Update on the Genetics of Dystonia

Epidemiological study on pediatric-onset dystonia in Japan: A questionnaire-based survey

OBJECTIVE

This study aimed to investigate the clinical characteristics of pediatric-onset dystonia in Japan, addressing the diagnostic challenges arising from symptom variations and etiological diversity.

METHODS

From 2020 to 2022, questionnaires were distributed to 1218 board certified child neurologists (BCCNs) by Japanese Society of Child Neurology. In the primary survey, participants were asked to report the number of patients with pediatric-onset dystonia under their care. Subsequently, the follow-up secondary survey sought additional information on the clinical characteristics of these patients.

RESULTS

The primary survey obtained 550 responses (response rate: 45 %) from BCCNs for their 736 patients with dystonia. The predominant etiologies included inherited cases (with DYT10   being the most prevalent, followed by DYT5 and ATP1A3-related neurologic disorders), acquired cases (with perinatal abnormalities being the most common), and idiopathic cases. The secondary survey provided clinical insights into 308 cases from 82 BCCNs. Infancy-onset dystonia presented as persistent and generalized with diverse symptoms, primarily linked to ATP1A3-related neurologic disorders and other genetic disorders resembling acquired dystonia. Conversely, childhood/adolescent-onset dystonia showed paroxysmal, fluctuating courses, predominantly affecting limbs. The most common etiologies were DYT5 and DYT10 , leading to therapeutic diagnoses.

CONCLUSION

Pediatric-onset dystonia in Japan was treated by 28 % of BCCNs. The majority of cases were inherited, with high prevalence rates of DYT5 and DYT10 . Infancy-onset dystonia exhibits diverse etiologies and symptoms, emphasizing the utility of various examinations, including genetic testing. These findings significantly contribute to our understanding of pediatric-onset dystonia in Japan, although this study has the limitation of questionnaire survey.

Whole-exome sequencing in a cohort of Chinese patients with isolated cervical dystonia

Background

Dystonia is a kind of movement disorder but its pathophysiological mechanisms are still largely unknown. Recent evidence reveals that genetical defects may play important roles in the pathogenesis of dystonia.

Objectives and Methods

-To explore possible causative genes in Chinese dystonia patients, DNA samples from 42 sporadic patients with isolated cervical dystonia were subjected to whole-exome sequencing. Rare deleterious variants associated with dystonia phenotype were screened out and then classified according to the American College of Medical Genetics and Genomics (ACMG) criteria. Phenolyzer was used for analyzing the most probable candidates correlated with dystonia phenotype, and SWISS-MODEL server was for predicting the 3D structures of variant proteins.

Results

Among 42 patients (17 male and 25 female) recruited, a total of 36 potentially deleterious variants of dystonia-associated genes were found in 30 patients (30/42, 71.4 %). Four disease-causing variants including a pathogenic variant in PLA2G6 (c.797G > C) and three likely pathogenic variants in DCTN1 (c.73C > T), SPR (c.1A > C) and TH (c.56C > G) were found in four patients separately. Other 32 variants were classified as uncertain significance in 26 patients. Phenolyzer prioritized genes TH, PLA2G6 and DCTN1 as the most probable candidates correlated with dystonia phenotype. Although 3D prediction of DCTN1 and PLA2G6 variant proteins detected no obvious structural alterations, the mutation in DCTN1 (c.73C > T:p.Arg25Trp) was closely adjacent to its key functional domain.

Conclusion

Our whole-exome sequencing results identified a novel variant in DCTN1 in sporadic Chinese patients with isolated cervical dystonia, which however, needs our further study on its exact role in dystonia pathogenesis.

The role of genetics in the treatment of dystonia with deep brain stimulation: Systematic review and Meta-analysis

BACKGROUND

Dystonia is a movement disorder characterized by sustained or intermittent muscle contractions that lead to involuntary postures or repetitive movements. Genetic mutations are being increasingly recognized as a cause of dystonia. Deep brain stimulation (DBS) is one of the limited treatment options available. However, there are varying reports on its efficacy in genetic dystonias. This systematic review of the characteristics of genetic dystonias treated with DBS and their outcomes aims to aid in the evaluation of eligibility for such treatment.

METHODS

We performed a PUBMED search of all papers related to genetic dystonias and DBS up until April 2022. In addition to performing a systematic review, we also performed a meta-analysis to assess the role of the mutation on DBS response. We included cases that had a confirmed genetic mutation and DBS along with pre-and post-operative BFMDRS.

RESULTS

Ninety-one reports met our inclusion criteria and from them, 235 cases were analyzed. Based on our analysis DYT-TOR1A dystonia had the best evidence for DBS response and Rapid-Onset Dystonia Parkinsonism was among the least responsive to DBS.

CONCLUSION

While our report supports the role of genetics in DBS selection and response, it is limited by the rarity of the individual genetic conditions, the reliance on case reports and case series, and the limited ability to obtain genetic testing on a large scale in real-time as opposed to retrospectively as in many cases.

Physiology of Dystonia: Animal Studies

Dystonia is currently ranked as the third most prevalent motor disorder. It is typically characterized by involuntary muscle over- or co-contractions that can cause painful abnormal postures and jerky movements. Dystonia is a heterogenous disorder-across patients, dystonic symptoms vary in their severity, body distribution, temporal pattern, onset, and progression. There are also a growing number of genes that are associated with hereditary dystonia. In addition, multiple brain regions are associated with dystonic symptoms in both genetic and sporadic forms of the disease. The heterogeneity of dystonia has made it difficult to fully understand its underlying pathophysiology. However, the use of animal models has been used to uncover the complex circuit mechanisms that lead to dystonic behaviors. Here, we summarize findings from animal models harboring mutations in dystonia-associated genes and phenotypic animal models with overt dystonic motor signs resulting from spontaneous mutations, neural circuit perturbations, or pharmacological manipulations. Taken together, an emerging picture depicts dystonia as a result of brain-wide network dysfunction driven by basal ganglia and cerebellar dysfunction. In the basal ganglia, changes in dopaminergic, serotonergic, noradrenergic, and cholinergic signaling are found across different animal models. In the cerebellum, abnormal burst firing activity is observed in multiple dystonia models. We are now beginning to unveil the extent to which these structures mechanistically interact with each other. Such mechanisms inspire the use of pre-clinical animal models that will be used to design new therapies including drug treatments and brain stimulation.

A novel compound heterozygous mutation of COL6A3 in Chinese patients with isolated cervical dystonia

Background

The etiology and pathogenesis of idiopathic dystonia remain obscure. Recent studies revealed that compound heterozygous mutations in collagen type VI alpha-3 gene COL6A3 may cause recessive isolated dystonia (DYT)-27. However, whether COL6A3 mutations are associated with Chinese patients with isolated dystonia is not yet reported.

Methods

In this study, 45 Chinese patients with isolated cervical dystonia were recruited, and their blood DNA samples were subjected to whole-exome sequencing. The potential causal variants of COL6A3 were identified based on the criteria of the American College of Medical Genetics and Genomics and by prediction software.

Results

Among 45 isolated cervical dystonia patients, 18 patients (10 female patients and eight male patients) were found to have seven potential causal variants in the COL6A3 gene. Among these variants, a compound heterozygous mutation was found in one patient. One allele had a c.1264G>A mutation in exon 4 that resulted in an amino acid substitution of methionine for valine at codon 422 (p.Val422Met) and the other a c.8965+9G>A mutation involving a splicing change in exon 40. In addition, other five missense variants, including c.958G>A (p.Ala320Thr), c.1478T>C (p.Val493Ala), c.1597C>T (p.Arg533Cys), c.1762G>A (p.Asp588Asn), and c.4912G>A (p.Ala1638Thr), were identified as well.

Conclusion

We identified a novel deleterious compound heterozygous mutation as well as five missense variants in the COL6A3 gene of Chinese patients with cervical dystonia. These findings may expand the spectrum of the COL6A3 genotype in isolated dystonia.

PhenoExam: gene set analyses through integration of different phenotype databases

BACKGROUND

Gene set enrichment analysis (detecting phenotypic terms that emerge as significant in a set of genes) plays an important role in bioinformatics focused on diseases of genetic basis. To facilitate phenotype-oriented gene set analysis, we developed PhenoExam, a freely available R package for tool developers and a web interface for users, which performs: (1) phenotype and disease enrichment analysis on a gene set; (2) measures statistically significant phenotype similarities between gene sets and (3) detects significant differential phenotypes or disease terms across different databases.

RESULTS

PhenoExam generates sensitive and accurate phenotype enrichment analyses. It is also effective in segregating gene sets or Mendelian diseases with very similar phenotypes. We tested the tool with two similar diseases (Parkinson and dystonia), to show phenotype-level similarities but also potentially interesting differences. Moreover, we used PhenoExam to validate computationally predicted new genes potentially associated with epilepsy.

CONCLUSIONS

We developed PhenoExam, a freely available R package and Web application, which performs phenotype enrichment and disease enrichment analysis on gene set G, measures statistically significant phenotype similarities between pairs of gene sets G and G' and detects statistically significant exclusive phenotypes or disease terms, across different databases. We proved with simulations and real cases that it is useful to distinguish between gene sets or diseases with very similar phenotypes. Github R package URL is https://github.com/alexcis95/PhenoExam . Shiny App URL is https://alejandrocisterna.shinyapps.io/phenoexamweb/ .

Adult-onset idiopathic dystonia: A national data-linkage study to determine epidemiological, social deprivation, and mortality characteristics

BACKGROUND AND PURPOSE

Accurate epidemiological information is essential for the improved understanding of dystonia syndromes, as well as better provisioning of clinical services and providing context for diagnostic decision-making. Here, we determine epidemiological, social deprivation, and mortality characteristics of adult-onset idiopathic dystonia in the Welsh population.

METHODS

A retrospective population-based cohort study using anonymized electronic health care data in Wales was conducted to identify individuals with dystonia between 1 January 1994 and 31 December 2017. We developed a case-ascertainment algorithm to determine dystonia incidence and prevalence, as well as characterization of the dystonia cohort, based on social deprivation and mortality.

RESULTS

The case-ascertainment algorithm (79% sensitivity) identified 54,966 cases; of these cases, 41,660 had adult-onset idiopathic dystonia (≥20 years). Amongst the adult-onset form, the median age at diagnosis was 41 years, with males significantly older at time of diagnosis compared to females. Prevalence rates ranged from 0.02% in 1994 to 1.2% in 2017. The average annual incidence was 87.7/100,000/year, increasing from 49.9/100,000/year (1994) to 96.21/100,000/year (2017). In 2017, people with dystonia had a similar life expectancy to the Welsh population.

CONCLUSIONS

We have developed a case-ascertainment algorithm, supported by the introduction of a neurologist-reviewed validation cohort, providing a platform for future population-based dystonia studies. We have established robust population-level prevalence and incidence values for adult-onset idiopathic forms of dystonia, with this reflecting increasing clinical recognition and identification of causal genes. Underlying causes of death mirrored those of the general population, including circulatory disorders, respiratory disorders, cancers, and dementia.

Approach to Tremor Disorders

Tremor disorders are diverse and complex. Historical clues and examination features play a major role in diagnosing these disorders, but diagnosis can be challenging due to phenotypic overlap. Ancillary testing, such as neuroimaging or laboratory testing, is driven by the history and examination, and should be performed particularly when there are other neurological or systemic manifestations. The pathophysiology of tremor is not entirely understood, but likely involves multiple networks along with the cerebello-thalamo-cortical pathways. Treatment options include medications, botulinum toxin, surgery, and nonpharmacologic interventions utilizing physical and occupational therapies and assistive devices. Further work is needed in developing accurate diagnostic tests and better treatment options for tremor disorders.

A Homozygous Missense Variant in PPP1R1B/DARPP-32 Is Associated With Generalized Complex Dystonia

BACKGROUND

The dystonias are a heterogeneous group of hyperkinetic disorders characterized by sustained or intermittent muscle contractions that cause abnormal movements and/or postures. Although more than 200 causal genes are known, many cases of primary dystonia have no clear genetic cause.

OBJECTIVES

To identify the causal gene in a consanguineous family with three siblings affected by a complex persistent generalized dystonia, generalized epilepsy, and mild intellectual disability.

METHODS

We performed exome sequencing in the parents and two affected siblings and characterized the expression of the identified gene by immunohistochemistry in control human and zebrafish brains.

RESULTS

We identified a novel missense variant (c.142G>A (NM_032192); p.Glu48Lys) in the protein phosphatase 1 regulatory inhibitor subunit 1B gene (PPP1R1B) that was homozygous in all three siblings and heterozygous in the parents. This gene is also known as dopamine and cAMP-regulated neuronal phosphoprotein 32 (DARPP-32) and has been involved in the pathophysiology of abnormal movements. The uncovered variant is absent in public databases and modifies the conserved glutamate 48 localized close to the serine 45 phosphorylation site. The PPP1R1B protein was shown to be expressed in cells and regions involved in movement control, including projection neurons of the caudate-putamen, substantia nigra neuropil, and cerebellar Purkinje cells. The latter cells were also confirmed to be positive for PPP1R1B expression in the zebrafish brain.

CONCLUSIONS

We report the association of a PPP1R1B/DARPP-32 variant with generalized dystonia in man. It might be relevant to include the sequencing of this new gene in the diagnosis of patients with otherwise unexplained movement disorders. © 2021 International Parkinson and Movement Disorder Society.

Pharmacological perturbation reveals deficits in D2 receptor responses in Thap1 null mice

The primary dystonia DYT6 is caused by mutations in the transcription factor Thanatos‐associated protein 1 (THAP1). To understand THAP1’s functions, we generated mice lacking THAP1 in the nervous system. THAP1 loss causes locomotor deficits associated with transcriptional changes. Since many of the genes misregulated involve dopaminergic signaling, we pharmacologically challenged the two striatal canonical dopamine pathways: the direct, regulated by the D1 receptor, and the indirect, regulated by the D2 receptor. We discovered that depleting THAP1 specifically interferes with the D2 receptor responses, pointing to a selective misregulation of the indirect pathway in DYT6 with implications for pathogenesis and treatment.

Dystonia-specific mutations in THAP1 alter transcription of genes associated with neurodevelopment and myelin

Dystonia is a neurologic disorder associated with an increasingly large number of genetic variants in many genes, resulting in characteristic disturbances in volitional movement. Dissecting the relationships between these mutations and their functional outcomes is critical in understanding the pathways that drive dystonia pathogenesis. Here we established a pipeline for characterizing an allelic series of dystonia-specific mutations. We used this strategy to investigate the molecular consequences of genetic variation in THAP1, which encodes a transcription factor linked to neural differentiation. Multiple pathogenic mutations associated with dystonia cluster within distinct THAP1 functional domains and are predicted to alter DNA-binding properties and/or protein interactions differently, yet the relative impact of these varied changes on molecular signatures and neural deficits is unclear. To determine the effects of these mutations on THAP1 transcriptional activity, we engineered an allelic series of eight alterations in a common induced pluripotent stem cell background and differentiated these lines into a panel of near-isogenic neural stem cells (n = 94 lines). Transcriptome profiling followed by joint analysis of the most robust signatures across mutations identified a convergent pattern of dysregulated genes functionally related to neurodevelopment, lysosomal lipid metabolism, and myelin. On the basis of these observations, we examined mice bearing Thap1-disruptive alleles and detected significant changes in myelin gene expression and reduction of myelin structural integrity relative to control mice. These results suggest that deficits in neurodevelopment and myelination are common consequences of dystonia-associated THAP1 mutations and highlight the potential role of neuron-glial interactions in the pathogenesis of dystonia.

Childhood-onset dystonia-causing KMT2B variants result in a distinctive genomic hypermethylation profile

Background

Dystonia is a clinically and genetically heterogeneous movement disorder characterized by sustained or intermittent muscle contractions causing abnormal, often repetitive, movements and/or postures. Heterozygous variants in lysine methyltransferase 2B (KMT2B), encoding a histone H3 methyltransferase, have been associated with a childhood-onset, progressive and complex form of dystonia (dystonia 28, DYT28). Since 2016, more than one hundred rare KMT2B variants have been reported, including frameshift, nonsense, splice site, missense and other in-frame changes, many having an uncertain clinical impact.

Results

We characterize the genome-wide peripheral blood DNA methylation profiles of a cohort of 18 patients with pathogenic and unclassified KMT2B variants. We resolve the “episignature” associated with KMT2B haploinsufficiency, proving that this approach is robust in diagnosing clinically unsolved cases, properly classifying them with respect to other partially overlapping dystonic phenotypes, other rare neurodevelopmental disorders and healthy controls. Notably, defective KMT2B function in DYT28 causes a non-random DNA hypermethylation across the genome, selectively involving promoters and other regulatory regions positively controlling gene expression.

Conclusions

We demonstrate a distinctive DNA hypermethylation pattern associated with DYT28, provide an epigenetic signature for this disorder enabling accurate diagnosis and reclassification of ambiguous genetic findings and suggest potential therapeutic approaches.

Supplementary Information

The online version contains supplementary material available at 10.1186/s13148-021-01145-y.

Gut Microbiome and Serum Metabolome Alterations Associated with Isolated Dystonia

Dystonia is a complex neurological movement disorder characterized by involuntary muscle contractions. Increasing studies implicate the microbiome as a possible key susceptibility factor for neurological disorders, but the relationship between the gut microbiota and dystonia remains poorly explored. Here, the gut microbiota of 57 patients with isolated dystonia and 27 age- and environment-matched healthy controls was analyzed by 16S rRNA gene amplicon sequencing. Further, integrative analysis of the gut microbiome and serum metabolome measured by high-performance liquid chromatography-mass spectrometry was performed. No difference in α-diversity was found, while β-diversity was significantly different, with a more heterogeneous community structure among dystonia patients than among controls. The most significant changes in dystonia highlighted an increase in Clostridiales, including Blautia obeum, Dorea longicatena, and Eubacterium hallii, and a reduction in Bacteroides vulgatus and Bacteroides plebeius. The functional analysis revealed that genes related to tryptophan and purine biosynthesis were more abundant in gut microbiota from patients with dystonia, while genes linked to citrate cycle, vitamin B₆, and glycan metabolism were less abundant. The evaluation of serum metabolites revealed altered levels of l-glutamic acid, taurine, and d-tyrosine, suggesting changes in neurotransmitter metabolism. The most modified metabolites strongly inversely correlated with the abundance of members belonging to the Clostridiales, revealing the effect of the gut microbiota on neurometabolic activity. This study is the first to reveal gut microbial dysbiosis in patients with isolated dystonia and identified potential links between gut microbiota and serum neurotransmitters, providing new insight into the pathogenesis of isolated dystonia.

IMPORTANCE Dystonia is the third most common movement disorder after essential tremor and Parkinson’s disease. However, the cause for the majority of cases is not known. This is the first study so far that reveals significant alterations of gut microbiome and correlates the alteration of serum metabolites with gut dysbiosis in patients with isolated dystonia. We demonstrated a general overrepresentation of Clostridiales and underrepresentation of Bacteroidetes in patients with dystonia in comparison with healthy controls. The functional analysis found that genes related to the biosynthesis of tryptophan, which is the precursor of the neurotransmitter serotonin, were more active in isolated dystonia patients. Altered levels of several serum metabolites were found to be associated with microbial changes, such as d-tyrosine, taurine, and glutamate, indicating differences in neurotransmitter metabolism in isolated dystonia. Integrative analysis suggests that neurotransmitter system dysfunction may be a possible pathway by which the gut microbiome participates in the development of dystonia. The gut microbiome changes provide new insight into the pathogenesis of dystonia, suggesting new potential therapeutic directions.

[Update on the etiology and pathogenesis of muscle dystonia]

Muscle dystonia is one of the most common extrapyramidal diseases and is the third most common after essential tremor and Parkinson's disease. The introduction of diagnostic methods expanded the understanding of the genetic basis of muscle dystonia and neurophysiological mechanisms of dystonic phenomena. However, the questions of the etiology and pathogenesis of dystonia still remain the subject of close interest of researchers. The review provides up-to-date information about the etiology and pathogenesis of muscle dystonia. Recent changes in the genetic nomenclature of dystonia are described. Modern ideas about the pathogenetic significance of such mechanisms as abnormalities of neural inhibition, disturbances of sensorimotor integration, and abnormalities of neural plasticity are considered. Recent research data support the concept of systemic sensorimotor disintegration, including not only basal ganglia dysfunction, but also motor network disorders involving the cerebellum, cortex, midbrain, thalamus and other areas.

Reduced Expression of GABA A Receptor Alpha2 Subunit Is Associated With Disinhibition of DYT-THAP1 Dystonia Patient-Derived Striatal Medium Spiny Neurons

DYT-THAP1 dystonia (formerly DYT6) is an adolescent-onset dystonia characterized by involuntary muscle contractions usually involving the upper body. It is caused by mutations in the gene THAP1 encoding for the transcription factor Thanatos-associated protein (THAP) domain containing apoptosis-associated protein 1 and inherited in an autosomal-dominant manner with reduced penetrance. Alterations in the development of striatal neuronal projections and synaptic function are known from transgenic mice models. To investigate pathogenetic mechanisms, human induced pluripotent stem cell (iPSC)-derived medium spiny neurons (MSNs) from two patients and one family member with reduced penetrance carrying a mutation in the gene THAP1 (c.474delA and c.38G > A) were functionally characterized in comparison to healthy controls. Calcium imaging and quantitative PCR analysis revealed significantly lower Ca²⁺ amplitudes upon GABA applications and a marked downregulation of the gene encoding the GABA_A receptor alpha2 subunit in THAP1 MSNs indicating a decreased GABAergic transmission. Whole-cell patch-clamp recordings showed a significantly lower frequency of miniature postsynaptic currents (mPSCs), whereas the frequency of spontaneous action potentials (APs) was elevated in THAP1 MSNs suggesting that decreased synaptic activity might have resulted in enhanced generation of APs. Our molecular and functional data indicate that a reduced expression of GABA_A receptor alpha2 subunit could eventually lead to limited GABAergic synaptic transmission, neuronal disinhibition, and hyperexcitability of THAP1 MSNs. These data give pathophysiological insight and may contribute to the development of novel treatment strategies for DYT-THAP1 dystonia.

Deep Brain Stimulation in KMT2B-Related Dystonia: Case Report and Review of the Literature With Special Emphasis on Dysarthria and Speech

Objective: KMT2B-related dystonia is a progressive childhood-onset movement disorder, evolving from lower-limb focal dystonia into generalized dystonia. With increasing age, children frequently show prominent laryngeal or facial dystonia manifesting in dysarthria. Bilateral deep brain stimulation of the globus pallidus internus (GPi-DBS) is reported to be an efficient therapeutic option. Especially improvement of dystonia and regaining of independent mobility is commonly described, but detailed information about the impact of GPi-DBS on dysarthria and speech is scarce. Methods: We report the 16-months outcome after bilateral GPi-DBS in an 8-year-old child with KMT2B-related dystonia caused by a de-novo c.3043C>T (p.Arg1015^*) non-sense variant with special emphasis on dysarthria and speech. We compare the outcome of our patient with 59 patients identified through a PubMed literature search. Results: A remarkable improvement of voice, articulation, respiration and prosodic characteristics was seen 16 months after GPi-DBS. The patients' speech intelligibility improved. His speech became much more comprehensible not only for his parents, but also for others. Furthermore, his vocabulary and the possibility to express his feelings and wants expanded considerably. Conclusion: A positive outcome of GPi-DBS on speech and dysarthria is rarely described in the literature. This might be due to disease progression, non-effectiveness of DBS or due to inadvertent spreading of the electrical current to the corticobulbar tract causing stimulation induced dysarthria. This highlights the importance of optimal lead placement, the possibility of horizontal steering of the electrical field by applying directional stimulation with segmented leads as well as the use of the lowest possible effective stimulation intensity.

Genotype-Phenotype Relations for Isolated Dystonia Genes: MDSGene Systematic Review

This comprehensive MDSGene review is devoted to 7 genes - TOR1A, THAP1, GNAL, ANO3, PRKRA, KMT2B, and HPCA - mutations in which may cause isolated dystonia. It followed MDSGene's standardized data extraction protocol and screened a total of ~1200 citations. Phenotypic and genotypic data on ~1200 patients with 254 different mutations were curated and analyzed. There were differences regarding age at onset, site of onset, and distribution of symptoms across mutation carriers in all 7 genes. Although carriers of TOR1A, THAP1, PRKRA, KMT2B, or HPCA mutations mostly showed childhood and adolescent onset, patients with GNAL and ANO3 mutations often developed first symptoms in adulthood. GNAL and KMT2B mutation carriers frequently have 1 predominant site of onset, that is, the neck (GNAL) or the lower limbs (KMT2B), whereas site of onset in DYT-TOR1A, DYT-THAP1, DYT-ANO3, DYT-PRKRA, and DYT-HPCA was broader. However, in most DYT-THAP1 and DYT-ANO3 patients, dystonia first manifested in the upper half of the body (upper limb, neck, and craniofacial/laryngeal), whereas onset in DYT-TOR1A, DYT-PRKRA and DYT-HPCA was frequently observed in an extremity, including both upper and lower ones. For ANO3, a segmental/multifocal distribution was typical, whereas TOR1A, PRKRA, KMT2B, and HPCA mutation carriers commonly developed generalized dystonia. THAP1 mutation carriers presented with focal, segmental/multifocal, or generalized dystonia in almost equal proportions. GNAL mutation carriers rarely showed generalization. This review provides a comprehensive overview of the current knowledge of hereditary isolated dystonia. The data are also available in an online database (http://www.mdsgene.org), which additionally offers descriptive summary statistics. © 2021 The Authors. Movement Disorders published by Wiley Periodicals LLC on behalf of International Parkinson and Movement Disorder Society.

Fifteen-minute consultation: Approach to investigation and management of childhood dystonia

Dystonia is a hyperkinetic movement disorder characterised by sustained or intermittent muscle contractions causing abnormal movements, postures or both. Dystonia is a challenging condition to diagnose and treat. Dystonia is often under-recognised in children, particularly in cerebral palsy, and frequently coexists with spasticity. This guide aims to simplify the approach to diagnosis, investigation and treatment of childhood-onset dystonia. The principle of treatment is similar regardless of the underlying aetiology: identification of potential triggers and consideration of both pharmacological and surgical options.

Biallelic variants in TSPOAP1, encoding the active-zone protein RIMBP1, cause autosomal recessive dystonia

Dystonia is a debilitating hyperkinetic movement disorder, which can be transmitted as a monogenic trait. Here, we describe homozygous frameshift, nonsense, and missense variants in TSPOAP1, which encodes the active-zone RIM-binding protein 1 (RIMBP1), as a genetic cause of autosomal recessive dystonia in 7 subjects from 3 unrelated families. Subjects carrying loss-of-function variants presented with juvenile-onset progressive generalized dystonia, associated with intellectual disability and cerebellar atrophy. Conversely, subjects carrying a pathogenic missense variant (p.Gly1808Ser) presented with isolated adult-onset focal dystonia. In mice, complete loss of RIMBP1, known to reduce neurotransmission, led to motor abnormalities reminiscent of dystonia, decreased Purkinje cell dendritic arborization, and reduced numbers of cerebellar synapses. In vitro analysis of the p.Gly1808Ser variant showed larger spike-evoked calcium transients and enhanced neurotransmission, suggesting that RIMBP1-linked dystonia can be caused by either reduced or enhanced rates of spike-evoked release in relevant neural networks. Our findings establish a direct link between dysfunction of the presynaptic active zone and dystonia and highlight the critical role played by well-balanced neurotransmission in motor control and disease pathogenesis.

Dystonia genes functionally converge in specific neurons and share neurobiology with psychiatric disorders

Dystonia is a neurological disorder characterized by sustained or intermittent muscle contractions causing abnormal movements and postures, often occurring in absence of any structural brain abnormality. Psychiatric comorbidities, including anxiety, depression, obsessive-compulsive disorder and schizophrenia, are frequent in patients with dystonia. While mutations in a fast-growing number of genes have been linked to Mendelian forms of dystonia, the cellular, anatomical, and molecular basis remains unknown for most genetic forms of dystonia, as does its genetic and biological relationship to neuropsychiatric disorders. Here we applied an unbiased systems-biology approach to explore the cellular specificity of all currently known dystonia-associated genes, predict their functional relationships, and test whether dystonia and neuropsychiatric disorders share a genetic relationship. To determine the cellular specificity of dystonia-associated genes in the brain, single-nuclear transcriptomic data derived from mouse brain was used together with expression-weighted cell-type enrichment. To identify functional relationships among dystonia-associated genes, we determined the enrichment of these genes in co-expression networks constructed from 10 human brain regions. Stratified linkage-disequilibrium score regression was used to test whether co-expression modules enriched for dystonia-associated genes significantly contribute to the heritability of anxiety, major depressive disorder, obsessive-compulsive disorder, schizophrenia, and Parkinson's disease. Dystonia-associated genes were significantly enriched in adult nigral dopaminergic neurons and striatal medium spiny neurons. Furthermore, 4 of 220 gene co-expression modules tested were significantly enriched for the dystonia-associated genes. The identified modules were derived from the substantia nigra, putamen, frontal cortex, and white matter, and were all significantly enriched for genes associated with synaptic function. Finally, we demonstrate significant enrichments of the heritability of major depressive disorder, obsessive-compulsive disorder and schizophrenia within the putamen and white matter modules, and a significant enrichment of the heritability of Parkinson's disease within the substantia nigra module. In conclusion, multiple dystonia-associated genes interact and contribute to pathogenesis likely through dysregulation of synaptic signalling in striatal medium spiny neurons, adult nigral dopaminergic neurons and frontal cortical neurons. Furthermore, the enrichment of the heritability of psychiatric disorders in the co-expression modules enriched for dystonia-associated genes indicates that psychiatric symptoms associated with dystonia are likely to be intrinsic to its pathophysiology.

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.

Pathogenic convergence of CNVs in genes functionally associated to a severe neuromotor developmental delay syndrome

BACKGROUND

Complex developmental encephalopathy syndromes might be the consequence of unknown genetic alterations that are likely to contribute to the full neurological phenotype as a consequence of pathogenic gene combinations.

METHODS

To identify the additional genetic contribution to the neurological phenotype, we studied as a test case a boy, with a KCNQ2 exon-7 partial duplication, by single-nucleotide polymorphism (SNP) microarray to detect copy-number variations (CNVs).

RESULTS

The proband presented a cerebral palsy like syndrome with a severe motor and developmental encephalopathy. The SNP array analysis detected in the proband several de novo CNVs, nine partial gene losses (LRRC55, PCDH9, NALCN, RYR3, ELAVL2, CDH13, ATP1A2, SLC17A5, ANO3), and two partial gene duplications (PCDH19, EFNA5). The biological functions of these genes are associated with ion channels such as calcium, chloride, sodium, and potassium with several membrane proteins implicated in neural cell-cell interactions, synaptic transmission, and axon guidance. Pathogenically, these functions can be associated to cerebral palsy, seizures, dystonia, epileptic crisis, and motor neuron dysfunction, all present in the patient.

CONCLUSIONS

Severe motor and developmental encephalopathy syndromes of unknown origin can be the result of a phenotypic convergence by combination of several genetic alterations in genes whose physiological function contributes to the neurological pathogenic mechanism.

Rare functional missense variants in CACNA1H: What can we learn from Writer's cramp?

Writer's cramp (WC) is a task-specific focal dystonia that occurs selectively in the hand and arm during writing. Previous studies have shown a role for genetics in the pathology of task-specific focal dystonia. However, to date, no causal gene has been reported for task-specific focal dystonia, including WC. In this study, we investigated the genetic background of a large Dutch family with autosomal dominant‒inherited WC that was negative for mutations in known dystonia genes. Whole exome sequencing identified 4 rare variants of unknown significance that segregated in the family. One candidate gene was selected for follow-up, Calcium Voltage-Gated Channel Subunit Alpha1 H, CACNA1H, due to its links with the known dystonia gene Potassium Channel Tetramerization Domain Containing 17, KCTD17, and with paroxysmal movement disorders. Targeted resequencing of CACNA1H in 82 WC cases identified another rare, putative damaging variant in a familial WC case that did not segregate. Using structural modelling and functional studies in vitro, we show that both the segregating p.Arg481Cys variant and the non-segregating p.Glu1881Lys variant very likely cause structural changes to the Cav3.2 protein and lead to similar gains of function, as seen in an accelerated recovery from inactivation. Both mutant channels are thus available for re-activation earlier, which may lead to an increase in intracellular calcium and increased neuronal excitability. Overall, we conclude that rare functional variants in CACNA1H need to be interpreted very carefully, and additional studies are needed to prove that the p.Arg481Cys variant is the cause of WC in the large Dutch family.

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

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

DYT-TUBB4A (DYT4 Dystonia): New Clinical and Genetic Observations

OBJECTIVE

To report 4 novel TUBB4A mutations leading to laryngeal and cervical dystonia with frequent generalization.

METHODS

We screened 4 families including a total of 11 definitely affected members with a clinical picture resembling the original description.

RESULTS

Four novel variants in the TUBB4A gene have been identified: D295N, R46M, Q424H, and R121W. In silico modeling showed that all variants have characteristics similar to R2G. The variants segregate with the disease in 3 of the families with evidence of incomplete penetrance in 2 of them. All 4 variants would be classified as likely pathogenic. The clinical picture particularly included laryngeal dystonia (often the site of onset), associated with cervical and upper limb dystonia and frequent generalization. Laryngeal dystonia was extremely prevalent (>90%) both in the original cases and in this case series. The hobby horse gait was evident in only 1 patient in this case series.

CONCLUSIONS

Our interpretation is that laryngeal involvement is a hallmark feature of DYT-TUBB4A. Nevertheless, TUBB4A mutations remain an exceedingly rare cause of laryngeal or other isolated dystonia.

A case report of DOPA-responsive dystonia in a young woman

Dopa-responsive dystonia (DRD) is a rare progressive genetically heterogenous disorder with pediatric onset. DRD is 3 times as prevalent in women than in men. This article reports a clinical case of DRD in a young female presenting with paraparesis, foot dystonia (more pronounced in the right foot) and pronounced walking impairment, who was admitted for emergency treatment to a Neurology Unit. Based on the additional tests, which included a levodopa trial and Sanger sequencing, the patient was diagnosed with DRD. Levodopa caused a considerable improvement of the symptoms. The article describes the clinical features of the disease, talks about its differential diagnosis, genetic predisposition and treatment strategy.

Successful Pallidal Stimulation in a Patient with KMT2B-Related Dystonia

Although the KMT2B gene was identified as a causative gene for early-onset generalized dystonia, the efficacy of deep brain stimulation (DBS) in KMT2B-related dystonia has not been clearly elucidated. Here, we describe a 28-year-old woman who developed generalized dystonia with developmental delay, microcephaly, short stature, and cognitive decline. She was diagnosed with KMT2B- related dystonia using whole-exome sequencing with a heterozygous frameshift insertion of c.515dupC (p.T172fs) in the KMT2B gene. Oral medications and botulinum toxin injection were not effective. The dystonia markedly improved with bilateral pallidal DBS (the Burke-Fahn-Marsden Dystonia Rating Scale score was reduced from 30 to 5 on the dystonia movement scale and from 11 to 1 on the disability scale), and she could walk independently. From this case, we suggest that bilateral globus pallidus internus DBS can be an effective treatment option for patients with KMT2B-related generalized dystonia.

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.

Differential response to pallidal deep brain stimulation among monogenic dystonias: systematic review and meta-analysis

OBJECTIVE

Genetic subtypes of dystonia may respond differentially to deep brain stimulation of the globus pallidus pars interna (GPi DBS). We sought to compare GPi DBS outcomes among the most common monogenic dystonias.

METHODS

This systematic review and meta-analysis followed the Preferred Reporting Items for Systematic Reviews and Meta-analyses and Meta-analysis of Observational Studies in Epidemiology guidelines. We searched PubMed for studies on genetically confirmed monogenic dystonia treated with GPi DBS documenting pre-surgical and post-surgical assessments using the Burke-Fahn-Marsden Dystonia Rating Scale Motor Score (BFMMS) and Burke-Fahn-Marsden Disability Score (BFMDS). We performed (i) meta-analysis for each gene mutation; (ii) weighted ordinary linear regression analyses to compare BFMMS and BFMDS outcomes between DYT-TOR1A and other monogenic dystonias, adjusting for age and disease duration and (iii) weighted linear regression analysis to estimate the effect of age, sex and disease duration on GPi DBS outcomes. Results were summarised with mean change and 95% CI.

RESULTS

DYT-TOR1A (68%, 38.4 points; p<0.001), DYT-THAP1 (37% 14.5 points; p<0.001) and NBIA/DYT-PANK2 (27%, 21.4 points; p<0.001) improved in BFMMS; only DYT-TOR1A improved in BFMDS (69%, 9.7 points; p<0.001). Improvement in DYT-TOR1A was significantly greater than in DYT-THAP1 (BFMMS -31%), NBIA/DYT-PANK2 (BFMMS -35%; BFMDS -53%) and CHOR/DYT-ADCY5 (BFMMS -36%; BFMDS -42%). Worse motor outcomes were associated with longer dystonia duration and older age at dystonia onset in DYT-TOR1A, longer dystonia duration in DYT/PARK-TAF1 and younger age at dystonia onset in DYT-SGCE.

CONCLUSIONS

GPi DBS outcomes vary across monogenic dystonias. These data serve to inform patient selection and prognostic counselling.

Unraveling Molecular Mechanisms of THAP1 Missense Mutations in DYT6 Dystonia

Mutations in THAP1 (THAP domain-containing apoptosis-associated protein 1) are responsible for DYT6 dystonia. Until now, more than eighty different mutations in THAP1 gene have been found in patients with primary dystonia, and two third of them are missense mutations. The potential pathogeneses of these missense mutations in human are largely elusive. In the present study, we generated stable transfected human neuronal cell lines expressing wild-type or mutated THAP1 proteins found in DYT6 patients. Transcriptional profiling using microarrays revealed a set of 28 common genes dysregulated in two mutated THAP1 (S21T and F81L) overexpression cell lines suggesting a common mechanism of these mutations. ChIP-seq showed that THAP1 can bind to the promoter of one of these genes, superoxide dismutase 2 (SOD2). Overexpression of THAP1 in SK-N-AS cells resulted in increased SOD2 protein expression, whereas fibroblasts from THAP1 patients have less SOD2 expression, which indicates that SOD2 is a direct target gene of THAP1. In addition, we show that some THAP1 mutations (C54Y and F81L) decrease the protein stability which might also be responsible for altered transcription regulation due to dosage insufficiency. Taking together, the current study showed different potential pathogenic mechanisms of THAP1 mutations which lead to the same consequence of DYT6 dystonia.

The matter of significance - Has the p.(Glu121Lys) variant of TOR1A gene a pathogenic role in dystonia or Parkinson disease?

Next Generation Sequencing (NGS), has now become a very powerful tool for decoding variants of genes involved in pathogenesis of number of human disorders. One of the challenges of this method is to decipher the real pathogenic variants from a number of identified, not related to the disorder in analyzed case. Another issue is recognition of new phenotypes previously unrecognized but related to new variants combinations' in known genes. The other aspect is the HGMD or ClinVar mutation databases usage in data interpretation. The aim of this paper is to discuss pathogenicity of p.(Glu121Lys) missense mutation in the TOR1A gene previously described as dystonia causing variant. The patient diagnosed with typical Parkinson disease and positive family history was included into analysis. Also the internal whole exome sequencing (WES) database containing 600 subjects who has performed WES due to different causes was searched. All subjects had WES performed on SureSelect Human All Exon v.6 enrichment, Illumina NovaSeq 6000 platform, (annotations according to internal Institute Mother and Child's pipeline). The TOR1A p.(Glu121Lys) heterozygous mutation was revealed in 1 patient diagnosed with PD and 2 healthy subjects who has no dystonia symptoms. To conclude the TOR1A p.Glu121Lys variant should not be recognized as clearly pathogenic now.

Pallidal Deep Brain Stimulation in DYT6 Dystonia: Clinical Outcome and Predictive Factors for Motor Improvement

Pallidal deep brain stimulation is an established treatment in dystonia. Available data on the effect in DYT-THAP1 dystonia (also known as DYT6 dystonia) are scarce and long-term follow-up studies are lacking. In this retrospective, multicenter follow-up case series of medical records of such patients, the clinical outcome of pallidal deep brain stimulation in DYT-THAP1 dystonia, was evaluated. The Burke Fahn Marsden Dystonia Rating Scale served as an outcome measure. Nine females and 5 males were enrolled, with a median follow-up of 4 years and 10 months after implant. All benefited from surgery: dystonia severity was reduced by a median of 58% (IQR 31-62, p = 0.001) at last follow-up, as assessed by the Burke Fahn Marsden movement subscale. In the majority of individuals, there was no improvement of speech or swallowing, and overall, the effect was greater in the trunk and limbs as compared to the cranio-cervical and orolaryngeal regions. No correlation was found between disease duration before surgery, age at surgery, or preoperative disease burden and the outcome of deep brain stimulation. Device- and therapy-related side-effects were few. Accordingly, pallidal deep brain stimulation should be considered in clinically impairing and pharmaco-resistant DYT-THAP1 dystonia. The method is safe and effective, both short- and long-term.

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.

A Novel Transgenic Mouse Model to Investigate the Cell-Autonomous Effects of torsinA(ΔE) Expression in Striatal Output Neurons

Dystonia is a disabling neurological syndrome characterized by abnormal movements and postures that result from intermittent or sustained involuntary muscle contractions; mutations of DYT1/TOR1A are the most common cause of childhood-onset, generalized, inherited dystonia. Patient and mouse model data strongly support dysregulation of the nigrostriatal dopamine neurotransmission circuit in the presence of the DYT1-causing mutation. To determine striatal medium spiny neuron (MSN) cell-autonomous and non-cell autonomous effects relevant to dopamine transmission, we created a transgenic mouse in which expression of mutant torsinA in forebrain is restricted to MSNs. We assayed electrically evoked and cocaine-enhanced dopamine release and locomotor activity, dopamine uptake, gene expression of dopamine-associated neuropeptides and receptors, and response to the muscarinic cholinergic antagonist, trihexyphenidyl. We found that over-expression of mutant torsinA in MSNs produces complex cell-autonomous and non-cell autonomous alterations in nigrostriatal dopaminergic and intrastriatal cholinergic function, similar to that found in pan-cellular DYT1 mouse models. These data introduce targets for future studies to identify which are causative and which are compensatory in DYT1 dystonia, and thereby aid in defining appropriate therapies.

High Prevalence of Dystonia in the Faroe Islands: A Population-Based Study

BACKGROUND

There are fewer than 5 population-based studies of dystonia worldwide. Only one utilized a movement disorders neurologist. Given the potential for founder effects, and the highly genetic nature of dystonia, the Faroe Islands provide a particularly interesting setting to study the prevalence of dystonia.

OBJECTIVE

To estimate the prevalence of dystonia.

METHODS

We used a 2-phase, population-based design, screening 1,334 randomly selected Faroese individuals aged ≥40 years from which a subsample of 227 participated in an in-person clinical evaluation. Dystonia was assessed by 2 movement disorder neurologists using videotaped examinations.

RESULTS

Two of 227 (0.88%, 95% CI -0.33 to 2.09%) were diagnosed with cervical or segmental dystonia. An unusual form of thumb flexion dystonia was noted in 75 more, yielding a combined prevalence of 33.92% (95% CI 27.73-40.11%).

CONCLUSIONS

The prevalence of cervical or segmental dystonia was as high as in one prior population-based study using similar methods. Furthermore, an unusual form of thumb flexion dystonia was uncovered, which yielded an extraordinarily high prevalence of dystonia in this population. Although our methods likely contributed to more complete capture of subtle dystonia, founder effects are highly likely to have been an additional major contributor to these findings.

A Novel SGCE Nonsense Variant Associated With Marked Intrafamilial Variability in a Turkish Family With Myoclonus-Dystonia

Background

Myoclonus-Dystonia syndrome (M-D) is an autosomal-dominant movement disorder related to SGCE gene pathogenic variants. Although there can be observed variability in clinical findings, here we describe intrafamilial variability in a Turkish family with a novel nonsense SGCE pathogenic variant.

Methods

A family with variable clinical symptoms resembling M-D were referred to our clinic. After preliminary diagnosis, patients were tested for mutations in the SGCE gene by Sanger sequencing.

Results

Novel pathogenic heterozygous nonsense mutation in exon 3, c.272T>G; p.Leu91* (NM_003919.2) were observed in affected family members.

Conclusion

Intrafamilial clinical variability, despite the same pathogenic variant described in this work, suggests that there are regulatory factors, epigenetic or environmental modifiers, which are the subject of a matter for future studies.

Anoctamin 3: A Possible Link between Cluster Headache and Ca2+ Signaling

Cluster headache is a severe primary headache characterized by extremely painful attacks of unilateral headache. Verapamil is commonly used as a prophylactic treatment with good effect. In order to search for new pathways involved in the pathophysiology of cluster headache, we analyzed genetic variants that were previously linked to verapamil response in migraine in a Swedish cluster headache case-control sample. We used TaqMan qPCR for genetic screening and performed a gene expression analysis on associated genes in patient-derived fibroblasts, and further investigated which reference genes were suitable for analysis in fibroblasts from cluster headache patients. We discovered a significant association between anoctamin 3, a gene encoding a calcium-activated ion channel, and cluster headache. The association was not dependent on verapamil treatment since the associated variant, rs1531394, was also overrepresented in patients not using verapamil. No difference was found in the anoctamin 3 gene expression between controls and patients. Also, we determined that TBP, IPO8 and PDHB were suitable reference genes in cluster headache fibroblasts. This finding is the first report of an association between a variant in a gene encoding an ion-channel and cluster headache, and the first significant genetic evidence of calcium involvement in cluster headache pathophysiology.

Diverse Mechanisms Lead to Common Dysfunction of Striatal Cholinergic Interneurons in Distinct Genetic Mouse Models of Dystonia

Clinical and experimental data indicate striatal cholinergic dysfunction in dystonia, a movement disorder typically resulting in twisted postures via abnormal muscle contraction. Three forms of isolated human dystonia result from mutations in the TOR1A (DYT1), THAP1 (DYT6), and GNAL (DYT25) genes. Experimental models carrying these mutations facilitate identification of possible shared cellular mechanisms. Recently, we reported elevated extracellular striatal acetylcholine by in vivo microdialysis and paradoxical excitation of cholinergic interneurons (ChIs) by dopamine D2 receptor (D2R) agonism using ex vivo slice electrophysiology in Dyt1 ^ΔGAG/+ mice. The paradoxical excitation was caused by overactive muscarinic receptors (mAChRs), leading to a switch in D2R coupling from canonical G_i/o to noncanonical β-arrestin signaling. We sought to determine whether these mechanisms in Dyt1 ^ΔGAG/+ mice are shared with Thap1 ^C54Y/+ knock-in and Gnal ^+/- knock-out dystonia models and to determine the impact of sex. We found Thap1 ^C54Y/+ mice of both sexes have elevated extracellular striatal acetylcholine and D2R-induced paradoxical ChI excitation, which was reversed by mAChR inhibition. Elevated extracellular acetylcholine was absent in male and female Gnal ^+/- mice, but the paradoxical D2R-mediated ChI excitation was retained and only reversed by inhibition of adenosine A2ARs. The G_i/o-preferring D2R agonist failed to increase ChI excitability, suggesting a possible switch in coupling of D2Rs to β-arrestin, as seen previously in a DYT1 model. These data show that, whereas elevated extracellular acetylcholine levels are not always detected across these genetic models of human dystonia, the D2R-mediated paradoxical excitation of ChIs is shared and is caused by altered function of distinct G-protein-coupled receptors.SIGNIFICANCE STATEMENT Dystonia is a common and often disabling movement disorder. The usual medical treatment of dystonia is pharmacotherapy with nonselective antagonists of muscarinic acetylcholine receptors, which have many undesirable side effects. Development of new therapeutics is a top priority for dystonia research. The current findings, considered in context with our previous investigations, establish a role for cholinergic dysfunction across three mouse models of human genetic dystonia: DYT1, DYT6, and DYT25. The commonality of cholinergic dysfunction in these models arising from diverse molecular etiologies points the way to new approaches for cholinergic modulation that may be broadly applicable in dystonia.

Identification of Novel KMT2B Variants in Chinese Dystonia Patients via Whole-Exome Sequencing

Background: Dystonia is a movement disorder with high clinical and genetic heterogeneity. Recently mutations in lysine-specific histone methyltransferase 2B (KMT2B) gene have been reported to be associated with early-onset progressive dystonia.

Methods: We performed whole-exome sequencings (WES) in a cohort of early-onset dystonia patients from China. Bioinformatics analysis and cosegregation testings were conducted to select candidate causal variants. The effects of identified variants were classified according to the American College of Medical Genetics and Genomics (ACMG) standards and guidelines.

Results: Three novel KMT2B variants were identified, including p.Q1359^* in patient 1, p.R1487AfsTer7 in patient 2, and p.R152W in patient 3. Among these variants, the nonsense variant p.Q1359^* and the frameshift variant p.R1487AfsTer7 showed high pathogenicity and were rated as pathogenic according to the ACMG guideline. Regarding the phenotypes of these two patients with pathogenic variants, patient 2 showed the similar presentation as reported whereas patient 1 seemly harbored the atypical presentations, including later onset age, atypical sites of onset and milder degree of dystonia.

Conclusions: We further report three dystonia patients with novel variants in KMT2B and expand the spectrums of genotype and phenotype of KMT2B.

Loss of the dystonia gene Thap1 leads to transcriptional deficits that converge on common pathogenic pathways in dystonic syndromes

Dystonia is a movement disorder characterized by involuntary and repetitive co-contractions of agonist and antagonist muscles. Dystonia 6 (DYT6) is an autosomal dominant dystonia caused by loss-of-function mutations in the zinc finger transcription factor THAP1. We have generated Thap1 knock-out mice with a view to understanding its transcriptional role. While germ-line deletion of Thap1 is embryonic lethal, mice lacking one Thap1 allele-which in principle should recapitulate the haploinsufficiency of the human syndrome-do not show a discernable phenotype. This is because mice show autoregulation of Thap1 mRNA levels with upregulation at the non-affected locus. We then deleted Thap1 in glial and neuronal precursors using a nestin-conditional approach. Although these mice do not exhibit dystonia, they show pronounced locomotor deficits reflecting derangements in the cerebellar and basal ganglia circuitry. These behavioral features are associated with alterations in the expression of genes involved in nervous system development, synaptic transmission, cytoskeleton, gliosis and dopamine signaling that link DYT6 to other primary and secondary dystonic syndromes.

Frequency and phenotypic spectrum of KMT2B dystonia in childhood: A single-center cohort study

BACKGROUND

Childhood-onset dystonia is often genetically determined. Recently, KMT2B variants have been recognized as an important cause of childhood-onset dystonia.

OBJECTIVE

To define the frequency of KMT2B mutations in a cohort of dystonic patients aged <18 years at onset, the associated clinical and radiological phenotype, and the natural history of disease.

METHODS

Whole-exome sequencing or customized gene panels were used to screen a cohort of 65 patients who had previously tested negative for all other known dystonia-associated genes.

RESULTS

We identified 14 patients (21.5%) carrying KMT2B variants, of which 1 was classified as a variant of unknown significance. We also identified 2 additional patients carrying pathogenic mutations in GNAO1 and ATM. Overall, we established a definitive genetic diagnosis in 23% of cases. We observed a spectrum of clinical manifestations in KMT2B variant carriers, ranging from generalized dystonia to short stature or intellectual disability alone, even within the same family. In 78.5% of cases, dystonia involved the lower limbs at onset, with later caudocranial generalization. Eight patients underwent pallidal DBS with a median decrease of Burke-Fahn-Marsden Dystonia Rating Scale-Motor score of 38.5% in the long term. We also report on 4 asymptomatic carriers, suggesting that some KMT2B mutations may be associated with incomplete disease penetrance.

CONCLUSIONS

KMT2B mutations are frequent in childhood-onset dystonia and cause a complex neurodevelopmental syndrome, often featuring growth retardation and intellectual disability as additional phenotypic features. A dramatic and long-lasting response to DBS is characteristic of DYT-KMT2B dystonia. © 2019 International Parkinson and Movement Disorder Society.

Novel mutations in KMT2B offer pathophysiological insights into childhood-onset progressive dystonia

Rapid progress has recently been made in the elucidation of the genetic basis of childhood-onset inherited generalized dystonia (IGD) due to the implementation of genomic sequencing methodologies. We identified four patients with childhood-onset IGD harboring novel disease-causing mutations in lysine-specific histone methyltransferase 2B gene (KMT2B) by whole-exome sequencing. The main focus of this paper is to gain novel pathophysiological insights through understanding the molecular consequences of these mutations. The disease course is mostly progressive, evolving from lower limbs into generalized dystonia, which could be associated with dysarthria, dysphonia, intellectual disability, orofacial dyskinesia, and sometimes distinct dysmorphic facial features. In two patients, motor performances improved after bilateral implantation of deep brain stimulation in the globus pallidus internus (GPi-DBS). Pharmacotherapy with trihexyphenidyl reduced dystonia in two patients. We discovered three novel KMT2B mutations. Our analyses revealed that the mutation in patient 1 (c.7463A > G, p.Y2488C) is localized in the highly conserved FYRC domain of KMT2B. This mutation holds the potential to alter the inter-domain FYR interactions, which could lead to KMT2B instability. The mutations in patients 2 and 3 (c.3596_3697insC, p.M1202Dfs*22; c.4229delA, p.Q1410Rfs*12) lead to predicted unstable transcripts, likely to be subject to degradation by non-sense-mediated decay. Childhood-onset progressive dystonia with orofacial involvement is one of the main clinical manifestations of KMT2B mutations. In all, 26% (18/69) of the reported cases have T2 signal alterations of the globus pallidus internus, mostly at a younger age. Anticholinergic medication and GPi-DBS are promising treatment options and shall be considered early.