Epsilon-sarcoglycan mutations found in combination with other dystonia gene mutations

The G protein modifier KCTD5 tunes the decoding of neuromodulatory signals necessary for motor function in striatal neurons

G proteins (Gα and Gβγ subtypes) drive adenylyl cyclase type 5 (AC5) synthesis of cAMP in striatal neurons, which is essential for motor coordination. KCTD5 directly interacts with Gβγ to delimit signaling events, yet downstream impact of KCTD5 in striatal circuits is not known. Here, generation of a conditional Kctd5 knockout mouse identified that loss of striatal KCTD5 leads to a dystonic phenotype, coordination deficits, and skewed transitions between behavioral syllables. 2-photon imaging of a cAMP biosensor revealed electrically evoked dopaminergic responses were significantly augmented in the absence of KCTD5 in striatal circuits. cAMP sensitization was rescued in situ by expression of a Gβγ-scavenging nanobody and motor deficits were partially rescued in vivo by pharmacological antagonism of the indirect striatal cAMP pathway. Therefore, KCTD5 acts as a brake on cAMP signaling in striatal neurons important for tuning dopaminergic signaling and motor coordination.

KCTD1 regulation of Adenylyl cyclase type 5 adjusts striatal cAMP signaling

Dopamine transfers information to striatal neurons, and disrupted neurotransmission leads to motor deficits observed in movement disorders. Striatal dopamine converges downstream to Adenylyl Cyclase Type 5 (AC5)-mediated synthesis of cAMP, indicating the essential role of signal transduction in motor physiology. However, the relationship between dopamine decoding and AC5 regulation is unknown. Here, we utilized an unbiased global protein stability screen to identify Potassium Channel Tetramerization Domain 1 (KCTD1) as a key regulator of AC5 level that is mechanistically tied to N-linked glycosylation. We then implemented a CRISPR/SaCas9 approach to eliminate KCTD1 in striatal neurons expressing a Förster resonance energy transfer (FRET)-based cAMP biosensor. 2-photon imaging of striatal neurons in intact circuits uncovered that dopaminergic signaling was substantially compromised in the absence of KCTD1. Finally, knockdown of KCTD1 in genetically defined dorsal striatal neurons significantly altered motor behavior in mice. These results reveal that KCTD1 acts as an essential modifier of dopaminergic signaling by stabilizing striatal AC5.

Detection of a new deleterious SGCE gene variant in Moroccan family with inherited myoclonus-dystonia

Myoclonus-dystonia (M-D) is a pleiotropic neuropsychiatric disorder with autosomal dominant mode of inheritance with variable severity and incomplete penetrance. Pathogenic variants in ξ-sarcoglycan gene SGCE are the most frequently known genetic cause of M-D with maternal imprinting, and in most cases, a symptomatic individual inherits the pathogenic variant from his or her father. This work reported a missense mutation c.662G> T inherited in the M-D Moroccan family described for the first time, which is deleterious based on protein modeling analysis.

Monozygotic twins with DYT-TOR1A showing jerking movements and levodopa responsiveness

BACKGROUND

DYT-TOR1A is caused by a GAG deletion in the TOR1A gene. While it usually manifests as early-onset dystonia, its phenotype is extremely diverse, even within one family. Recent reports have revealed that some DYT-TOR1A cases have novel mutations in the TOR1A gene while others have mutations in both TOR1A and another DYT gene (THAP1 or SGCE). Our understanding of the correlation between genotype and phenotype is becoming increasingly complicated.

CASE PRESENTATIONS

Here, we report on monozygotic twins who developed dystonia in childhood. The two children had different presentations in terms of onset age and dominant disturbances, but both exhibited marked diurnal fluctuation and jerking movements of the limbs as well as levodopa/levodopa-carbidopa responsiveness. These features are commonly associated with DYT/PARK-GCH1 and DYT-SGCE, yet these twins had no mutations in the GCH1 or SGCE genes. Whole exome sequencing eventually revealed a single GAG deletion in the TOR1A gene.

CONCLUSION

Monozygotic twins whose only mutation was a GAG deletion in TOR1A exhibited DYT/PARK-GCH1-asssociated features and jerking movements reminiscent of myoclonus. This finding may expand the spectrum of phenotypes associated with DYT-TOR1A, and suggests that levodopa has potential as a treatment for DYT-TOR1A with DYT/PARK-GCH1-associated features.

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.

Membrane defects and genetic redundancy: Are we at a turning point for DYT1 dystonia?

Heterozygosity for a 3-base pair deletion (ΔGAG) in TOR1A/torsinA is one of the most common causes of hereditary dystonia. In this review, we highlight current understanding of how this mutation causes disease from research spanning structural biochemistry, cell science, neurobiology, and several model organisms. We now know that homozygosity for ΔGAG has the same effects as Tor1a^KO , implicating a partial loss of function mechanism in the ΔGAG/+ disease state. In addition, torsinA loss specifically affects neurons in mice, even though the gene is broadly expressed, apparently because of differential expression of homologous torsinB. Furthermore, certain neuronal subtypes are more severely affected by torsinA loss. Interestingly, these include striatal cholinergic interneurons that display abnormal responses to dopamine in several Tor1a animal models. There is also progress on understanding torsinA molecular cell biology. The structural basis of how ΔGAG inhibits torsinA ATPase activity is defined, although mutant torsinA^ΔGAG protein also displays some characteristics suggesting it contributes to dystonia by a gain-of-function mechanism. Furthermore, a consistent relationship is emerging between torsin dysfunction and membrane biology, including an evolutionarily conserved regulation of lipid metabolism. Considered together, these findings provide major advances toward understanding the molecular, cellular, and neurobiological pathologies of DYT1/TOR1A dystonia that can hopefully be exploited for new approaches to treat this disease. © 2016 International Parkinson and Movement Disorder Society.

Distribution and Coexistence of Myoclonus and Dystonia as Clinical Predictors of SGCE Mutation Status: A Pilot Study

Introduction

Myoclonus–dystonia (M–D) is a young onset movement disorder typically involving myoclonus and dystonia of the upper body. A proportion of the cases are caused by mutations to the autosomal dominantly inherited, maternally imprinted, epsilon-sarcoglycan gene (SGCE). Despite several sets of diagnostic criteria, identification of patients most likely to have an SGCE mutation remains difficult.

Methods

Forty consecutive patients meeting pre-existing diagnostic clinical criteria for M–D underwent a standardized clinical examination (20 SGCE mutation positive and 20 negative). Each video was reviewed and systematically scored by two assessors blinded to mutation status. In addition, the presence and coexistence of myoclonus and dystonia was recorded in four body regions (neck, arms, legs, and trunk) at rest and with action.

Results

Thirty-nine patients were included in the study (one case was excluded owing to insufficient video footage). Based on previously proposed diagnostic criteria, patients were subdivided into 24 “definite,” 5 “probable,” and 10 “possible” M–D. Motor symptom severity was higher in the SGCE mutation-negative group. Myoclonus and dystonia were most commonly observed in the neck and upper limbs of both groups. Truncal dystonia with action was significantly seen more in the mutation-negative group (p < 0.05). Coexistence of myoclonus and dystonia in the same body part with action was more commonly seen in the mutation-negative cohort (p < 0.05).

Conclusion

Truncal action dystonia and coexistence of myoclonus and dystonia in the same body part with action might suggest the presence of an alternative mutation in patients with M–D.

Dilated cardiomyopathy mutations in δ-sarcoglycan exert a dominant-negative effect on cardiac myocyte mechanical stability

Delta-sarcoglycan is a component of the sarcoglycan subcomplex within the dystrophin-glycoprotein complex located at the plasma membrane of muscle cells. While recessive mutations in δ-sarcoglycan cause limb girdle muscular dystrophy 2F, dominant mutations in δ-sarcoglycan have been linked to inherited dilated cardiomyopathy (DCM). The purpose of this study was to investigate functional cellular defects present in adult cardiac myocytes expressing mutant δ-sarcoglycans harboring the dominant inherited DCM mutations R71T or R97Q. This study demonstrates that DCM mutant δ-sarcoglycans can be stably expressed in adult rat cardiac myocytes and traffic similarly to wild-type δ-sarcoglycan to the plasma membrane, without perturbing assembly of the dystrophin-glycoprotein complex. However, expression of DCM mutant δ-sarcoglycan in adult rat cardiac myocytes is sufficient to alter cardiac myocyte plasma membrane stability in the presence of mechanical strain. Upon cyclical cell stretching, cardiac myocytes expressing mutant δ-sarcoglycan R97Q or R71T have increased cell-impermeant dye uptake and undergo contractures at greater frequencies than myocytes expressing normal δ-sarcoglycan. Additionally, the R71T mutation creates an ectopic N-linked glycosylation site that results in aberrant glycosylation of the extracellular domain of δ-sarcoglycan. Therefore, appropriate glycosylation of δ-sarcoglycan may also be necessary for proper δ-sarcoglycan function and overall dystrophin-glycoprotein complex function. These studies demonstrate that DCM mutations in δ-sarcoglycan can exert a dominant negative effect on dystrophin-glycoprotein complex function leading to myocardial mechanical instability that may underlie the pathogenesis of δ-sarcoglycan-associated DCM.

Sporadic and familial myoclonic dystonia: Report of three cases and review of literature

Myoclonic dystonia refers to a clinical syndrome characterized by rapid jerky movements along with dystonic posturing of the limbs. Clinically, it is characterized by sudden, brief, electric shock-like movements, mostly involving the upper extremities, shoulders, neck and trunk. Characteristically, the movements wane with consumption of small dose of alcohol in about 50% of cases. Additionally, dystonic contractions are observed in most of the patients in the affected body parts and some patients may exhibit cervical dystonia or graphospasm as well. It may manifest as an autosomal dominant condition or sometimes, as a sporadic entity, though there are doubts whether these represent cases with reduced penetrance. The condition is usually treated with a combination of an anticholinergic agent like, benztropine, pimozide and tetrabenazine. We report one sporadic case and one familial case where the father and the son are affected. The cases were collected from the Movement Disorders Clinic of Bangur Institute of Neurosciences, Kolkata, West Bengal in a period of ten months. Myoclonic dystonia is a rare condition and to the best of our knowledge, this series is the first one reported from our country. Videos of the patients are also provided with the article.

Phenotype of non-c.907_909delGAG mutations in TOR1A: DYT1 dystonia revisited

BACKGROUND

In addition to the most frequent TOR1A/DYT1 mutation (c.907_909delGAG), a growing number of TOR1A sequence variants are found in dystonia patients. For most, functional characterization has demonstrated pathogenicity at different levels, implying that TOR1A genetic testing should not be limited to screening for c.907_909delGAG.

METHODS

We tested 461 Serbian patients with isolated or combined dystonia for changes in the TOR1A gene and performed a systematic literature review of the clinical characteristics of patients carrying TOR1A mutations other than c.907_909delGAG.

RESULTS

One likely pathogenic TOR1A mutation (c.385G>A, p.Val129Ile) was detected in an adult-onset cervical dystonia patient. This change is in proximity to the previously reported p.Glu121Lys mutation and predicted to decrease the stability of TOR1A-encoded protein TorsinA.

CONCLUSIONS

Our patient and three other reported carriers of non-c.907_909delGAG-mutations within the first three exons of TOR1A showed similar phenotypes of adult-onset focal or segmental cervical dystonia. This observation raises the possibility of genotype-phenotype correlations in DYT1 and indicates that the clinical spectrum of this type of dystonia might be broader then previous classic descriptions.

Behavioral and electrophysiological characterization of Dyt1 heterozygous knockout mice

DYT1 dystonia is an inherited movement disorder caused by mutations in DYT1 (TOR1A), which codes for torsinA. Most of the patients have a trinucleotide deletion (ΔGAG) corresponding to a glutamic acid in the C-terminal region (torsinA(ΔE)). Dyt1 ΔGAG heterozygous knock-in (KI) mice, which mimic ΔGAG mutation in the endogenous gene, exhibit motor deficits and deceased frequency of spontaneous excitatory post-synaptic currents (sEPSCs) and normal theta-burst-induced long-term potentiation (LTP) in the hippocampal CA1 region. Although Dyt1 KI mice show decreased hippocampal torsinA levels, it is not clear whether the decreased torsinA level itself affects the synaptic plasticity or torsinA(ΔE) does it. To analyze the effect of partial torsinA loss on motor behaviors and synaptic transmission, Dyt1 heterozygous knock-out (KO) mice were examined as a model of a frame-shift DYT1 mutation in patients. Consistent with Dyt1 KI mice, Dyt1 heterozygous KO mice showed motor deficits in the beam-walking test. Dyt1 heterozygous KO mice showed decreased hippocampal torsinA levels lower than those in Dyt1 KI mice. Reduced sEPSCs and normal miniature excitatory post-synaptic currents (mEPSCs) were also observed in the acute hippocampal brain slices from Dyt1 heterozygous KO mice, suggesting that the partial loss of torsinA function in Dyt1 KI mice causes action potential-dependent neurotransmitter release deficits. On the other hand, Dyt1 heterozygous KO mice showed enhanced hippocampal LTP, normal input-output relations and paired pulse ratios in the extracellular field recordings. The results suggest that maintaining an appropriate torsinA level is important to sustain normal motor performance, synaptic transmission and plasticity. Developing therapeutics to restore a normal torsinA level may help to prevent and treat the symptoms in DYT1 dystonia.

Combined occurrence of a novel TOR1A and a THAP1 mutation in primary dystonia

BACKGROUND

The ΔGAG deletion of the TOR1A gene (DYT1) is responsible for DYT1 dystonia. However, no other TOR1A mutation has been reported in the Chinese population.

METHODS

Two hundred one dystonia patients without the ΔGAG deletion were screened for other mutations in TOR1A. Gene function changes were analyzed by subcellular distribution and luciferase reporter assay.

RESULTS

A novel TOR1A mutation (c.581A>T, p.Asp194Val) was found in a patient with early-onset segmental dystonia harboring a THAP1 mutation (c.539T>C, p.Leu180Ser). Overexpression of mutant TOR1A Asp194Val protein induces inclusion formation in SK-N-AS cell lines, and the repressive activity of the mutant THAP1 Leu180Ser protein on TOR1A gene expression is decreased compared with wild-type THAP1.

CONCLUSIONS

This is the first report about a dystonia patient harboring two distinct dystonia gene mutations. Functional analysis indicated a potential additive effect of these two mutations, which might provoke the occurrence of dystonic symptoms in this patient.

Bilateral globus pallidus interna deep-brain stimulation in a patient with myoclonus-dystonia: a case report

OBJECTIVE

Myoclonus-dystonia is a movement disorder characterized by childhood onset of myoclonus and dystonia. We report a case of the epsilon-sarcoglycan mutation-negative myoclonus-dystonia patient who underwent bilateral globus pallidus interna deep-brain stimulation with subsequent improvement of both myoclonus and dystonia.

CASE REPORT

A 37-year-old woman with myoclonic jerks and dystonia affecting predominantly the lower limbs was treated with chronic bilateral globus pallidus interna deep-brain stimulation.

RESULTS

The movement subscore of the Burke-Fahns-Marsden Dystonia Rating Scale was 38 before surgery and improved to 7 after 3 years. The disability subscore of the Burke-Fahns-Marsden Dystonia Rating Scale improved from 7 to 2. The Unified Myoclonus Rating Scale also decreased significantly from 93 to 39. No hardware- or stimulation-related complications occurred during follow-up.

CONCLUSION

This report suggests that patients with myoclonus-dystonia may significantly benefit from bilateral globus pallidus interna deep-brain stimulation. Larger studies of this patient population are needed to confirm the optimal target.

Pre-synaptic release deficits in a DYT1 dystonia mouse model

DYT1 early-onset generalized torsion dystonia (DYT1 dystonia) is an inherited movement disorder caused by mutations in one allele of DYT1 (TOR1A), coding for torsinA. The most common mutation is a trinucleotide deletion (ΔGAG), which causes a deletion of a glutamic acid residue (ΔE) in the C-terminal region of torsinA. Although recent studies using cultured cells suggest that torsinA contributes to protein processing in the secretory pathway, endocytosis, and the stability of synaptic proteins, the nature of how this mutation affects synaptic transmission remains unclear. We previously reported that theta-burst-induced long-term potentiation (LTP) in the CA1 region of the hippocampal slice is not altered in Dyt1 ΔGAG heterozygous knock-in (KI) mice. Here, we examined short-term synaptic plasticity and synaptic transmission in the hippocampal slices. Field recordings in the hippocampal Schaffer collaterals (SC) pathway revealed significantly enhanced paired pulse ratios (PPRs) in Dyt1 ΔGAG heterozygous KI mice, suggesting an impaired synaptic vesicle release. Whole-cell recordings from the CA1 neurons showed that Dyt1 ΔGAG heterozygous KI mice exhibited normal miniature excitatory post-synaptic currents (mEPSC), suggesting that action-potential independent spontaneous pre-synaptic release was normal. On the other hand, there was a significant decrease in the frequency, but not amplitude or kinetics, of spontaneous excitatory post-synaptic currents (sEPSC) in Dyt1 ΔGAG heterozygous KI mice, suggesting that the action-potential dependent pre-synaptic release was impaired. Moreover, hippocampal torsinA was significantly reduced in Dyt1 ΔGAG heterozygous KI mice. Although the hippocampal slice model may not represent the neurons directly associated with dystonic symptoms, impaired release of neurotransmitters caused by partial dysfunction of torsinA in other brain regions may contribute to the pathophysiology of DYT1 dystonia.

Hereditäre Dystonien

Dystonien sind eine klinisch und ätiologisch heterogene Gruppe von Bewegungsstörungen. Charakteristisch sind unwillkürliche Muskelkontraktionen, die zu drehenden, schraubenden und repetitiven Bewegungen führen und sehr schmerzhaft sein können. Die Dystonie kann dabei das einzige Symptom sein („isolierte Dystonie“) oder von anderen Symptomen begleitet werden („kombinierte Dystonie“), sie kann aber auch eine Manifestation jedweder das Zentralnervensystem betreffenden Erkrankung sein, die das motorische System in Mitleidenschaft zieht (z. B. neurodegenerative, ischämische, traumatische Prozesse). In den letzten 20 Jahren hat die Entwicklung neuer molekulargenetischer Technologien zur Entdeckung neuer Gene geführt, die vielen Dystoniesubtypen zugrunde liegen, und eine verbesserte Klassifizierung sowie einen tieferen Einblick in die Pathophysiologie ermöglicht. Es wird eine aktuelle Übersicht über die genetisch determinierten Dystonien mit Fokus auf den sog. isolierten bzw. kombinierten Formen vorgelegt. Die Zusammenstellung phänotypischer Charakteristika zu spezifischen genetischen Veränderungen soll dem Kliniker ermöglichen, anhand konkreter klinischer Manifestationen eine entsprechende molekulargenetische Abklärung in die Wege zu leiten.

The genetics of dystonias

Dystonia has been defined as a syndrome of involuntary, sustained muscle contractions affecting one or more sites of the body, frequently causing twisting and repetitive movements or abnormal postures. Dystonia is also a clinical sign that can be the presenting or prominent manifestation of many neurodegenerative and neurometabolic disorders. Etiological categories include primary dystonia, secondary dystonia, heredodegenerative diseases with dystonia, and dystonia plus. Primary dystonia includes syndromes in which dystonia is the sole phenotypic manifestation with the exception that tremor can be present as well. Most primary dystonia begins in adults, and approximately 10% of probands report one or more affected family members. Many cases of childhood- and adolescent-onset dystonia are due to mutations in TOR1A and THAP1. Mutations in THAP1 and CIZ1 have been associated with sporadic and familial adult-onset dystonia. Although significant recent progress had been made in defining the genetic basis for most of the dystonia-plus and heredodegenerative diseases with dystonia, a major gap remains in understanding the genetic etiologies for most cases of adult-onset primary dystonia. Common themes in the cellular biology of dystonia include G1/S cell cycle control, monoaminergic neurotransmission, mitochondrial dysfunction, and the neuronal stress response.

Improved motor performance in Dyt1 ΔGAG heterozygous knock-in mice by cerebellar Purkinje-cell specific Dyt1 conditional knocking-out

Early-onset generalized torsion dystonia (dystonia 1) is an inherited movement disorder caused by mutations in DYT1 (TOR1A), which codes for torsinA. Most patients have a 3-base pair deletion (ΔGAG) in one allele of DYT1, corresponding to a loss of a glutamic acid residue (ΔE) in the C-terminal region of the protein. Functional alterations in basal ganglia circuits and the cerebellum have been reported in dystonia. Pharmacological manipulations or mutations in genes that result in functional alterations of the cerebellum have been reported to have dystonic symptoms and have been used as phenotypic rodent models. Additionally, structural lesions in the abnormal cerebellar circuits, such as cerebellectomy, have therapeutic effects in these models. A previous study has shown that the Dyt1 ΔGAG heterozygous knock-in (KI) mice exhibit motor deficits in the beam-walking test. Both Dyt1 ΔGAG heterozygous knock-in (KI) and Dyt1 Purkinje cell-specific knockout (Dyt1 pKO) mice exhibit dendritic alterations of cerebellar Purkinje cells. Here, Dyt1 pKO mice exhibited significantly less slip numbers in the beam-walking test, suggesting better motor performance than control littermates, and normal gait. Furthermore, Dyt1 ΔGAG KI/Dyt1 pKO double mutant mice exhibited significantly lower numbers of slips than Dyt1 ΔGAG heterozygous KI mice, suggesting Purkinje-cell specific knockout of Dyt1 wild-type (WT) allele in Dyt1 ΔGAG heterozygous KI mice rescued the motor deficits. The results suggest that molecular lesions of torsinA in Purkinje cells by gene therapy or intervening in the signaling pathway downstream of the cerebellar Purkinje cells may rescue motor symptoms in dystonia 1.

A gain-of-glycosylation mutation associated with myoclonus-dystonia syndrome affects trafficking and processing of mouse ε-sarcoglycan in the late secretory pathway

Missense mutations in the SGCE gene encoding ε-sarcoglycan account for approximately 15% of SGCE-positive cases of myoclonus-dystonia syndrome (MDS) in humans. In this study, we show that while the majority of MDS-associated missense mutants modeled with a murine ε-sarcoglycan cDNA are substrates for endoplasmic reticulum-associated degradation, one mutant, M68T (analogous to human c.275T>C, p.M92T), located in the Ig-like domain of ε-sarcoglycan, results in a gain-of-glycosylation mutation producing a protein that is targeted to the plasma membrane, albeit at reduced levels compared to wild-type ε-sarcoglycan. Removal of the ectopic N-linked glycan failed to restore efficient plasma membrane targeting of M68T demonstrating that the substitution rather than the glycan was responsible for the trafficking defect of this mutant. M68T also colocalized with CD63-positive vesicles in the endosomal-lysosomal system and was found to be more susceptible to lysosomal proteolysis than wild-type ε-sarcoglycan. Finally, we demonstrate impaired ectodomain shedding of M68T, a process that occurs physiologically for ε-sarcoglycan resulting in the lysosomal trafficking of the intracellular C-terminal domain of the protein. Our findings show that functional analysis of rare missense mutations can provide a mechanistic insight into the pathogenesis of MDS and the physiological role of ε-sarcoglycan.

Myoclonus-dystonia syndrome

Myoclonus dystonia syndrome (MDS) refers to a group of heterogeneous nondegenerative clinical conditions characterized by the association of myoclonus and dystonia as the only or prominent symptom. The "core" of MDS is represented by inherited myoclonus-dystonia (M-D), a disorder with autosomal-dominant inheritance and reduced penetrance, beginning in early childhood with a relatively benign course, with myoclonus as the most predominant and disabling symptom. Alcohol responsiveness and psychiatric symptoms are characteristic features. Mutations in the epsilon-sarcoglycan gene (SGCE, DYT11) represent the major genetic cause, but M-D is genetically heterogeneous. In a variable proportion of M-D patients no mutation is found, and at least one other locus (DYT15) has been linked to the disease. Patients with primary dystonia, with or without the DYT1 mutation, may show irregular and arrhythmic jerky movements associated with dystonia. Usually dystonia is the prominent symptom and the myoclonic jerk involves the same body region; this condition, currently defined as "myoclonic dystonia," is included in the spectrum of MDS. Dopa-responsive dystonia due to mutation in the GTP-CH gene and vitamin E deficiency can present with a phenotype of dystonia and myoclonus in combination; both conditions should be considered in the diagnostic approach to patients since they are potentially treatable.

Earlier onset of motor deficits in mice with double mutations in Dyt1 and Sgce

DYT1 early-onset generalized torsion dystonia is an inherited movement disorder caused by mutations in DYT1 coding for torsinA with ∼30% penetrance. Most of the DYT1 dystonia patients exhibit symptoms during childhood and adolescence. On the other hand, DYT1 mutation carriers without symptoms during these periods mostly do not exhibit symptoms later in their life. Little is known about what controls the timing of the onset, a critical issue for DYT1 mutation carriers. DYT11 myoclonus-dystonia is caused by mutations in SGCE coding for ε-sarcoglycan. Two dystonia patients from a single family with double mutations in DYT1 and SGCE exhibited more severe symptoms. A recent study suggested that torsinA contributes to the quality control of ε-sarcoglycan. Here, we derived mice carrying mutations in both Dyt1 and Sgce and found that these double mutant mice showed earlier onset of motor deficits in beam-walking test. A novel monoclonal antibody against mouse ε-sarcoglycan was developed by using Sgce knock-out mice to avoid the immune tolerance. Western blot analysis suggested that functional deficits of torsinA and ε-sarcoglycan may independently cause motor deficits. Examining additional mutations in other dystonia genes may be beneficial to predict the onset in DYT1 mutation carriers.

TorsinA and DYT1 dystonia: a synaptopathy?

DYT1 dystonia is an autosomal dominant movement disorder, characterized by early onset of involuntary sustained muscle contractions. It is caused by a 3-bp deletion in the DYT1 gene, which results in the deletion of a single glutamate residue in the C-terminus of the protein TA (torsinA). TA is a member of the AAA+ (ATPase associated with various cellular activities) family of chaperones with multiple functions in the cell. There is no evidence of neurodegeneration in DYT1 dystonia, which suggests that mutant TA leads to functional neuronal abnormalities, leading to dystonic movements. In recent years, different functional roles have been attributed to TA, including being a component of the cytoskeleton and the NE (nuclear envelope), and involvement in the secretory pathway and SV (synaptic vesicle) machinery. The aim of the present review is to summarize these findings and the different models proposed, which have contributed to our current understanding of the function of TA, and also to discuss the evidence implicating TA in SV function.

Is psychopathology part of the phenotypic spectrum of myoclonus-dystonia?: a study of a large Dutch M-D family

BACKGROUND

Myoclonus-dystonia (M-D) is a movement disorder frequently caused by mutations in the epsilon-sarcoglycan gene (SGCE, DYT11). In several M-D families, psychiatric symptoms accompanying the motor symptoms have been reported, but a shared genetic etiology remains unclear.

OBJECTIVE

To assess neuropsychologic functioning and psychopathology in DYT11 mutation carriers (MC) and their family members using standardized neuropsychologic and psychiatric measures.

METHODS

Cognitive and behavioural characteristics of 27 DYT11 MC (14 symptomatic and 13 asymptomatic) and 42 control subjects from 1 large Dutch M-D family were studied. Neuropsychologic tests encompassed memory, language, mental speed, concentration, visuospatial function, and executive functions. Psychiatric assessment addressed qualitative (according to Diagnostic and Statistical Manual-IV criteria) as well as quantitative measures of depression, anxiety, panic attacks, and obsessive-compulsive disorder (OCD), using selfadministered and interview-based scales.

RESULTS

No differences were observed on tests of cognitive functioning between DYT11 MC and controls. The frequency of Diagnostic and Statistical Manual-IV diagnoses was higher in the symptomatic DYT11 MC than in controls. The symptomatic DYT11 MC showed more depressive and anxiety symptoms, including panic attacks but no increase of OCD compared with controls. No differences were found between asymptomatic DYT11 MC and controls on any of the psychopathologic tests.

CONCLUSIONS

Neither cognitive dysfunction nor OCD seems to be associated with the DYT11 phenotype in this large Dutch pedigree. Depressive and anxiety symptoms are increased in symptomatic, but not in asymptomatic DYT11 MC. Future research has to be carried out to determine whether the psychiatric symptoms are part of or secondary to the DYT11 phenotype.

Myoclonus-dystonia: an update

Our knowledge of the clinical, neurophysiological, and genetic aspects of myoclonus-dystonia (M-D) has improved markedly in the recent years. Basic research has provided new insights into the complex dysfunctions involved in the pathogenesis of M-D. On the basis of a comprehensive literature search, this review summarizes current knowledge on M-D, with a focus on recent findings. We also propose modified diagnostic criteria and recommendations for clinical management.

Printor, a novel torsinA-interacting protein implicated in dystonia pathogenesis

Early onset generalized dystonia (DYT1) is an autosomal dominant neurological disorder caused by deletion of a single glutamate residue (torsinA DeltaE) in the C-terminal region of the AAA(+) (ATPases associated with a variety of cellular activities) protein torsinA. The pathogenic mechanism by which torsinA DeltaE mutation leads to dystonia remains unknown. Here we report the identification and characterization of a 628-amino acid novel protein, printor, that interacts with torsinA. Printor co-distributes with torsinA in multiple brain regions and co-localizes with torsinA in the endoplasmic reticulum. Interestingly, printor selectively binds to the ATP-free form but not to the ATP-bound form of torsinA, supporting a role for printor as a cofactor rather than a substrate of torsinA. The interaction of printor with torsinA is completely abolished by the dystonia-associated torsinA DeltaE mutation. Our findings suggest that printor is a new component of the DYT1 pathogenic pathway and provide a potential molecular target for therapeutic intervention in dystonia.

TorsinA and dystonia: from nuclear envelope to synapse

A GAG deletion in the DYT1 gene is responsible for the autosomal dominant movement disorder, early onset primary torsion dystonia, which is characterised by involuntary sustained muscle contractions and abnormal posturing of the limbs. The mutation leads to deletion of a single glutamate residue in the C-terminus of the protein torsinA, a member of the AAA+ ATPase family of proteins with multiple functions. Since no evidence of neurodegeneration has been found in DYT1 patients, the dystonic phenotype is likely to be the result of neuronal functional defect(s), the nature of which is only partially understood. Biochemical, structural and cell biological studies have been performed in order to characterise torsinA. These studies, together with the generation of several animal models, have contributed to identify cellular compartments and pathways, including the cytoskeleton and the nuclear envelope, the secretory pathway and the synaptic vesicle machinery where torsinA function may be crucial. However, the role of torsinA and the correlation between the dysfunction caused by the mutation and the dystonic phenotype remain unclear. This review provides an overview of the findings of the last ten years of research on torsinA, a critical evaluation of the different models proposed and insights towards future avenues of research.

Myoclonus and tremor response to thalamic deep brain stimulation parameters in a patient with inherited myoclonus-dystonia syndrome

We present a 74-year-old woman with inherited myoclonus-dystonia, with predominant myoclonus and a novel mutation in the epsilon-sarcoglycan gene. The patient reports a life-long history of rapid, jerking movements, most severe in the upper extremities as well as a postural and action tremor. Bilateral deep brain stimulation (DBS) of the ventral intermediate nucleus of the thalamus was performed, and the patient demonstrated moderate clinical improvement in myoclonus. We studied the effects on myoclonus and tremor of varying DBS frequency and amplitude. The frequency tuning curve for myoclonus was similar to that of tremor, suggesting similar mechanisms by which DBS alleviates both disorders.

High-throughput mutational analysis of TOR1A in primary dystonia

BACKGROUND

Although the c.904_906delGAG mutation in Exon 5 of TOR1A typically manifests as early-onset generalized dystonia, DYT1 dystonia is genetically and clinically heterogeneous. Recently, another Exon 5 mutation (c.863G>A) has been associated with early-onset generalized dystonia and some DeltaGAG mutation carriers present with late-onset focal dystonia. The aim of this study was to identify TOR1A Exon 5 mutations in a large cohort of subjects with mainly non-generalized primary dystonia.

METHODS

High resolution melting (HRM) was used to examine the entire TOR1A Exon 5 coding sequence in 1014 subjects with primary dystonia (422 spasmodic dysphonia, 285 cervical dystonia, 67 blepharospasm, 41 writer's cramp, 16 oromandibular dystonia, 38 other primary focal dystonia, 112 segmental dystonia, 16 multifocal dystonia, and 17 generalized dystonia) and 250 controls (150 neurologically normal and 100 with other movement disorders). Diagnostic sensitivity and specificity were evaluated in an additional 8 subjects with known DeltaGAG DYT1 dystonia and 88 subjects with DeltaGAG-negative dystonia.

RESULTS

HRM of TOR1A Exon 5 showed high (100%) diagnostic sensitivity and specificity. HRM was rapid and economical. HRM reliably differentiated the TOR1A DeltaGAG and c.863G>A mutations. Melting curves were normal in 250/250 controls and 1012/1014 subjects with primary dystonia. The two subjects with shifted melting curves were found to harbor the classic DeltaGAG deletion: 1) a non-Jewish Caucasian female with childhood-onset multifocal dystonia and 2) an Ashkenazi Jewish female with adolescent-onset spasmodic dysphonia.

CONCLUSION

First, HRM is an inexpensive, diagnostically sensitive and specific, high-throughput method for mutation discovery. Second, Exon 5 mutations in TOR1A are rarely associated with non-generalized primary dystonia.

A novel mutation of the epsilon-sarcoglycan gene in a Chinese family with myoclonus-dystonia syndrome

In a Chinese myoclonus-dystonia syndrome (MDS) family presented with a phenotype including a typical MDS, cervical dystonia, and writer's cramp, genetic analyses revealed a novel 662 + 1insG heterozygous mutation in exon 5 in the epsilon-sarcoglycan (SGCE) gene, leading to a frameshift with a down stream stop codon. Low SGCE mRNA levels were detected in the mutation carriers by real-time PCR, suggesting that the nonsense mutation might interfere with the stability of SGCE mRNA. This is the first report on Chinese with a SGCE mutation leading to MDS. Our data support the fact that same mutation of SGCE gene can lead to a varied phenotype, even in the same family.

Dystonia-associated mutations cause premature degradation of torsinA protein and cell-type-specific mislocalization to the nuclear envelope

An in-frame 3 bp deletion in the torsinA gene resulting in the loss of a glutamate residue at position 302 or 303 (torsinA DeltaE) is the major cause for early-onset torsion dystonia (DYT1). In addition, an 18 bp deletion in the torsinA gene resulting in the loss of residues 323-328 (torsinA Delta323-8) has also been associated with dystonia. Here we report that torsinA DeltaE and torsinA Delta323-8 mutations cause neuronal cell-type-specific mislocalization of torsinA protein to the nuclear envelope without affecting torsinA oligomerization. Furthermore, both dystonia-associated mutations destabilize torsinA protein in dopaminergic cells. We find that wild-type torsinA protein is degraded primarily through the macroautophagy-lysosome pathway. In contrast, torsinA DeltaE and torsinA Delta323-8 mutant proteins are degraded by both the proteasome and macroautophagy-lysosome pathways. Our findings suggest that torsinA mutation-induced premature degradation may contribute to the pathogenesis of dystonia via a loss-of-function mechanism and underscore the importance of both the proteasome and macroautophagy in the clearance of dystonia-associated torsinA mutant proteins.

Myoclonus-dystonia syndrome: clinical presentation, disease course, and genetic features in 11 families

Myoclonus-dystonia syndrome (MDS) is an inherited movement disorder with clinical and genetic heterogeneity. The epsilon sarcoglycan (SGCE) gene is an important cause of MDS. We report the results of a clinical and genetic study of 20 patients from 11 families. We disclosed six novel and two previously described mutations in nine families. The majority of patients had a phenotype of myoclonus and dystonia in combination, but clinical findings considered atypical, such a very early onset, distal myoclonus, and legs involvement, were detected in a significant proportion of cases. The disease course was variable, from progression to spontaneous remission of the motor symptoms. There were no obvious differences between mutation-positive and -negative cases.

The pathophysiological basis of dystonias

Dystonias comprise a group of movement disorders that are characterized by involuntary movements and postures. Insight into the nature of neuronal dysfunction has been provided by the identification of genes responsible for primary dystonias, the characterization of animal models and functional evaluations and in vivo brain imaging of patients with dystonia. The data suggest that alterations in neuronal development and communication within the brain create a susceptible substratum for dystonia. Although there is no overt neurodegeneration in most forms of dystonia, there are functional and microstructural brain alterations. Dystonia offers a window into the mechanisms whereby subtle changes in neuronal function, particularly in sensorimotor circuits that are associated with motor learning and memory, can corrupt normal coordination and lead to a disabling motor disorder.

Autosomal dominant myoclonus-dystonia and Tourette syndrome in a family without linkage to theSGCEgene

The objective of this study was to report clinical details and results of genetic testing for mutations in the epsilon-sarcoglycan (SGCE) gene, the Slit and Trk-like 1 (SLITRK1) gene and for linkage to the DYT15, DYT1, and DRD2 gene loci in a family with autosomal dominant myoclonus-dystonia (M-D) and Gilles de la Tourette syndrome (GTS). Fourteen family members, from three generations, underwent a detailed clinical assessment and donated DNA samples. The SGCE and the SLITRK1 gene were sequenced and investigated by gene dosage analysis in selected family members. Linkage to the SGCE, DYT15, DYT1, DRD2, and SLITRK1 loci was also tested.

RESULTS

We included three healthy and 11 affected family members with M-D (n = 3), dystonia alone (n = 2), GTS (n = 1), tics (n = 1) or a combination of these with obsessive compulsive disorder (OCD) (M-D + OCD: n = 2; dystonia+OCD: n = 1; M-D + GTS + OCD: n = 1). There was no linkage to the SGCE, DYT15, DYT1 or DRD2 loci. No changes were found in the SLITRK1 gene. The presence of both M-D and GTS in one family, in which all known M-D loci and a recently discovered GTS locus were excluded, suggests a novel susceptibility gene for both M-D and GTS.

Refinement of the DYT15 locus in myoclonus dystonia

Inherited myoclonus dystonia (MD) is an autosomal dominant disorder in which we previously mapped a novel locus to chromosome18p11 (OMIM number: 607488). Since no further informative STS markers were found within the flanking shared regions, we utilized single nucleotide polymorphisms (SNP) for fine-mapping. All known or predicted genes within this region were directly sequenced. We identified three recombinant SNPs in the distal region but none from the proximal region. Our previous linked region has now been reduced to 3.18 Mb but direct sequencing of all seven known and four predicted genes with EST support did not identify any mutations..

Obsessive-compulsive disorder is not a clinical manifestation of the DYT1 dystonia gene

Prior studies suggest that obsessive-compulsive symptoms (OCS) and disorder (OCD) are co-morbid with dystonia. We tested if OCS/OCD is a clinical manifestation of the DYT1 dystonia mutation by interviewing members of families with an identified DYT1 mutation, and classifying by manifesting carriers (MC), non-manifesting carriers (NMC), and non-carriers (NC). We found that OCD/OCS are not increased in DYT1 mutation carriers compared with NC, nor is OCD associated with manifesting DYT1 dystonia.

SGCE missense mutations that cause myoclonus-dystonia syndrome impair epsilon-sarcoglycan trafficking to the plasma membrane: modulation by ubiquitination and torsinA

Myoclonus-dystonia syndrome (MDS) is a genetically heterogeneous disorder characterized by myoclonic jerks often seen in combination with dystonia and psychiatric co-morbidities and epilepsy. Mutations in the gene encoding epsilon-sarcoglycan (SGCE) have been found in some patients with MDS. SGCE is a maternally imprinted gene with the disease being inherited in an autosomal dominant pattern with reduced penetrance upon maternal transmission. In the central nervous system, epsilon-sarcoglycan is widely expressed in neurons of the cerebral cortex, basal ganglia, hippocampus, cerebellum and the olfactory bulb. epsilon-Sarcoglycan is located at the plasma membrane in neurons, muscle and transfected cells. To determine the effect of MDS-associated mutations on the function of epsilon-sarcoglycan we examined the biosynthesis and trafficking of wild-type and mutant proteins in cultured cells. In contrast to the wild-type protein, disease-associated epsilon-sarcoglycan missense mutations (H36P, H36R and L172R) produce proteins that are undetectable at the cell surface and are retained intracellularly. These mutant proteins become polyubiquitinated and are rapidly degraded by the proteasome. Furthermore, torsinA, that is mutated in DYT1 dystonia, a rare type of primary dystonia, binds to and promotes the degradation of epsilon-sarcoglycan mutants when both proteins are co-expressed. These data demonstrate that some MDS-associated mutations in SGCE impair trafficking of the mutant protein to the plasma membrane and suggest a role for torsinA and the ubiquitin proteasome system in the recognition and processing of misfolded epsilon-sarcoglycan.

Some genetic and biochemical aspects of myoclonus

Can a gene defect be responsible for the occurrence in an individual, at a particular age, of such a muscle twitch followed by relaxation called: "myoclonus" and defined as sudden, brief, shock-like movements? Genetic defects could indeed determine a subsequent cascade of molecular events (caused by abnormal encoded proteins) that would produce new aberrant cellular relationships in a particular area of the CNS leading to re-built "myoclonogenic" neuronal networks. This can be illustrated reviewing some inherited neurological entities that are characterized by a predominant myoclonic picture and among which a clear gene defect has been identified. In the second part of this chapter, we will also propose a new point of view on how some structural genes could, under certain conditions, when altered, produced idiopathic generalized epilepsy with myoclonic jerks, taking juvenile myoclonic epilepsy (JME) and the myoclonin (EFHC-1) gene as examples.

Intrafamilial phenotypic and genetic heterogeneity of dystonia

Most cases of early-onset primary torsion dystonia are caused by the same 3-bp (GAG) deletion in the DYT1 gene. We describe a large Serbian family with significant intrafamilial variability of the DYT1 phenotype, from asymptomatic carrier status to late-onset focal, and generalized jerky dystonia. Seven mutation carriers (six proven by direct analysis and one by inferred haplotype) were identified, but only two of them were affected by dystonia (penetrance reduced to 29%). In addition, three GAG-deletion-negative family members also developed dystonia (two multifocal dystonia and one torticollis), suggesting that their involuntary movements are due to some other etiological factor(s) (i.e., another dystonia gene), or may be psychogenic.

Myoclonus, Motor Deficits, Alterations in Emotional Responses and Monoamine Metabolism in ε-Sarcoglycan Deficient Mice

Mutations of epsilon-sarcoglycan gene (SGCE) have been implicated in myoclonus-dystonia (M-D), a movement disorder. To determine the pathophysiology of M-D, we produced Sgce knockout mice and found that the knockout mice exhibited myoclonus, motor impairments, hyperactivity, anxiety, depression, significantly higher levels of striatal dopamine and its metabolites, and an inverse correlation between the dopamine and serotonin metabolites. The results suggest that the diverse symptoms associated with M-D are indeed resulted from a single SGCE gene mutation that leads to alterations of dopaminergic and serotonergic systems. Therefore, antipsychotic agents and serotonin reuptake inhibitors may offer potential benefits for M-D patients.

A mutation of beta -actin that alters depolymerization dynamics is associated with autosomal dominant developmental malformations, deafness, and dystonia

Actin, one of the major filamentous cytoskeletal molecules, is involved in a variety of cellular functions. Whereas an association between muscle actin mutations and skeletal and cardiac myopathies has been well documented, reports of human disease arising from mutations of nonmuscle actin genes have been rare. We have identified a missense point mutation in the gene coding for beta -actin that results in an arginine-to-tryptophan substitution at position 183. The disease phenotype includes developmental midline malformations, sensory hearing loss, and a delayed-onset generalized dystonia syndrome in monozygotic twins. Cellular studies of a lymphoblastoid cell line obtained from an affected patient demonstrated morphological abnormalities of the actin cytoskeleton and altered actin depolymerization dynamics in response to latrunculin A, an actin monomer-sequestering drug. Resistance to latrunculin A was also observed in NIH 3T3 cells expressing the mutant actin. These findings suggest that mutations in nonmuscle actins may be associated with a broad spectrum of developmental malformations and/or neurological abnormalities such as dystonia.

Movement disorders and alcohol misuse

Many movement disorders, including tics, chorea, tremor, myoclonus and parkinsonism, may result from substance abuse. However, alcohol in particular is associated in a more complex manner with two specific movement disorders, essential tremor (ET) and myoclonus-dystonia (M-D). In this review we discuss the comorbidity of alcohol abuse in both ET and M-D, the ameliorative effects of alcohol in both diseases, and review the data evaluating alcohol abuse secondary to self-medication. We also discuss shared pathophysiologic mechanisms in the understanding of both of these disorders, as the elucidation of the mechanisms by which alcohol exerts its effects may lead to novel therapeutic approaches.