Loss-of-function mutations in SGCE found in Japanese patients with myoclonus-dystonia.

SGCE myoclonus-dystonia is a monogenic form of dystonia with an autosomal dominant mode of inheritance that co-occurs with a myoclonic jerk. In this study, we present 12 Japanese patients from nine families with this disease. Targeted next-generation sequencing covering major causative genes for monogenic dystonias identified nine distinct SGCE mutations from each of the families: three nonsense, two frameshift, two missense, one in-frame 15 bp deletion, and one splice donor site mutations, of which four were previously unreported. One missense mutation (c.662G>T, p.Gly221Val) was located at the 3' end of exon 5 (NM_001099400), which was predicted to cause aberrant splicing according to in silico predictions. Minigene assays performed together with the c.825+1G>C mutation demonstrated complete skipping of exon 5 and 6, respectively, in their transcripts. The other missense (c.1345A>G, p.Met449Val) and 15 bp deletion (c.168_182del, p.Phe58_Leu62del) mutations showed a significant reduction in cell membrane expression via HiBiT bioluminescence assay. Therefore, we concluded that all the detected mutations were disease-causing. Unlike the other detected mutations, p.Met449Val affects only isoform 3 (NP_001092870 encoded by NM_001099400) among the variously known isoforms of SGCE. This isoform is brain-specific and is mostly expressed in the cerebellum, which supports recent studies showing that cerebellar dysfunction is a key element in the pathophysiology of SGCE myoclonus-dystonia.

Perampanel as a novel treatment for subcortical myoclonus in myoclonus-dystonia syndrome.

BACKGROUND: Myoclonus-dystonia (MD) is a syndrome characterized by subcortical myoclonus and milder dystonia. The main causative gene is the epsilon sarcoglycan gene (SGCE), but other genes may be involved. Response to medications is variable, with poor tolerability limiting their use. CASE PRESENTATION: We present the case of a patient with severe myoclonic jerks and mild dystonia since childhood. At first neurological visit at the age of 46 years old, she presented brief myoclonic jerks predominating in the upper limbs and neck, mild at rest and elicited by action, posture and tactile stimulus. Myoclonus was accompanied by mild neck and right arm dystonia. Neurophysiological tests suggested subcortical origin of myoclonus, brain MRI was unremarkable. Myoclonus-dystonia was diagnosed, and genetic testing identified a novel mutation in SGCE gene (c.907delC) in heterozygosis. Over time she assumed a large variety of anti-epileptics without beneficial effect on myoclonus and low tolerability. Add-on treatment with Perampanel was started, with a beneficial effect. No adverse events were reported. Perampanel is the first selective non-competitive AMPA receptor antagonist approved in add-on for focal and generalized tonic-clonic seizures. To our knowledge, this is the first trial of Perampanel in MD. CONCLUSIONS: We presented the case of a patient with MD due to SGCE mutation who was treated with Perampanel with beneficial effects. We propose Perampanel as a novel treatment for myoclonus in MD.

Bilateral Pallidal Stimulation in a Family With Myoclonus Dystonia Syndrome Due to a Mutation in the Sarcoglycan Gene.

OBJECTIVES: The study aimed to present a family with myoclonus dystonia (M-D) syndrome due to a mutation in the epsilon sarcoglycan gene (SGCE). Three members of the family suffered from treatment-refractory severe myoclonic jerks of the neck, trunk, and upper extremities. The mild dystonic symptoms recognized as cervical dystonia or truncal dystonia affected all individuals. The efficacy of pharmacotherapy, including anticholinergic, dopaminergic, and serotoninergic drugs, has failed. One individual developed an alcohol dependency and suffered from alcoholic epilepsy. MATERIALS AND METHODS: The patients were referred for stereotactic surgery. All individuals underwent bilateral implantation of deep brain stimulation (DBS) leads into the posteroventrolateral segment of the globus pallidus internus (GPi). Surgeries were uneventful. The formal preoperative objective assessment included the Unified Myoclonus Rating Scale (UMRS) and the Burke-Fahn-Marsden Dystonia Rating Scale (BFMDRS). The postoperative UMRS and BFMDRS assessments were done only under continuous stimulation at 3, 6, and 12 months after the surgery and at the last available follow-up ranging from 6 to 15 months (mean, 10 months follow-up). RESULTS: At the last follow-up visit, the rest and action parts of UMRS were improved by 93.3% and 88.2%, respectively, when compared to the baseline scores. The motor and disability scales of BFMDRS were improved by 77% and 43% at the last follow-up visit compared to the baseline BFMDRS scores. There were no hardware or stimulation-induced complications over the follow-up period. Positive social adjustment allowed two patients to regain jobs and one patient continued his education and hobbies. CONCLUSION: Our experience gathered in three individuals in the family with a mutation in SGCE indicates that bilateral GPi DBS can be an effective and safe treatment for disabling pharmacological resistant, intractable M-D syndrome.

Combined dystonias: clinical and genetic updates.

The genetic combined dystonias are a clinically and genetically heterogeneous group of neurologic disorders defined by the overlap of dystonia and other movement disorders such as parkinsonism or myoclonus. The number of genes associated with combined dystonia syndromes has been increasing due to the wider recognition of clinical features and broader use of genetic testing. Nevertheless, these diseases are still rare and represent only a small subgroup among all dystonias. Dopa-responsive dystonia (DYT/PARK-GCH1), rapid-onset dystonia-parkinsonism (DYT/PARK-ATP1A3), X-linked dystonia-parkinsonism (XDP, DYT/PARK-TAF1), and young-onset dystonia-parkinsonism (DYT/PARK-PRKRA) are monogenic combined dystonias accompanied by parkinsonian features. Meanwhile, MYC/DYT-SGCE and MYC/DYT-KCTD17 are characterized by dystonia in combination with myoclonus. In the past, common molecular pathways between these syndromes were the center of interest. Although the encoded proteins rather affect diverse cellular functions, recent neurophysiological evidence suggests similarities in the underlying mechanism in a subset. This review summarizes recent developments in the combined dystonias, focusing on clinico-genetic features and neurophysiologic findings. Disease-modifying therapies remain unavailable to date; an overview of symptomatic therapies for these disorders is also presented.

Successful Unilateral Surgical Approach to Internal Globus Pallidus and Ventral Intermediate Nucleus of the Thalamus in 3 Cases of Myoclonus-Dystonia Syndrome.

Surgical approaches of internal globus pallidus (GPi) and ventral intermediate thalamic nucleus (Vim) have been used to treat different movement disorders. Three subjects with myoclonus-dystonia syndrome were surgically treated, one of them with GPi and Vim stimulation, while radiofrequency ablation of these structures was performed in the other 2 subjects. Surgical approach of both targets was performed simultaneously on each subject. Mean follow-up was of 33.3 months (22-48 months), the Unified Myoclonus Rating Scale action myoclonus (AM), functional tests (FT), patient questionnaire (PQ) sub-scores, and the Unified Dystonia Rating Scale (UDRS) were used during assessments. Improvement in all scales were seen 6 months after surgery (AM: 74%, FT: 60%, PQ: 63%, UDRS: 65%), and this benefit persisted throughout follow-up (AM: 61%, FT:62%, PQ: 65%, UDRS: 86%). No adverse events were noticed. Simultaneous unilateral procedures of GPi and Vim by either stimulation or ablation techniques improve both motor and functional scores in myoclonus-dystonia syndrome.

Deep brain stimulation for myoclonus dystonia syndrome: a meta-analysis with individual patient data.

Good outcomes have been reported in deep brain stimulation (DBS) for myoclonus-dystonia syndrome (M-D), a heritable disease characterized by childhood-onset myoclonic jerks and dystonia in the upper body. This meta-analysis was to evaluate the clinical outcomes consecutively, compare the stimulation targets, and identify potential prognostic factors. A systematic literature search was performed on PubMed, Web of Science, and Embase. The primary outcome was the percent improvement in Burke-Fahn-Marsden Dystonia Rating Scale movement (BFMDRS-M) scores for dystonia and Unified Myoclonus Rating Scale (UMRS) scores for myoclonus at the last follow-up visit. BFMDRS-disability scores of the patients were also summarized. Pearson correlation analyses were performed to identify the myoclonus and dystonia outcome predictors. Thirty-one studies reporting 71 patients were included. There were significant improvements in BFMDRS-M and BFMDRS-disability scores in each time category and at the last follow-up visit. Mean improvement (%) in UMRS was 79.5 ± 18.2, and 94.1% of the patients showed > 50% improvement in UMRS scores at the last follow-up visit. There was a significant trend toward improved myoclonus outcome with older age at onset and shorter disease duration. Most of the adverse events were mild and transient, and pallidal stimulation seemed to be better with respect to fewer stimulation-induced events. Based on the current data, DBS is effective for even the severe M-D. Surgery at an early stage may predict a better outcome. Although targets do not serve as the outcome predictors, pallidal stimulation may be preferred due to fewer stimulation-induced events.

Functional and Molecular Properties of DYT-SGCE Myoclonus-Dystonia Patient-Derived Striatal Medium Spiny Neurons.

Myoclonus-dystonia (DYT-SGCE, formerly DYT11) is characterized by alcohol-sensitive, myoclonic-like appearance of fast dystonic movements. It is caused by mutations in the SGCE gene encoding ε-sarcoglycan leading to a dysfunction of this transmembrane protein, alterations in the cerebello-thalamic pathway and impaired striatal plasticity. To elucidate underlying pathogenic mechanisms, we investigated induced pluripotent stem cell (iPSC)-derived striatal medium spiny neurons (MSNs) from two myoclonus-dystonia patients carrying a heterozygous mutation in the SGCE gene (c.298T>G and c.304C>T with protein changes W100G and R102X) in comparison to two matched healthy control lines. Calcium imaging showed significantly elevated basal intracellular Ca2+ content and lower frequency of spontaneous Ca2+ signals in SGCE MSNs. Blocking of voltage-gated Ca2+ channels by verapamil was less efficient in suppressing KCl-induced Ca2+ peaks of SGCE MSNs. Ca2+ amplitudes upon glycine and acetylcholine applications were increased in SGCE MSNs, but not after GABA or glutamate applications. Expression of voltage-gated Ca2+ channels and most ionotropic receptor subunits was not altered. SGCE MSNs showed significantly reduced GABAergic synaptic density. Whole-cell patch-clamp recordings displayed elevated amplitudes of miniature postsynaptic currents and action potentials in SGCE MSNs. Our data contribute to a better understanding of the pathophysiology and the development of novel therapeutic strategies for myoclonus-dystonia.

Visual sensory processing is altered in myoclonus dystonia.

BACKGROUND: Abnormal sensory processing, including temporal discrimination threshold, has been described in various dystonic syndromes. OBJECTIVE: To investigate visual sensory processing in DYT-SGCE and identify its structural correlates. METHODS: DYT-SGCE patients without DBS (DYT-SGCE-non-DBS) and with DBS (DYT-SGCE-DBS) were compared to healthy volunteers in three tasks: a temporal discrimination threshold, a movement orientation discrimination, and movement speed discrimination. Response times attributed to accumulation of sensory visual information were computationally modelized, with µ parameter indicating sensory mean growth rate. We also identified the structural correlates of behavioral performance for temporal discrimination threshold. RESULTS: Twenty-four DYT-SGCE-non-DBS, 13 DYT-SGCE-DBS, and 25 healthy volunteers were included in the study. In DYT-SGCE-DBS, the discrimination threshold was higher in the temporal discrimination threshold (P = 0.024), with no difference among the groups in other tasks. The sensory mean growth rate (µ) was lower in DYT-SGCE in all three tasks (P < 0.01), reflecting a slower rate of sensory accumulation for the visual information in these patients independent of DBS. Structural imaging analysis showed a thicker left primary visual cortex (P = 0.001) in DYT-SGCE-non-DBS compared to healthy volunteers, which also correlated with lower µ in temporal discrimination threshold (P = 0.029). In DYT-SGCE-non-DBS, myoclonus severity also correlated with a lower µ in the temporal discrimination threshold task (P = 0.048) and with thicker V1 on the left (P = 0.022). CONCLUSION: In DYT-SGCE, we showed an alteration of the visual sensory processing in the temporal discrimination threshold that correlated with myoclonus severity and structural changes in the primary visual cortex. © 2019 International Parkinson and Movement Disorder Society.

A novel SGCE variant is associated with myoclonus-dystonia with phenotypic variability.

Myoclonus-dystonia associated with epsilon-sarcoglycan gene (SGCE) is a rare disorder characterized by myoclonus involving the upper body (neck, trunk, upper limbs) and proximal muscles associated with dystonia in more than half of the patients. When the clinical picture is clearly identified, more than half of the cases are associated with mutations in the SGCE gene. We herein describe a family with myoclonus-dystonia associated with a novel mutation in exon 7 of SGCE, c.904A>T (p.Lys302Ter) [Chr7:(GRCh38):g.94600779 T>A], which was absent in a non-affected member. A video recording of two of the affected members is provided. While the index case presents a severe cervical dystonia even affecting back posture, his sibling shows a much milder phenotype with mild myoclonic jerks. None of them had alcohol responsiveness or psychiatric comorbidity.

Clinical phenotype heterogeneity in a family with ε-sarcoglycan gene mutation.

AIM OF THE STUDY: This paper describes six cases of patients with myoclonus-dystonia syndrome who are members of a family in which an SGCE gene mutation has been confirmed. CLINICAL RATIONALE FOR THE STUDY: Myoclonus-dystonia syndrome is a very rare disease, with an incidence in Europe of about 2 in every million. Due to the fact that only a few case reports of this illness are accessible in the literature, the material we collected seems to be valuable for clinical practice. MATERIALS AND METHODS: A history was taken, and physical and genetic examinations of the patients were performed. Furthermore, the clinical examination of three patients was video-recorded. RESULTS: The clinical picture of the disease varied significantly between the described individuals, from a healthy carrier of the SGCE mutation to patients presenting mild to moderate symptoms. The differences concerned the age at onset of the disease, the initial symptoms, the intensity of involuntary movements, and the predominant symptoms. In addition to the typical movement disorders which are myoclonus and dystonia, in the described family there was also the coexistence of epilepsy, obsessive-compulsive behaviour, dyslexia, dysgraphia, non-harmonious development of cognitive processes, as well as mild phenotypic features of muscular dystrophy. The mutation (NM_001099401.2:c.806-809delACTG) found in the presented family has not been described elsewhere. CONCLUSIONS AND CLINICAL IMPLICATIONS: Our description of six cases of patients demonstrates the heterogeneity of the natural course of the disease, even in patients with the same mutation. It seems reasonable to regularly examine relatives of patients with myoclonus-dystonia syndrome, who should be observed for involuntary movements as well as non-motor symptoms.

Myoclonus-dystonia (DYT11, DYT-SGCE) - a channelopathy?

INTRODUCTION: Kaczynska et al. reported a family with myoclonus-dystonia (M-D) caused by a truncating SGCE mutation, in which two members had epilepsy. Further, patients had mild psychiatric and developmental deficits. CLINICAL REFLECTIONS: Characteristic motor features of M-D include myoclonus, dystonia and tremor. A wide range of additional disease manifestations are known. A few patients with M-D have seizures. CLINICAL IMPLICATIONS: Altered neuronal excitability has been found in the pathogenesis of M-D. This may explain the partial effectiveness of antiepileptics and a lower seizure threshold, and could encourage trials of other membrane stabilisers. Careful clinical observations of seemingly well-known diseases remain important.

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.

Long-term GPi-DBS improves motor features in myoclonus-dystonia and enhances social adjustment.

BACKGROUND: Good short-term results of pallidal deep brain stimulation have been reported in myoclonus-dystonia. Efficacy and safety in the long term remain to be established. In addition, the actual impact of DBS treatment on social inclusion is unknown. The objective of this study was to assess the long-term clinical outcome, quality of life, and social adjustment of GPi-DBS in patients with ε-sarcoglycan (DYT11)-positive myoclonus-dystonia. METHODS: Consecutive myoclonus-dystonia patients with ε-sarcoglycan mutations who underwent GPi-DBS were evaluated at least 5 years postoperatively. Motor symptoms were assessed using the Burke-Fahn-Marsden Dystonia Rating Scale including the Disability Scale, a composite score combining the rest and action parts of the Unified Myoclonus Rating Scale and modified Abnormal Involuntary Movement Scale. Standardized video-protocols were assessed by a blinded and external movement disorder specialist. Social adjustment, cognition, and mood were evaluated. RESULTS: Nine patients (5 women) with long-term GPi-DBS (8.7 ± 3.1 years) were included. There was significant improvement in the composite myoclonus score (94.1% ± 4% improvement; P = 0.008). Dystonia severity was also markedly improved (71.4% ± 28.33% improvement; P = 0.008) as well as motor disability (88.3% ± 20% improvement; P = 0.008) and abnormal involuntary movement score (71.1% ± 15.0% improvement; P = 0.008). No patients experienced postoperative speech or gait problems or any permanent adverse effects. Eight of the 9 patients had fully enhanced social adjustment and personal achievement, with little or no mood or behavioral disorders. CONCLUSIONS: GPi-DBS seems to be a safe and efficacious treatment for medically refractory ɛ-sarcoglycan myoclonus-dystonia, with sustained motor benefit, good quality of life, and social adjustment in long-term follow-up. © 2018 International Parkinson and Movement Disorder Society.

ADCY5-related dyskinesia presenting as familial myoclonus-dystonia.

We describe a family with an autosomal dominant familial dyskinesia resembling myoclonus-dystonia associated with a novel missense mutation in ADCY5, found through whole-exome sequencing. A tiered analytical approach was used to analyse whole-exome sequencing data from an affected grandmother-granddaughter pair. Whole-exome sequencing identified 18,000 shared variants, of which 46 were non-synonymous changes not present in a local cohort of control exomes (n = 422). Further filtering based on predicted splicing effect, minor allele frequency in the 1000 Genomes Project and on phylogenetic conservation yielded 13 candidate variants, of which the heterozygous missense mutation c.3086T>G, p. M1029R in ADCY5 most closely matched the observed phenotype. This report illustrates the utility of whole-exome sequencing in cases of undiagnosed movement disorders with clear autosomal dominant inheritance. Moreover, ADCY5 mutations should be considered in cases with apparent myoclonus-dystonia, particularly where SCGE mutations have been excluded. ADCY5-related dyskinesia may manifest variable expressivity within a single family, and affected individuals may be initially diagnosed with differing neurological phenotypes.

[Parasomnia and paroxysmal dyskinesia]. / Parasomnien und paroxysmale Dyskinesien.

Short involuntary paroxysmal movements or behavioral patterns are an important differential diagnosis to epileptic seizures, especially when occurring for the first time. Typically, these attacks are not witnessed by medically trained personnel and the patient anamnesis or observations by a third party are often not specific enough to differentiate between epileptic seizures and the differential diagnoses. This review presents the epidemiology, the clinical presentation, the necessary diagnostic steps and the differential diagnostic approach to parasomnias and dyskinesias. The focus is on the clinical aspects, and therapeutic principles are also briefly described.

Progression of neuropsychiatric and cognitive features due to exons 2 to 5 deletion in the epsilon-sarcoglycan gene: a case report.

Physical symptoms of myoclonus dystonia due to epsilon-sarcoglycan mutations are well documented; however, the progression of neuropsychiatric and cognitive symptoms remains unclear. We present a case of a 34-year-old woman with early childhood onset of myoclonic jerks, dystonic posture and developmental delay due to exons 2 to 5 deletion in the epsilon-sarcoglycan gene. Over time, she developed neuropsychiatric symptoms. She underwent bilateral deep brain stimulation of the ventral intermediate nucleus of the thalamus for her motor symptoms, which greatly improved but she exhibited slow deterioration of her neuropsychiatric and cognitive symptoms, particularly apathy, aggression and severe executive dysfunction.

Bilateral pallidal deep brain stimulation in myoclonus-dystonia: our experience in three cases and their follow-up.

BACKGROUND: Myoclonus-dystonia syndrome (MDS) is an autosomal dominant movement disorder caused by mutations in the SGCE gene. MDS is characterized by mild dystonia and myoclonic jerks, and a constellation of psychiatric manifestations. Deep brain stimulation (DBS) of bilateral internal globus pallidus (GPi) has recently been introduced as a new and beneficial technique to improve motor symptoms in MDS. METHODS: We report three proven genetically MDS cases with successful response to DBS, and their clinical evolution over years. RESULTS: DBS improves significantly the Unified Myoclonus Rating Scale and Burke-Fahn-Marsden Dystonia Rating Scale in all three patients. This improvement is sustained over the years and no major adverse events were recorded. DBS stimulation parameters employed are justified and compared with cases reported throughout the literature. DISCUSSION: DBS of bilateral GPi is an effective and safe therapy to be considered in MDS refractory cases. Careful neuropsychological evaluation is essential inside the presurgery planning. Correct location of the DBS electrodes and individualized selection of stimulation parameters in each case are the main determinants of the best clinical response.

RELN rare variants in myoclonus-dystonia.

BACKGROUND: Myoclonus-dystonia (M-D) is a hyperkinetic movement disorder with predominant myoclonic symptoms combined with dystonia of the upper part of the body. A proportion of M-D cases are caused by mutations in the epsilon-sarcoglycan gene. In remaining M-D patients, no genetic factor has been established, indicating genetic heterogeneity. METHODS: Patients were included in a prospective clinical database and recruited from referral centers and general neurology clinics in The Netherlands. To investigate new genetic causal factors in M-D syndrome, we performed homozygosity mapping combined with exome sequencing in a three-generation M-D family and genetically screened 24 additional patients with M-D. RESULTS: We found co-segregation of the rare missense variant Thr1904Met in the RELN gene. By additional screening of an M-D cohort, we identified co-segregation of RELN variants in two families (Thr1904Met, Ile1217Met) and identified two sporadic RELN mutation carriers (Pro1703Arg, Leu411Ile). Taken together, five of 25 SGCE-negative M-D patients carried RELN rare missense variants. CONCLUSION: We propose that RELN mutations contribute to the genetic heterogeneity of M-D. Reelin is a large secreted glycoprotein that plays essential roles in the cytoarchitecture of laminated brain structures and modulation of synaptic transmission and plasticity.

Pallidal activity in myoclonus dystonia correlates with motor signs.

BACKGROUND: Myoclonus-dystonia related to epsilon-sarcoglycan gene mutations is characterized by myoclonic jerks and mild to moderate dystonia. The role of basal ganglia dysfunction in the pathogenesis is unknown. METHODS: Pallidal neuronal activity was recorded in six myoclonus-dystonia and six primary generalized dystonia patients operated on for internal globus pallidus deep brain stimulation. RESULTS: In myoclonus-dystonia patients compared with primary-dystonia patients, internal pallidum neurons showed higher burst frequency, lower mean burst, and pause durations. External pallidum neurons showed higher mean pause frequency. Oscillatory activity was present in 33% and 35% of internal pallidum neurons in myoclonus-dystonia and primary-dystonia patients, respectively, predominantly in the theta frequency band (3-8 Hz). In myoclonus-dystonia patients with more severe myoclonus, internal pallidum neurons exhibited a higher bursting activity with high intraburst frequency and lower oscillatory activity frequency. CONCLUSIONS: Myoclonus-dystonia appears to be related to specific changes in internal pallidum activity, leading to disruption in striato-pallido-thalamo-cortical circuits. © 2015 International Parkinson and Movement Disorder Society.