Paroxysmal Movement Disorders

Clinical characterization of a novel episodic ataxia in young working Cocker Spaniels

BACKGROUND

Episodic ataxias (EAs) are a rare group of paroxysmal movement disorders (PMD) described in human medicine with only one suspected case described in veterinary literature.

HYPOTHESIS/OBJECTIVES

This study aimed to provide clinical description of a suspected primary EA in working Cocker Spaniel (WCS) dogs.

ANIMALS

Seven WCS dogs with suspected primary EA.

METHODS

Descriptive, retrospecitve, multicenter study. Clinical signs, video footage, investigations, treatment, and outcome were reviewed. Owners of affected dogs were invited to complete a questionnaire.

RESULTS

The mean age at clinical onset was 4 months. Signs were acute and included episodic body swaying, titubation, cerebellar ataxia, wide-base stance, and hypermetria, all while mentation remained unaltered. Neither autonomic nor vestibular signs nor hyperkinetic movements were observed. Duration of episodes ranged from 30 minutes up to 24 hours, and their frequency varied from weekly to once every 5 months. When investigations were performed, results revealed no abnormalities except for 1 dog that had increased gluten antibody titers. None of the dogs deteriorated, and in dogs with available follow-up (5/7) the frequency of episodes decreased or completely resolved, from which the majority (4/5) received gluten-free diet.

CONCLUSION AND CLINICAL IMPORTANCE

A novel PMD was identified in young WCS, manifesting as EA. The condition is suspected to have a primary (genetic) etiology, although the cause of this manifestation has not yet been identified. Episodic ataxia in our WCS had a good prognosis. Veterinarians must be aware of this presentation, and further investigations are needed to determine the origin of the clinical signs.

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.

Genetic testing for non-parkinsonian movement disorders: Navigating the diagnostic maze

Genetic testing has become a valuable diagnostic tool for movement disorders due to substantial advancements in understanding their genetic basis. However, the heterogeneity of movement disorders poses a significant challenge, with many genes implicated in different subtypes. This paper aims to provide a neurologist's perspective on approaching patients with hereditary hyperkinetic disorders with a focus on select forms of dystonia, paroxysmal dyskinesia, chorea, and ataxia. Age at onset, initial symptoms, and their severity, as well as the presence of any concurrent neurological and non-neurological features, contribute to the individual clinical profiles of hereditary non-parkinsonian movement disorders, aiding in the selection of appropriate genetic testing strategies. There are also more specific diagnostic clues that may facilitate the decision-making process and may be highly specific for certain conditions, such as diurnal fluctuations and l-dopa response in dopa-responsive dystonia, and triggering factors, duration and frequency of attacks in paroxysmal dyskinesia. While the genetic and mutational spectrum across non-parkinsonian movement disorders is broad, certain groups of diseases tend to be associated with specific types of pathogenic variants, such as repeat expansions in many of the ataxias. Some of these pathogenic variants cannot be detected by standard methods, such as panel or exome sequencing, but require the investigation of intronic regions for repeat expansions, such as Friedreich's or FGF14-linked ataxia. With our advancing knowledge of the genetic underpinnings of movement disorders, the incorporation of precise and personalized diagnostic strategies can enhance patient care, prognosis, and the application and development of targeted therapeutic interventions.

Genetics and Pathogenesis of Dystonia

Dystonia is a clinically and genetically highly heterogeneous neurological disorder characterized by abnormal movements and postures caused by involuntary sustained or intermittent muscle contractions. A number of groundbreaking genetic and molecular insights have recently been gained. While they enable genetic testing and counseling, their translation into new therapies is still limited. However, we are beginning to understand shared pathophysiological pathways and molecular mechanisms. It has become clear that dystonia results from a dysfunctional network involving the basal ganglia, cerebellum, thalamus, and cortex. On the molecular level, more than a handful of, often intertwined, pathways have been linked to pathogenic variants in dystonia genes, including gene transcription during neurodevelopment (e.g., KMT2B, THAP1), calcium homeostasis (e.g., ANO3, HPCA), striatal dopamine signaling (e.g., GNAL), endoplasmic reticulum stress response (e.g., EIF2AK2, PRKRA, TOR1A), autophagy (e.g., VPS16), and others. Thus, different forms of dystonia can be molecularly grouped, which may facilitate treatment development in the future.

Genotype-phenotype relations for episodic ataxia genes: MDSGene systematic review

BACKGROUND

Most episodic ataxias (EA) are autosomal dominantly inherited and characterized by recurrent attacks of ataxia and other paroxysmal and non-paroxysmal features. EA is often caused by pathogenic variants in the CACNA1A, KCNA1, PDHA1, and SLC1A3 genes, listed as paroxysmal movement disorders (PxMD) by the MDS Task Force on the Nomenclature of Genetic Movement Disorders. Little is known about the genotype-phenotype correlation of the different genetic EA forms.

METHODS

We performed a systematic review of the literature to identify individuals affected by an episodic movement disorder harboring pathogenic variants in one of the four genes. We applied the standardized MDSGene literature search and data extraction protocol to summarize the clinical and genetic features. All data are available via the MDSGene protocol and platform on the MDSGene website (https://www.mdsgene.org/).

RESULTS

Information on 717 patients (CACNA1A: 491, KCNA1: 125, PDHA1: 90, and SLC1A3: 11) carrying 287 different pathogenic variants from 229 papers was identified and summarized. We show the profound phenotypic variability and overlap leading to the absence of frank genotype-phenotype correlation aside from a few key 'red flags'.

CONCLUSION

Given this overlap, a broad approach to genetic testing using a panel or whole exome or genome approach is most practical in most circumstances.

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.

A TNR Frameshift Variant in Weimaraner Dogs with an Exercise-Induced Paroxysmal Movement Disorder

BACKGROUND

Some paroxysmal movement disorders remain without an identified genetic cause.

OBJECTIVES

The aim was to identify the causal genetic variant for a paroxysmal dystonia-ataxia syndrome in Weimaraner dogs.

METHODS

Clinical and diagnostic investigations were performed. Whole genome sequencing of one affected dog was used to identify private homozygous variants against 921 control genomes.

RESULTS

Four Weimaraners were presented for episodes of abnormal gait. Results of examinations and diagnostic investigations were unremarkable. Whole genome sequencing revealed a private frameshift variant in the TNR (tenascin-R) gene in an affected dog, XM_038542431.1:c.831dupC, which is predicted to truncate more than 75% of the open read frame. Genotypes in a cohort of 4 affected and 70 unaffected Weimaraners showed perfect association with the disease phenotype.

CONCLUSIONS

We report the association of a TNR variant with a paroxysmal dystonia-ataxia syndrome in Weimaraners. It might be relevant to include sequencing of this gene in diagnosing humans with unexplained paroxysmal movement disorders. © 2023 The Authors. Movement Disorders published by Wiley Periodicals LLC on behalf of International Parkinson and Movement Disorder Society.

Diagnostic Uncertainties: Chorea

Chorea is a hyperkinetic movement disorder with a multitude of potential etiologies, both acquired and inherited. Although the differential diagnosis for new-onset chorea is extensive, there are often clues in the history, exam, and basic testing that can help to narrow the options. Evaluation for treatable or reversible causes should take priority, as rapid diagnosis can lead to more favorable outcomes. While Huntington's disease is most common genetic cause of chorea, multiple phenocopies also exist and should be considered if Huntington gene testing is negative. The decision of what additional genetic testing to pursue should be based on both clinical and epidemiological factors. The following review provides an overview of the many possible etiologies as well as a practical approach for a patient presenting with new-onset chorea.

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.

Paroxysmal movement disorders: Paroxysmal dyskinesia and episodic ataxia

Paroxysmal movement disorders have traditionally been classified into paroxysmal dyskinesia (PxD), which consists in attacks of involuntary movements (mainly dystonia and/or chorea) without loss of consciousness, and episodic ataxia (EA), which features spells of cerebellar dysfunction with or without interictal neurological manifestations. In this chapter, PxD will be discussed first according to the trigger-based classification, thus reviewing clinical, genetic, and molecular features of paroxysmal kinesigenic dyskinesia, paroxysmal nonkinesigenic dyskinesia, and paroxysmal exercise-induced dyskinesia. EA will be presented thereafter according to their designated gene or genetic locus. Clinicogenetic similarities among paroxysmal movement disorders have progressively emerged, which are herein highlighted along with growing evidence that their pathomechanisms overlap those of epilepsy and migraine. Advances in our comprehension of the biological pathways underlying paroxysmal movement disorders, which involve ion channels as well as proteins associated with the vesical synaptic cycle or implicated in neuronal energy metabolism, may represent the cornerstone for defining a shared pathophysiologic framework and developing target-specific therapies.

On-demand cell-autonomous gene therapy for brain circuit disorders

Several neurodevelopmental and neuropsychiatric disorders are characterized by intermittent episodes of pathological activity. Although genetic therapies offer the ability to modulate neuronal excitability, a limiting factor is that they do not discriminate between neurons involved in circuit pathologies and "healthy" surrounding or intermingled neurons. We describe a gene therapy strategy that down-regulates the excitability of overactive neurons in closed loop, which we tested in models of epilepsy. We used an immediate early gene promoter to drive the expression of Kv1.1 potassium channels specifically in hyperactive neurons, and only for as long as they exhibit abnormal activity. Neuronal excitability was reduced by seizure-related activity, leading to a persistent antiepileptic effect without interfering with normal behaviors. Activity-dependent gene therapy is a promising on-demand cell-autonomous treatment for brain circuit disorders.

Preliminary study on pathogenic mechanism of first Chinese family with PNKD

Background

The first Chinese family with paroxysmal non-kinesigenic dystonia (PNKD) was confirmed to harbour a PNKD mutation. However, the pathogenic mechanism of the PNKD-causing gene mutation was unclear.

Methods

Wild-type and mutant PNKD-L plasmids were prepared and transfected into the C6 cell line to study the distribution and stability of PNKD protein in C6 cells and its effect on the glutathione content. The blood and cerebrospinal fluid (CSF) of 3 PNKD patients and 3 healthy controls were collected. The differentially expressed proteins were identified using isobaric tags for relative and absolute quantitation. Furthermore, Gene Ontology (GO) and Kyoto Encyclopaedia of Genes and Genomes (KEGG) enrichment analyses were performed, and the protein–protein interaction network was constructed.

Results

Wild-type PNKD protein was mainly distributed in the membranes, whereas mutant PNKD protein was distributed throughout the C6 cells. After transfection with mutant PNKD-L plasmid, the glutathione content decreased significantly in C6 cells; the stability of the mutant PNKD protein was significantly low. There were 172 and 163 differentially expressed proteins in CSF and plasma, respectively, of PNKD patients and healthy controls. For these proteins, blood microparticle and complex activation (classical pathway) were the common GO enrichment term, and complex and coordination cascade pathway were the common KEGG enrichment pathway. Recombinant mothers against decapentaplegic homolog 4 (SMAD4) was one of the differentially expressed proteins; it exhibited a relationship with the aforementioned enrichment GO terms and KEGG pathway.

Conclusion

PNKD protein was mainly distributed in cell membranes. PNKD-L mutation affected subcellular localisation, PNKD protein stability, and glutathione content. SMAD4 was found to be a potential biomarker for PNKD diagnosis.

Lisdexamfetamine Therapy in Paroxysmal Non-kinesigenic Dyskinesia Associated with the KCNMA1-N999S Variant

BACKGROUND

KCNMA1-linked channelopathy is a rare movement disorder first reported in 2005. Paroxysmal non-kinesigenic dyskinesia (PNKD) in KCNMA1-linked channelopathy is the most common symptom in patients harboring the KCNMA1-N999S mutation. PNKD episodes occur up to hundreds of times daily with significant morbidity and limited treatment options, often in the context of epilepsy.

CASES

We report 6 cases with the KCNMA1-N999S variant treated with lisdexamfetamine (0.7-1.25 mg/kg/day), a pro-drug of dextroamphetamine. Data were collected retrospectively from interviews and chart review. Parent-reported daily PNKD episode counts were reduced under treatment, ranging from a 10-fold decrease to complete resolution.

CONCLUSION

Our findings suggest that lisdexamfetamine is an effective therapy for PNKD3 (KCNMA1-associated PNKD). Treatment produced dramatic reductions in debilitating dyskinesia episodes, without provocation or exacerbation of other KCNMA1-associated symptoms such as seizures.