Medical management of myoclonus-dystonia and implications for underlying pathophysiology

Sodium Oxybate-Treated Familial Myoclonus-Dystonia Syndrome Due to Novel SGCE Variant

Myoclonus-dystonia syndrome (MDS, OMIM #159900) is an autosomal-dominant movement disorder caused by heterozygous variants in the epsilon sarcoglycan gene (SGCE) and characterized by a combination of myoclonic jerks, dystonia, and psychiatric comorbidities. Patients with MDS have a normal life expectancy with markedly reduced quality of life. Here, we report four family members diagnosed with MDS of variable severity due to a novel heterozygous splicing variant in SGCE (c.341-2A>G), including a 13-year-old female who presented with disabling dystonic spasms, myoclonic jerks, and psychiatric symptoms. She had shown little or no response to several conventional MDS treatments. However, disabling axial dystonia was significantly improved by sodium oxybate (1 g, twice daily). Although there was less effect on myoclonus, sodium oxybate treatment significantly improved the overall quality of life at the 3-years follow-up. Clinical trials are warranted to assess the clinical efficacy and safety of sodium oxybate for MDS-associated dystonia.

Multivariate Pattern Analysis of fMRI Reveals Striato-Cortical Network Changes in Myoclonus-Dystonia

BACKGROUND

Currently, the pathophysiology of myoclonus-dystonia (M-D) remains insufficiently understood. This study addresses this gap by adding innovative multivariate pattern analysis (MVPA) to traditional univariate analysis of functional magnetic resonance imaging (fMRI) data.

METHODS

Data from 18 M-D patients and 18 age-matched healthy volunteers who performed a finger tapping fMRI task were analyzed. Whole-brain univariate and searchlight (MVPA) analysis with varying hemodynamic response function (HRF) delays were employed to examine brain responses associated with the visually guided motor task.

RESULTS

Distinguishing response patterns between M-D patients and healthy volunteers revealed significant response reductions in the putamen, insula, and visual cortex. Compared to univariate analysis, searchlight analysis was more sensitive for brain activity patterns associated with finger tapping in both M-D patients and healthy volunteers. At short HRF delays, increased (pre)motor cortical responses were evident in M-D patients, whereas such responses emerged at a later HRF delay in healthy volunteers.

CONCLUSION

The task-related effects observed in M-D patients support the involvement of the basal ganglia-thalamo-cortical network. Notably, cerebellar involvement was not strongly implicated in our study. We postulate that inherent deficits in the putamen trigger either premature or downstream compensatory (motor) cortical effects. The potential involvement of the visual cortex in the M-D pathophysiology is new, but its role has been suggested by a previous study investigating visual sensory processing in SGCE gene-positive M-D patients. Our findings, including the innovative searchlight method, pave the way for further studies investigating the complex interplay between brain regions and networks and their role in M-D pathogenesis.

Deciphering the Pathophysiological Mechanisms Underpinning Myoclonus Dystonia Using Pluripotent Stem Cell-Derived Cellular Models

Dystonia is a movement disorder with an estimated prevalence of 1.2% and is characterised by involuntary muscle contractions leading to abnormal postures and pain. Only symptomatic treatments are available with no disease-modifying or curative therapy, in large part due to the limited understanding of the underlying pathophysiology. However, the inherited monogenic forms of dystonia provide an opportunity for the development of disease models to examine these mechanisms. Myoclonus Dystonia, caused by SGCE mutations encoding the ε-sarcoglycan protein, represents one of now >50 monogenic forms. Previous research has implicated the involvement of the basal ganglia-cerebello-thalamo-cortical circuit in dystonia pathogenesis, but further work is needed to understand the specific molecular and cellular mechanisms. Pluripotent stem cell technology enables a patient-derived disease modelling platform harbouring disease-causing mutations. In this review, we discuss the current understanding of the aetiology of Myoclonus Dystonia, recent advances in producing distinct neuronal types from pluripotent stem cells, and their application in modelling Myoclonus Dystonia in vitro. Future research employing pluripotent stem cell-derived cellular models is crucial to elucidate how distinct neuronal types may contribute to dystonia and how disruption to neuronal function can give rise to dystonic disorders.

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.

Efficacy and Safety of Zolpidem for Focal Dystonia After Neurosurgical Treatments: A Retrospective Cohort Study

Although there are several reports of the significant efficacy of zolpidem for treating dystonia, zolpidem is still considered an anecdotal treatment. Here, we evaluated the efficacy and safety of zolpidem for treating residual dystonia in patients who previously received various neurosurgical treatments majorly including deep brain stimulation and radiofrequency ablation. We retrospectively reviewed medical records from January 2021 to September 2021 to identify patients with dystonia who had been prescribed zolpidem after undergoing neurosurgery. Twenty patients were enrolled in this study, including those with blepharospasm (two), tongue dystonia (four), mouth dystonia (one), spasmodic dysphonia (two), cervical dystonia (six), focal hand dystonia (three), hemidystonia (two), blepharospasm with cervical dystonia (one), and mouth dystonia with cervical dystonia (one). Single doses of zolpidem ranged between 2.5 and 10 mg, while daily dosages ranged from 10 to 30 mg. The zolpidem dose prescribed was 5–10 mg, with single and daily doses of 7 ± 2.9 and 14.5 ± 6.0 mg, respectively. With zolpidem administration, the participants' Burke-Fahn-Marsden Dystonia Rating Scale-Movement Scale score significantly improved from 8.1 ± 6.7 to 3.7 ± 2.5 (50.6% improvement, p < 0.0001). Improvements in arm dystonia, blepharospasm, and spasmodic dysphonia were observed using the Arm Dystonia Disability Scale, Jankovic Rating Scale, and Voice Handicap Index, respectively. No improvements were observed in cervical dystonia on the Toronto Western Spasmodic Torticollis Rating Scale. Drowsiness, including three cases each of mild and moderate drowsiness, was the most frequent adverse effect (30%), which persisted for 2–3 h. Transient amnesia and rapid eye movement sleep behavior disorder occurred in two patients and one patient, respectively. Although our findings suggest that zolpidem can be a valuable treatment option for patients with residual dystonia after neurosurgical treatments, the beneficial effects for cervical dystonia were limited.

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.