The phenotypic spectrum of DYT24 due to ANO3 mutations

Exploring the early drivers of pain in Parkinson's disease

Pain is a common and complex non-motor symptom in people with Parkinson's disease (PWP). Little is known about the genetic drivers of pain in PWP, and progress in its study has been challenging. Here, we conducted two genome-wide association studies (GWAS) to identify genetic variants associated with pain experienced during the earliest stages of Parkinson's disease. The study population consisted of 4,159 PWP of European ancestry who were mapped to five previously-described, longitudinal pain trajectories. In the first GWAS, the extreme pain trajectories (highest burden versus no significant pain over time) were compared, and in the second GWAS, a multinomial approach was undertaken. While no variant reached genome-wide significance, we identified promising associations, such as rs117108018 (ORGWAS-Extreme=8.96, pGWAS-Extreme=2.5 × 10- 7), a brain/nerve eQTL for L3MBTL3 and EPB41L2, and rs61881484 (pGWAS-Multinomial=2 × 10- 7), which intersects a transcription factor peak targeting CREB1, critical in sensory neuron synaptic plasticity and neuropathic pain regulation. Gene-based tests implicated CTNNB1 (pGWAS-Extreme=3.2 × 10- 5), KLK7 (pGWAS-Extreme=7 × 10- 5), and SLITRK3 (pGWAS-Multinomial=3.2 × 10- 5), which have been associated with neurodevelopment. At the pathway-level, there was an enrichment for genes involved in neurotransmitter regulation and opioid dependence. This study implicates neuropathic pain mechanisms as prominent drivers of elevated pain in PWP, suggests potential therapeutic genetic targets for further research.

TMEM16 proteins: Ca2+‑activated chloride channels and phospholipid scramblases as potential drug targets (Review)

TMEM16 proteins, which function as Ca2+‑activated Cl‑ channels are involved in regulating a wide variety of cellular pathways and functions. The modulators of Cl‑ channels can be used for the molecule‑based treatment of respiratory diseases, cystic fibrosis, tumors, cancer, osteoporosis and coronavirus disease 2019. The TMEM16 proteins link Ca2+ signaling, cellular electrical activity and lipid transport. Thus, deciphering these complex regulatory mechanisms may enable a more comprehensive understanding of the physiological functions of the TMEM16 proteins and assist in ascertaining the applicability of these proteins as potential pharmacological targets for the treatment of a range of diseases. The present review examined the structures, functions and characteristics of the different types of TMEM16 proteins, their association with the pathogenesis of various diseases and the applicability of TMEM16 modulator‑based treatment methods.

Missense variants in ANO4 cause sporadic encephalopathic or familial epilepsy with evidence for a dominant-negative effect

Anoctamins are a family of Ca2+-activated proteins that may act as ion channels and/or phospholipid scramblases with limited understanding of function and disease association. Here, we identified five de novo and two inherited missense variants in ANO4 (alias TMEM16D) as a cause of fever-sensitive developmental and epileptic or epileptic encephalopathy (DEE/EE) and generalized epilepsy with febrile seizures plus (GEFS+) or temporal lobe epilepsy. In silico modeling of the ANO4 structure predicted that all identified variants lead to destabilization of the ANO4 structure. Four variants are localized close to the Ca2+ binding sites of ANO4, suggesting impaired protein function. Variant mapping to the protein topology suggests a preliminary genotype-phenotype correlation. Moreover, the observation of a heterozygous ANO4 deletion in a healthy individual suggests a dysfunctional protein as disease mechanism rather than haploinsufficiency. To test this hypothesis, we examined mutant ANO4 functional properties in a heterologous expression system by patch-clamp recordings, immunocytochemistry, and surface expression of annexin A5 as a measure of phosphatidylserine scramblase activity. All ANO4 variants showed severe loss of ion channel function and DEE/EE associated variants presented mild loss of surface expression due to impaired plasma membrane trafficking. Increased levels of Ca2+-independent annexin A5 at the cell surface suggested an increased apoptosis rate in DEE-mutant expressing cells, but no changes in Ca2+-dependent scramblase activity were observed. Co-transfection with ANO4 wild-type suggested a dominant-negative effect. In summary, we expand the genetic base for both encephalopathic sporadic and inherited fever-sensitive epilepsies and link germline variants in ANO4 to a hereditary disease.

Tremor in cervical dystonia

Background

Cervical dystonia (CD) is the most common form of focal dystonia encountered in the clinic. Approximately one-third of CD patients have co-existing tremor in the head and hands. Assessment of tremor as regular or irregular in context of its oscillation trajectory, frequency, and amplitude is a major clinical challenge and can confound the diagnosis of CD. The misdiagnosis may lead to therapeutic failures, poor quality of life, and poor utilization of medical and financial resources.

Methods

We analyzed the largest cohort of CD patients (n = 3117) available to date, collected from 37 movement disorder centers in North America, Europe, and Asia. We used machine learning to determine what clinical features from clinician reports predicted the presence of tremor as well as its regular or irregular appearance.

Results

Out of 3,117 CD patients, 1,367 had neck tremor. The neck tremor was interpreted as irregular in 1,022, regular in 345, and mixed (both irregular and regular) in 442. A feature importance analysis determined that greater severity of CD, longer disease duration, and older age, in descending order, predicted the presence of neck tremor. The probability of neck tremor was reduced if the dystonia affected other body parts in addition to the neck. We also found a significantly heightened risk for developing neck tremor in women. An additional feature importance analysis indicated that increased severity of dystonia affecting other body parts, severity of CD, and prolonged disease duration was associated with a lower likelihood of regular neck tremor while increased age predicted a higher likelihood.

Conclusion

Machine learning recognized the most relevant clinical features that can predict concurrent neck tremor and its irregularity in a large multi-center dystonia cohort. These results may facilitate a more accurate description of neck tremor and improved care path in CD.

The Clinical Spectrum of ANO3-Report of a New Family and Literature Review

BACKGROUND

Mutations in ANO3 are a rare cause of autosomal dominant isolated or combined dystonia, mainly presenting in adulthood.

CASES

We extensively characterize a new, large ANO3 family with six affected carriers. The proband is a young girl who had suffered from tremor and painful dystonic movements in her right arm since the age of 11 years. She later developed a diffuse dystonic tremor and mild extrapyramidal signs (ie, rigidity and hypodiadochokinesis) in her right arm. She also suffered from psychomotor delay and learning difficulties. Repeated structural and functional neuroimaging were unremarkable. A dystonic tremor was also present in her two sisters. Her paternal aunt, father, and a third older sister presented episodic postural tremor in the arms. The father and one sister also presented learning difficulties. The heterozygous p.G6V variant in ANO3 was identified in all affected subjects.

LITERATURE REVIEW

Stratification by age at onset divided ANO3 cases into two major groups, where younger patients displayed a more severe phenotype, probably due to variants near the scrambling domain.

CONCLUSIONS

We describe the phenotype of a new ANO3 family and highlight the need for functional studies to explore the impact of ANO3 variants on its phospholipid scrambling activity.

The role of laboratory investigations in the classification of tremors

INTRODUCTION

Tremor is the most common movement disorder. Although clinical examination plays a significant role in evaluating patients with tremor, laboratory tests are useful to classify tremors according to the recent two-axis approach proposed by the International Parkinson and Movement Disorders Society.

METHODS

In the present review, we will discuss the usefulness and applicability of the various diagnostic methods in classifying and diagnosing tremors. We will evaluate a number of techniques, including laboratory and genetic tests, neurophysiology, and neuroimaging. The role of newly introduced innovative tremor assessment methods will also be discussed.

RESULTS

Neurophysiology plays a crucial role in tremor definition and classification, and it can be useful for the identification of specific tremor syndromes. Laboratory and genetic tests and neuroimaging may be of paramount importance in identifying specific etiologies. Highly promising innovative technologies are being developed for both clinical and research purposes.

CONCLUSIONS

Overall, laboratory investigations may support clinicians in the diagnostic process of tremor. Also, combining data from different techniques can help improve understanding of the pathophysiological bases underlying tremors and guide therapeutic management.

A novel ANO3 variant in two siblings with different phenotypes

INTRODUCTION

Dystonia type 24 is due to the mutation of the ANO3 gene. It generally consists of craniocervical dystonia associated with tremor; however, other neurological manifestations may also occur. Scientific literature has been expanding on its phenotype over the past few years.

CASE

Here we present two siblings affected by dystonia 24 associated to a novel missense mutation of the ANO3 gene. Description of their phenotype, with regard to motor and non-motor features, may improve the knowledge on DYT 24. Consistent with previous reports, our patients presented with cranio-cervical involvement, and they also exhibited different severity and phenotypes. However non-motor symptoms were present too.

CONCLUSION

Dystonia 24 spectrum is continuously expanding. This case suggests that the ANO3 missense mutation should be sought in all cases of dystonia and isolated tremor and that non-motor symptoms are an integral part of dystonic syndromes. It also shows that clinical and treatment features may vary from patient to patient, even if they may present the same mutation.

Dystonia and tremor: Do they have a shared biology?

Dystonia and tremor are the two most commonly encountered hyperkinetic movement disorders encountered in clinical practice. While there has been substantial progress in the research on these two disorders, there also exists a lot of gray areas. Entities such as dystonic tremor and tremor associated with dystonia occupy a major portion of the "gray zone". In addition, there is a marked clinical heterogeneity and overlap of several clinical and epidemiological features among dystonia and tremor. These facts raise the possibility that dystonia and tremor could be having shared biology. In this chapter, we revisit critical aspects of this possibility that may have important clinical and research implications in the future. We comprehensively review the points in favor and against the theory that dystonia and tremor have shared biology from clinical, epidemiological, genetic and neuroimaging studies.

A novel variant in the transmembrane 4 domain of ANO3 identified in a two-year-old girl with developmental delay and tremor

ANO3 encodes Anoctamin-3, also known as TMEM16C, a calcium-activated chloride channel. Heterozygous variants of ANO3 can cause dystonia 24, an adult-onset focal dystonia. Some pediatric cases have been reported, but most patients were intellectually normal with some exceptions. Here, we report a two-year-old girl who showed mild to moderate developmental delay, tremor, and ataxic gait, but no obvious dystonia. Trio exome sequencing identified a heterozygous de novo missense variant NM_031418.4:c.1809T>G, p.(Asn603Lys) in the ANO3 gene. Three cases with ANO3 variants and intellectual disability have been reported, including the present case. These variants were predicted to face in the same direction on the same alpha-helix (the transmembrane 4 domain), suggesting an association between these variants and childhood-onset movement disorder with intellectual disability. In pediatric cases with developmental delay and movement disorders such as tremor and ataxia, specific variants in the transmembrane 4 domain of ANO3 may be a cause, even in the absence of dystonia.

The Patho-Neurophysiological Basis and Treatment of Focal Laryngeal Dystonia: A Narrative Review and Two Case Reports Applying TMS over the Laryngeal Motor Cortex

Focal laryngeal dystonia (LD) is a rare, idiopathic disease affecting the laryngeal musculature with an unknown cause and clinically presented as adductor LD or rarely as abductor LD. The most effective treatment options include the injection of botulinum toxin (BoNT) into the affected laryngeal muscle. The aim of this narrative review is to summarize the patho-neuro-physiological and genetic background of LD, as well as the standard recommended therapy (BoNT) and pharmacological treatment options, and to discuss possible treatment perspectives using neuro-modulation techniques such as repetitive transcranial magnetic stimulation (rTMS) and vibrotactile stimulation. The review will present two LD cases, patients with adductor and abductor LD, standard diagnostic procedure, treatments and achievement, and the results of cortical excitability mapping the primary motor cortex for the representation of the laryngeal muscles in the assessment of corticospinal and corticobulbar excitability.

Is essential tremor a family of diseases or a syndrome? A syndrome

In a consensus statement, a task force of the "International Parkinson and Movement Disorder Society" (IPMDS) has recently proposed a two axes classification for tremor: axis I (clinical manifestations) and axis II (etiology). In the axis, I, the clinical features of tremor in a given patient are specified in terms of medical history, tremor characteristics, associated signs, and laboratory tests for some tremors leading to the discovery of axis 2 etiologies. Based on axis I sign and symptoms a specific clinical syndrome is diagnosed which have been categorized as isolated tremor syndrome (a syndrome consisting only of tremor) and combined tremor syndrome (consisting of tremor and other systemic or neurological signs). The IPMDS task force defined essential tremor as an isolated tremor syndrome of bilateral upper limb action tremor of at least 3years duration with or without a tremor in other locations (e.g., head, voice or lower limbs) in absence of other neurological signs, such as dystonia, ataxia, or parkinsonism. Patients with neurological signs of uncertain significance (such as impaired tandem gait, questionable dystonic posturing, or memory impairment) are classified as essential tremor plus. In this paper, the author will make the argument that essential tremor is a syndrome with multiple causes.

A Clinical and Integrated Genetic Study of Isolated and Combined Dystonia in Taiwan

Dystonia is a clinically and genetically heterogeneous movement disorder. However, genetic causes of dystonia remain largely unknown in Asian subjects. To address this, we applied an integrated two-step approach that included gene dosage analysis and a next-generation sequencing panel containing 72 known genes causative for dystonia and related movement disorders to 318 Taiwanese patients with isolated or combined dystonia. Whole-genome sequencing was performed for one multiplex family with no known causative variant. The panel confirmed the genetic diagnosis in 40 probands (12.6%). A genetic diagnosis was more likely with juvenile onset compared with adult onset (24.2% vs 10.8%; P = 0.03) and those with combined features, especially with myoclonus, compared with isolated dystonia (35.3% vs 10.5%; P = 0.004). The most common causative genes were SGCE followed by GCH1, TH, CACNA1B, PRRT2, MR1, CIZ1, PLA2G6, and PRKN. Genetic causes were identified from single cases in TOR1A, TUBB4A, THAP1, ATP1A3, ANO3, GNAL, KMT2B, SLC6A3, ADCY5, CYP27A1, PANK2, C19orf12, and SPG11. The whole-genome sequencing analysis identified a novel intragenic deletion in OPHN1 in a multiplex family with X-linked dystonia and intellectual delay. Our findings delineate the genetic architecture and clinical spectrum of dystonia-causing pathogenic variants in an Asian population.

Polymodal Control of TMEM16x Channels and Scramblases

The TMEM16A/anoctamin-1 calcium-activated chloride channel (CaCC) contributes to a range of vital functions, such as the control of vascular tone and epithelial ion transport. The channel is a founding member of a family of 10 proteins (TMEM16x) with varied functions; some members (i.e., TMEM16A and TMEM16B) serve as CaCCs, while others are lipid scramblases, combine channel and scramblase function, or perform additional cellular roles. TMEM16x proteins are typically activated by agonist-induced Ca2+ release evoked by Gq-protein-coupled receptor (GqPCR) activation; thus, TMEM16x proteins link Ca2+-signalling with cell electrical activity and/or lipid transport. Recent studies demonstrate that a range of other cellular factors—including plasmalemmal lipids, pH, hypoxia, ATP and auxiliary proteins—also control the activity of the TMEM16A channel and its paralogues, suggesting that the TMEM16x proteins are effectively polymodal sensors of cellular homeostasis. Here, we review the molecular pathophysiology, structural biology, and mechanisms of regulation of TMEM16x proteins by multiple cellular factors.

Mixed Motor Disorder: Essential Tremor Families With Heterogeneous Motor Phenomenology

Background and Objectives

Essential tremor (ET) is one of the most prevalent movement disorders. Because ET is so common, individuals with other neurologic disorders may also have ET. There is evidence, however, that the cooccurrence of ET with Parkinson disease (PD) and/or dystonia is not merely a chance cooccurrence. We have observed combinations of these 3 movement disorders within individuals and across individuals within families containing multiple individuals with ET. This observation has a number of implications. Our objective is to present 4 ET families in whom motor phenomenology was heterogeneous and discuss the implications of this finding.

Methods

ET cases and their relatives were enrolled in the Family Study of Essential Tremor (2015-present). Phenotyping was performed by a senior movement disorders neurologist based on neurologic examination.

Results

We present 4 families, including 14 affected individuals, among whom assigned diagnoses were ET, PD, ET + PD, and ET + dystonia. In those with ET and another movement disorder, the predominant and earliest phenotype was ET.

Discussion

There are assortments of these 3 involuntary motor disorders, ET, dystonia, and PD, both within individuals and in different individuals within ET families. This observation has mechanistic implications. Furthermore, we believe that the concept of the mixed motor disorder should enter into and inform the clinical dialogue. In assigning diagnoses, clinicians are swayed by family history information, and they should be prepared to observe a mix of different motor disorders to manifest within particular families.

A Novel Heterozygous ANO3 Mutation in a Child Presenting Tremor with Dystonia and Review of the Literature

Mutations in ANO3 have recently been identified as an autosomal dominant cause of dystonia (dystonia-24). Since then, the phenotypic spectrum has also been extended in children. Here, we reported a case of a 10-year-old Turkish girl child patient with a novel variant (NM_001313726: c.221dupA, p.Tyr74*), who exhibited tremor with mild dystonia. This report expands the phenotype caused by ANO3 variants and reveals an essential clinical aspect for patients and medical staff.

Tremor Syndromes: An Updated Review

Tremor is the most commonly encountered movement disorder in clinical practice. A wide range of pathologies may manifest with tremor either as a presenting or predominant symptom. Considering the marked etiological and phenomenological heterogeneity, it would be desirable to develop a classification of tremors that reflects their underlying pathophysiology. The tremor task force of the International Parkinson Disease and Movement Disorders Society has worked toward this goal and proposed a new classification system. This system has remained a prime topic of scientific communications on tremor in recent times. The new classification is based on two axes: 1. based on the clinical features, history, and tremor characteristics and 2. based on the etiology of tremor. In this article, we discuss the key aspects of the new classification, review various tremor syndromes, highlight some of the controversies in the field of tremor, and share the potential future perspectives.

Tremor in Primary Monogenic Dystonia

PURPOSE OF REVIEW

Tremor is an important phenotypic feature of dystonia with wide variability in the reported prevalence ranging from 14 to 86.67%. This variability may be due to the types of dystonia patients reported in different studies. This article reviews research articles reporting tremor in primary monogenic dystonia.

RECENT FINDINGS

We searched the MDS gene data and selected all research articles reporting tremor in primary monogenic dystonia. Tremor was reported in nine dystonia genes, namely DYT-HPCA, DYT-ANO3, DYT-KCTD17, DYT-THAP1, DYT-PRKRA, DYT-GNAL, DYT-TOR1A, DYT-KMT2B, and DYT-SGCE in the descending order of its frequency. HPCA gene mutation is rare, but all reported patients had tremor. Similarly, tremor was reported in eight genes associated with dystonia parkinsonism, namely DYT-SLC6A3, DYT-TH, DYT-SPR, DYT-PTS, DYT-GCH1, DYT-TAF1, DYT-QDPR, and DYT-SCL30A10 in the descending order of its prevalence. DYT-HPCA and DYT-ANO3 gene showed the highest prevalence of tremor in isolated dystonia, and DYT-SLC6A3 has the highest prevalence of tremor in combined dystonia.

Another Twist in the Tale: Intrafamilial Phenotypic Heterogeneity in ANO3-Related Dystonia

Background

Mutations in the anoctamin 3 (ANO3) gene cause autosomal dominant craniocervical dystonia (DYT24), presenting from childhood to mid-life. However, in the past years, the clinical spectrum of this disorder has widened. We present a family with heterogeneous presentation, exemplifying phenotypic diversity in DYT24.

Cases

The index case presented with myoclonic dystonia at age 10. His family history was remarkable for cervical dystonia with myoclonus in his grandfather, cervical and upper limb dystonia along with dopa-responsive parkinsonism in his father and lower-limb dystonia in his teenage sister. Magnetic resonance imaging and blood work-ups of all the affected family members were normal. The genetic panel for inherited forms of dystonia disclosed a point mutation c.1787C > A (p.Ser596Tyr) segregated in all affected family members.

Conclusions

ANO3 mutations usually present with craniocervical dystonia and rarely generalized or leg dystonia. This family exemplifies the heterogeneous presentation of this disorder as well as a wide phenotypic variability within the same family.

Exploring Interrater Disagreement on Essential Tremor Using a Standardized Tremor Elements Assessment

Background

Patients with upper limb action tremor frequently exhibit additional neurological signs of uncertain significance. Clinicians vary in their interpretation, and interrater agreement on the final diagnosis is poor.

Objectives

A new clinical tool for assessing the presence or absence of clinical signs that are important in axis‐1 classification of tremor patients is introduced: the Standardized Tremor Elements Assessment (STEA). Interrater agreement is determined, and signs leading to disagreement in the final diagnosis are identified.

Methods

Three tremor‐focussed and one dystonia‐focussed movement disorder specialists rated 59 videos of patients with upper limb action tremor syndromes using STEA. Interrater agreements for final diagnosis and STEA items were calculated.

Results

Interrater agreement regarding the final diagnosis was higher within the group of tremor specialists and poor between dystonia and tremor specialists. Greater agreement was found for items characterizing tremor than for signs of dystonia.

Conclusions

Clinical signs leading to diagnostic disagreement were identified with STEA, and STEA should therefore be useful in future studies of diagnostic disagreement. The thresholds for considering neurological signs as soft versus significant for ataxia, parkinsonism, dystonia, etc. are critically important in tremor classification and must be studied across movement disorder subspecialties, not simply within a pool of tremor specialists.

Atxn2-CAG100-KnockIn mouse spinal cord shows progressive TDP43 pathology associated with cholesterol biosynthesis suppression

Large polyglutamine expansions in Ataxin-2 (ATXN2) cause multi-system nervous atrophy in Spinocerebellar Ataxia type 2 (SCA2). Intermediate size expansions carry a risk for selective motor neuron degeneration, known as Amyotrophic Lateral Sclerosis (ALS). Conversely, the depletion of ATXN2 prevents disease progression in ALS. Although ATXN2 interacts directly with RNA, and in ALS pathogenesis there is a crucial role of RNA toxicity, the affected functional pathways remain ill defined. Here, we examined an authentic SCA2 mouse model with Atxn2-CAG100-KnockIn for a first definition of molecular mechanisms in spinal cord pathology. Neurophysiology of lower limbs detected sensory neuropathy rather than motor denervation. Triple immunofluorescence demonstrated cytosolic ATXN2 aggregates sequestrating TDP43 and TIA1 from the nucleus. In immunoblots, this was accompanied by elevated CASP3, RIPK1 and PQBP1 abundance. RT-qPCR showed increase of Grn, Tlr7 and Rnaset2 mRNA versus Eif5a2, Dcp2, Uhmk1 and Kif5a decrease. These SCA2 findings overlap well with known ALS features. Similar to other ataxias and dystonias, decreased mRNA levels for Unc80, Tacr1, Gnal, Ano3, Kcna2, Elovl5 and Cdr1 contrasted with Gpnmb increase. Preterminal stage tissue showed strongly activated microglia containing ATXN2 aggregates, with parallel astrogliosis. Global transcriptome profiles from stages of incipient motor deficit versus preterminal age identified molecules with progressive downregulation, where a cluster of cholesterol biosynthesis enzymes including Dhcr24, Msmo1, Idi1 and Hmgcs1 was prominent. Gas chromatography demonstrated a massive loss of crucial cholesterol precursor metabolites. Overall, the ATXN2 protein aggregation process affects diverse subcellular compartments, in particular stress granules, endoplasmic reticulum and receptor tyrosine kinase signaling. These findings identify new targets and potential biomarkers for neuroprotective therapies.

The expanding clinical and genetic spectrum of ANO3 dystonia

INTRODUCTION

Dystonia is a movement disorder with high clinical and genetic heterogeneity. Mutations in Anoctamin-3 (ANO3) gene have been reported to cause dystonia 24 (DYT24). This study aims to clarify the spectrum and frequency of ANO3 rare variants in Chinese populations with primary dystonia and understand the clinical and genetic features of DYT24.

METHODS

Sanger sequencing was used to screen all exons and exon-intron boundaries of ANO3 for rare variants in 115 primary dystonia patients. The clinical manifestations of patients with ANO3 variants in our study and previously reported literatures were further characterized.

RESULTS

Four distinct variants of ANO3 (c.1127A > G, c.1235 T > A, c.1531-3T > C, c.-11G > T) were identified in six unrelated individuals. Combined with our work and literature review, a total of 35 different rare variants distributed in ANO3 were identified in 62 dystonia patients. The predominant phenotype is cranio-cervical dystonia and more than half of patients develop head/limb tremor. Most of patients presented with isolated dystonia whereas few of them showed combined dystonia. The age of onset ranged from 1 to 69 years and peaked in late adulthood, while for generalized dystonia it peaked in a young age. Half of patients with generalized dystonia experienced deep brain stimulation (DBS). And all of them showed improvement of dystonia by DBS.

CONCLUSIONS

This study confirms a relatively high frequency of rare ANO3 variants in Chinese patients with dystonia and indicates that the late adulthood-onset, cranio-cervical dystonia seems to be an important feature of the ANO3 phenotype. Further functional studies are warranted to understand the role of ANO3 in dystonia.

[Diagnostic procedures and therapy in tremor disorders: current clinical concepts]

Tremor is the most common movement disorder, occurring as an isolated tremor syndrome, as a symptom of neurological diseases or diseases from other medical specialty fields, or after the intake of drugs / toxins. The heterogeneous variety of the clinical presentations, the etiologies, and the therapeutical options require the continuous development of the clinical concepts in tremor disorders. This review summarizes the current state of the art of the clinical recommendations for the diagnostic and therapeutic procedures in tremor.

Dystonia and Tremor: A Cross-Sectional Study of the Dystonia Coalition Cohort

OBJECTIVE

To assess the clinical manifestations and predictors of different types of tremors in individuals with different types of isolated dystonia.

METHODS

Clinical manifestations of tremor were assessed in a multicenter, international cross-sectional, cohort study of 2,362 individuals with all types of isolated dystonia (focal, segmental, multifocal, and generalized) recruited through the Dystonia Coalition.

RESULTS

Methodical and standardized assessments of all participants in this cohort revealed the overall prevalence of any type of tremor was 53.3%. The prevalence of dystonic tremor varied from 36.9% to 48.4%, depending on criteria used to define it. To identify the factors associated with tremors in dystonia, the data were analyzed by generalized linear modeling and cluster analyses. Generalized linear modeling indicated 2 of the strongest factors associated with tremor included body region affected by dystonia and recruitment center. Tremor was also associated with severity of dystonia and duration of dystonia, but not with sex or race. The cluster analysis distinguished 8 subgroups within the whole cohort; defined largely by body region with dystonia, and secondarily by other clinical characteristics.

CONCLUSION

The large number of cases evaluated by an international team of movement disorder experts facilitated the dissection of several important factors that influence the apparent prevalence and phenomenology of tremor in dystonia. These results are valuable for understanding the many differences reported in prior studies, and for guiding future studies of the nosology of tremor and dystonia.

ANO3 and early-onset dyskinetic encephalopathy

Mutations in the ANO3 gene have been associated with autosomal dominant craniocervical dystonia. However, little else is known about the genotype-phenotype characteristics of this disorder. Here we describe a 3 years-old girl with distal myoclonic dystonia. Whole exome sequencing in trio revealed a de novo missense ANO3 variant not previously described in international databases. A global psychomotor regression was observed once dystonia was present. Brain MRI changes paralleled these findings: whereas MRI at the age of 18 months was normal, mild brain and cerebellar atrophy was observed 18 months later. These results suggest that missense mutations in ANO3 may underlie complex disorders particularly characterized by early psychomotor regression and dystonia.

Do We Belittle Essential Tremor by Calling It a Syndrome Rather Than a Disease? No

A task force of the International Parkinson and Movement Disorder Society (MDS) recently published a tremor classification scheme that is based on the nosologic principle of two primary axes for classifying an illness: clinical manifestations (Axis 1) and etiology (Axis 2). An Axis 1 clinical syndrome is a recurring group of clinical symptoms, signs (physical findings), and possibly laboratory results that suggests the presence of at least one underlying Axis 2 etiology. Syndromes must be defined and used consistently to be of value in finding specific etiologies and effective treatments. The MDS task force concluded that essential tremor is a common neurological syndrome that has never been defined consistently by clinicians and researchers. The MDS task force defined essential tremor as a syndrome of bilateral upper limb action tremor of at least 3 years duration, with or without tremor in other locations (e.g., head, voice, or lower limbs), in the absence of other neurological signs (e.g., dystonia, parkinsonism, myoclonus, ataxia, peripheral neuropathy, and cognitive impairment). Deviations from this definition should not be labeled as essential tremor. Patients with additional questionably-abnormal signs or with signs of uncertain relevance to tremor are classified as essential tremor plus. The MDS classification scheme encourages a thorough unbiased phenotyping of patients with tremor, with no assumptions of etiology, pathology, pathophysiology, or relationship to other neurological disorders. The etiologies, pathology, and clinical course of essential tremor are too heterogeneous for this syndrome to be viewed as a disease or a family of diseases.

Isolated and combined genetic tremor syndromes: a critical appraisal based on the 2018 MDS criteria

The 2018 consensus statement on the classification of tremors proposes a two-axis categorization scheme based on clinical features and etiology. It also defines "isolated" and "combined" tremor syndromes depending on whether tremor is the sole clinical manifestation or is associated with other neurological or systemic signs. This syndromic approach provides a guide to investigate the underlying etiology of tremors, either genetic or acquired. Several genetic defects have been proven to cause tremor disorders, including autosomal dominant and recessive, X-linked, and mitochondrial diseases, as well as chromosomal abnormalities. Furthermore, some tremor syndromes are recognized in individuals with a positive family history, but their genetic confirmation is pending. Although most genetic tremor disorders show a combined clinical picture, there are some distinctive conditions in which tremor may precede the appearance of other neurological signs by years or remain the prominent manifestation throughout the disease course, previously leading to misdiagnosis as essential tremor (ET). Advances in the knowledge of genetically determined tremors may have been hampered by the inclusion of heterogeneous entities in previous studies on ET. The recent classification of tremors therefore aims to provide more consistent clinical data for deconstructing the genetic basis of tremor syndromes in the next-generation and long-read sequencing era. This review outlines the wide spectrum of tremor disorders with defined or presumed genetic etiology, both isolated and combined, unraveling diagnostic clues of these conditions and focusing mainly on ET-like phenotypes. Furthermore, we suggest a phenotype-to-genotype algorithm to support clinicians in identifying tremor syndromes and guiding genetic investigations.

Systematic clinical approach for diagnosing upper limb tremor

Tremor is the most common movement disorder worldwide, but diagnosis is challenging. In 2018, the task force on tremor of the International Parkinson and Movement Disorder Society published a consensus statement that proposes a tremor classification along two independent axes: a clinical tremor syndrome and its underlying aetiology. In line with this statement, we here propose a stepwise diagnostic approach that leads to the correct clinical and aetiological classification of upper limb tremor. We also describe the typical clinical signs of each clinical tremor syndrome. A key feature of our algorithm is the distinction between isolated and combined tremor syndromes, in which tremor is accompanied by bradykinesia, cerebellar signs, dystonia, peripheral neuropathy or brainstem signs. This distinction subsequently informs the selection of appropriate diagnostic tests, such as neurophysiology, laboratory testing, structural and dopaminergic imaging and genetic testing. We highlight treatable metabolic causes of tremor, as well as drugs and toxins that can provoke tremor. The stepwise approach facilitates appropriate diagnostic testing and avoids unnecessary investigations. We expect that the approach offered in this article will reduce diagnostic uncertainty and increase the diagnostic yield in patients with tremor.

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.

Rest tremor in dystonia: epidemiology, differential diagnosis, and pathophysiology

BACKGROUND

The most common type of tremor reported in dystonia patients is postural and kinetic. There is uncertainty regarding the prevalence of rest tremor in dystonia.

OBJECTIVE

This review focuses on the clinical and neurophysiological features of rest tremor in dystonia, its differential diagnosis, and methods to distinguish it from other rest tremor syndromes.

METHODS

A PubMed search was done, and the available literature identified. Bibliography of the available literature was reviewed for relevant references.

RESULTS

Rest tremor in dystonia has been reported with a variable frequency of 1.81-12.05%. The most common body distribution is arm, and it tends to be asymmetric. Most of the affected patients have multifocal and segmental dystonia. Rest tremor is a late-onset phenomenon associated with severe and spreading dystonia. Clinically, it is difficult to distinguish rest tremor in dystonia from other rest tremor syndromes based on tremor characteristics; however, other neurological signs can provide clues to differentiate these syndromes. Surface electromyography and other neurophysiological tests can help differentiate the various rest tremor syndromes.

CONCLUSION

Rest tremor in dystonia can be differentiated from other rest tremor syndromes based on neurophysiological techniques. There is some evidence to suggest that SWEDDs could be a form of dystonic tremor, but further studies are required to clarify this diagnostic dilemma. Data regarding the treatment of rest tremor in dystonia are virtually nonexistent, and there is an urgent need for prospective studies focusing its medical management and to know the surgical targets.

COL6A3 mutation associated early-onset isolated dystonia (DYT)-27: Report of a new case and review of published literature

BACKGROUND

Still, the genetic basis of a large number of cases of early-onset isolated dystonia continues to be a mystery. In recent years, many new candidate genes are being identified as putative pathogenic factors in children with isolated dystonia due to the easy availability of whole-exome sequencing. Recently biallelic mutations in the COL6A3 gene were identified as a cause of rare dystonia (DYT)-27 syndrome. Till date, only six cases of DYT27 have been reported in the literature.

METHODS

We report a new case of COL6A3 mutation associated early-onset isolated dystonia-DYT27. We did a review of the previously published cases of DYT27. Citations were identified through PubMed, Embase, Web of Science and Google scholar searches using the search terms (including variations), "Dystonia-27 or DYT27" or/and "COL6A3 mutation associated early-onset isolated dystonia", combined with study filters for original research, case reports and case series.

RESULTS

Next-generation sequencing in the index patient revealed two pathogenic compound heterozygous loss of function mutations in exon 10 and exon 12 of the COL6A3 gene coding for the alpha(α)3(VI) chain of type VI collagen. Together with the presented case, seven cases (five males) were available for analysis. The median age at onset was 22 years (range: 6-61). Dystonic symptoms were started from hands in five and from the neck in the remaining two patients. Five patients had favorable outcomes with trihexyphenidyl and botulinum toxin while tetrabenazine and levodopa were ineffective.

CONCLUSIONS

Although it is a new entity that is only recently discovered, in future years many more new cases suffering from this particular entity are likely to be reported and the already heterogeneous clinical spectrum is likely to be further widespread in years to come.

Longitudinal follow-up with VIM thalamic deep brain stimulation for dystonic or essential tremor

OBJECTIVE

To assess longitudinal tremor outcomes with ventral intermediate nucleus deep brain stimulation (VIM DBS) in patients with dystonic tremor (DT) and to compare with DBS outcomes in essential tremor (ET).

METHODS

We retrospectively investigated VIM DBS outcomes for 163 patients followed at our center diagnosed with either DT or ET. The Fahn-Tolosa-Marin tremor rating scale (TRS) was used to assess change in tremor and activities of daily living (ADL) at 6 months, 1 year, 2-3 years, 4-5 years, and ≥6 years after surgery.

RESULTS

Twenty-six patients with DT and 97 patients with ET were analyzed. Compared to preoperative baseline, there were significant improvements in TRS motor up to 4-5 years (52.2%; p = 0.032) but this did not reach statistical significance at ≥6 years (46.0%, p = 0.063) in DT, which was comparable to the outcomes in ET. While the improvements in the upper extremity tremor, head tremor, and axial tremor were also comparable between DT and ET throughout the follow-up, the ADL improvements in DT were lost at 2-3 years follow-up.

CONCLUSION

Overall, tremor control with VIM DBS in DT and ET was comparable and remained sustained at long term likely related to intervention at the final common node in the pathologic tremor network. However, the long-term ADL improvements in DT were not sustained, possibly due to inadequate control of concomitant dystonia symptoms. These findings from a large cohort of DT indicate that VIM targeting is reasonable if the tremor is considerably more disabling than the dystonic features.

CLASSIFICATION OF EVIDENCE

This study provides Class IV evidence that VIM DBS improves tremor in patients with DT or ET.

ANO3 Mutations in Chinese Dystonia: A Genetic Screening Study Using Next-Generation Sequencing

Background: Dystonia-24 (DYT24) is a monogenic autosomal dominant dystonia caused by mutations in the gene ANO3, which has shown phenotypic and genotypic heterogeneity according to previous reports.

Objective: To screen and identify ANO3 mutations in a cohort of patients with dystonia in China and to expand the spectrum of DYT24.

Methods: This study screened ANO3 mutations in 187 Chinese dystonia patients using next-generation sequencing (NGS). In silico investigations were conducted in detected ANO3 variants and co-segregation analysis was carried out if applicable. The effects of identified variants were classified according to the standards and guidelines of the American College of Medical Genetics and Genomics (ACMG).

Results: Four different variants were identified in four unrelated dystonia patients, including three missense variants [c.1789G>C (p.V600L), c.182A>C (p.E61A), c.787A>G (p.M263V)] and one splice site change (c.1714-3T>C). The novel missense mutation c.1798G>C (p.V600L), identified in a teenaged girl with generalized dystonia, showed high pathogenicity and was classified as “likely pathogenic” according to ACMG guidelines. Of note, she responded well to deep brain stimulation.

Conclusion: Our study helps expand the mutational and clinical spectrum of DYT24 due to ANO3 mutations by further reporting four variants. Rare ANO3 variants appear to represent an uncommon cause of dystonia in China.

Temporal discrimination is altered in patients with isolated asymmetric and jerky upper limb tremor

BACKGROUND

Unilateral or very asymmetric upper limb tremors with a jerky appearance are poorly investigated. Their clinical classification is an unsolved problem because their classification as essential tremor versus dystonic tremor is uncertain. To avoid misclassification as essential tremor or premature classification as dystonic tremor, the term indeterminate tremor was suggested.

OBJECTIVES

The aim of this study was to characterize this tremor subgroup electrophysiologically and evaluate whether diagnostically meaningful electrophysiological differences exist compared to patients with essential tremor and dystonic tremor.

METHODS

We enrolled 29 healthy subjects and 64 patients with tremor: 26 with dystonic tremor, 23 with essential tremor, and 15 patients with upper limb tremor resembling essential tremor but was unusually asymmetric and jerky (indeterminate tremor). We investigated the somatosensory temporal discrimination threshold, the short-interval intracortical inhibition, and the cortical plasticity by paired associative stimulation.

RESULTS

Somatosensory temporal discrimination threshold was significantly increased in patients with dystonic tremor and indeterminate tremor, but it was normal in the essential tremor patients and healthy controls. Significant differences in short-interval intracortical inhibition and paired associative stimulation were not found among the three patient groups and controls.

CONCLUSION

These results indicate that indeterminate tremor, as defined in this study, shares electrophysiological similarities with dystonic tremor rather than essential tremor. Therefore, we propose that indeterminate tremor should be considered as a separate clinical entity from essential tremor and that it might be dystonic in nature. Somatosensory temporal discrimination appears to be a useful tool in tremor classification. © 2019 International Parkinson and Movement Disorder Society.

Nomenclature of Genetically Determined Myoclonus Syndromes: Recommendations of the International Parkinson and Movement Disorder Society Task Force

Genetically determined myoclonus disorders are a result of a large number of genes. They have wide clinical variation and no systematic nomenclature. With next-generation sequencing, genetic diagnostics require stringent criteria to associate genes and phenotype. To improve (future) classification and recognition of genetically determined movement disorders, the Movement Disorder Society Task Force for Nomenclature of Genetic Movement Disorders (2012) advocates and renews the naming system of locus symbols. Here, we propose a nomenclature for myoclonus syndromes and related disorders with myoclonic jerks (hyperekplexia and myoclonic epileptic encephalopathies) to guide clinicians in their diagnostic approach to patients with these disorders. Sixty-seven genes were included in the nomenclature. They were divided into 3 subgroups: prominent myoclonus syndromes, 35 genes; prominent myoclonus syndromes combined with another prominent movement disorder, 9 genes; disorders that present usually with other phenotypes but can manifest as a prominent myoclonus syndrome, 23 genes. An additional movement disorder is seen in nearly all myoclonus syndromes: ataxia (n = 41), ataxia and dystonia (n = 6), and dystonia (n = 5). However, no additional movement disorders were seen in related disorders. Cognitive decline and epilepsy are present in the vast majority. The anatomical origin of myoclonus is known in 64% of genetic disorders: cortical (n = 34), noncortical areas (n = 8), and both (n = 1). Cortical myoclonus is commonly seen in association with ataxia, and noncortical myoclonus is often seen with myoclonus-dystonia. This new nomenclature of myoclonus will guide diagnostic testing and phenotype classification. © 2019 The Authors. Movement Disorders published by Wiley Periodicals, Inc. on behalf of International Parkinson and Movement Disorder Society.

The Phenotypic Variation of a Parkin-Related Parkinson's Disease Family and the Role of Heterozygosity

Background

Parkinson's disease (PD) is a common neurodegenerative disorder with both sporadic occurrence and Mendelian heredity, as it is true for autosomal recessive parkin-related PD (PARK-parkin). Parkin-related PD is characterized by early onset, slow progression, frequent lower limb dystonia, and a robust response to levodopa. Clinicians are increasingly confronted with heterozygous PD patients mimicking dominant inheritance. Nevertheless, the exact clinical implications of heterozygosity are not fully understood.

Cases

We present an illustrative PARK-parkin family with 2 affected sisters (compound heterozygous) and their father (heterozygous). One sister expresses the classical phenotype, whereas the other has isolated jerky tremor. The father has left-sided action tremor of the hand with some dystonic posturing without clear bradykinesia and normal DaTSCAN.

Conclusion

This case series illustrates the phenotypic variability in parkin-related PD with 1 classical phenotype and 1 patient with isolated jerky tremor. Unilateral hand tremor of the heterozygous father could mislead genetic testing by mimicking dominant inheritance.

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.

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.

[The new tremor classification of the International Parkinson and Movement Disorder Society : Update on frequent tremors]

Tremor is one of the most frequent movement disorders. The recently published new classification of the Movement Disorder Society separates the clinical description of tremor syndromes as so-called axis 1 symptom constellations from the etiologies of tremor (axis 2). The same tremor syndromes can therefore be combined with different causes and vice versa. The terminology used in this classification is precisely defined and thereby also the necessary language for medical communication. Frequent tremor syndromes, such as enhanced physiologic tremor, dystonic and parkinsonian tremor as well as focal tremors and task and position-specific tremors are discussed with respect to the phenomenology, and current therapy.