Evolving concepts in the pathogenesis of dystonia

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.

Genetic Update and Treatment for Dystonia

A neurological condition called dystonia results in abnormal, uncontrollable postures or movements because of sporadic or continuous muscular spasms. Several varieties of dystonia can impact people of all ages, leading to severe impairment and a decreased standard of living. The discovery of genes causing variations of single or mixed dystonia has improved our understanding of the disease's etiology. Genetic dystonias are linked to several genes, including pathogenic variations of VPS16, TOR1A, THAP1, GNAL, and ANO3. Diagnosis of dystonia is primarily based on clinical symptoms, which can be challenging due to overlapping symptoms with other neurological conditions, such as Parkinson's disease. This review aims to summarize recent advances in the genetic origins and management of focal dystonia.

MRI-Guided Focused Ultrasound for the Treatment of Dystonia: A Narrative Review

Contemporary surgical management of dystonia includes neuromodulation via deep brain stimulation (DBS) or ablative techniques such as radiofrequency (RF) ablation. MRI-guided focused ultrasound (MRgFUS) is an emerging modality that uses high-intensity ultrasound to precisely ablate targets in the brain; this is incisionless, potentially avoiding the surgical risks of a burr hole and transcortical tract to reach the anatomical target. There is some evidence of efficacy in essential tremor and Parkinson's disease (PD), but, to date, there is no study aggregating the evidence of MRgFUS in dystonia. In this narrative review, we searched Medline, Embase, CINAHL, EBSCO, and ClinicalTrials.gov for primary studies and clinical trials on MRgFUS in the treatment of dystonia. Data were analyzed concerning dystonia phenotype, reported outcomes, and complications. PD-related dystonia was also included within the scope of the review. Using our search criteria, six articles on the use of MRgFUS in adult dystonia and three articles on the use of FUS in dystonia in PD were included. Four trials on the use of FUS in dystonia were also found on ClinicalTrials.gov, one of which was completed in December 2013. All included studies showed evidence of symptomatic improvement, mostly in focal hand dystonia; improvements were also found in dystonia-associated tremor, cervicobrachial dystonia, and dystonia-associated chronic neuropathic pain as well as PD-related dystonia. Reported complications included transient neurological deficits and persistent arm pain in one study. However, the evidence is limited to level-4 case series at present. MRgFUS is an emerging modality that appears to be safe and effective, particularly in focal hand dystonia, without major adverse effects. However, the quality of evidence is low at present, and long-term outcomes are unknown. High-quality prospective studies comparing MRgFUS to other surgical techniques will be useful in determining its role in the management of dystonia.

Cerebellar dysfunction in rodent models with dystonia, tremor, and ataxia

Dystonia is a movement disorder characterized by involuntary co- or over-contractions of the muscles, which results in abnormal postures and movements. These symptoms arise from the pathophysiology of a brain-wide dystonia network. There is mounting evidence suggesting that the cerebellum is a central node in this network. For example, manipulations that target the cerebellum cause dystonic symptoms in mice, and cerebellar neuromodulation reduces these symptoms. Although numerous findings provide insight into dystonia pathophysiology, they also raise further questions. Namely, how does cerebellar pathophysiology cause the diverse motor abnormalities in dystonia, tremor, and ataxia? Here, we describe recent work in rodents showing that distinct cerebellar circuit abnormalities could define different disorders and we discuss potential mechanisms that determine the behavioral presentation of cerebellar diseases.

Spastic dystonia: Still a valid term

Hypertonia in childhood may arise because of a variable combination of neuronal and non-neuronal factors. Involuntary muscle contraction may be due to spasticity or dystonia, which represent disorders of the spinal reflex arch and of central motor output respectively. Whilst consensus definitions for dystonia have been established, definitions of spasticity vary, highlighting the lack of a single unifying nomenclature in the field of clinical movement science. The term spastic dystonia refers to involuntary tonic muscle contraction in the context of an upper motor neuron (UMN) lesion. This review considers the utility of the term spastic dystonia, exploring our understanding of the pathophysiology of dystonia and the UMN syndrome. An argument is advanced that spastic dystonia is a valid construct that warrants further exploration. WHAT THIS PAPER ADDS: There is no single universally accepted definitions for terms commonly used to describe motor disorders. Spasticity and dystonia are phenomenologically and pathophysiologically distinct entities. Spastic dystonia represents a subset of dystonia, but with pathophysiological mechanisms more in common with spasticity.

Blood neurofilament light chain as a surrogate marker for dystonia

BACKGROUND AND PURPOSE

Dystonia is a heterogeneous movement disorder, and it remains unclear whether neurodegeneration is involved. Neurofilament light chain (NfL) is a biosignature of neurodegeneration. We aimed to investigate whether plasma NfL levels were elevated and associated with disease severity in patients with dystonia.

METHOD

We enrolled 231 unrelated dystonia patients (isolated dystonia n = 203; combined dystonia n = 28) and 54 healthy controls from movement disorder clinics. Clinical severity was evaluated using the Fahn Marsden Dystonia Rating Scale, the Unified Dystonia Rating Scale, and the Global Dystonia Rating Scale. Blood NfL levels were measured by single-molecule array.

RESULTS

Plasma NfL levels were significantly higher in those with generalized dystonia compared to those with focal dystonia (20.1 ± 8.8 vs. 11.7 ± 7.2 pg/mL; p = 0.01) or controls (p < 0.01), while the level was comparable between the focal dystonia group and controls (p = 0.08). Furthermore, the dystonia combined with parkinsonism group had higher NfL levels than the isolated dystonia group (17.4 ± 6.2 vs. 13.5 ± 7.5 pg/mL; p = 0.04). Notably, whole-exome sequencing was performed in 79 patients and two patients were identified as having likely pathogenic variants: one had a heterozygous c.122G>A (p.R41H) variant in THAP1 (DYT6) and the other carried a c.1825G>A (p.D609N) substitution in ATP1A3 (DYT12). No significant correlation was found between plasma NfL levels and dystonia rating scores.

CONCLUSION

Plasma NfL levels are elevated in patients with generalized dystonia and dystonia combined with parkinsonism, suggesting that neurodegeneration is involved in the disease process of this subgroup of patients.

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.

Dystonia genes and their biological pathways

High-throughput sequencing has been instrumental in uncovering the spectrum of pathogenic genetic alterations that contribute to the etiology of dystonia. Despite the immense heterogeneity in monogenic causes, studies performed during the past few years have highlighted that many rare deleterious variants associated with dystonic presentations affect genes that have roles in certain conserved pathways in neural physiology. These various gene mutations that appear to converge towards the disruption of interconnected cellular networks were shown to produce a wide range of different dystonic disease phenotypes, including isolated and combined dystonias as well as numerous clinically complex, often neurodevelopmental disorder-related conditions that can manifest with dystonic features in the context of multisystem disturbances. In this chapter, we summarize the manifold dystonia-gene relationships based on their association with a discrete number of unifying pathophysiological mechanisms and molecular cascade abnormalities. The themes on which we focus comprise dopamine signaling, heavy metal accumulation and calcifications in the brain, nuclear envelope function and stress response, gene transcription control, energy homeostasis, lysosomal trafficking, calcium and ion channel-mediated signaling, synaptic transmission beyond dopamine pathways, extra- and intracellular structural organization, and protein synthesis and degradation. Enhancing knowledge about the concept of shared etiological pathways in the pathogenesis of dystonia will motivate clinicians and researchers to find more efficacious treatments that allow to reverse pathologies in patient-specific core molecular networks and connected multipathway loops.

Pathophysiology of Dyt1-Tor1a dystonia in mice is mediated by spinal neural circuit dysfunction

Dystonia, a neurological disorder defined by abnormal postures and disorganized movements, is considered to be a neural circuit disorder with dysfunction arising within and between multiple brain regions. Given that spinal neural circuits constitute the final pathway for motor control, we sought to determine their contribution to this movement disorder. Focusing on the most common inherited form of dystonia in humans, DYT1-TOR1A, we generated a conditional knockout of the torsin family 1 member A (Tor1a) gene in the mouse spinal cord and dorsal root ganglia (DRG). We found that these mice recapitulated the phenotype of the human condition, developing early-onset generalized torsional dystonia. Motor signs emerged early in the mouse hindlimbs before spreading caudo-rostrally to affect the pelvis, trunk, and forelimbs throughout postnatal maturation. Physiologically, these mice bore the hallmark features of dystonia, including spontaneous contractions at rest and excessive and disorganized contractions, including cocontractions of antagonist muscle groups, during voluntary movements. Spontaneous activity, disorganized motor output, and impaired monosynaptic reflexes, all signs of human dystonia, were recorded from isolated mouse spinal cords from these conditional knockout mice. All components of the monosynaptic reflex arc were affected, including motor neurons. Given that confining the Tor1a conditional knockout to DRG did not lead to early-onset dystonia, we conclude that the pathophysiological substrate of this mouse model of dystonia lies in spinal neural circuits. Together, these data provide new insights into our current understanding of dystonia pathophysiology.

Impaired trunk control and its relationship with balance, functional mobility, and disease severity in patients with cervical dystonia

BACKGROUND

Impaired trunk control is common in neurological disorders; however, trunk control has not been examined in patients with cervical dystonia (CD). Therefore, the primary aim was to compare trunk control between patients with CD and healthy people. The secondary aim was to investigate the relationship between trunk control and balance, functional mobility, and disease severity in patients with CD.

METHODS

]This cross-sectional study included 32 patients with CD and 32 healthy people. Trunk control was compared using the trunk impairment scale (TIS) that consists of three subscales: static sitting balance, dynamic sitting balance, and trunk coordination between two groups. Balance was assessed using Berg Balance Scale, four square step test, and one-leg stance test. The Timed Up and Go Test was measured to determine functional mobility. Toronto Western Spasmodic Torticollis Rating Scale was used to evaluate disease severity.]></AbstractText> <AbstractText Label="RESULTS"><![CDATA[ Patients with CD demonstrated worse performance on the TIS-total with TIS-dynamic sitting subscale and TIS-trunk coordination subscale (p < 0.001, p < 0.001, and p < 0.001), except for TIS-static sitting subscale (p = 0.078) compared to healthy people. TIS-total scores had moderate to strong correlations with balance, functional mobility, and disease severity (range r between 0.786 and 0.536, p < 0.05 for all). There was no correlation between TIS-total scores and disease severity (p = 0.102).

DISCUSSION

Patients with CD had impaired trunk control, especially in dynamic sitting balance and trunk coordination. Impaired trunk control was also associated with balance and functional mobility but not disease severity. These findings suggest that trunk control deficits should receive attention in the assessment and treatment of patients with CD.

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.

Electromyography as a Method for Distinguishing Dystonia in Mice

Electromyography (EMG) methods allow quantitative analyses of motor function. The techniques include intramuscular recordings that are performed in vivo. However, recording muscle activity in freely moving mice, particularly in models of motor disease, often creates challenges that prevent the acquisition of clean signals. Recording preparations must be stable enough for the experimenter to collect an adequate number of signals for statistical analyses. Instability results in a low signal-to-noise ratio that prohibits proper isolation of EMG signals from the target muscle during the behavior of interest. Such insufficient isolation prevents the analysis of full electrical potential waveforms. In this case, resolving the shape of a waveform to differentiate individual spikes and bursts of muscle activity can be difficult. A common source of instability is an inadequate surgery. Poor surgical techniques cause blood loss, tissue damage, poor healing, encumbered movement, and unstable implantation of the electrodes. Here, we describe an optimized surgical procedure that ensures electrode stability for in vivo muscle recordings. We implement our technique to obtain recordings from agonist and antagonist muscle pairs in the hindlimbs of freely moving adult mice. We validate the stability of our method by holding EMG recordings during dystonic behavior. Our approach is ideal for studying normal and abnormal motor function in actively behaving mice and valuable for recording intramuscular activity when considerable motion is expected.

Cortical mechanisms of sensory trick in cervical dystonia

Patients with cervical dystonia (CD) often show an improvement in dystonic posture after sensory trick (ST), though the mechanisms underlying ST remain unclear. In this study, we aimed to investigate the effects of ST on cortical activity in patients with CD and to explore the contribution of motor and sensory components to ST mechanisms. To this purpose, we studied 15 CD patients with clinically effective ST, 17 without ST, and 14 healthy controls (HCs) who mimicked the ST. We used electroencephalographic (EEG) recordings and electromyography (EMG) data from bilateral sternocleidomastoid (SCM) muscles. We compared ST-related EEG spectral changes from sensorimotor and posterior parietal areas and EMG power changes between groups. To better understand the contribution of motor and sensory components to ST, we tested EEG and EMG correlates of three different conditions mimicking ST, the first without skin touch ("no touch" condition), the second without voluntary movements ("passive" condition), and finally without arm movements ("examiner touch" condition). Results showed ST-related alpha desynchronization in the sensorimotor cortex and theta desynchronization in the sensorimotor and posterior parietal cortex. Both spectral changes were more significant during maneuver execution in CD patients with ST than in CD patients without ST and HCs who mimicked the ST. Differently, the "no touch", "passive", or "examiner touch" conditions did not show significant differences in EEG or EMG changes determined by ST execution/mimicking between CD patients with or without ST. A higher desynchronization within alpha and theta bands in the sensorimotor and posterior parietal areas correlated with a more significant activity decrease in the contralateral SCM muscle, Findings from this study suggest that ST-related changes in the activity of sensorimotor and posterior parietal areas may restore dystonic posture and that both motor and sensory components contribute to the ST effect.

Cerebellar Dysfunction as a Source of Dystonic Phenotypes in Mice

There is now a substantial amount of compelling evidence demonstrating that the cerebellum may be a central locus in dystonia pathogenesis. Studies using spontaneous genetic mutations in rats and mice, engineered genetic alleles in mice, shRNA knockdown in mice, and conditional genetic silencing of fast neurotransmission in mice have all uncovered a common set of behavioral and electrophysiological defects that point to cerebellar cortical and cerebellar nuclei dysfunction as a source of dystonic phenotypes. Here, we revisit the Ptf1a^Cre/+;Vglut2^flox/flox mutant mouse to define fundamental phenotypes and measures that are valuable for testing the cellular, circuit, and behavioral mechanisms that drive dystonia. In this model, excitatory neurotransmission from climbing fibers is genetically eliminated and, as a consequence, Purkinje cell and cerebellar nuclei firing are altered in vivo, with a prominent and lasting irregular burst pattern of spike activity in cerebellar nuclei neurons. The resulting impact on behavior is that the mice have developmental abnormalities, including twisting of the limbs and torso. These behaviors continue into adulthood along with a tremor, which can be measured with a tremor monitor or EMG. Importantly, expression of dystonic behavior is reduced upon cerebellar-targeted deep brain stimulation. The presence of specific combinations of disease-like features and therapeutic responses could reveal the causative mechanisms of different types of dystonia and related conditions. Ultimately, an emerging theme places cerebellar dysfunction at the center of a broader dystonia brain network.

Dystonia, chorea, hemiballismus and other dyskinesias

Hyperkinesias are heterogeneous involuntary movements that significantly differ in terms of clinical and semeiological manifestations, including rhythm, regularity, speed, duration, and other factors that determine their appearance or suppression. Hyperkinesias are due to complex, variable, and largely undefined pathophysiological mechanisms that may involve different brain areas. In this chapter, we specifically focus on dystonia, chorea and hemiballismus, and other dyskinesias, specifically, levodopa-induced, tardive, and cranial dyskinesia. We address the role of neurophysiological studies aimed at explaining the pathophysiology of these conditions. We mainly refer to human studies using surface and invasive in-depth recordings, as well as spinal, brainstem, and transcortical reflexology and non-invasive brain stimulation techniques. We discuss the extent to which the neurophysiological abnormalities observed in hyperkinesias may be explained by pathophysiological models. We highlight the most relevant issues that deserve future research efforts. The potential role of neurophysiological assessment in the clinical context of hyperkinesia is also discussed.

Haloperidol-induced isolated lingual dystonia

A 28-year-old woman presenting with agitation and mania with psychotic features developed symptoms of isolated lingual dystonia shortly after the initiation of a haloperidol concentrate regimen.

A cross-sectional study of walking, balance and upper limb assessment scales in people with cervical dystonia

Cervical dystonia (CD) is a neurological movement disorder causing the neck to move involuntarily away from the neutral position. CD is a network disorder, involving multiple brain areas and, therefore, may impair movement in parts of the body other than the neck. This study used clinical assessments to investigate walking, balance and upper limb function (UL) in people with CD; the reliability of scoring these assessments and examined for relationship between CD severity, usual exercise and clinical assessments. We conducted a prospective observational cohort study of participants with isolated, focal, idiopathic CD. Participants were assessed by experienced physiotherapists and completed three questionnaires and eight clinical assessments of fear of falling, balance confidence, walking, balance, UL function and usual exercise. Results were compared to published data from healthy adults and other neurological populations. Twenty-two people with mild to moderate CD participated. Fear of falling, gross UL function and usual exercise were worse in people with CD compared with healthy adults, while walking, balance and distal UL function were similar to healthy populations. All assessments were reliably performed by physiotherapists, and we found no correlations between the severity of dystonia or usual exercise and performance on the physical assessments. Routine performance of clinical assessment of walking and balance are likely not required in people with mild to moderate CD; however, fear of falling and gross upper limb function should be assessed to determine any problems which may be amenable to therapy.

Smell and taste in idiopathic blepharospasm

The pathophysiology of blepharospasm is incompletely understood. Current concepts suggest that blepharospasm is a network disorder, involving basal ganglia, thalamus, cortex, and, possibly, the cerebellum. Tracing, imaging, and clinical studies revealed that these structures are also concerned with olfaction and taste. Because of this anatomical overlap, dysfunction of the chemical senses in blepharospasm is expected. Injections of botulinum toxin into the eyelid muscles are the first-line treatment of blepharospasm. Yet, the effects of botulinum toxin on the chemical senses have not been systematically assessed. To contribute to a better understanding of blepharospasm, olfactory and gustatory abilities were assessed in 17 subjects with blepharospasm and 17 age-/sex-matched healthy controls. Sniffin Sticks were used to assess odor threshold, odor discrimination, and odor identification. Results of these three Sniffin Sticks subtests were added to the composite olfactory score. The Taste Strips were applied to assess taste. In an adjacent study, we assessed the sense of smell and taste in eight subjects with blepharospasm before and 4 weeks after botulinum toxin treatment. Subjects with blepharospasm had significantly lower (= worse) scores for odor threshold and for the composite olfactory score than healthy controls, while odor discrimination, odor identification, and the composite taste score were not different between groups. The adjacent study revealed that botulinum toxin did not impact the chemical senses. In this study, subjects with blepharospasm had a lower (= worse) odor threshold than healthy controls. As olfaction is important in daily life, findings justify further research of olfaction in blepharospasm.

[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.

Neurobiological mechanisms associated with antipsychotic drug-induced dystonia

Dystonia is by far the most intrusive and invalidating extrapyramidal side effect of potent classical antipsychotic drugs. Antipsychotic drug-induced dystonia is classified in both acute and tardive forms. The incidence of drug-induced dystonia is associated with the affinity to inhibitory dopamine D2 receptors. Particularly acute dystonia can be treated with anticholinergic drugs, but the tardive form may also respond to such antimuscarinic treatment, which contrasts their effects in tardive dyskinesia. Combining knowledge of the pathophysiology of primary focal dystonia with the anatomical and pharmacological organization of the extrapyramidal system may shed some light on the mechanism of antipsychotic drug-induced dystonia. A suitable hypothesis is derived from the understanding that focal dystonia may be due to a faulty processing of somatosensory input, so leading to inappropriate execution of well-trained motor programmes. Neuroplastic alterations of the sensitivity of extrapyramidal medium-sized spiny projection neurons to stimulation, which are induced by the training of specific complex movements, lead to the sophisticated execution of these motor plans. The sudden and non-selective disinhibition of indirect pathway medium-sized spiny projection neurons by blocking dopamine D2 receptors may distort this process. Shutting down the widespread influence of tonically active giant cholinergic interneurons on all medium-sized spiny projection neurons by blocking muscarinic receptors may result in a reduction of the influence of extrapyramidal cortical-striatal-thalamic-cortical regulation. Furthermore, striatal cholinergic interneurons have an important role to play in integrating cerebellar input with the output of cerebral cortex, and are also targeted by dopaminergic nigrostriatal fibres affecting dopamine D2 receptors.

Deep brain stimulation: a review of the open neural engineering challenges

OBJECTIVE

Deep brain stimulation (DBS) is an established and valid therapy for a variety of pathological conditions ranging from motor to cognitive disorders. Still, much of the DBS-related mechanism of action is far from being understood, and there are several side effects of DBS whose origin is unclear. In the last years DBS limitations have been tackled by a variety of approaches, including adaptive deep brain stimulation (aDBS), a technique that relies on using chronically implanted electrodes on 'sensing mode' to detect the neural markers of specific motor symptoms and to deliver on-demand or modulate the stimulation parameters accordingly. Here we will review the state of the art of the several approaches to improve DBS and summarize the main challenges toward the development of an effective aDBS therapy.

APPROACH

We discuss models of basal ganglia disorders pathogenesis, hardware and software improvements for conventional DBS, and candidate neural and non-neural features and related control strategies for aDBS.

MAIN RESULTS

We identify then the main operative challenges toward optimal DBS such as (i) accurate target localization, (ii) increased spatial resolution of stimulation, (iii) development of in silico tests for DBS, (iv) identification of specific motor symptoms biomarkers, in particular (v) assessing how LFP oscillations relate to behavioral disfunctions, and (vi) clarify how stimulation affects the cortico-basal-ganglia-thalamic network to (vii) design optimal stimulation patterns.

SIGNIFICANCE

This roadmap will lead neural engineers novel to the field toward the most relevant open issues of DBS, while the in-depth readers might find a careful comparison of advantages and drawbacks of the most recent attempts to improve DBS-related neuromodulatory strategies.

Olfaction as a Marker for Dystonia: Background, Current State and Directions

Dystonia is a heterogeneous group of hyperkinetic movement disorders. The unifying descriptor of dystonia is the motor manifestation, characterized by continuous or intermittent contractions of muscles that cause abnormal movements and postures. Additionally, there are psychiatric, cognitive, and sensory alterations that are possible or putative non-motor manifestations of dystonia. The pathophysiology of dystonia is incompletely understood. A better understanding of dystonia pathophysiology is highly relevant in the amelioration of significant disability associated with motor and non-motor manifestations of dystonia. Recently, diminished olfaction was found to be a potential non-motor manifestation that may worsen the situation of subjects with dystonia. Yet, this finding may also shed light into dystonia pathophysiology and yield novel treatment options. This article aims to provide background information on dystonia and the current understanding of its pathophysiology, including the key structures involved, namely, the basal ganglia, cerebellum, and sensorimotor cortex. Additionally, involvement of these structures in the chemical senses are reviewed to provide an overview on how olfactory (and gustatory) deficits may occur in dystonia. Finally, we describe the present findings on altered chemical senses in dystonia and discuss directions of research on olfactory dysfunction as a marker in dystonia.

Bilateral polymicrogyria associated with dystonia: A new neurogenetic syndrome?

The clinical presentation of bilateral perisylvian polymicrogyria (PMG) is highly variable, including oromotor dysfunction, epilepsy, intellectual disability, and pyramidal signs. Extrapyramidal features are extremely rare. We present four apparently unrelated patients with a unique association of PMG with dystonia. The clinical, genetic, and radiologic features are described and possible mechanisms of dystonia are discussed. All patients were female and two were born to consanguineous families. All presented with early childhood onset dystonia. Other neurologic symptoms and signs classically seen in bilateral perisylvian PMG were observed, including oromotor dysfunction and speech abnormalities ranging from dysarthria to anarthria (4/4), pyramidal signs (3/4), hypotonia (3/4), postnatal microcephaly (1/4), and seizures (1/4). Neuroimaging showed a unique pattern of bilateral PMG with an infolded cortex originating primarily from the perisylvian region in three out of four patients. Whole exome sequencing was performed in two out of four patients and did not reveal pathogenic variants in known genes for cortical malformations or movement disorders. The dystonia seen in our patients is not described in bilateral PMG and suggests an underlying mechanism of impaired connectivity within the motor network or compromised cortical inhibition. The association of bilateral PMG with dystonia in our patients may represent a new neurogenetic disorder.

Hyperkinetic manifestations in superficial siderosis: evidence for pathogenic network disruption

Superficial siderosis (SS) of central nervous system is a rare condition characterized by hemosiderin deposition diffusely involving supratentorial and infratentorial compartments. SS usually manifests with ataxia and sensorineural hearing loss. Basal ganglia are almost always spared by the degenerative process, and movement disorders are only rarely reported. We describe the case of an aged woman with apparently idiopathic SS presenting with cerebellar ataxia, hearing loss, and orofacial dyskinesias. Together with some previously reported patients affected by SS and presenting with dystonic manifestations, our case reinforces the current hypothesis supporting a wide network disruption, rather than a direct basal ganglia damage, as the likely underlying cause of some dystonic syndromes.

Cortical Oscillations in Cervical Dystonia and Dystonic Tremor

Dystonia involves sustained or repetitive muscle contractions, affects different skeletal muscles, and may be associated with tremor. Few studies have investigated if cortical pathophysiology is impaired even when dystonic muscles are not directly engaged and during the presence of dystonic tremor (DT). Here, we recorded high-density electroencephalography and time-locked behavioral data in 2 cohorts of patients and controls during the performance of head movements, upper limb movements, and grip force. Patients with cervical dystonia had reduced movement-related desynchronization in the alpha and beta bands in the bilateral sensorimotor cortex during head turning movements, produced by dystonic muscles. Reduced desynchronization in the upper beta band in the ipsilateral motor and bilateral sensorimotor cortex was found during upper limb planar movements, produced by non-dystonic muscles. In a precision grip task, patients with DT had reduced movement-related desynchronization in the alpha and beta bands in the bilateral sensorimotor cortex. We observed a general pattern of abnormal sensorimotor cortical desynchronization that was present across the head and upper limb motor tasks, in patients with and without DT when compared with controls. Our findings suggest that abnormal cortical desynchronization is a general feature of dystonia that should be a target of pharmacological and other therapeutic interventions.

Awareness of Dystonic Posture in Patients With Cervical Dystonia

Background

Cervical dystonia (CD) is a focal dystonia characterized by sensorimotor integration abnormalities and proprioceptive dysfunction. Since proprioception is essential for bodily awareness, we hypothesized that CD patients may have an impairment in dystonic posture awareness. More information on this issue could be useful to better understand whether dystonic posture affects bodily perception in CD and could help in the development of specific rehabilitation strategies based on proprioceptive input manipulation to restore bodily awareness.

Objectives

The aim of our study was to investigate dystonic posture and head tremor awareness in CD patients by comparing evaluations performed by CD patients with those performed by a neurologist expert in movement disorders.

Methods

We enrolled 25 CD patients. We investigated dystonic posture and head tremor awareness in CD patients using a standardized protocol in which patients were asked to describe the type of dystonic pattern, both while viewing standardized images of different CD subtypes (torticollis, laterocollis, anterocollis, and retrocollis) and after watching a video recording of their dystonic posture and head tremor.

Results

We found that 72% of CD patients correctly recognized their dystonic posture when viewing standardized images, whereas 84% of CD patients were able to identify their dystonic pattern when watching a video recording of themselves. CD patients also displayed a preserved awareness of their head tremor. We did not find any associations between dystonic pattern awareness and clinical or demographic features.

Conclusion

Contrary to our hypothesis, the majority of CD patients have a preserved awareness of their dystonic pattern and tremor.

A survey of falls in people with dystonia

OBJECTIVE

Dystonia is a chronic and sometimes progressive neurological disorder causing abnormalities in movement and function. We conducted a preliminary survey to investigate whether people with dystonia experience falls and to identify contributing factors to falls in this population.

METHODS

An online survey of people with dystonia was conducted in November 2015. Respondents were asked to complete demographic information, three questionnaires (the Falls Self-Efficacy Scale International [FES-I], the Activities-based Balance Confidence Scale [ABC] and the Functional Disability Questionnaire [FDQ]), and to report any falls sustained during the previous 6 months.

RESULTS

Thirty-nine percent of the 122 respondents reported falling in the previous 6 months and 65% of fallers were diagnosed with dystonia not affecting the lower limbs. Fallers reported lower falls self-efficacy and balance confidence with higher functional disability. Both falling scales correlated with self-reported functional disability. Linear regression analysis for falls prediction revealed the variables FES-I and FDQ accounted for almost 30% of the falls in this dystonia population.

CONCLUSION

This survey indicates that fear of falling and balance confidence are impaired in people with dystonia, possibly impacting on function and falls. Further investigation into balance, function and falls in this population is required.

Consensus Paper: Experimental Neurostimulation of the Cerebellum

The cerebellum is best known for its role in controlling motor behaviors. However, recent work supports the view that it also influences non-motor behaviors. The contribution of the cerebellum towards different brain functions is underscored by its involvement in a diverse and increasing number of neurological and neuropsychiatric conditions including ataxia, dystonia, essential tremor, Parkinson's disease (PD), epilepsy, stroke, multiple sclerosis, autism spectrum disorders, dyslexia, attention deficit hyperactivity disorder (ADHD), and schizophrenia. Although there are no cures for these conditions, cerebellar stimulation is quickly gaining attention for symptomatic alleviation, as cerebellar circuitry has arisen as a promising target for invasive and non-invasive neuromodulation. This consensus paper brings together experts from the fields of neurophysiology, neurology, and neurosurgery to discuss recent efforts in using the cerebellum as a therapeutic intervention. We report on the most advanced techniques for manipulating cerebellar circuits in humans and animal models and define key hurdles and questions for moving forward.

Dystonia and dopamine: From phenomenology to pathophysiology

A line of evidence suggests that the pathophysiology of dystonia involves the striatum, whose activity is modulated among other neurotransmitters, by the dopaminergic system. However, the link between dystonia and dopamine appears complex and remains unclear. Here, we propose a physiological approach to investigate the clinical and experimental data supporting a role of the dopaminergic system in the pathophysiology of dystonic syndromes. Because dystonia is a disorder of motor routines, we first focus on the role of dopamine and striatum in procedural learning. Second, we consider the phenomenology of dystonia from every angle in order to search for features giving food for thought regarding the pathophysiology of the disorder. Then, for each dystonic phenotype, we review, when available, the experimental and imaging data supporting a connection with the dopaminergic system. Finally, we propose a putative model in which the different phenotypes could be explained by changes in the balance between the direct and indirect striato-pallidal pathways, a process critically controlled by the level of dopamine within the striatum. Search strategy and selection criteria References for this article were identified through searches in PubMed with the search terms « dystonia », « dopamine", « striatum », « basal ganglia », « imaging data », « animal model », « procedural learning », « pathophysiology », and « plasticity » from 1998 until 2018. Articles were also identified through searches of the authors' own files. Only selected papers published in English were reviewed. The final reference list was generated on the basis of originality and relevance to the broad scope of this review.

Update on current and emerging therapies for dystonia

Treatment strategies for dystonia depend on the focal, segmental or generalized distribution of symptoms. Chemodenervation with botulinum toxin remains the treatment of choice for focal- or select-body regions in generalized and segmental dystonia. A potentially longer acting formulation of botulinum toxin is being investigated besides the currently available formulations. Electromyography increases toxin injection accuracy and may reduce injection number, frequency, side effects and costs by identifying dystonic muscle activity. Oral anticholinergics, baclofen and clonazepam are used off-label, but novel drugs in development include sodium oxybate, zonisamide and perampanel. Characterizing dystonia as a sensorimotor circuit disorder has prompted the use of noninvasive neuromodulation procedures. These techniques need further study but simultaneous rehabilitation techniques appear to also improve outcomes. Pallidal deep-brain stimulation is beneficial for medication-refractory primary generalized and possibly focal dystonia such as cervical dystonia. Certain genetic conditions are amenable to specific therapies and future gene-targeted therapies could benefit selected dystonia patients.

Toward Electrophysiology-Based Intelligent Adaptive Deep Brain Stimulation for Movement Disorders

Deep brain stimulation (DBS) represents one of the major clinical breakthroughs in the age of translational neuroscience. In 1987, Benabid and colleagues demonstrated that high-frequency stimulation can mimic the effects of ablative neurosurgery in Parkinson's disease (PD), while offering two key advantages to previous procedures: adjustability and reversibility. Deep brain stimulation is now an established therapeutic approach that robustly alleviates symptoms in patients with movement disorders, such as Parkinson's disease, essential tremor, and dystonia, who present with inadequate or adverse responses to medication. Currently, stimulation electrodes are implanted in specific target regions of the basal ganglia-thalamic circuit and stimulation pulses are delivered chronically. To achieve optimal therapeutic effect, stimulation frequency, amplitude, and pulse width must be adjusted on a patient-specific basis by a movement disorders specialist. The finding that pathological neural activity can be sampled directly from the target region using the DBS electrode has inspired a novel DBS paradigm: closed-loop adaptive DBS (aDBS). The goal of this strategy is to identify pathological and physiologically normal patterns of neuronal activity that can be used to adapt stimulation parameters to the concurrent therapeutic demand. This review will give detailed insight into potential biomarkers and discuss next-generation strategies, implementing advances in artificial intelligence, to further elevate the therapeutic potential of DBS by capitalizing on its modifiable nature. Development of intelligent aDBS, with an ability to deliver highly personalized treatment regimens and to create symptom-specific therapeutic strategies in real-time, could allow for significant further improvements in the quality of life for movement disorders patients with DBS that ultimately could outperform traditional drug treatment.

A unique de novo gain-of-function variant in CAMK4 associated with intellectual disability and hyperkinetic movement disorder

Calcium/calmodulin-dependent protein kinases (CaMKs) are key mediators of calcium signaling and underpin neuronal health. Although widely studied, the contribution of CaMKs to Mendelian disease is rather enigmatic. Here, we describe an unusual neurodevelopmental phenotype, characterized by milestone delay, intellectual disability, autism, ataxia, and mixed hyperkinetic movement disorder including severe generalized dystonia, in a proband who remained etiologically undiagnosed despite exhaustive testing. We performed trio whole-exome sequencing to identify a de novo essential splice-site variant (c.981+1G>A) in CAMK4, encoding CaMKIV. Through in silico evaluation and cDNA analyses, we demonstrated that c.981+1G>A alters CAMK4 pre-mRNA processing and results in a stable mRNA transcript containing a 77-nt out-of-frame deletion and a premature termination codon within the last exon. The expected protein, p.Lys303Serfs*28, exhibits selective loss of the carboxy-terminal regulatory domain of CaMKIV and bears striking structural resemblance to previously reported synthetic mutants that confer constitutive CaMKIV activity. Biochemical studies in proband-derived cells confirmed an activating effect of c.981+1G>A and indicated that variant-induced excessive CaMKIV signaling is sensitive to pharmacological manipulation. Additionally, we found that variants predicted to cause selective depletion of CaMKIV's regulatory domain are unobserved in diverse catalogs of human variation, thus revealing that c.981+1G>A is a unique molecular event. We propose that our proband's phenotype is explainable by a dominant CAMK4 splice-disrupting mutation that acts through a gain-of-function mechanism. Our findings highlight the importance of CAMK4 in human neurodevelopment, provide a foundation for future clinical research of CAMK4, and suggest the CaMKIV signaling pathway as a potential drug target in neurological disease.

Benefits of pallidal stimulation in dystonia are linked to cerebellar volume and cortical inhibition

Clinical benefits of pallidal deep brain stimulation (GPi DBS) in dystonia increase relatively slowly suggesting slow plastic processes in the motor network. Twenty-two patients with dystonia of various distribution and etiology treated by chronic GPi DBS and 22 healthy subjects were examined for short-latency intracortical inhibition of the motor cortex elicited by paired transcranial magnetic stimulation. The relationships between grey matter volume and intracortical inhibition considering the long-term clinical outcome and states of the GPi DBS were analysed. The acute effects of GPi DBS were associated with a shortening of the motor response whereas the grey matter of chronically treated patients with a better clinical outcome showed hypertrophy of the supplementary motor area and cerebellar vermis. In addition, the volume of the cerebellar hemispheres of patients correlated with the improvement of intracortical inhibition which was generally less effective in patients than in controls regardless of the DBS states. Importantly, good responders to GPi DBS showed a similar level of short-latency intracortical inhibition in the motor cortex as healthy controls whereas non-responders were unable to increase it. All these results support the multilevel impact of effective DBS on the motor networks in dystonia and suggest potential biomarkers of responsiveness to this treatment.

Striatal Cholinergic Interneurons in a Knock-in Mouse Model of L-DOPA-Responsive Dystonia

Striatal cholinergic dysfunction is a common phenotype associated with various forms of dystonia in which anti-cholinergic drugs have some therapeutic benefits. However, the underlying substrate of striatal cholinergic defects in dystonia remain poorly understood. In this study, we used a recently developed knock-in mouse model of dopamine-responsive dystonia (DRD) with strong symptomatic responses to anti-cholinergic drugs, to assess changes in the prevalence and morphology of striatal cholinergic interneurons (ChIs) in a model of generalized dystonia. Unbiased stereological neuronal counts and Sholl analysis were used to address these issues. To determine the potential effect of aging on the number of ChIs, both young (3 months old) and aged (15 months old) mice were used. For purpose of comparisons with ChIs, the number of GABAergic parvalbumin (PV)-immunoreactive striatal interneurons was also quantified in young mice. Overall, no significant change in the prevalence of ChIs and PV-immunoreactive cells was found throughout various functional regions of the striatum in young DRD mice. Similar results were found for ChIs in aged animals. Subtle changes in the extent and complexity of the dendritic tree of ChIs were found in middle and caudal regions of the striatum in DRD mice. Additional immunohistochemical data also suggested lack of significant change in the expression of striatal cholinergic M1 and M4 muscarinic receptors immunoreactivity in DRD mice. Thus, together with our previous data from a knock-in mouse model of DYT-1 dystonia (Song et al., 2013), our data further suggest that the dysregulation of striatal cholinergic transmission in dystonia is not associated with major neuroplastic changes in the morphology or prevalence of striatal ChIs.

Highlights-

There is no significant change in the number of striatal ChIs in young and aged mice model of DRD

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There is no significant change in the prevalence of striatal GABAergic PV-containing interneurons in the striatum of young mice models of DRD

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Subtle morphological changes in the dendritic arborization of striatal ChIs are found in the middle and caudal tiers of the striatum in young mice models of DRD

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The levels of both M1 and M4 muscarinic receptors immunoreactivity are not significantly changed in the striatum of DRD mice

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Major changes in the prevalence and morphology of striatal ChIs are unlikely to underlie striatal cholinergic dysfunction in DRD

The influence of occlusal stabilization appliances on cervical dystonia symptoms

Objectives

The aim of this study was to assess the therapeutic efficiency of the occlusal stabilization appliance (OSA) in patients with cervical dystonia (CD).

Methods

The study included 11 patients aged between 29 and 80 years, 7 women and 4 men, diagnosed with primary CD. The patients underwent an extra- and intra-oral clinical examination, followed by para-clinical examinations, necessary for the specifications of the OSA. The following data were recorded: demographic parameters, CD duration, management of the disease, dental impression, recording of the centric relationship, recording of the position of the upper jaw with the facial bow. A standardized OSA was manufactured in a private dental laboratory. Patients received instructions for wearing the OSA for 24 hours. Patients filled a questionnaire designed by us, which evaluated the effects of wearing the OSA over a 24-hours period on the symptoms of CD: muscles contraction, pain, discomfort while walking, sleep quality, tremor. The patients kept the dental appliances, and after three months they completed the questionnaire one more time.

Results

The OSA was applied on the lower arch in 3 (27.3%) patients and on the upper arch in 8 (72.7%) patients. The OSA wearing time for the first 24 h was on average 19.2±6 hours. Total relaxation of dystonic muscles was reported by 9 (81.8%) patients, while 2 (18.2%) patients related partial muscle relaxation. Seven (63.6%) patients reported a pain decrease. Increased comfort while walking was observed by 8 (72.7%) patients. Two (18.2%) patients described an increase of sleep quality. In two (18.2%) patients the tremor disappeared. All patients reported difficulties while eating and removed the OSA during meals. Patients who wore the OSA for more hours, experienced a pain decrease (p=0.08), an increase in sleep quality (p=0.1), the disappearance of the tremor (p=0.1). After three months, only seven patients continued to use the OSA. More patients described a pain decrease after three months (5 (71.4%) vs. 4 (57.1%); p=0.5), relaxation of dystonic muscles (7 (100%) vs. 6 (85.7%); p=0.3).

Conclusions

The use of OSA might be beneficial in CD patients, as it reduced the dystonic symptoms, pain severity and improved the quality of sleep.

Pallidal DBS for dystonia in the age of personalized medicine

In response to the correspondence by Albanese and co-workers, we discuss etiology as a factor predicting outcome of pallidal DBS in dystonia, reanalysing our dataset on causes of non-response to pallidal DBS in isolated dystonia by looking only at patients with a diagnosis of idiopathic dystonia at time of surgery.