Myoclonus-dystonia and spinocerebellar ataxia type 14 presenting with similar phenotypes: Trunk tremor, myoclonus, and dystonia

Tremor in Spinocerebellar Ataxia: A Scoping Review

Background

Spinocerebellar ataxia (SCA) denotes an expanding list of autosomal dominant cerebellar ataxias. Although tremor is an important aspect of the clinical spectrum of the SCAs, its prevalence, phenomenology, and pathophysiology are unknown.

Objectives

This review aims to describe the various types of tremors seen in the different SCAs, with a discussion on the pathophysiology of the tremors, and the possible treatment modalities.

Methods

The authors conducted a literature search on PubMed using search terms including tremor and the various SCAs. Relevant articles were included in the review after excluding duplicate publications.

Results

While action (postural and intention) tremors are most frequently associated with SCA, rest and other rare tremors have also been documented. The prevalence and types of tremors vary among the different SCAs. SCA12, common in certain ethnic populations, presents a unique situation, where the tremor is typically the principal manifestation. Clinical manifestations of SCAs may be confused with essential tremor or Parkinson's disease. The pathophysiology of tremors in SCAs predominantly involves the cerebellum and its networks, especially the cerebello-thalamo-cortical circuit. Additionally, connections with the basal ganglia, and striatal dopaminergic dysfunction may have a role. Medical management of tremor is usually guided by the phenomenology and associated clinical features. Deep brain stimulation surgery may be helpful in treatment-resistant tremors.

Conclusions

Tremor is an elemental component of SCAs, with diverse phenomenology, and emphasizes the role of the cerebellum in tremor. Further studies will be useful to delineate the clinical, pathophysiological, and therapeutic aspects of tremor in SCAs.

Two Cases of Monozygotic Twins with Early-onset Isolated (DYT1) Dystonia Effectively Treated with Bilateral Globus Pallidus Internus Stimulation

Early-onset isolated (DYT1) dystonia is one of the most common forms of primary dystonia in childhood, and deep brain stimulation of the globus pallidus internus (GPi-DBS) is a highly effective treatment for it. However, the effectiveness of GPi-DBS in monozygotic twins with DYT1 dystonia has never been reported globally. Here, we report the cases of monozygotic twins with DYT1 dystonia who were treated using GPi-DBS, and we include a literature review. The younger brother showed an abnormal gait, with external rotation of the right lower leg at 6 years old. The symptoms gradually became so severe that he had difficulty walking on his own at 9 years of age. Treatment with levodopa-carbidopa partially resolved his symptoms, but most of the symptoms remained. Meanwhile, the older brother developed dystonia in both upper limbs at 8 years of age, with gradual symptom progression. At 13 years of age, they were diagnosed with DYT1 dystonia. Bilateral GPi-DBS was performed in both patients at 16 years of age. Their symptoms remarkably improved after surgery. The Burke-Fahn-Marsden dystonia rating scale (BFMDRS) movement score was reduced from 52 to 2 points for the younger brother and from 35 to 1 point for the older brother. Even if monozygotic twins have the same genes, the onset and severity of symptoms might vary in accordance with differences in epigenomic profiles. However, GPi-DBS treatment was very effective for the two cases; thus, we should consider the surgical interventions for each patient.

Pearls & Oy-sters: SCA21 Due to TMEM240 Mutation Presenting as Myoclonus Dystonia Syndrome

Spinocerebellar ataxia (SCA) 21 due to TMEM240 mutation characteristically presents insidiously with a delay in language, motor, and social skill acquisition. The condition typically progresses to severe cognitive impairment. We report a patient with SCA21, who presented with myoclonus dystonia (M-D) syndrome, whose dystonia showed a modest response to levodopa. Affected family members (mother and sibling of the proband) also had a similar phenotype. Neuropsychology evaluation of proband and afflicted family members revealed moderate impairments in attention, executive function, short-term and episodic memory, and marked impairments in planning, abstract reasoning, language and visuospatial functions. Normal electroencephalogram, alpha-fetoprotein levels and somatosensory evoked potentials helped to delineate SCA21 from other differential diagnoses. Motor impairment, pyramidal signs, and sensory impairment are usually absent in SCA21. This case highlights the importance of genetic testing in patients with M-D syndrome and supports a trial of levodopa for patients with dystonia from SCA21 due to TMEM240 mutation.

Two cases with postural axial tremor: Consider a genetic origin

We present two cases with postural axial tremor predominantly involving the head, trunk, and shoulders. In the first patient, the postural tremor occurred in multiple attacks a day lasting approximately 10 min. The second patient developed a progressive tremor of his head and arms, worsened during sitting and standing. Electrophysiological supported the postural axial tremor in both patients with a varying 3-10 Hz tremor frequency between different muscles and within the same muscles at different times. Postural axial tremor is a rare and complex movement disorder. The majority of cases are caused by acquired cerebellar pathology. However, isolated cases with underlying genetic disorders are described in literature. Here, we illustrate how to differentiate paroxysmal axial tremor from other axial hyperkinetic movement disorders and extend the genetic heterogeneity of this intriguing movement disorder phenotype.

Myoclonus-Ataxia Syndromes: A Diagnostic Approach

Background

A myriad of disorders combine myoclonus and ataxia. Most causes are genetic and an increasing number of genes are being associated with myoclonus-ataxia syndromes (MAS), due to recent advances in genetic techniques. A proper etiologic diagnosis of MAS is clinically relevant, given the consequences for genetic counseling, treatment, and prognosis.

Objectives

To review the causes of MAS and to propose a diagnostic algorithm.

Methods

A comprehensive and structured literature search following PRISMA criteria was conducted to identify those disorders that may combine myoclonus with ataxia.

Results

A total of 135 causes of combined myoclonus and ataxia were identified, of which 30 were charted as the main causes of MAS. These include four acquired entities: opsoclonus-myoclonus-ataxia syndrome, celiac disease, multiple system atrophy, and sporadic prion diseases. The distinction between progressive myoclonus epilepsy and progressive myoclonus ataxia poses one of the main diagnostic dilemmas.

Conclusions

Diagnostic algorithms for pediatric and adult patients, based on clinical manifestations including epilepsy, are proposed to guide the differential diagnosis and corresponding work-up of the most important and frequent causes of MAS. A list of genes associated with MAS to guide genetic testing strategies is provided. Priority should be given to diagnose or exclude acquired or treatable disorders.

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.

Twenty years on: Myoclonus-dystonia and ε-sarcoglycan - neurodevelopment, channel, and signaling dysfunction

Myoclonus-dystonia is a clinical syndrome characterized by a typical childhood onset of myoclonic jerks and dystonia involving the neck, trunk, and upper limbs. Psychiatric symptomatology, namely, alcohol dependence and phobic and obsessive-compulsive disorder, is also part of the clinical picture. Zonisamide has demonstrated effectiveness at reducing both myoclonus and dystonia, and deep brain stimulation seems to be an effective and long-lasting therapeutic option for medication-refractory cases. In a subset of patients, myoclonus-dystonia is associated with pathogenic variants in the epsilon-sarcoglycan gene, located on chromosome 7q21, and up to now, more than 100 different pathogenic variants of the epsilon-sarcoglycan gene have been described. In a few families with a clinical phenotype resembling myoclonus-dystonia associated with distinct clinical features, variants have been identified in genes involved in novel pathways such as calcium channel regulation and neurodevelopment. Because of phenotypic similarities with epsilon-sarcoglycan gene-related myoclonus-dystonia, these conditions can be collectively classified as "myoclonus-dystonia syndromes." In the present article, we present myoclonus-dystonia caused by epsilon-sarcoglycan gene mutations, with a focus on genetics and underlying disease mechanisms. Second, we review those conditions falling within the spectrum of myoclonus-dystonia syndromes, highlighting their genetic background and involved pathways. Finally, we critically discuss the normal and pathological function of the epsilon-sarcoglycan gene and its product, suggesting a role in the stabilization of the dopaminergic membrane via regulation of calcium homeostasis and in the neurodevelopmental process involving the cerebello-thalamo-pallido-cortical network. © 2019 International Parkinson and Movement Disorder Society.

Spinocerebellar ataxia type 14 caused by a nonsense mutation in the PRKCG gene

Spinocerebellar ataxia type 14 (SCA14) is an autosomal dominant neurodegenerative disorder characterized by cerebellar ataxia with myoclonus, dystonia, spasticity, and rigidity. Although missense mutations and a deletion mutation have been found in the protein kinase C gamma (PRKCG) gene encoding protein kinase C γ (PKCγ) in SCA14 families, a nonsense mutation has not been reported. The patho-mechanisms underlying SCA14 remain poorly understood. However, gain-of-function mechanisms and loss-of-function mechanisms, but not dominant negative mechanisms, were reported the patho-mechanism of SCA14. We identified the c.226C>T mutation of PRKCG, which caused the p.R76X in PKCγ by whole-exome sequencing in patients presenting cerebellar atrophy with cognitive and hearing impairment. To investigate the patho-mechanism of our case, we studied aggregation formation, cell death, and PKC inhibitory effect by confocal microscopy, western blotting with cleaved caspase 3, and pSer PKC motif antibodies, respectively. PKCγ(R76X)-GFP have aggregations the same as wild-type (WT) PKCγ-GFP. The PKCγ(R76X)-GFP inhibited PKC phosphorylation activity more than GFP alone. It also induced more apoptosis in COS7 and SH-SY5Y cells compared to WT-PKCγ-GFP and GFP. We first reported SCA14 patients with p.R76X in PKCγ who have cerebellar atrophy with cognitive and hearing impairment. Our results suggest that a dominant negative mechanism due to truncated peptides produced by p.R76X may be at least partially responsible for the cerebellar atrophy.

Profile of extrapyramidal manifestations in 85 patients with spinocerebellar ataxia type 1, 2 and 3

This study aimed to determine the prevalence and type of extrapyramidal signs (EPS) in spinocerebellar ataxia (SCA) type 1, 2 and 3. Eighty-five patients with genetically confirmed SCA (SCA1=40, SCA2=28, SCA3=17) were evaluated for the prevalence and types of EPS. Forty-one SCA patients (48.2%) had one or more types of EPS. The prevalence of EPS was 60.7% in SCA2, 52.9% in SCA3, and 37.5% in SCA1. Among SCA2 patients, bradykinesia was the most frequent (35.3%), followed by reduced facial expression, postural tremor and dystonia (29.4% each), rest tremor, titubation and rigidity (23.5% each), and lip/jaw tremor and chorea (11.8% each). In SCA3 the common EPS were bradykinesia (44.4%), staring look, postural tremor and dystonia (33.3% each), and reduced facial expression and rigidity (22.2% each). In SCA1, staring look was the most common (53.3%), followed by dystonia and bradykinesia (33.3% each), and postural tremor (26.7%). In all three groups, there was no significant difference in the mean length of repeat of the abnormal allele between those with and without EPS. To conclude bradykinesia, staring look, dystonia and postural tremor were the most frequent EPS observed in SCA. In SCA1, these signs were seen more often in younger patients with early onset of symptoms.

Hereditäre Ataxien

Hereditäre Ataxien stellen aufgrund der Vielfalt der möglichen genetischen Ursachen eine große diagnostische Herausforderung für die medizinische Genetik dar. Dieses Problem wird dadurch verstärkt, dass zwar die Zahl der neu identifizierten Gene in den letzten 3 Jahren durch neue Sequenziertechnologien rasant zugenommen hat, häufig jedoch nur wenige Familien weltweit Mutationen in diesen Genen aufweisen, d. h. sie extrem selten sind. Der vorliegende Artikel gibt eine Übersicht über dominante und rezessive Ataxien und berücksichtigt dabei auch die neu identifizierten Ataxie-Gene. Um den Anforderungen einer praktisch-orientierten genetischen Diagnostik gerecht zu werden, versuchen wir dabei auch, Häufigkeitseinschätzungen der betroffenen Genorte zu geben und – sofern möglich – phänotypische Eigenschaften und Biomarker zu definieren, die eine genetische Diagnostik erfolgversprechend leiten können, insbesondere bei rezessiven Ataxien. Diese diagnostischen Indikatoren werden in Form von diagnostischen Pfaden zusammengefasst, die eine Orientierung bei der mehrstufigen genetischen Diagnostik dominanter und rezessiver Ataxien geben sollen. Aufgrund der Vielzahl der Genkandidaten und des großen phänotypischen Überlappungsbereichs wird es in den meisten Fällen jedoch am zeiteffizientesten und kostengünstigsten sein, Panel-Untersuchungen mittels Next-Generation-Sequencing-Technologien durchzuführen.

Spinocerebellar ataxia type 14

SCA14 is an autosomal dominant hereditary cerebellar ataxia that usually has an onset in early to mid adult life, with slow progression and normal lifespan. Although generally an uncomplicated cerebellar ataxia with gait imbalance, dysarthria, and nystagmus, there is occasionally sensory loss, hyperactive tendon reflexes, cognitive decline, or myoclonus. Brain MRI shows cerebellar atrophy. A single autopsy has shown loss of cerebellar Purkinje cells. The disease is caused by mutations in the protein kinase C gamma (PKCγ, PRKCG) gene with a hotspot for mutations in exon 4. Genetic testing for SCA14 is clinically available.