ADCY5-related dyskinesia: Broader spectrum and genotype-phenotype correlations

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.

Structure of adenylyl cyclase 5 in complex with Gβγ offers insights into ADCY5-related dyskinesia

The nine different membrane-anchored adenylyl cyclase isoforms (AC1-9) in mammals are stimulated by the heterotrimeric G protein, Gαs, but their response to Gβγ regulation is isoform specific. In the present study, we report cryo-electron microscope structures of ligand-free AC5 in complex with Gβγ and a dimeric form of AC5 that could be involved in its regulation. Gβγ binds to a coiled-coil domain that links the AC transmembrane region to its catalytic core as well as to a region (C1b) that is known to be a hub for isoform-specific regulation. We confirmed the Gβγ interaction with both purified proteins and cell-based assays. Gain-of-function mutations in AC5 associated with human familial dyskinesia are located at the interface of AC5 with Gβγ and show reduced conditional activation by Gβγ, emphasizing the importance of the observed interaction for motor function in humans. We propose a molecular mechanism wherein Gβγ either prevents dimerization of AC5 or allosterically modulates the coiled-coil domain, and hence the catalytic core. As our mechanistic understanding of how individual AC isoforms are uniquely regulated is limited, studies such as this may provide new avenues for isoform-specific drug development.

NOTCH3 C201R variant causes cerebral autosomal dominant arteriopathy with subcortical infarcts and leukoencephalopathy (CADASIL) that can be confused with early-onset Alzheimer's disease

BACKGROUND

NOTCH3 is the causative gene for autosomal dominant cerebral arteriopathy with subcortical infarctions and leukoencephalopathy (CADASIL) which is associated with both stroke and dementia. When CADASIL presents primarily as dementia it can be difficult to distinguish from Alzheimer's disease (AD) at both the clinical and neuropathological levels.

METHODS

We performed exome sequencing of several affected individuals from a large family affected with AD. PCR amplification and direct Sanger sequencing were used to verify variants detected by exome analysis and to screen family members at-risk to carry those variants. Neuropathologic brain evaluation by immunohistochemistry and MRI were performed for the carriers of the NOTCH3 variant.

RESULTS

In a three-generation family with AD, we found a c.601 T > C p.Cys201Arg variant in the NOTCH3 gene that caused clinical and neuropathological manifestations of CADASIL. These features included earlier onset of dementia accompanied by behavioral abnormalities in the father and son and white matter abnormalities in the asymptomatic grandson. The family is one branch of a large pedigree studied by the Alzheimer's Disease Sequencing Project (ADSP). As part of the ADSP linkage analysis and whole genome sequencing endeavor, an ABCA1 variant, p.Ala937Val, was previously found associated with AD in this pedigree.

CONCLUSIONS

Our findings, together with other reported pathogenic missense variants of the C201 codon in NOTCH3, support the role of cysteine 201 as a mutation hotspot for CADASIL and highlight the genetic complexity both clinically and pathologically of AD and related dementia.

Scoping Review on ADCY5-Related Movement Disorders

Background

Adenylyl cyclase 5 (ADCY5)-related movement disorder (ADCY5-RMD) is a rare, childhood-onset disease resulting from pathogenic variants in the ADCY5 gene. The clinical features, diagnostic options, natural history, and treatments for this disease are poorly characterized and have never been established through a structured approach.

Objective

This scoping review attempts to summarize all available clinical literature on ADCY5-RMD.

Methods

Eighty-seven articles were selected for inclusion in this scoping review. The majority of articles identified were case reports or case series.

Results

These articles demonstrate that patients with ADCY5-RMD suffer from permanent and/ or paroxysmal hyperkinetic movements. The paroxysmal episodes can be worsened by environmental triggers, in particular the sleep-wake transition phase in the early morning. Occurrence of nocturnal paroxysmal dyskinesias and perioral twitches are highly suggestive of the diagnosis when present. In the majority of patients intellectual capacity is preserved. ADCY5-RMD is considered a non-progressive disorder, with inter-individual variations in evolution with aging. Somatic mosaicism, mode of inheritance and the location of the mutation within the protein can influence phenotype.

Conclusions

The current evidence for therapeutic options for ADCY5-RMD is limited: caffeine, benzodiazepines and deep brain stimulation have been consistently reported to be useful in case reports and case series.

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.

Isoform Specific Regulation of Adenylyl Cyclase 5 by Gβγ

The nine different membrane-anchored adenylyl cyclase isoforms (AC1-9) in mammals are stimulated by the heterotrimeric G protein Gαs, but their response to Gβγ regulation is isoform-specific. For example, AC5 is conditionally activated by Gβγ. Here, we report cryo-EM structures of ligand-free AC5 in complex with Gβγ and of a dimeric form of AC5 that could be involved in its regulation. Gβγ binds to a coiled-coil domain that links the AC transmembrane region to its catalytic core as well as to a region (C1b) that is known to be a hub for isoform-specific regulation. We confirmed the Gβγ interaction with both purified proteins and cell-based assays. The interface with Gβγ involves AC5 residues that are subject to gain-of-function mutations in humans with familial dyskinesia, indicating that the observed interaction is important for motor function. A molecular mechanism wherein Gβγ either prevents dimerization of AC5 or allosterically modulates the coiled-coil domain, and hence the catalytic core, is proposed. Because our mechanistic understanding of how individual AC isoforms are uniquely regulated is limited, studies such as this may provide new avenues for isoform-specific drug development.

Genetic Links to Episodic Movement Disorders: Current Insights

Episodic or paroxysmal movement disorders (PxMD) are conditions, which occur episodically, are transient, usually have normal interictal periods, and are characterized by hyperkinetic disorders, including ataxia, chorea, dystonia, and ballism. Broadly, these comprise paroxysmal dyskinesias (paroxysmal kinesigenic and non-kinesigenic dyskinesia [PKD/PNKD], paroxysmal exercise-induced dyskinesias [PED]) and episodic ataxias (EA) types 1-9. Classification of paroxysmal dyskinesias has traditionally been clinical. However, with advancement in genetics and the discovery of the molecular basis of several of these disorders, it is becoming clear that phenotypic pleiotropy exists, that is, the same variant may give rise to a variety of phenotypes, and the classical understanding of these disorders requires a new paradigm. Based on molecular pathogenesis, paroxysmal disorders are now categorized as synaptopathies, transportopathies, channelopathies, second-messenger related disorders, mitochondrial or others. A genetic paradigm also has an advantage of identifying potentially treatable disorders, such as glucose transporter 1 deficiency syndromes, which necessitates a ketogenic diet, and ADCY5-related disorders, which may respond to caffeine. Clues for a primary etiology include age at onset below 18 years, presence of family history and fixed triggers and attack duration. Paroxysmal movement disorder is a network disorder, with both the basal ganglia and the cerebellum implicated in pathogenesis. Abnormalities in the striatal cAMP turnover pathway may also be contributory. Although next-generation sequencing has restructured the approach to paroxysmal movement disorders, the genetic underpinnings of several entities remain undiscovered. As more genes and variants continue to be reported, these will lead to enhanced understanding of pathophysiological mechanisms and precise treatment.

Effects of theophylline on ADCY5 activation-From cellular studies to improved therapeutic options for ADCY5-related dyskinesia patients

We show the effects of the three purine derivatives, caffeine, theophylline, and istradefylline, on cAMP production by adenylyl cyclase 5 (ADCY5)-overexpressing cell lines. A comparison of cAMP levels was performed for ADCY5 wild-type and R418W mutant cells. ADCY5-catalyzed cAMP production was reduced with all three purine derivatives, while the most pronounced effects on cAMP reduction were observed for ADCY5 R418W mutant cells. The gain-of-function ADCY5 R418W mutant is characterized by an increased catalytic activity resulting in elevated cAMP levels that cause kinetic disorders or dyskinesia in patients. Based on our findings in ADCY5 cells, a slow-release formulation of theophylline was administered to a preschool-aged patient with ADCY5-related dyskinesia. A striking improvement of symptoms was observed, outperforming the effects of caffeine that had previously been administered to the same patient. We suggest considering theophylline as an alternative therapeutic option to treat ADCY5-related dyskinesia in patients.

Elective and Emergency Deep Brain Stimulation in Refractory Pediatric Monogenetic Movement Disorders Presenting with Dystonia: Current Practice Illustrated by Two Cases

BACKGROUND

Dystonia is characterized by sustained or intermittent muscle contractions, leading to abnormal posturing and twisting movements. In pediatric patients, dystonia often negatively influences quality of life. Pharmacological treatment for dystonia is often inadequate and causes adverse effects. Deep brain stimulation (DBS) appears to be a valid therapeutic option for pharmacoresistant dystonia in children.

METHODS

To illustrate the current clinical practice, we hereby describe two pediatric cases of monogenetic movement disorders presenting with dystonia and treated with DBS. We provide a literature review of similar previously described cases and on different clinical aspects of DBS in pediatric dystonia.

RESULTS

The first patient, a 6-year-old girl with severe dystonia, chorea, and myoclonus due to an ADCY5 gene mutation, received DBS in an elective setting. The second patient, an 8-year-old boy with GNAO1-related dystonia and chorea, underwent emergency DBS due to a pharmacoresistant status dystonicus. A significant amelioration of motor symptoms (65% on the Burke-Fahn-Marsden Dystonia Rating Scale) was observed postoperatively in the first patient and her personal therapeutic goals were achieved. DBS was previously reported in five patients with ADCY5-related movement disorders, of which three showed objective improvement. Emergency DBS in our second patient resulted in the successful termination of his GNAO1-related status dystonicus, this being the eighth case reported in the literature.

CONCLUSION

DBS can be effective in monogenetic pediatric dystonia and should be considered early in the disease course. To better evaluate the effects of DBS on patients' functioning, patient-centered therapeutic goals should be discussed in a multidisciplinary approach.

Gαs, adenylyl cyclase, and their relationship to the diagnosis and treatment of depression

The relationship between depression, its etiology and therapy, and the cAMP signaling system have been studies for decades. This review will focus on cAMP, G proteins and adenylyl cyclase and depression or antidepressant action. Both human and animal studies are compared and contrasted. It is concluded that there is some synteny in the findings that cAMP signaling is attenuated in depression and that this is reversed by successful antidepressant therapy. The G protein that activates adenylyl cyclase, Gα_s, appears to have diminished access to adenylyl cyclase in depression, and this is rectified by successful antidepressant treatment. Unfortunately, attempts to link specific isoforms of adenylyl cyclase to depression or antidepressant action suffer from discontinuity between human and animal studies.

Functional abnormalities in the cerebello-thalamic pathways in a mouse model of DYT25 dystonia

Dystonia is often associated with functional alterations in the cerebello-thalamic pathways, which have been proposed to contribute to the disorder by propagating pathological firing patterns to the forebrain. Here, we examined the function of the cerebello-thalamic pathways in a model of DYT25 dystonia. DYT25 (Gnal^+/−) mice carry a heterozygous knockout mutation of the Gnal gene, which notably disrupts striatal function, and systemic or striatal administration of oxotremorine to these mice triggers dystonic symptoms. Our results reveal an increased cerebello-thalamic excitability in the presymptomatic state. Following the first dystonic episode, Gnal^+/- mice in the asymptomatic state exhibit a further increase of the cerebello-thalamo-cortical excitability, which is maintained after θ-burst stimulations of the cerebellum. When administered in the symptomatic state induced by a cholinergic activation, these stimulations decreased the cerebello-thalamic excitability and reduced dystonic symptoms. In agreement with dystonia being a multiregional circuit disorder, our results suggest that the increased cerebello-thalamic excitability constitutes an early endophenotype, and that the cerebellum is a gateway for corrective therapies via the depression of cerebello-thalamic pathways.

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.

Physiological Roles of Mammalian Transmembrane Adenylyl Cyclase Isoforms

Adenylyl cyclases (ACs) catalyze the conversion of ATP to the ubiquitous second messenger cAMP. Mammals possess nine isoforms of transmembrane ACs, dubbed AC1-9, that serve as major effector enzymes of G protein-coupled receptors. The transmembrane ACs display varying expression patterns across tissues, giving potential for them having a wide array of physiologic roles. Cells express multiple AC isoforms, implying that ACs have redundant functions. Furthermore, all transmembrane ACs are activated by Gα_s so it was long assumed that all ACs are activated by Gα_s-coupled GPCRs. AC isoforms partition to different microdomains of the plasma membrane and form prearranged signaling complexes with specific GPCRs that contribute to cAMP signaling compartments. This compartmentation allows for a diversity of cellular and physiological responses by enabling unique signaling events to be triggered by different pools of cAMP. Isoform specific pharmacological activators or inhibitors are lacking for most ACs, making knockdown and overexpression the primary tools for examining the physiological roles of a given isoform. Much progress has been made in understanding the physiological effects mediated through individual transmembrane ACs. GPCR-AC-cAMP signaling pathways play significant roles in regulating functions of every cell and tissue, so understanding each AC isoform's role holds potential for uncovering new approaches for treating a vast array of pathophysiological conditions.

Paroxysmal Movement Disorders

Paroxysmal movement disorders (PxMDs) are a clinical and genetically heterogeneous group of movement disorders characterized by episodic involuntary movements (dystonia, dyskinesia, chorea and/or ataxia). Historically, PxMDs were classified clinically (triggers and characteristics of the movements) and this directed single-gene testing. With the advent of next-generation sequencing (NGS), how we classify and investigate PxMDs has been transformed. Next-generation sequencing has enabled new gene discovery (RHOBTB2, TBC1D24), expansion of phenotypes in known PxMDs genes and a better understanding of disease mechanisms. However, PxMDs exhibit phenotypic pleiotropy and genetic heterogeneity, making it challenging to predict genotype based on the clinical phenotype. For example, paroxysmal kinesigenic dyskinesia is most commonly associated with variants in PRRT2 but also variants identified in PNKD, SCN8A, and SCL2A1. There are no radiological or biochemical biomarkers to differentiate genetic causes. Even with NGS, diagnosis rates are variable, ranging from 11 to 51% depending on the cohort studied and technology employed. Thus, a large proportion of patients remain undiagnosed compared to other neurological disorders such as epilepsy, highlighting the need for further genomic research in PxMDs. Whole-genome sequencing, deep-sequencing, copy number variant analysis, detection of deep-intronic variants, mosaicism and repeat expansions, will improve diagnostic rates. Identifying the underlying genetic cause has a significant impact on patient care, modification of treatment, long-term prognostication and genetic counseling. This paper provides an update on the genetics of PxMDs, description of PxMDs classified according to causative gene rather than clinical phenotype, highlighting key clinical features and providing an algorithm for genetic testing of PxMDs.

An Update on the Phenotype, Genotype and Neurobiology of ADCY5-Related Disease

Adenylyl cyclase 5 (ADCY5)-related phenotypes comprise an expanding disease continuum, but much remains to be understood about the underlying pathogenic mechanisms of the disease. ADCY5-related disease comprises a spectrum of hyperkinetic disorders involving chorea, myoclonus, and/or dystonia, often with paroxysmal exacerbations. Hypotonia, developmental delay, and intellectual disability may be present. The causative gene encodes adenylyl cyclase, the enzyme responsible for the conversion of adenosine triphosphate (ATP) to cyclic adenosine-3',5'-monophosphate (cAMP). cAMP is a second messenger that exerts a wide variety of effects via several intracellular signaling pathways. ADCY5 is the most commonly expressed isoform of adenylyl cyclase in medium spiny neurons (MSNs) of the striatum, and it integrates and controls dopaminergic signaling. Through cAMP pathway, ADCY5 is a key regulator of the cortical and thalamic signaling that control initiation of voluntary movements and prevention of involuntary movements. Gain-of-function mutations in ADCY5 have been recently linked to a rare genetic disorder called ADCY5-related dyskinesia, where dysregulation of the cAMP pathway leads to reduced inhibitory activity and involuntary hyperkinetic movements. Here, we present an update on the neurobiology of ADCY5, together with a detailed overview of the reported clinical phenotypes and genotypes. Although a range of therapeutic approaches has been trialed, there are currently no disease-modifying treatments. Improved in vitro and in vivo laboratory models will no doubt increase our understanding of the pathogenesis of this rare genetic movement disorder, which will improve diagnosis, and also facilitate the development of precision medicine approaches for this, and other forms of hyperkinesia. © 2021 The Authors. Movement Disorders published by Wiley Periodicals LLC on behalf of International Parkinson and Movement Disorder Society.

Genetic updates on paroxysmal dyskinesias

The paroxysmal dyskinesias are a diverse group of genetic disorders that manifest as episodic movements, with specific triggers, attack frequency, and duration. With recent advances in genetic sequencing, the number of genetic variants associated with paroxysmal dyskinesia has dramatically increased, and it is now evident that there is significant genotype-phenotype overlap, reduced (or incomplete) penetrance, and phenotypic variability. In addition, a variety of genetic conditions can present with paroxysmal dyskinesia as the initial symptom. This review will cover the 34 genes implicated to date and propose a diagnostic workflow featuring judicious use of whole-exome or -genome sequencing. The goal of this review is to provide a common understanding of paroxysmal dyskinesias so basic scientists, geneticists, and clinicians can collaborate effectively to provide diagnoses and treatments for patients.

Homozygous ADCY5 mutation causes early-onset movement disorder with severe intellectual disability

BACKGROUND

Mutations of theADCY5 have been identified in patients with familial dyskinesia, early-onsetautosomal dominant chorea and dystonia, and benign hereditary chorea. Most ofthe ADCY5 mutations are de novo or transmitted in an autosomal dominantfashion. Only two pedigrees are known to show autosomal recessive inheritance.

OBJECTIVES

We report twosiblings with severe ID, dystonic movement, and growth failure with unknownetiology.

METHODS

We planned a proband-parentapproach using whole exome sequencing.

RESULTS

Homozygous mutationin exon 21 of the ADCY5 (p.R1238W) was identified in the siblings. Althoughtheir parents were heterozygous for the mutation, they were free from clinicalmanifestations.

CONCLUSIONS

Our results furtherexpand the phenotype/genotype correlations of the ADCY5-related disorders.Mutations of ADCY5 should be considered in pediatric patients with ID andinvoluntary movement.

Compartmentalized Signaling in Aging and Neurodegeneration

The cyclic AMP (cAMP) signalling cascade is necessary for cell homeostasis and plays important roles in many processes. This is particularly relevant during ageing and age-related diseases, where drastic changes, generally decreases, in cAMP levels have been associated with the progressive decline in overall cell function and, eventually, the loss of cellular integrity. The functional relevance of reduced cAMP is clearly supported by the finding that increases in cAMP levels can reverse some of the effects of ageing. Nevertheless, despite these observations, the molecular mechanisms underlying the dysregulation of cAMP signalling in ageing are not well understood. Compartmentalization is widely accepted as the modality through which cAMP achieves its functional specificity; therefore, it is important to understand whether and how this mechanism is affected during ageing and to define which is its contribution to this process. Several animal models demonstrate the importance of specific cAMP signalling components in ageing, however, how age-related changes in each of these elements affect the compartmentalization of the cAMP pathway is largely unknown. In this review, we explore the connection of single components of the cAMP signalling cascade to ageing and age-related diseases whilst elaborating the literature in the context of cAMP signalling compartmentalization.

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.

Striatal Dopamine Induced ERK Phosphorylation Is Altered in Mouse Models of Monogenic Dystonia

BACKGROUND

Similar to some monogenic forms of dystonia, levodopa-induced dyskinesia is a hyperkinetic movement disorder with abnormal nigrostriatal dopaminergic neurotransmission. Molecularly, it is characterized by hyper-induction of phosphorylation of extracellular signal-related kinase in response to dopamine in medium spiny neurons of the direct pathway.

OBJECTIVES

The objective of this study was to determine if mouse models of monogenic dystonia exhibit molecular features of levodopa-induced dyskinesia.

METHODS

Western blotting and quantitative immunofluorescence was used to assay baseline and/or dopamine-induced levels of the phosphorylated kinase in the striatum in mouse models of DYT1, DYT6, and DYT25 expressing a reporter in dopamine D1 receptor-expressing projection neurons. Cyclic adenosine monophosphate (cAMP) immunoassay and adenylyl cyclase activity assays were also performed.

RESULTS

In DYT1 and DYT6 models, blocking dopamine reuptake with cocaine leads to enhanced extracellular signal-related kinase phosphorylation in dorsomedial striatal medium spiny neurons in the direct pathway, which is abolished by pretreatment with the N-methyl-d-aspartate antagonist MK-801. Phosphorylation is decreased in a model of DYT25. Levels of basal and stimulated cAMP and adenylyl cyclase activity were normal in the DYT1 and DYT6 mice and decreased in the DYT25 mice. Oxotremorine induced increased abnormal movements in the DYT1 knock-in mice.

CONCLUSIONS

The increased dopamine induction of extracellular signal-related kinase phosphorylation in 2 genetic types of dystonia, similar to what occurs in levodopa-induced dyskinesia, and its decrease in a third, suggests that abnormal signal transduction in response to dopamine in the postsynaptic nigrostriatal pathway might be a point of convergence for dystonia and other hyperkinetic movement disorders, potentially offering common therapeutic targets. © 2021 International Parkinson and Movement Disorder Society.

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.

Treatment of Paroxysmal Dyskinesia

Paroxysmal dyskinesia (PxD) is a heterogeneous group of syndromes characterized by recurrent attacks of abnormal movements, triggered by detectable factors, without loss of consciousness. According to the precipitating factors, they are classified as paroxysmal kinesigenic dyskinesia (PKD), paroxysmal non-kinesigenic dyskinesia (PNKD), and paroxysmal exercise-induced dystonia (PED). PxD treatment is based on the combination of nonpharmacologic and pharmacologic approaches. Pharmacologic and nonpharmacologic treatments effective for PNKD and PED also are available. In PxD refractory to conventional treatment, surgery might be an alternative therapeutic option. The course of PRRT2-PKD and MR-1-PNKD is benign, and treatment might not be needed with advancing age.

Deep brain stimulation reduces (nocturnal) dyskinetic exacerbations in patients with ADCY5 mutation: a case series

Mutations in the ADCY5 gene can cause a complex hyperkinetic movement disorder. Episodic exacerbations of dyskinesia are a particularly disturbing symptom as they occur predominantly during night and interrupt sleep. We present the clinical short- and long-term effects of pallidal deep brain stimulation (DBS) in three patients with a confirmed pathogenic ADCY5 mutation. Patients were implanted with bilateral pallidal DBS at the age of 34, 20 and 13 years. Medical records were reviewed for clinical history. Pre- and postoperative video files were assessed using the “Abnormal Involuntary Movement Scale” (AIMS) as well as the motor part of the “Burke Fahn Marsden Dystonia Rating Scale” (BFMDRS). All patients reported subjective general improvement ranging from 40 to 60%, especially the reduction of nocturnal episodic dyskinesias (80–90%). Objective scales revealed only a mild decrease of involuntary movements in all and reduced dystonia in one patient. DBS-induced effects were sustained up to 13 years after implantation. We demonstrate that treatment with pallidal DBS was effective in reducing nocturnal dyskinetic exacerbations in patients with ADCY5-related movement disorder, which was sustained over the long term.

Medical management of myoclonus-dystonia and implications for underlying pathophysiology

Myoclonus-dystonia is an early onset genetic disorder characterised by subcortical myoclonus and less prominent dystonia. Its primary causative gene is the epsilon-sarcoglycan gene but the syndrome of "myoclonic dystonia" has been shown to be a heterogeneous group of genetic disorders. The underlying pathophysiology of myoclonus-dystonia is incompletely understood, although it may relate to dysfunction of striatal monoamine neurotransmission or disruption of cerebellothalamic networks (possibly via a GABAergic deficit of Purkinje cells). A broad range of oral medical therapies have been used in the treatment of myoclonus-dystonia with a varying response, and limited data relating to efficacy and tolerability, yet this condition responds dramatically to alcohol. Few well conducted randomized controlled trials have been undertaken leading to an empirical ad hoc approach for many patients. We review the current evidence for pharmacological therapies in myoclonus-dystonia, discuss implications for underlying pathogenesis of the condition and propose a treatment algorithm for these patients.

Biallelic PDE2A variants: a new cause of syndromic paroxysmal dyskinesia

Cause of complex dyskinesia remains elusive in some patients. A homozygous missense variant leading to drastic decrease of PDE2A enzymatic activity was reported in one patient with childhood-onset choreodystonia preceded by paroxysmal dyskinesia and associated with cognitive impairment and interictal EEG abnormalities. Here, we report three new cases with biallelic PDE2A variants identified by trio whole-exome sequencing. Mitochondria network was analyzed after Mitotracker™ Red staining in control and mutated primary fibroblasts. Analysis of retrospective video of patients' movement disorder and refinement of phenotype was carried out. We identified a homozygous gain of stop codon variant c.1180C>T; p.(Gln394*) in PDE2A in siblings and compound heterozygous variants in young adult: a missense c.446C>T; p.(Pro149Leu) and splice-site variant c.1922+5G>A predicted and shown to produce an out of frame transcript lacking exon 22. All three patients had cognitive impairment or developmental delay. The phenotype of the two oldest patients, aged 9 and 26, was characterized by childhood-onset refractory paroxysmal dyskinesia initially misdiagnosed as epilepsy due to interictal EEG abnormalities. The youngest patient showed a proven epilepsy at the age of 4 months and no paroxysmal dyskinesia at 15 months. Interestingly, analysis of the fibroblasts with the biallelic variants in PDE2A variants revealed mitochondria network morphology changes. Together with previously reported case, our three patients confirm that biallelic PDE2A variants are a cause of childhood-onset refractory paroxysmal dyskinesia with cognitive impairment, sometimes associated with choreodystonia and interictal baseline EEG abnormalities or epilepsy.

Heterozygous STUB1 missense variants cause ataxia, cognitive decline, and STUB1 mislocalization

OBJECTIVE

To identify the genetic cause of autosomal dominant ataxia complicated by behavioral abnormalities, cognitive decline, and autism in 2 families and to characterize brain neuropathologic signatures of dominant STUB1-related ataxia and investigate the effects of pathogenic variants on STUB1 localization.

METHODS

Clinical and research-based exome sequencing was used to identify the causative variants for autosomal dominant ataxia in 2 families. Gross and microscopic neuropathologic evaluations were performed on the brains of 4 affected individuals in these families.

RESULTS

Mutations in STUB1 have been primarily associated with childhood-onset autosomal recessive ataxia, but here we report heterozygous missense variants in STUB1 (p.Ile53Thr and p.The37Leu) confirming the recent reports of autosomal dominant inheritance. Cerebellar atrophy on imaging and cognitive deficits often preceded ataxia. Unique neuropathologic examination of the 4 brains showed the marked loss of Purkinje cells (PCs) without microscopic evidence of significant pathology outside the cerebellum. The normal pattern of polarized somatodendritic STUB1 protein expression in PCs was lost, resulting in aberrant STUB1 localization in the distal PC dendritic arbors.

CONCLUSIONS

This study confirms a dominant inheritance pattern in STUB1-ataxia in addition to a recessive one and documents its association with cognitive and behavioral disability, including autism. In the most extensive analysis of cerebellar pathology in this disease, we demonstrate disruption of STUB1 protein in PCs as part of the underlying pathogenesis.

Chorea

PURPOSE OF REVIEW

This article provides an overview of the approach to chorea in clinical practice, beginning with a discussion of the phenomenologic features of chorea and how to differentiate it from other movement disorders. The diagnostic approach, clinical features of important acquired and genetic choreas, and therapeutic principles are also discussed. Practical clinical points and caveats are included.

RECENT FINDINGS

C9orf72 disease is the most common Huntington disease phenocopy, according to studies in the European population. Anti-IgLON5 disease can present with chorea. The role of immunotherapies in Sydenham chorea has increased, and further clinical studies may be useful. Benign hereditary chorea is a syndrome or phenotype due to mutations in several genes, including NKX2-1, ADCY5, GNAO1, and PDE10A. New-generation presynaptic dopamine-depleting agents provide more options for symptomatic treatment of chorea with fewer adverse effects. Deep brain stimulation has been performed in several choreic disorders, but features other than chorea and the neurodegenerative nature should be taken into consideration. Studies on genetic interventions for Huntington disease are ongoing.

SUMMARY

Clinical features remain crucial in guiding the differential diagnosis and appropriate investigations in chorea. Given the complexity of most choreic disorders, treating only the chorea is not sufficient. A comprehensive and multidisciplinary approach is required.

Nosology and Phenomenology of Psychosis in Movement Disorders

Background

Psychotic symptoms, such as delusions and hallucinations, are part of the clinical picture of several conditions presenting movement disorders. Phenomenology and epidemiology of psychosis in Parkinson's disease have received wide attention; however, the presence of psychosis in other movement disorders is, comparatively, less well known.

Objectives

To review psychotic symptoms present in different movement disorders.

Methods

A comprehensive and structured literature search was performed to identify and analyze data on patients with movement disorders and comorbid psychosis.

Results

In monogenic parkinsonisms, such as PARK-GBA, PARK-LRRK2, and PARK-SNCA, visual hallucinations related to dopamine replacement therapy are frequent as well as are delusions in PARK-LRRK2 and PARK-SNCA, but not in PARK-GBA. Different types of delusions and hallucinations are found in Huntington's disease and other choreic disorders. In Tourette's syndrome, paranoid delusions as well as visual, olfactory, and auditory hallucinations have been described, which usually develop after an average of 10 years of disease. Delusions in ataxias are more frequent in ATX-TBP, ATX-ATN1, and ATX-ATXN3, whereas it is rare in Friedreich's ataxia. Psychosis is also a prominent and frequent clinical feature in Fahr's disease, Wilson's disease, neurodegeneration with brain iron accumulation, and some lysosomal storage disorders, whereas it is uncommon in atypical parkinsonisms and dystonia. Psychosis usually occurs at late disease stages, but may appear as onset symptoms of the disease, especially in Wilson's disease, Huntington's disease, late-onset Tays-Sachs, and Niemann-Pick.

Conclusion

Psychosis is a frequent comorbidity in most hyper- and hypokinetic movement disorders. Appropriate recognition is relevant both in the early and late disease stages.

Hyperphosphorylated Tau, Increased Adenylate Cyclase 5 (ADCY5) Immunoreactivity, but No Neuronal Loss in ADCY5-Dyskinesia

BACKGROUND

Adenylate cyclase 5 (ADCY5)-related dyskinesia is a childhood-onset movement disorder. Manifestations vary in frequency and severity and may include chorea, tremor, dystonia, facial twitches, myoclonus, axial hypotonia, and limb hypertonia. Psychosis is likely part of the broader spectrum. ADCY5 is widely expressed in the brain, especially in the striatum. Previous reports of brain autopsies of 2 subjects with likely ADCY5-dyskinesia were limited by the absence of a molecular diagnosis. In 1 case, normal gross pathology was reported. In the other case, ADCY5 expression was not examined and neuropathological findings were confounded by age and comorbidities.

OBJECTIVES

To examine ADCY5 expression and neuropathological changes in ADCY5-dyskinesia.

METHODS

An extensive brain autopsy, including immunohistochemical analyses with antibodies to paired helical filament tau, α-synuclein, amyloid-β, microtubule-associated protein 2, and ADCY5, was performed.

RESULTS

The patient, with a p.M1029K ADCY5 variant, had severe dyskinesias from early childhood, later recurrent episodes of psychosis, and died at age 46. Gross pathology was unremarkable, but we detected increased immunoreactivity for ADCY5 in neurons in multiple brain regions. Despite no history of brain trauma to suggest chronic traumatic encephalopathy, we found tau deposits in the deep cortical sulci, midbrain, and hippocampus with minimal amyloid pathology and no Lewy bodies.

CONCLUSIONS

We present the first brain autopsy findings in a molecularly proven case of ADCY5-dyskinesia, showing increased ADCY5 immunoreactivity in neurons and evidence of tau deposition. Additional patients will need to be studied to determine whether increased immunoreactivity for ADCY5 is a signature for ADCY5-dyskinesia and whether this disease has a tauopathy component.

Clinical diagnostic exome sequencing in dystonia: Genetic testing challenges for complex conditions

Patients with dystonia are particularly appropriate for diagnostic exome sequencing (DES), due to the complex, diverse features and genetic heterogeneity. Personal and family history data were collected from test requisition forms and medical records from 189 patients with reported dystonia and available family members received for clinical DES. Of them, 20.2% patients had a positive genetic finding associated with dystonia. Detection rates for cases with isolated and combined dystonia were 22.4% and 25.0%, respectively. 71.4% of the cohort had co-occurring non-movement-related findings and a detection rate of 24.4%. Patients with childhood-onset dystonia trended toward higher detection rates (31.8%) compared to infancy (23.6%), adolescence (12.5%), and early-adulthood onset (16%). Uncharacterized gene findings were found in 6.7% (8/119) of cases that underwent analysis for genes without an established disease relationship. Patients with intellectual disability/developmental delay, seizures/epilepsy and/or multifocal dystonia were more likely to have positive findings (P = .0093, .0397, .0006). Four (2.1%) patients had findings in two genes, and seven (3.7%) had reclassification after the original report due to new literature, new clinical information or reanalysis request. Pediatric patients were more likely to have positive findings (P = .0180). Our observations show utility of family-based DES in patients with dystonia and illustrate the complexity of testing.

Diagnostic Yield of a Targeted Next-Generation Sequencing Gene Panel for Pediatric-Onset Movement Disorders: A 3-Year Cohort Study

In recent years, genetic techniques of diagnosis have shown rapid development, resulting in a modified clinical approach to many diseases, including neurological disorders. Movement disorders, in particular those arising in childhood, pose a diagnostic challenge. First, from a purely phenomenological point of view, the correct clinical classification of signs and symptoms may be difficult and require expert evaluation. This is because the clinical picture is often a mixture of hyperkinetic and hypokinetic disorders, and within hyperkinetic movement disorders, combined phenotypes are not unusual. Second, although several genes that cause movement disorders in children are now well-known, many of them have only been described in adult populations or discovered in patients after many years of disease. Furthermore, diseases that alter their mechanisms from childhood to adulthood are still little known, and many phenotypes in children are the result of a disruption of normal neurodevelopment. High-throughput gene screening addresses these difficulties and has modified the approach to genetic diagnosis. In the exome-sequencing era, customized genetic panels now offer the ability to perform fast and low-cost screening of the genes commonly involved in the pathogenesis of the disease. Here, we describe a 3-year study using a customized gene panel for pediatric-onset movement disorders in a selected cohort of children and adolescents. We report a satisfying diagnostic yield, further confirming the usefulness of gene panel analysis.

ADCY5-Related Dyskinesia: Improving Clinical Detection of an Evolving Disorder

Background

The phenotypic spectrum of adenylyl cyclase 5 (ADCY5)-related disease has expanded considerably since the first description of the disorder in 1978 as familial essential chorea in a multiplex family.

Objective

To examine recent advances in the understanding of ADCY5-related dyskinesia and outline a diagnostic approach to enhance clinical detection.

Methods

A pragmatic review of the ADCY5 literature was undertaken to examine unique genetic and pathophysiological features as well as distinguishing clinical features.

Results

With over 70 cases reported to date, the phenotype is recognized to be broad, although distinctive features include prominent facial dyskinesia, motor exacerbations during drowsiness or sleep arousal, episodic painful dystonic posturing increased with stress or illness, and axial hypotonia with delayed developmental milestones. Uncommon phenotypes include childhood-onset chorea, myoclonus-dystonia, isolated nongeneralized dystonia, and alternating hemiplegia.

Conclusion

The ongoing expansion in clinical features suggests that ADCY5 remains underdiagnosed and may account for a proportion of "idiopathic" hyperkinetic movement disorders. Enhanced understanding of its clinical features may help clinicians improve the detection of complex or uncommon cases.

The spectrum of paroxysmal dyskinesias

Paroxysmal dyskinesias (PxD) comprise a group of heterogeneous syndromes characterized by recurrent attacks of mainly dystonia and/or chorea, without loss of consciousness. PxD have been classified according to their triggers and duration as paroxysmal kinesigenic dyskinesia, paroxysmal nonkinesigenic dyskinesia and paroxysmal exertion-induced dyskinesia. Of note, the spectrum of genetic and nongenetic conditions underlying PxD is continuously increasing, but not always a phenotype–etiology correlation exists. This creates a challenge in the diagnostic work-up, increased by the fact that most of these episodes are unwitnessed. Furthermore, other paroxysmal disorders, included those of psychogenic origin, should be considered in the differential diagnosis. In this review, some key points for the diagnosis are provided, as well as the appropriate treatment and future approaches discussed.

Sleep in ADCY5-Related Dyskinesia: Prolonged Awakenings Caused by Abnormal Movements

STUDY OBJECTIVES

ADCY5 mutations cause early-onset hyperkinetic movement disorders comprising diurnal and nocturnal paroxysmal dyskinesia, and patient-reported sleep fragmentation. We aimed to characterize all movements occurring during sleep and in the transition from sleep to awakening, to ascertain if there is a primary sleep disorder, or if the sleep disturbance is rather a consequence of the dyskinesia.

METHODS

Using video polysomnography, we evaluated the nocturnal motor events and abnormal movements in 7 patients with ADCY5-related dyskinesia and compared their sleep measures with those of 14 age- and sex-matched healthy controls.

RESULTS

We observed an increased occurrence of abnormal movements during wake periods compared to sleep in patients with ADCY5-related dyskinesia. While asleep, abnormal movements occurred more frequently during stage N2 and REM sleep, in contrast with stage N3 sleep. Abnormal movements were also more frequent during morning awakenings compared to wake periods before falling asleep. The pattern of the nocturnal abnormal movements mirrored those observed during waking hours. Compared to controls, patients with ADCY5-related dyskinesia had lower sleep efficiencies due to prolonged awakenings secondary to the abnormal movements, but no other differences in sleep measures. Notably, sleep onset latency was short and devoid of violent abnormal movements.

CONCLUSIONS

In this series of patients with ADCY5-related dyskinesia, nocturnal paroxysmal dyskinesia were not associated with drowsiness or delayed sleep onset, but emerged during nighttime awakenings with subsequent delayed sleep, whereas sleep architecture was normal.

Paroxysmal Movement Disorders: Recent Advances

PURPOSE OF REVIEW

Recent advancements in next-generation sequencing (NGS) have enabled techniques such as whole exome sequencing (WES) and whole genome sequencing (WGS) to be used to study paroxysmal movement disorders (PMDs). This review summarizes how the recent genetic advances have altered our understanding of the pathophysiology and treatment of the PMDs. Recently described disease entities are also discussed.

RECENT FINDINGS

With the recognition of the phenotypic and genotypic heterogeneity that occurs amongst the PMDs, an increasing number of gene mutations are now implicated to cause the disorders. PMDs can also occur as part of a complex phenotype. The increasing complexity of PMDs challenges the way we view and classify them. The identification of new causative genes and their genotype-phenotype correlation will shed more light on the underlying pathophysiology and will facilitate development of genetic testing guidelines and identification of novel drug targets for PMDs.

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.

Restless Legs Syndrome in NKX2-1-related chorea: An expansion of the disease spectrum

BACKGROUND

Molecular technologies are expanding our knowledge about genetic variability underlying early-onset non-progressive choreic syndromes. Focusing on NKX2-1-related chorea, the clinical phenotype and sleep related disorders have been only partially characterized.

METHODS

We propose a retrospective and longitudinal observational study in 7 patients with non-progressive chorea due to NKX2-1 mutations. In all subjects sleep and awake EEG, brain MRI with study of pituitary gland, chest X-rays, endocrinological investigations were performed. Movement disorders, pattern of sleep and related disorders were investigated using structured clinical evaluation and several validated questionnaires.

RESULTS

In patients carrying NKX2-1 mutations, chorea was mainly distributed in the upper limbs and tended to improve with age. All patients presented clinical or subclinical hypothyroidism and delayed motor milestones. Three subjects had symptoms consistent with Restless Legs Syndrome (RLS) that improved with Levodopa.

CONCLUSIONS

Patients with NKX2-1 gene mutations should be investigated for RLS, which, similarly to chorea, can sometimes be ameliorated by Levodopa.