Phenomenology and clinical course of movement disorder in GNAO1 variants: Results from an analytical review

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.

Gnao1 is a molecular switch that regulates the Rho signaling pathway in differentiating neurons

GNAO1 encodes G protein subunit alpha O1 (Gαo). Pathogenic variations in GNAO1 cause developmental delay, intractable seizures, and progressive involuntary movements from early infancy. Because the functional role of GNAO1 in the developing brain remains unclear, therapeutic strategies are still unestablished for patients presenting with GNAO1-associated encephalopathy. We herein report that siRNA-mediated depletion of Gnao1 perturbs the expression of transcripts associated with Rho GTPase signaling in Neuro2a cells. Consistently, siRNA treatment hampered neurite outgrowth and extension. Growth cone formation was markedly disrupted in monolayer neurons differentiated from iPSCs from a patient with a pathogenic variant of Gαo (p.G203R). This variant disabled neuro-spherical assembly, acquisition of the organized structure, and polarized signals of phospho-MLC2 in cortical organoids from the patient's iPSCs. We confirmed that the Rho kinase inhibitor Y27632 restored these morphological phenotypes. Thus, Gαo determines the self-organizing process of the developing brain by regulating the Rho-associated pathway. These data suggest that Rho GTPase pathway might be an alternative target of therapy for patients with GNAO1-associated encephalopathy.

Genetic pathways in cerebral palsy: a review of the implications for precision diagnosis and understanding disease mechanisms

ABSTRACT

Cerebral palsy is a diagnostic term utilized to describe a group of permanent disorders affecting movement and posture. Patients with cerebral palsy are often only capable of limited activity, resulting from non-progressive disturbances in the fetal or neonatal brain. These disturbances severely impact the child's daily life and impose a substantial economic burden on the family. Although cerebral palsy encompasses various brain injuries leading to similar clinical outcomes, the understanding of its etiological pathways remains incomplete owing to its complexity and heterogeneity. This review aims to summarize the current knowledge on the genetic factors influencing cerebral palsy development. It is now widely acknowledged that genetic mutations and alterations play a pivotal role in cerebral palsy development, which can be further influenced by environmental factors. Despite continuous research endeavors, the underlying factors contributing to cerebral palsy remain are still elusive. However, significant progress has been made in genetic research that has markedly enhanced our comprehension of the genetic factors underlying cerebral palsy development. Moreover, these genetic factors have been categorized based on the identified gene mutations in patients through clinical genotyping, including thrombosis, angiogenesis, mitochondrial and oxidative phosphorylation function, neuronal migration, and cellular autophagy. Furthermore, exploring targeted genotypes holds potential for precision treatment. In conclusion, advancements in genetic research have substantially improved our understanding of the genetic causes underlying cerebral palsy. These breakthroughs have the potential to pave the way for new treatments and therapies, consequently shaping the future of cerebral palsy research and its clinical management. The investigation of cerebral palsy genetics holds the potential to significantly advance treatments and management strategies. By elucidating the underlying cellular mechanisms, we can develop targeted interventions to optimize outcomes. A continued collaboration between researchers and clinicians is imperative to comprehensively unravel the intricate genetic etiology of cerebral palsy.

The Prodrug DHED Delivers 17β-Estradiol into the Retina for Protection of Retinal Ganglion Cells and Preservation of Visual Function in an Animal Model of Glaucoma

We report a three-pronged phenotypic evaluation of the bioprecursor prodrug 10β,17β-dihydroxyestra-1,4-dien-3-one (DHED) that selectively produces 17β-estradiol (E2) in the retina after topical administration and halts glaucomatous neurodegeneration in a male rat model of the disease. Ocular hypertension (OHT) was induced by hyperosmotic saline injection into an episcleral vein of the eye. Animals received daily DHED eye drops for 12 weeks. Deterioration of visual acuity and contrast sensitivity by OHT in these animals were markedly prevented by the DHED-derived E2 with concomitant preservation of retinal ganglion cells and their axons. In addition, we utilized targeted retina proteomics and a previously established panel of proteins as preclinical biomarkers in the context of OHT-induced neurodegeneration as a characteristic process of the disease. The prodrug treatment provided retina-targeted remediation against the glaucomatous dysregulations of these surrogate endpoints without increasing circulating E2 levels. Collectively, the demonstrated significant neuroprotective effect by the DHED-derived E2 in the selected animal model of glaucoma supports the translational potential of our presented ocular neuroprotective approach owing to its inherent therapeutic safety and efficacy.

Neomorphic Gαo mutations gain interaction with Ric8 proteins in GNAO1 encephalopathies

GNAO1 mutated in pediatric encephalopathies encodes the major neuronal G protein Gαo. Of the more than 80 pathogenic mutations, most are single amino acid substitutions spreading across the Gαo sequence. We performed extensive characterization of Gαo mutants, showing abnormal GTP uptake and hydrolysis and deficiencies in binding Gβγ and RGS19. Plasma membrane localization of Gαo was decreased for a subset of mutations that leads to epilepsy; dominant interactions with GPCRs also emerged for the more severe mutants. Pathogenic mutants massively gained interaction with Ric8A and, surprisingly, Ric8B proteins, relocalizing them from cytoplasm to Golgi. Of these 2 mandatory Gα-subunit chaperones, Ric8A is normally responsible for the Gαi/Gαo, Gαq, and Gα12/Gα13 subfamilies, and Ric8B solely responsible for Gαs/Gαolf. Ric8 mediates the disease dominance when engaging in neomorphic interactions with pathogenic Gαo through imbalance of 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 uncovers the neomorphic molecular mechanism of mutations underlying pediatric encephalopathies and offers insights into other maladies caused by G protein malfunctioning and further genetic diseases.

Dyskinetic crisis in GNAO1-related disorders: clinical perspectives and management strategies

Background

GNAO1-related disorders (GNAO1-RD) encompass a diverse spectrum of neurodevelopmental and movement disorders arising from variants in the GNAO1 gene. Dyskinetic crises, marked by sudden and intense exacerbations of abnormal involuntary movements, present a significant challenge in GNAO1-RD.

Objectives

This study aimed to establish a standardized framework for understanding dyskinetic crises, addressing crucial aspects such as definition, triggers, diagnostic criteria, complications, and management strategies.

Methods

A Delphi consensus process was conducted involving international experts in GNAO1-RD. The panel of thirteen experts participated in three voting rounds, discussing 90 statements generated through a literature review and clinical expertise.

Results

Consensus was achieved on 31 statements, defining dyskinetic crises as abrupt, paroxysmal episodes involving distinct abnormal movements in multiple body regions, triggered by emotional stress or infections. Dyskinetic crises may lead to functional impairment and complications, emphasizing the need for prompt recognition. While individualized pharmacological recommendations were not provided, benzodiazepines and clonidine were suggested for acute crisis management. Chronic treatment options included tetrabenazine, benzodiazepines, gabapentin, and clonidine. Deep brain stimulation should be considered early in the treatment of refractory or prolonged dyskinetic crisis.

Conclusion

This consensus provides a foundation for understanding and managing dyskinetic crises in GNAO1-RD for clinicians, caregivers, and researchers. The study emphasizes the importance of targeted parental and caregiver education, which enables early recognition and intervention, thereby potentially minimizing both short- and long-term complications. Future research should concentrate on differentiating dyskinetic crises from other neurological events and investigating potential risk factors that influence their occurrence and nature. The proposed standardized framework improves clinical management, stakeholder communication, and future GNAO1-RD research.

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.

Molecular and in silico analyses of SYN III gene variants in autism spectrum disorder

BACKGROUND

Defects in neurotransmission and synaptogenesis are noteworthy in the pathogenesis of ASD. Synapsin III (SYN III) is defined as a synaptic vesicle protein that plays an important role in synaptogenesis and regulation of neurotransmitter release and neurite outgrowth. Therefore, SYN III may associate with many neurodevelopmental diseases, including ASD.

AIM

The aim of this study was to investigate whether the SYN III gene -631 C > G (rs133946) and -196 G > A (rs133945) polymorphisms are associated with susceptibility to ASD.

METHODS

SYN III variants and the risk of ASD were investigated in 26 healthy children and 24 ASD children. SYN III gene variants were genotyped by PCR-RFLP methods. The differences in genotype and allele frequencies between the ASD and control groups were calculated using the chi-square (χ2). We analysed the SYN III gene using web-based tools.

RESULTS

Our results suggest that the presence of the AA genotype of the SYN III -196 G > A (rs133945) polymorphism affects the characteristics and development of ASD in children (p = 0.012). SYN III -631 C > G (rs133946) polymorphism was not associated with ASD (p = 0.524). We have shown the prediction of gene-gene interaction that SYN III is co-expressed with 17 genes, physical interaction with 3 genes, and co-localization with 12 genes. The importance of different genes (SYN I, II, III, GABRD, NOS1AP, GNAO1) for ASD pathogenesis was revealed by GO analysis.

CONCLUSION

Considering the role of SYN III and related genes, especially in the synaptic vesicle pathway and neurotransmission, its effect on ASD can be further investigated.

Movement Disorders in Patients With Genetic Developmental and Epileptic Encephalopathies

BACKGROUND AND OBJECTIVES

Movement disorders (MDs) are underrecognized in the developmental and epileptic encephalopathies (DEEs). There are now more than 800 genes implicated in causing the DEEs; relatively few of these rare genetic diseases are known to be associated with MDs. We identified patients with genetic DEEs who had MDs, classified the nature of their MDs, and asked whether specific patterns correlated with the underlying mechanism.

METHODS

We classified the type of MDs associated with specific genetic DEEs in a large international cohort of patients and analyzed whether specific patterns of MDs reflected the underlying biological dysfunction.

RESULTS

Our cohort comprised 77 patients with a genetic DEE with a median age of 9 (range 1-38) years. Stereotypies (37/77, 48%) and dystonia (34/77, 44%) were the most frequent MDs, followed by chorea (18/77, 23%), myoclonus (14/77, 18%), ataxia (9/77, 12%), tremor (7/77, 9%), and hypokinesia (6/77, 8%). In 47% of patients, a combination of MDs was seen. The MDs were first observed at a median age of 18 months (range day 2-35 years). Dystonia was more likely to be observed in nonambulatory patients, while ataxia was less likely. In 46% of patients, therapy was initiated with medication (34/77, 44%), deep brain stimulation (1/77, 1%), or intrathecal baclofen (1/77, 1%). We found that patients with channelopathies or synaptic vesicle trafficking defects were more likely to experience dystonia; whereas, stereotypies were most frequent in individuals with transcriptional defects.

DISCUSSION

MDs are often underrecognized in patients with genetic DEEs, but recognition is critical for the management of these complex neurologic diseases. Distinguishing MDs from epileptic seizures is important in tailoring patient treatment. Understanding which MDs occur with different biological mechanisms will inform early diagnosis and management.

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.

Efficacy of perampanel in pediatric epilepsy with known and presumed genetic etiology

OBJECTIVE

The efficacy of perampanel (PER) in pediatric epilepsy with specific etiologies has not been well established. Here, we investigated outcome and predictors of PER treatment in a pediatric cohort with known and presumed genetic etiology.

METHODS

We included pediatric patients with potential genetic epilepsy who received PER treatment and underwent whole-exome sequencing (WES) from January 2020 to September 2021. All patients were followed up for >12 months.

RESULTS

A total of 124 patients were included. Overall response rates were 51.6% and 49.6% at 6 months and 12 months, respectively. Pathogenic or likely pathogenic variants in 27 multiple genes were detected among 58 patients (46.8%) by WES. On performing multivariate logistic regression analysis, only developmental delay (OR = 0.406, P = 0.042) was a negative predictor of treatment response. However, the seizure onset age, positive WES results, and number of ASMs before PER administration were not significantly. Thirteen carriers with variants in the SCN1A gene showed a better response compared to eight patients with other sodium channels (P = 0.007), and to the other 45 patients with positive WES results (OR = 7.124, 95% CI = 1.306-38.860, P = 0.023). Adverse events were only reported in 23 patients, the most common being emotional problems.

INTERPRETATION

PER is safe and efficacious in pediatric patients with known and presumed genetic etiology. The response rate is comparable to that reported in other pediatric populations, and lower among those with developmental delay. A gene-specific response to PER is found along with better efficacy links to pathogenic variants in the SCN1A gene.

The changing face of reported status dystonicus - A systematic review

BACKGROUND

Status Dystonicus (SD) represents the most severe end of the spectrum of dystonia. We aimed to explore whether reported features of cases of SD have changed over time.

METHODS

A systematic review of cases of SD reported from 2017 to 2023 and comparison of features to data extracted from 2 previous literature reviews (epochs 2012-2017 and pre-2012).

RESULTS

From 53 papers, a total 206 SD episodes in 168 patients were identified from 2017 to 2023. Combining data from all 3 epochs, a total of 339 SD episodes were reported from 277 patients. SD episodes occurred mostly in children, with a trigger identified in 63.4% of episodes, most commonly infection/inflammation. Most reported underlying aetiologies were genetic (e.g. 49.5% between 2017 and 2023), including new associated aetiologies in each epoch. Deep Brain Stimulation (DBS)-related SD increased over time. Neurosurgical interventions were more frequently reported in later epochs. Across the epochs, return to or improvement post SD episode, compared to baseline was reported above 70%. Reported mortality was 4.9% most recently, compared to 11.4% and 7.9%, previously.

CONCLUSIONS

SD episodes reported have more than doubled in the last 5 years. Reports of medication change-induced SD have become less frequent, whilst episodes of DBS-related SD have become more frequent. More dystonia aetiologies, including novel aetiologies have been reported in recent cohorts, reflecting advances in genetic diagnosis. Neurosurgical interventions are increasingly reported in the management of SD episodes, including novel use of intraventricular baclofen. Overall outcomes from SD remain largely unchanged over time. No prospective epidemiological studies of SD were identified.

Pharmacotherapy for Sydenham's chorea: where are we and where do we need to be?

INTRODUCTION

Sydenham's chorea (SC) is the most common cause of acquired chorea in children. The existing literature describes it as a benign, self-remitting condition. However, recent evidence discloses the persistence of long-course neuropsychiatric and cognitive complications in adulthood, which imposes to redefine the concept of 'benignity' of such condition. In addition, therapies are mostly empirical and non-evidence based.

AREAS COVERED

Here, we conducted an electronic exploration of the PubMed database and selected 165 relevant studies directly correlated to SC treatment. Critical data from selected articles were synthesized to provide an update on pharmacotherapy in SC, which basically consists of three pillars: antibiotic, symptomatic and immunomodulant treatments. Moreover, since SC mostly affects females with recurrences occurring in pregnancy (chorea gravidarum), we focused on the management in pregnancy.

EXPERT OPINION

SC is still a major burden in developing countries. The first therapeutic strategy should be the primary prevention of group A beta-hemolytic streptococcal (GABHS) infection. Secondary antibiotic prophylaxis should be performed in every SC patient as the World Health Organization (WHO) guidelines recommend. Symptomatic or immunomodulant treatments are administered according to clinical judgment. However, a greater effort to understand SC physiopathology is needed, together with larger trials, to outline appropriate therapeutic indications.

GNAO1-related movement disorder: An update on phenomenology, clinical course, and response to treatments

AIM

To evaluate clinical phenotype and molecular findings of 157 cases with GNAO1 pathogenic or likely pathogenic variants delineating the clinical spectrum, course, and response to treatments.

METHOD

Clinical phenotype, genetic data, and pharmacological and surgical treatment history of 11 novel cases and 146 previously published patients were analyzed.

RESULTS

Complex hyperkinetic movement disorder (MD) characterizes 88% of GNAO1 patients. Severe hypotonia and prominent disturbance of postural control seem to be hallmarks in the early stages preceding the hyperkinetic MD. In a subgroup of patients, paroxysmal exacerbations became so severe as to require admission to intensive care units (ICU). Almost all patients had a good response to deep brain stimulation (DBS). Milder phenotypes with late-onset focal/segmental dystonia, mild to moderate intellectual disability, and other minor neurological signs (i.e., parkinsonism and myoclonus) are emerging. MRI, previously considered noncontributory to a diagnosis, can show recurrent findings (i.e., cerebral atrophy, myelination and/or basal ganglia abnormalities). Fifty-eight GNAO1 pathogenic variants, including missense changes and a few recurrent splice site defects, have been reported. Substitutions at residues Gly²⁰³, Arg²⁰⁹ and Glu²⁴⁶, together with the intronic c.724-8G > A change, account for more than 50% of cases.

INTERPRETATION

Infantile or childhood-onset complex hyperkinetic MD (chorea and/or dystonia) with or without paroxysmal exacerbations, associated hypotonia, and developmental disorders should prompt research for GNAO1 mutations. DBS effectively controls and prevents severe exacerbations and should be considered early in patients with specific GNAO1 variants and refractory MD. Prospective and natural history studies are necessary to define genotype-phenotype correlations further and clarify neurological outcomes.

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.

Gln52 mutations in GNAO1-related disorders and personalized drug discovery

•Gln52 mutations have been found in patients with GNAO1-related disorders.•Gln52 can be mutated to Pro and Arg, leading to different clinical manifestations.•Personalized drug discovery is tailored to specific GNAO1 mutations.

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.

[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.

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 regulatory role of Gnao1 protein in diabetic encephalopathy in KK-Ay mice and streptozotocin-induced diabetic rats

AIMS

To investigate the regulation and functional role of Gnao1 in the brain of diabetic encephalopathy (DE) in various animal models.

RESULTS

Data from the biochemical and behavioral studies showed that DE models were successful induced in streptozotocin treatment animals and KK-Ay mice. Gnao1 was down regulated in the brain tissues of these two diabetes animal models with significant cognition deficiency. It suggested that the changes in DE are also related to dementia such as Alzheimer's disease (AD). Our study also showed that the expression of adrenergic α2 receptor (Adr-α2R), the upstream protein of Gnao1, was decreased in DE animal models. Furthermore, many downstream proteins of Gnao1 also altered, among which cAMP and PKA proteins were increased, CREB and BDNF proteins were decreased both in animal models and in the cell levels. In addition, Gnao1 silencing leads to the increase of reactive oxygen species (ROS) and the decreased proliferation in cultured primary astrocytes, which means that the deficiency of Gnao1 might not be benefit for DE.

CONCLUSION

Our findings demonstrated the importance of Gnao1 in DE and suggested Gnao1 as a novel marker and a promising therapeutic target for DE and dementia in animal models.

Motor, epileptic, and developmental phenotypes in genetic disorders affecting G protein coupled receptors-cAMP signaling

Over the last years, a constantly increasing number of genetic diseases associated with epilepsy and movement disorders have been recognized. An emerging group of conditions in this field is represented by genetic disorders affecting G-protein-coupled receptors (GPCRs)–cAMP signaling. This group of postsynaptic disorders includes genes encoding for proteins highly expressed in the central nervous system and involved in GPCR signal transduction and cAMP production (e.g., GNAO1, GNB1, ADCY5, GNAL, PDE2A, PDE10A, and HPCA genes). While the clinical phenotype associated with ADCY5 and GNAL is characterized by movement disorder in the absence of epilepsy, GNAO1, GNB1, PDE2A, PDE10A, and HPCA have a broader clinical phenotype, encompassing movement disorder, epilepsy, and neurodevelopmental disorders. We aimed to provide a comprehensive phenotypical characterization of genetic disorders affecting the cAMP signaling pathway, presenting with both movement disorders and epilepsy. Thus, we reviewed clinical features and genetic data of 203 patients from the literature with GNAO1, GNB1, PDE2A, PDE10A, and HPCA deficiencies. Furthermore, we delineated genotype–phenotype correlation in GNAO1 and GNB1 deficiency. This group of disorders presents with a highly recognizable clinical phenotype combining distinctive motor, epileptic, and neurodevelopmental features. A severe hyperkinetic movement disorder with potential life-threatening exacerbations and high susceptibility to a wide range of triggers is the clinical signature of the whole group of disorders. The existence of a distinctive clinical phenotype prompting diagnostic suspicion and early detection has relevant implications for clinical and therapeutic management. Studies are ongoing to clarify the pathophysiology of these rare postsynaptic disorders and start to design disease-specific treatments.

Defining causal variants in rare epilepsies: an essential team effort between biomedical scientists, geneticists and epileptologists

In the last few years, with the advent of next generation sequencing (NGS), our knowledge of genes associated with monogenic epilepsies has significantly improved. NGS is also a powerful diagnostic tool for patients with epilepsy, through gene panels, exomes and genomes. This has improved diagnostic yield, reducing the time between the first seizure and a definitive molecular diagnosis. However, these developments have also increased the complexity of data interpretation, due to the large number of variants identified in a given patient and due to the phenotypic variability associated with many of the epilepsy-related genes. In this paper, we present examples of variant classification in "real life" clinic situations. We emphasize the importance of accurate phenotyping of the epilepsies including recognising variable/milder phenotypes and expansion of previously described phenotypes. There are some important issues specific to rare epilepsies - mosaicism and reduced penetrance - which affect genetic counselling. These challenges may be overcome through multidisciplinary meetings including epileptologists, pediatric neurologists, and clinical and molecular geneticists, in which every specialist learns from the others in a process which leads to for rapid and accurate diagnosis. This is an important milestone to achieve as targeted therapiesbased on the functional effects of pathogenic variants become available.

Deep brain stimulation in a young child with GNAO1 mutation – Feasible and helpful

Background:

GNAO1 is an emerging disorder characterized with hypotonia, developmental delay, epilepsy, and movement disorder, which can be potentially life threatening during acute exacerbation. In the USA, deep brain stimulation (DBS) has been licensed for treating children with chronic, treatment-resistant primary dystonia, who are 7 years old or older.

Case Description:

A 4-year-old girl diagnosed to have GNAO1-related dyskinesia and severe global developmental delay. She had severe dyskinesia precipitated by intercurrent infection, requiring prolonged intensive care for heavy sedation and related complications. Her dyskinesia improved dramatically after DBS implantation. Technical difficulties and precautions of DBS in preschool children were discussed.

Conclusion:

DBS should be considered early in the treatment of drug-resistant movement disorders in young children with GNAO1, especially after dyskinetic crisis, as they tend to recur. Presurgical counseling to parents and close monitoring of complications is also important in the process.

Highlighting the Dystonic Phenotype Related to GNAO1

BACKGROUND

Most reported patients carrying GNAO1 mutations showed a severe phenotype characterized by early-onset epileptic encephalopathy and/or chorea.

OBJECTIVE

The aim was to characterize the clinical and genetic features of patients with mild GNAO1-related phenotype with prominent movement disorders.

METHODS

We included patients diagnosed with GNAO1-related movement disorders of delayed onset (>2 years). Patients experiencing either severe or profound intellectual disability or early-onset epileptic encephalopathy were excluded.

RESULTS

Twenty-four patients and 1 asymptomatic subject were included. All patients showed dystonia as prominent movement disorder. Dystonia was focal in 1, segmental in 6, multifocal in 4, and generalized in 13. Six patients showed adolescence or adulthood-onset dystonia. Seven patients presented with parkinsonism and 3 with myoclonus. Dysarthria was observed in 19 patients. Mild and moderate ID were present in 10 and 2 patients, respectively.

CONCLUSION

We highlighted a mild GNAO1-related phenotype, including adolescent-onset dystonia, broadening the clinical spectrum of this condition. © 2022 The Authors. Movement Disorders published by Wiley Periodicals LLC on behalf of International Parkinson and Movement Disorder Society.

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.

Nomenclature of Genetic Movement Disorders: Recommendations of the International Parkinson and Movement Disorder Society Task Force - An Update

In 2016, the Movement Disorder Society Task Force for the Nomenclature of Genetic Movement Disorders presented a new system for naming genetically determined movement disorders and provided a criterion-based list of confirmed monogenic movement disorders. Since then, a substantial number of novel disease-causing genes have been described, which warrant classification using this system. In addition, with this update, we further refined the system and propose dissolving the imaging-based categories of Primary Familial Brain Calcification and Neurodegeneration with Brain Iron Accumulation and reclassifying these genetic conditions according to their predominant phenotype. We also introduce the novel category of Mixed Movement Disorders (MxMD), which includes conditions linked to multiple equally prominent movement disorder phenotypes. In this article, we present updated lists of newly confirmed monogenic causes of movement disorders. We found a total of 89 different newly identified genes that warrant a prefix based on our criteria; 6 genes for parkinsonism, 21 for dystonia, 38 for dominant and recessive ataxia, 5 for chorea, 7 for myoclonus, 13 for spastic paraplegia, 3 for paroxysmal movement disorders, and 6 for mixed movement disorder phenotypes; 10 genes were linked to combined phenotypes and have been assigned two new prefixes. The updated lists represent a resource for clinicians and researchers alike and they have also been published on the website of the Task Force for the Nomenclature of Genetic Movement Disorders on the homepage of the International Parkinson and Movement Disorder Society (https://www.movementdisorders.org/MDS/About/Committees--Other-Groups/MDS-Task-Forces/Task-Force-on-Nomenclature-in-Movement-Disorders.htm). © 2022 The Authors. Movement Disorders published by Wiley Periodicals LLC on behalf of International Parkinson 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.

Mouse models characterize GNAO1 encephalopathy as a neurodevelopmental disorder leading to motor anomalies: from a severe G203R to a milder C215Y mutation

GNAO1 encephalopathy characterized by a wide spectrum of neurological deficiencies in pediatric patients originates from de novo heterozygous mutations in the gene encoding Gαo, the major neuronal G protein. Efficient treatments and even the proper understanding of the underlying etiology are currently lacking for this dominant disease. Adequate animal models of GNAO1 encephalopathy are urgently needed. Here we describe establishment and characterization of mouse models of the disease based on two point mutations in GNAO1 with different clinical manifestations. One of them is G203R leading to the early-onset epileptic seizures, motor dysfunction, developmental delay and intellectual disability. The other is C215Y producing much milder clinical outcomes, mostly-late-onset hyperkinetic movement disorder. The resultant mouse models show distinct phenotypes: severe neonatal lethality in GNAO1[G203R]/ + mice vs. normal vitality in GNAO1[C215Y]/ + . The latter model further revealed strong hyperactivity and hyperlocomotion in a panel of behavioral assays, without signs of epilepsy, recapitulating the patients' manifestations. Importantly, despite these differences the two models similarly revealed prenatal brain developmental anomalies, such as enlarged lateral ventricles and decreased numbers of neuronal precursor cells in the cortex. Thus, our work unveils GNAO1 encephalopathy as to a large extent neurodevelopmental malady. We expect that this understanding and the tools we established will be instrumental for future therapeutic developments.

Pediatric Encephalopathy: Clinical, Biochemical and Cellular Insights into the Role of Gln52 of GNAO1 and GNAI1 for the Dominant Disease

Heterotrimeric G proteins are immediate transducers of G protein-coupled receptors-the biggest receptor family in metazoans-and play innumerate functions in health and disease. A set of de novo point mutations in GNAO1 and GNAI1, the genes encoding the α-subunits (Gαo and Gαi1, respectively) of the heterotrimeric G proteins, have been described to cause pediatric encephalopathies represented by epileptic seizures, movement disorders, developmental delay, intellectual disability, and signs of neurodegeneration. Among such mutations, the Gln52Pro substitutions have been previously identified in GNAO1 and GNAI1. Here, we describe the case of an infant with another mutation in the same site, Gln52Arg. The patient manifested epileptic and movement disorders and a developmental delay, at the onset of 1.5 weeks after birth. We have analyzed biochemical and cellular properties of the three types of dominant pathogenic mutants in the Gln52 position described so far: Gαo[Gln52Pro], Gαi1[Gln52Pro], and the novel Gαo[Gln52Arg]. At the biochemical level, the three mutant proteins are deficient in binding and hydrolyzing GTP, which is the fundamental function of the healthy G proteins. At the cellular level, the mutants are defective in the interaction with partner proteins recognizing either the GDP-loaded or the GTP-loaded forms of Gαo. Further, of the two intracellular sites of Gαo localization, plasma membrane and Golgi, the former is strongly reduced for the mutant proteins. We conclude that the point mutations at Gln52 inactivate the Gαo and Gαi1 proteins leading to aberrant intracellular localization and partner protein interactions. These features likely lie at the core of the molecular etiology of pediatric encephalopathies associated with the codon 52 mutations in GNAO1/GNAI1.

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.

Cognitive Assessment in GNAO1 Neurodevelopmental Disorder Using an Eye Tracking System

GNAO1 gene mutations are associated with a neurodevelopmental disorder characterized by developmental delay, epilepsy, and movement disorder. Eye tracking and eye movement analysis are an intriguing method to assess cognitive and language function and, to the best of our knowledge, it has never been tested in a standardized way in GNAO1. GNAO1 children are usually wheelchair-bound and with numerous motor constrains, including dystonic movements and postures, heterotropia, and hypotonia, making the cognitive assessment arduous. These contribute to the burden and disability, with a high level of frustration of caregivers and patients. We have herein demonstrated that, through an eye tracking system, six GNAO1 patients evaluated showed variable degrees of communicative intent through intentionally directed gaze. Moreover, three of these were able to complete a cognitive evaluation, and showed normal fluid intelligence and lexical comprehension. In conclusion, in GNAO1-related disorders, the degree of cognitive development is underestimated; eye tracking technologies may help in overcome these boundaries.

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.

Adult-onset sporadic chorea: real-world data from a single-centre retrospective study

Background

Adult-onset sporadic chorea includes a wide and heterogeneous group of conditions whose differential diagnosis and treatments are often challenging and extensive.

Objectives

To analyse retrospectively cases of adult-onset sporadic chorea from a single Italian centre to provide insights for a practical approach in the management of these patients.

Methods

A total of 11,071 medical charts from a 9-year period (2012–2020) were reviewed, identifying 28 patients with adult-onset sporadic chorea (genetic forms excluded). All available data regarding phenomenology, diagnostic workup, aetiology, treatments, and long-term outcome from this cohort were collected and analysed.

Results

Adult-onset sporadic chorea occurred more frequently in females and presented with an acute-subacute onset. Cerebrovascular diseases accounted for 68% of aetiology; further causes were structural brain lesions, internal diseases, and other movement disorder syndromes. Clinical course was mild, with spontaneous resolution or minimal disturbances in 82% of cases. Neuroimaging was fundamental to diagnose 76% of adult-onset sporadic chorea, an appropriate clinical examination contributed to the 14% of diagnoses, whereas basic laboratory tests to the 10%.

Conclusions

Revision of real-world data of adult-onset sporadic chorea patients from a single Italian cohort suggests that an accurate clinical examination, neuroimaging, and routine laboratory tests are useful to identify those cases underlying potentially severe but treatable conditions. Although in the majority of cases adult-onset sporadic chorea has mild clinical course and good response to symptomatic treatments, it is essential to run a fast diagnostic workup.

COVID-19: dealing with a potential risk factor for chronic neurological disorders

SARS-CoV2 infection is responsible for a complex clinical syndrome, named Coronavirus Disease 2019 (COVID-19), whose main consequences are severe pneumonia and acute respiratory distress syndrome. Occurrence of acute and subacute neurological manifestations (encephalitis, stroke, headache, seizures, Guillain-Barrè syndrome) is increasingly reported in patients with COVID-19. Moreover, SARS-CoV2 immunopathology and tissue colonization in the gut and the central nervous system, and the systemic inflammatory response during COVID-19 may potentially trigger chronic autoimmune and neurodegenerative disorders. Specifically, Parkinson's disease, multiple sclerosis and narcolepsy present several pathogenic mechanisms that can be hypothetically initiated by SARS-CoV2 infection in susceptible individuals. In this short narrative review, we summarize the clinical evidence supporting the rationale for investigating SARS-CoV2 infection as risk factor for these neurological disorders, and suggest the opportunity to perform in the future SARS-CoV2 serology when diagnosing these disorders.

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.

KMT2B-related disorders: expansion of the phenotypic spectrum and long-term efficacy of deep brain stimulation

Heterozygous mutations in KMT2B are associated with an early-onset, progressive and often complex dystonia (DYT28). Key characteristics of typical disease include focal motor features at disease presentation, evolving through a caudocranial pattern into generalized dystonia, with prominent oromandibular, laryngeal and cervical involvement. Although KMT2B-related disease is emerging as one of the most common causes of early-onset genetic dystonia, much remains to be understood about the full spectrum of the disease. We describe a cohort of 53 patients with KMT2B mutations, with detailed delineation of their clinical phenotype and molecular genetic features. We report new disease presentations, including atypical patterns of dystonia evolution and a subgroup of patients with a non-dystonic neurodevelopmental phenotype. In addition to the previously reported systemic features, our study has identified co-morbidities, including the risk of status dystonicus, intrauterine growth retardation, and endocrinopathies. Analysis of this study cohort (n = 53) in tandem with published cases (n = 80) revealed that patients with chromosomal deletions and protein truncating variants had a significantly higher burden of systemic disease (with earlier onset of dystonia) than those with missense variants. Eighteen individuals had detailed longitudinal data available after insertion of deep brain stimulation for medically refractory dystonia. Median age at deep brain stimulation was 11.5 years (range: 4.5-37.0 years). Follow-up after deep brain stimulation ranged from 0.25 to 22 years. Significant improvement of motor function and disability (as assessed by the Burke Fahn Marsden's Dystonia Rating Scales, BFMDRS-M and BFMDRS-D) was evident at 6 months, 1 year and last follow-up (motor, P = 0.001, P = 0.004, and P = 0.012; disability, P = 0.009, P = 0.002 and P = 0.012). At 1 year post-deep brain stimulation, >50% of subjects showed BFMDRS-M and BFMDRS-D improvements of >30%. In the long-term deep brain stimulation cohort (deep brain stimulation inserted for >5 years, n = 8), improvement of >30% was maintained in 5/8 and 3/8 subjects for the BFMDRS-M and BFMDRS-D, respectively. The greatest BFMDRS-M improvements were observed for trunk (53.2%) and cervical (50.5%) dystonia, with less clinical impact on laryngeal dystonia. Improvements in gait dystonia decreased from 20.9% at 1 year to 16.2% at last assessment; no patient maintained a fully independent gait. Reduction of BFMDRS-D was maintained for swallowing (52.9%). Five patients developed mild parkinsonism following deep brain stimulation. KMT2B-related disease comprises an expanding continuum from infancy to adulthood, with early evidence of genotype-phenotype correlations. Except for laryngeal dysphonia, deep brain stimulation provides a significant improvement in quality of life and function with sustained clinical benefit depending on symptoms distribution.

Genetic Dystonias: Update on Classification and New Genetic Discoveries

PURPOSE OF REVIEW

Since the advent of next-generation sequencing, the number of genes associated with dystonia has been growing exponentially. We provide here a comprehensive review of the latest genetic discoveries in the field of dystonia and discuss how the growing knowledge of biology underlying monogenic dystonias may influence and challenge current classification systems.

RECENT FINDINGS

Pathogenic variants in genes without previously confirmed roles in human disease have been identified in subjects affected by isolated or combined dystonia (KMT2B, VPS16, HPCA, KCTD17, DNAJC12, SLC18A2) and complex dystonia (SQSTM1, IRF2BPL, YY1, VPS41). Importantly, the classical distinction between isolated and combined dystonias has become harder to sustain since many genes have been shown to determine multiple dystonic presentations (e.g., ANO3, GNAL, ADCY5, and ATP1A3). In addition, a growing number of genes initially linked to other neurological phenotypes, such as developmental delay, epilepsy, or ataxia, are now recognized to cause prominent dystonia, occasionally in an isolated fashion (e.g., GNAO1, GNB1, SCN8A, RHOBTB2, and COQ8A). Finally, emerging analyses suggest biological convergence of genes linked to different dystonic phenotypes. While our knowledge on the genetic basis of monogenic dystonias has tremendously grown, their clinical boundaries are becoming increasingly blurry. The current phenotype-based classification may not reflect the molecular structure of the disease, urging the need for new systems based on shared biological pathways among dystonia-linked genes.

Molecular Diagnostic Yield of Exome Sequencing in Patients With Cerebral Palsy

IMPORTANCE

Cerebral palsy is a common neurodevelopmental disorder affecting movement and posture that often co-occurs with other neurodevelopmental disorders. Individual cases of cerebral palsy are often attributed to birth asphyxia; however, recent studies indicate that asphyxia accounts for less than 10% of cerebral palsy cases.

OBJECTIVE

To determine the molecular diagnostic yield of exome sequencing (prevalence of pathogenic and likely pathogenic variants) in individuals with cerebral palsy.

DESIGN, SETTING, AND PARTICIPANTS

A retrospective cohort study of patients with cerebral palsy that included a clinical laboratory referral cohort with data accrued between 2012 and 2018 and a health care-based cohort with data accrued between 2007 and 2017.

EXPOSURES

Exome sequencing with copy number variant detection.

MAIN OUTCOMES AND MEASURES

The primary outcome was the molecular diagnostic yield of exome sequencing.

RESULTS

Among 1345 patients from the clinical laboratory referral cohort, the median age was 8.8 years (interquartile range, 4.4-14.7 years; range, 0.1-66 years) and 601 (45%) were female. Among 181 patients in the health care-based cohort, the median age was 41.9 years (interquartile range, 28.0-59.6 years; range, 4.8-89 years) and 96 (53%) were female. The molecular diagnostic yield of exome sequencing was 32.7% (95% CI, 30.2%-35.2%) in the clinical laboratory referral cohort and 10.5% (95% CI, 6.0%-15.0%) in the health care-based cohort. The molecular diagnostic yield ranged from 11.2% (95% CI, 6.4%-16.2%) for patients without intellectual disability, epilepsy, or autism spectrum disorder to 32.9% (95% CI, 25.7%-40.1%) for patients with all 3 comorbidities. Pathogenic and likely pathogenic variants were identified in 229 genes (29.5% of 1526 patients); 86 genes were mutated in 2 or more patients (20.1% of 1526 patients) and 10 genes with mutations were independently identified in both cohorts (2.9% of 1526 patients).

CONCLUSIONS AND RELEVANCE

Among 2 cohorts of patients with cerebral palsy who underwent exome sequencing, the prevalence of pathogenic and likely pathogenic variants was 32.7% in a cohort that predominantly consisted of pediatric patients and 10.5% in a cohort that predominantly consisted of adult patients. Further research is needed to understand the clinical implications of these findings.

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.

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.