein expression levels, but the cellular localization pattern of this mutant was partially shifted to the cytoplasm whereas WT was exclusively localized in the cellular membrane. Our report first clarified abnormal splicing and resulting mutant protein caused by the c.724-8G>A variant.

MICE WITH GNAO1-ASSOCIATED MOVEMENT DISORDER EXHIBIT REDUCED INHIBITORY SYNAPTIC INPUT TO CEREBELLAR PURKINJE CELLS

GNAO1 encodes Gα_o, a heterotrimeric G protein alpha subunit in the G_i/o family. In this report, we used a Gnao1 mouse model "G203R" previously described as a "gain-of-function" Gnao1 mutant with movement abnormalities and enhanced seizure susceptibility. Here, we report an unexpected second mutation resulting in a loss-of-function Gα_o protein and describe alterations in central synaptic transmission. Whole cell patch clamp recordings from Purkinje cells (PCs) in acute cerebellar slices from Gnao1 mutant mice showed significantly lower frequencies of spontaneous and miniature inhibitory postsynaptic currents (sIPSCs and mIPSCs) compared to WT mice. There was no significant change in sEPSCs or mEPSCs. Whereas mIPSC frequency was reduced, mIPSC amplitudes were not affected, suggesting a presynaptic mechanism of action. A modest decrease in the number of molecular layer interneurons was insufficient to explain the magnitude of IPSC suppression. Paradoxically, G_i/o inhibitors (pertussis toxin), enhanced the mutant-suppressed mIPSC frequency and eliminated the difference between WT and Gnao1 mice. While GABA_B receptor regulates mIPSCs, neither agonists nor antagonists of this receptor altered function in the mutant mouse PCs. This study is the first electrophysiological investigation of the role of G_i/o proteinin cerebellar synaptic transmission using an animal model with a loss-of-function G_i/o protein.

GNAO1 as a Novel Predictive Biomarker for Late Relapse in Hepatocellular Carcinoma

GNAO1, the alpha O1 subunit of G protein, was reported to be significantly downregulated in hepatocellular carcinoma (HCC), as well as being implicated in a variety of intracellular biological events; findings suggest that it may act as a tumor suppressor. Our goal was to further explore the expression of GNAO1 in HCC patients and its potential clinical significance. Oncomine and Kaplan–Meier plotter databases were used to assess the mRNA expression of GNAO1 in HCC tissues and patient survival time. Subsequently, immunohistochemistry (IHC) was used to measure GNAO1 protein level in tissue from 79 cases of HCC and paired adjacent tissues. The Kaplan–Meier survival analysis, Cox regression model, and prognostic nomogram were used to evaluate the prognostic role of GNAO1 in HCC. Results demonstrated that mRNA and protein expressions of GNAO1 were both lower in HCC tissues than in adjacent tissues (all p < 0.01). HCC patients with high expression of GNAO1 had better relapse-free survival (RFS) than those with low GNAO1 expression (all p < 0.05). A high expression of GNAO1, meanwhile, functioned as a good predictor of late relapse for HCC (p < 0.05). The nomogram consisting of GNAO1 expression and the tumor-node-metastasis (TNM) model presented good ability in predicting the 3-year relapse for HCC (C-index = 0.614). In conclusion, GNAO1 was a reliable biomarker of relapse prediction for HCC.

Caenorhabditis elegans provides an efficient drug screening platform for GNAO1-related disorders and highlights the potential role of caffeine in controlling dyskinesia

Dominant GNAO1 mutations cause an emerging group of childhood-onset neurological disorders characterized by developmental delay, intellectual disability, movement disorders, drug-resistant seizures and neurological deterioration. GNAO1 encodes the α-subunit of an inhibitory GTP/GDP-binding protein regulating ion channel activity and neurotransmitter release. The pathogenic mechanisms underlying GNAO1-related disorders remain largely elusive and there are no effective therapies. Here, we assessed the functional impact of two disease-causing variants associated with distinct clinical features, c.139A > G (p.S47G) and c.662C > A (p.A221D), using Caenorhabditis elegans as a model organism. The c.139A > G change was introduced into the orthologous position of the C. elegans gene via CRISPR/Cas9, whereas a knock-in strain carrying the p.A221D variant was already available. Like null mutants, homozygous knock-in animals showed increased egg laying and were hypersensitive to aldicarb, an inhibitor of acetylcholinesterase, suggesting excessive neurotransmitter release by different classes of motor neurons. Automated analysis of C. elegans locomotion indicated that goa-1 mutants move faster than control animals, with more frequent body bends and a higher reversal rate and display uncoordinated locomotion. Phenotypic profiling of heterozygous animals revealed a strong hypomorphic effect of both variants, with a partial dominant-negative activity for the p.A221D allele. Finally, caffeine was shown to rescue aberrant motor function in C. elegans harboring the goa-1 variants; this effect is mainly exerted through adenosine receptor antagonism. Overall, our findings establish a suitable platform for drug discovery, which may assist in accelerating the development of new therapies for this devastating condition, and highlight the potential role of caffeine in controlling GNAO1-related dyskinesia.

Genetic modeling of GNAO1 disorder delineates mechanisms of Gαo dysfunction

GNAO1 encephalopathy is a neurodevelopmental disorder with a spectrum of symptoms that include dystonic movements, seizures and developmental delay. While numerous GNAO1 mutations are associated with this disorder, the functional consequences of pathological variants are not completely understood. Here, we deployed the invertebrate C. elegans as a whole-animal behavioral model to study the functional effects of GNAO1 disorder-associated mutations. We tested several pathological GNAO1 mutations for effects on locomotor behaviors using a combination of CRISPR/Cas9 gene editing and transgenic overexpression in vivo. We report that all three mutations tested (G42R, G203R and R209C) result in strong loss of function defects when evaluated as homozygous CRISPR alleles. In addition, mutations produced dominant negative effects assessed using both heterozygous CRISPR alleles and transgenic overexpression. Experiments in mice confirmed dominant negative effects of GNAO1 G42R, which impaired numerous motor behaviors. Thus, GNAO1 pathological mutations result in conserved functional outcomes across animal models. Our study further establishes the molecular genetic basis of GNAO1 encephalopathy, and develops a CRISPR-based pipeline for functionally evaluating mutations associated with neurodevelopmental disorders.

Hidden etiology of cerebral palsy: genetic and clinical heterogeneity and efficient diagnosis by next-generation sequencing

Cerebral palsy (CP) is a heterogeneous neurodevelopmental disorder that causes movement and postural disabilities. Recent research studies focused on genetic diagnosis in patients with CP of unknown etiology. The present study was carried out in 20 families with one family member affected with idiopathic CP. Chromosomal microarray and exome sequencing techniques were performed in all patients. Chromosomal microarray analysis did not show any pathological or probable pathological structural variant. However, the next-generation sequencing study showed a high diagnostic yield. We report 11/20 patients (55%) with different pathogenic or potentially pathogenic variants detected by exome sequencing analysis: five patients with mutations in genes related to hereditary spastic paraplegia, two with mutations in genes related to Aicardi-Goutières syndrome, three with mutations in genes related to developmental/epileptic encephalopathies, and one with a mutation in the PGK1 gene. The accurate and precise patients' selection, the use of a high-throughput genetic platform, the selection of adequate target genes, and the application of rigorous criteria for the clinical interpretation are the most important elements for a good diagnostic performance. Based on our findings, next-generation sequencing should be considered in patients with cryptogenic CP as the first line of genetic workup. IMPACT: Sequencing techniques in CP of uncertain etiology provides a diagnostic yield of 55%. The appropriate selection of cases optimizes the diagnostic yield. NGS facilitate better understanding of new phenotypes of certain genetic diseases.

Phenotypes of GNAO1 Variants in a Chinese Cohort

This study aimed to analyze the genotypes and phenotypes of GNAO1 variants in a Chinese cohort. Seven male and four female patients with GNAO1 variants were enrolled, including siblings of brothers. Ten different GNAO1 variants (nine missense and one splicing site) were identified, among which six were novel. All the variants were confirmed to be de novo in peripheral blood DNA. Eight (73%, 8/11) patients had epilepsy; the seizure onset age ranged from 6 h after birth to 4 months (median age, 2.5 months). Focal seizures were observed in all eight patients, epileptic spasms occurred in six (75%, 6/8), tonic spasm in four (50%, 4/8), tonic seizures in two, atypical absence in one, and generalized tonic–clonic seizures in one. Seven patients had multiple seizure types. Eight (73%, 8/11) patients had movement disorders, seven of them having only dystonia, and one having dystonia with choreoathetosis. Varying degrees of developmental delay (DD) were present in all 11 patients. The phenotypes were diagnosed as early infantile epileptic encephalopathy (EIEE) in two (18%) patients, which were further diagnosed as West syndrome. Movement disorders (MD) with developmental delay were diagnosed in two (18%) brothers. EIEE and MD were overlapped in six (55%) patients, among which two were diagnosed with West syndrome, one with Ohtahara syndrome, and the other three with non-specific EIEE. One (9%) patient was diagnosed as DD alone. The onset age of GNAO1-related disorders was early infancy. The phenotypic spectrum of GNAO1 included EIEE, MD with DD, and DD alone.

GNAO1 mutation-related severe involuntary movements treated with gabapentin

BACKGROUND

Mutations in GNAO1 typically result in neurodevelopmental disorders, including involuntary movements. They may be improved using calcium-channel modulators.

CASE

The patient visited our hospital at age 2 years because of moderate global developmental delay. Her intermittent, generalized involuntary movements started at age 8 years. A de novo GNAO1 mutation, NM_020988.2:c.626G > A, (p.Arg209Cys), was identified by whole exome sequencing. At age 9 years, she experienced severe, intermittent involuntary movements, which led to rhabdomyolysis. She needed intensive care with administration of midazolam, dantrolene sodium hydrate, and plasma exchange. We started treating her with gabapentin (GBP), after which she recovered completely. At age 11 years, she developed continuous, generalized involuntary movements. This prompted us to increase the GBP dose, which again resolved the involuntary movements completely.

CONCLUSION

In the case of movement disorders associated with GNAO1 mutations, GBP treatment may be attempted before more invasive procedures are performed.

Early-Onset Developmental and Epileptic Encephalopathies of Infancy: An Overview of the Genetic Basis and Clinical Features

Our current knowledge of genetically determined forms of epilepsy has shortened the diagnostic pathway usually experienced by the families of infants diagnosed with early-onset developmental and epileptic encephalopathies. Genetic causes can be found in up to 80% of infants presenting with early-onset developmental and epileptic encephalopathies, often in the context of an uneventful perinatal history and with no clear underlying brain abnormalities. Although current disease-specific therapies remain limited and patient outcomes are often guarded, a genetic diagnosis may lead to early therapeutic intervention using new and/or repurposed therapies. In this review, an overview of epilepsy genetics, the indications for genetic testing in infants, the advantages and limitations of each test, and the challenges and ethical implications of genetic testing are discussed. In addition, the following causative genes associated with early-onset developmental and epileptic encephalopathies are discussed in detail: KCNT1, KCNQ2, KCNA2, SCN2A, SCN8A, STXBP1, CDKL5, PIGA, SPTAN1, and GNAO1. The epilepsy phenotypes, comorbidities, electroencephalgraphic findings, neuroimaging findings, and potential targeted therapies for each gene are reviewed.

Gαo is a major determinant of cAMP signaling in the pathophysiology of movement disorders

The G protein alpha subunit o (Gαo) is one of the most abundant proteins in the nervous system, and pathogenic mutations in its gene (GNAO1) cause movement disorder. However, the function of Gαo is ill defined mechanistically. Here, we show that Gαo dictates neuromodulatory responsiveness of striatal neurons and is required for movement control. Using in vivo optical sensors and enzymatic assays, we determine that Gαo provides a separate transduction channel that modulates coupling of both inhibitory and stimulatory dopamine receptors to the cyclic AMP (cAMP)-generating enzyme adenylyl cyclase. Through a combination of cell-based assays and rodent models, we demonstrate that GNAO1-associated mutations alter Gαo function in a neuron-type-specific fashion via a combination of a dominant-negative and loss-of-function mechanisms. Overall, our findings suggest that Gαo and its pathological variants function in specific circuits to regulate neuromodulatory signals essential for executing motor programs.

Muntean et al. describe biochemical, cellular, and physiological mechanisms by which the heterotrimeric G protein subunit Gαo controls neuromodulatory signaling in the striatum and elucidate mechanisms by which Gαo mutations compromise movements in GNAO1 disorder.

Spectrum of movement disorders in GNAO1 encephalopathy: in-depth phenotyping and case-by-case analysis

BACKGROUND

GNAO1 encephalopathy is a rare neurodevelopmental disorder characterized by distinct movement presentations and early onset epileptic encephalopathy. Here, we report the in-depth phenotyping of genetically confirmed patients with GNAO1 encephalopathy, focusing on movement presentations.

RESULTS

Six patients who participated in Korean Undiagnosed Disease Program were diagnosed to have pathogenic or likely pathogenic variants in GNAO1 using whole exome sequencing. All medical records and personal video clips were analyzed with a literature review. Three of the 6 patients were male. Median follow-up duration was 41 months (range 7-78 months) and age at last examination was 7.4 years (range 3.3-16.9 years). Initial complaints were hypotonia or developmental delay in 5 and right-hand clumsiness in 1 patient, which were noticed at median age of 3 months (range 0-75 months). All patients showed global developmental delay and 4 had severely retarded development. Five patients (5/6, 83.3%) had many different movement symptoms with various onset and progression. The symptoms included stereotyped hands movement, non-epileptic myoclonus, dyskinesia, dystonia and choreoathetosis. Whole exome sequencing identified 6 different variants in GNAO1. Three were novel de novo variants and atypical presentation was noted in a patient. One variant turned out to be inherited from patient's mother who had mosaic variant. Distinct and characteristics movement phenotypes in patients with variant p.Glu246Lys and p.Arg209His were elucidated by in-depth phenotyping and literature review.

CONCLUSIONS

We reported 6 patients with GNAO1 encephalopathy showing an extremely diverse clinical spectrum on video. Some characteristic movement features identified by careful inspection may also provide important diagnostic insight and practice guidelines.

Current challenges in the pathophysiology, diagnosis, and treatment of paroxysmal movement disorders

INTRODUCTION

Paroxysmal movement disorders mostly comprise paroxysmal dyskinesia and episodic ataxia, and can be the consequence of a genetic disorder or symptomatic of an acquired disease.

AREAS COVERED

In this review, the authors focused on certain hot-topic issues in the field: the respective contribution of the cerebellum and striatum to the generation of paroxysmal dyskinesia, the importance of striatal cAMP turnover in the pathogenesis of paroxysmal dyskinesia, the treatable causes of paroxysmal movement disorders not to be missed, with a special emphasis on the treatment strategy to bypass the glucose transport defect in paroxysmal movement disorders due to GLUT1 deficiency, and functional paroxysmal movement disorders.

EXPERT OPINION

Treatment of genetic causes of paroxysmal movement disorders is evolving towards precision medicine with targeted gene-specific therapy. Alteration of the cerebellar output and modulation of the striatal cAMP turnover offer new perspectives for experimental therapeutics, at least for paroxysmal movement disorders due to selected causes. Further characterization of cell-specific molecular pathways or network dysfunctions that are critically involved in the pathogenesis of paroxysmal movement disorders will likely result in the identification of new biomarkers and testing of innovative-targeted therapeutics.

GNAO1 organizes the cytoskeletal remodeling and firing of developing neurons

Developmental and epileptic encephalopathy (DEE) represents a group of neurodevelopmental disorders characterized by infantile-onset intractable seizures and unfavorable prognosis of psychomotor development. To date, hundreds of genes have been linked to the onset of DEE. GNAO1 is a DEE-associated gene encoding the alpha-O1 subunit of guanine nucleotide-binding protein (Gα_O ). Despite the increasing number of reported children with GNAO1 encephalopathy, the molecular mechanisms underlying their neurodevelopmental phenotypes remain elusive. We herein present that co-immunoprecipitation and mass spectrometry analyses identified another DEE-associated protein, SPTAN1, as an interacting partner of Gα_O . Silencing of endogenous Gnao1 attenuated the neurite outgrowth and calcium-dependent signaling. Inactivation of GNAO1 in human-induced pluripotent stem cells gave rise to anomalous brain organoids that only weakly expressed SPTAN1 and Ankyrin-G. Furthermore, GNAO1-deficient organoids failed to conduct synchronized firing to adjacent neurons. These data indicate that Gα_O and other DEE-associated proteins organize the cytoskeletal remodeling and functional polarity of neurons in the developing brain.

Humanization of Drosophila Gαo to Model GNAO1 Paediatric Encephalopathies

Several hundred genes have been identified to contribute to epilepsy-the disease affecting 65 million people worldwide. One of these genes is GNAO1 encoding Gαo, the major neuronal α-subunit of heterotrimeric G proteins. An avalanche of dominant de novo mutations in GNAO1 have been recently described in paediatric epileptic patients, suffering, in addition to epilepsy, from motor dysfunction and developmental delay. Although occurring in amino acids conserved from humans to Drosophila, these mutations and their functional consequences have only been poorly analysed at the biochemical or neuronal levels. Adequate animal models to study the molecular aetiology of GNAO1 encephalopathies have also so far been lacking. As the first step towards modeling the disease in Drosophila, we here describe the humanization of the Gαo locus in the fruit fly. A two-step CRISPR/Cas9-mediated replacement was conducted, first substituting the coding exons 2-3 of Gαo with respective human GNAO1 sequences. At the next step, the remaining exons 4-7 were similarly replaced, keeping intact the gene Cyp49a1 embedded in between, as well as the non-coding exons, exon 1 and the surrounding regulatory sequences. The resulting flies, homozygous for the humanized GNAO1 loci, are viable and fertile without any visible phenotypes; their body weight, locomotion, and longevity are also normal. Human Gαo-specific antibodies confirm the endogenous-level expression of the humanized Gαo, which fully replaces the Drosophila functions. The genetic model we established will make it easy to incorporate encephalopathic GNAO1 mutations and will permit intensive investigations into the molecular aetiology of the human disease through the powerful toolkit of Drosophila genetics.

EEG Monitoring of the Epileptic Newborn

PURPOSE OF REVIEW

Although differentiating neonatal-onset epilepsies from acute symptomatic neonatal seizures has been increasingly recognized as crucial, existing guidelines, and recommendations on EEG monitoring are mainly based on acute symptomatic seizures, especially secondary to hypoxic-ischemic encephalopathy. We aimed to narratively review current knowledge on neonatal-onset epilepsies of genetic, metabolic, and structural non-acquired origin, with special emphasis on EEG features and monitoring.

RECENT FINDINGS

A wide range of rare conditions are increasingly described, reducing undiagnosed cases. Although distinguishing features are identifiable in some, how to best monitor and detect less described etiologies is still an issue. A comprehensive approach considering onset, seizure evolution, ictal semiology, clinical, laboratory, EEG, and neuroimaging data is key to diagnosis. Phenotypic variability prevents precise recommendations, but a solid, consistent method moving from existing published guidelines helps in correctly assessing these newborns in order to provide better care, especially in view of expanding precision therapies.

Two cases of 16q12.1q21 deletions and refinement of the critical region

Interstitial deletions of 16q chromosome including 16q12.1q21 region are very rare, with only three cases reported to date. Main clinical features include dysmorphisms, short stature, microcephaly, eye abnormalities, epilepsy, development delay, intellectual disability, and autism spectrum disorder. We report two independent subjects with 16q12.1q21 deletion syndrome presenting with dysmorphic facial features, developmental delay, strabismus, and aggressive behavior. A minimal region of overlap spanning 1.7 Mb on chromosome 16, including IRX5, GNAO1, and NUDT21 genes was shared among these two cases and those previously reported. This minimal region of overlap suggests the potential pathogenic role of these genes, previously implicated in diseases of the central nervous system.

Discovering Biomarkers and Pathways Shared by Alzheimer's Disease and Ischemic Stroke to Identify Novel Therapeutic Targets

Background and objectives: Alzheimer's disease (AD) is a progressive neurodegenerative disease that results in severe dementia. Having ischemic strokes (IS) is one of the risk factors of the AD, but the molecular mechanisms that underlie IS and AD are not well understood. We thus aimed to identify common molecular biomarkers and pathways in IS and AD that can help predict the progression of these diseases and provide clues to important pathological mechanisms. Materials and Methods: We have analyzed the microarray gene expression datasets of IS and AD. To obtain robust results, combinatorial statistical methods were used to analyze the datasets and 26 transcripts (22 unique genes) were identified that were abnormally expressed in both IS and AD. Results: Gene Ontology (GO) and KEGG pathway analyses indicated that these 26 common dysregulated genes identified several altered molecular pathways: Alcoholism, MAPK signaling, glycine metabolism, serine metabolism, and threonine metabolism. Further protein-protein interactions (PPI) analysis revealed pathway hub proteins PDE9A, GNAO1, DUSP16, NTRK2, PGAM2, MAG, and TXLNA. Transcriptional and post-transcriptional components were then identified, and significant transcription factors (SPIB, SMAD3, and SOX2) found. Conclusions: Protein-drug interaction analysis revealed PDE9A has interaction with drugs caffeine, γ-glutamyl glycine, and 3-isobutyl-1-methyl-7H-xanthine. Thus, we identified novel putative links between pathological processes in IS and AD at transcripts levels, and identified possible mechanistic and gene expression links between IS and AD.

PDE10A mutations help to unwrap the neurobiology of hyperkinetic disorders

The dual-specific cAMP/cGMP phosphodiesterase PDE10A is exclusively localised to regions of the brain and specific cell types that control crucial brain circuits and behaviours. The downside to this expression pattern is that PDE10A is also positioned to be a key player in pathology when its function is perturbed. The last decade of research has seen a clear role emerge for PDE10A inhibition in modifying behaviours in animal models of psychosis and Huntington's disease. Unfortunately, this has not translated to the human diseases as expected. More recently, a series of families with hyperkinetic movement disorders have been identified with mutations altering the PDE10A protein sequence. As these mutations have been analysed and characterised in other model systems, we are beginning to learn more about PDE10A function and perhaps catch a glimpse into how PDE10A activity could be modified for therapeutic benefit.