Dystonia in spinocerebellar ataxia type 6

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.

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.

Dopa-responsive dystonia in spinocerebellar ataxia 6: A case report

Spinocerebellar ataxia 6 (SCA6) often presents with pure cerebellar ataxia. It is rarely accompanied by extrapyramidal symptoms, such as dystonia and parkinsonism. Here, we describe a case of SCA6 with dopa-responsive dystonia for the first time. A 75-year-old woman was admitted to the hospital with slowly progressive cerebellar ataxia and dystonia in the left upper limb for the past six years. Genetic testing confirmed the diagnosis of SCA6. Her dystonia improved with oral levodopa, and she was able to raise her left hand. Oral levodopa administration may provide early-phase therapeutic benefits for SCA6-associated dystonia.

Real-time machine learning classification of pallidal borders during deep brain stimulation surgery

OBJECTIVE

Deep brain stimulation (DBS) of the internal segment of the globus pallidus (GPi) in patients with Parkinson's disease and dystonia improves motor symptoms and quality of life. Traditionally, pallidal borders have been demarcated by electrophysiological microelectrode recordings (MERs) during DBS surgery. However, detection of pallidal borders can be challenging due to the variability of the firing characteristics of neurons encountered along the trajectory. MER can also be time-consuming and therefore costly. Here we show the feasibility of real-time machine learning classification of striato-pallidal borders to assist neurosurgeons during DBS surgery.

APPROACH

An electrophysiological dataset from 116 trajectories of 42 patients consisting of 11 774 MER segments of background spiking activity in five classes of disease was used to train the classification algorithm. The five classes included awake Parkinson's disease patients, as well as awake and lightly anesthetized genetic and non-genetic dystonia patients. A machine learning algorithm was designed to provide prediction of the striato-pallidal borders, based on hidden Markov models (HMMs) and the L₁-distance measure in normalized root mean square (NRMS) and power spectra of the MER. We tested its performance prospectively against the judgment of three electrophysiologists in the operating rooms of three hospitals using newly collected data.

MAIN RESULTS

The awake and the light anesthesia dystonia classes could be merged. Using MER NRMS and spectra, the machine learning algorithm was on par with the performance of the three electrophysiologists across the striatum-GPe, GPe-GPi, and GPi-exit transitions for all disease classes.

SIGNIFICANCE

Machine learning algorithms enable real-time GPi navigation systems to potentially shorten the duration of electrophysiological mapping of pallidal borders, while ensuring correct pallidal border detection.

Spinocerebellar ataxia type 2 presenting with involuntary movement: a diagnostic dilemma

Spinocerebellar ataxia type 2 (SCA2) is a rare disease characterized by slowly progressive ataxia, dysarthria, ophthalmoplegia, and slow saccade. SCA2 can present with a complex combination of hyperkinetic and hypokinetic movement disorders. Here, we describe a patient with SCA2 that partly mimicked the clinical manifestations of Huntington’s disease; similar symptoms had previously occurred in the patient’s family members. The findings in this report indicate that, when a patient exhibits choreiform movement (i.e., accompanying cerebellar ataxia), an SCA2-related mutation could be responsible for the onset of disease. In addition, this knowledge of the potential for extrapyramidal involvement in such patients is critical for clinicians.

The Comprehensive Management of Cerebellar Ataxia in Adults

PURPOSE OF REVIEW

In this review, we present the multidisciplinary approach to the management of the many neurological, medical, social, and emotional issues facing patients with cerebellar ataxia.

RECENT FINDINGS

Our holistic approach to treatment, developed over the past 25 years in the Massachusetts General Hospital Ataxia Unit, is centered on the compassionate care of the patient and their family, empowering them through engagement, and including the families as partners in the healing process. We present the management of ataxia in adults, beginning with establishing an accurate diagnosis, followed by treatment of the multiple symptoms seen in cerebellar disorders, with a view to maximizing quality of life and effectively living with the consequences of ataxia. We discuss the importance of a multidisciplinary approach to the management of ataxia, including medical and non-medical management and the evidence base that supports these interventions. We address the pharmacological treatment of ataxia, tremor, and other associated movement disorders; ophthalmological symptoms; bowel, bladder, and sexual symptoms; orthostatic hypotension; psychiatric and cognitive symptoms; neuromodulation, including deep brain stimulation; rehabilitation including physical therapy, occupational therapy and speech and language pathology and, as necessary, involving urology, psychiatry, and pain medicine. We discuss the role of palliative care in late-stage disease. The management of adults with ataxia is complex and a team-based approach is essential.

SCA2 presenting as a focal dystonia

BACKGROUND

Spinocerebellar ataxia 2 (SCA2) is an autosomal dominant neurodegenerative disorder caused by CAG repeat expansions in ATXN2 on chromosome 12q24. Patients present with adult-onset progressive gait ataxia, slow saccades, nystagmus, dysarthria and peripheral neuropathy. Dystonia is known to occur as SCA2 advances, but is rarely the presenting symptom.

CASE PRESENTATION

A 43-year-old right handed woman presented with focal dystonia of the right hand which started two years earlier with difficulty writing. There were only mild cerebellar signs. Her mother was reported to have a progressive gait disorder and we subsequently learned that she had SCA2. A total of 10 maternal family members were similarly affected. Over the course of 10 years, the patient's cerebellar signs progressed only mildly however the dystonia worsened to the extent of inability to use her right hand. Dystonia did not improve significantly with botulinum toxin, levodopa or trihexyphenidyl, but has shown marked improvement since DBS implantation in the GPi.

CONCLUSIONS

We describe a patient with SCA2 who presented with focal dystonia of the right upper extremity. Subtle cerebellar signs as well as the family history became especially important given the absence of predominant gait ataxia. Our case emphasizes that focal dystonia is not only a feature of SCA2, but can also rarely be the presenting sign as well as the most prominent feature during the disease course.

Recent advances in understanding and managing dystonia

Within the field of movement disorders, the conceptual understanding of dystonia has continued to evolve. Clinical advances have included improvements in recognition of certain features of dystonia, such as tremor, and understanding of phenotypic spectrums in the genetic dystonias and dystonia terminology and classification. Progress has also been made in the understanding of underlying biological processes which characterize dystonia from discoveries using approaches such as neurophysiology, functional imaging, genetics, and animal models. Important advances include the role of the cerebellum in dystonia, the concept of dystonia as an aberrant brain network disorder, additional evidence supporting the concept of dystonia endophenotypes, and new insights into psychogenic dystonia. These discoveries have begun to shape treatment approaches as, in parallel, important new treatment modalities, including magnetic resonance imaging-guided focused ultrasound, have emerged and existing interventions such as deep brain stimulation have been further refined. In this review, these topics are explored and discussed.

Whole-exome sequencing for variant discovery in blepharospasm

BACKGROUND

Blepharospasm (BSP) is a type of focal dystonia characterized by involuntary orbicularis oculi spasms that are usually bilateral, synchronous, and symmetrical. Despite strong evidence for genetic contributions to BSP, progress in the field has been constrained by small cohorts, incomplete penetrance, and late age of onset. Although several genetic etiologies for dystonia have been identified through whole-exome sequencing (WES), none of these are characteristically associated with BSP as a singular or predominant manifestation.

METHODS

We performed WES on 31 subjects from 21 independent pedigrees with BSP. The strongest candidate sequence variants derived from in silico analyses were confirmed with bidirectional Sanger sequencing and subjected to cosegregation analysis.

RESULTS

Cosegregating deleterious variants (GRCH37/hg19) in CACNA1A (NM_001127222.1: c.7261_7262delinsGT, p.Pro2421Val), REEP4 (NM_025232.3: c.109C>T, p.Arg37Trp), TOR2A (NM_130459.3: c.568C>T, p.Arg190Cys), and ATP2A3 (NM_005173.3: c.1966C>T, p.Arg656Cys) were identified in four independent multigenerational pedigrees. Deleterious variants in HS1BP3 (NM_022460.3: c.94C>A, p.Gly32Cys) and GNA14 (NM_004297.3: c.989_990del, p.Thr330ArgfsTer67) were identified in a father and son with segmental cranio-cervical dystonia first manifest as BSP. Deleterious variants in DNAH17, TRPV4, CAPN11, VPS13C, UNC13B, SPTBN4, MYOD1, and MRPL15 were found in two or more independent pedigrees. To our knowledge, none of these genes have previously been associated with isolated BSP, although other CACNA1A mutations have been associated with both positive and negative motor disorders including ataxia, episodic ataxia, hemiplegic migraine, and dystonia.

CONCLUSIONS

Our WES datasets provide a platform for future studies of BSP genetics which will demand careful consideration of incomplete penetrance, pleiotropy, population stratification, and oligogenic inheritance patterns.

A role for cerebellum in the hereditary dystonia DYT1

DYT1 is a debilitating movement disorder caused by loss-of-function mutations in torsinA. How these mutations cause dystonia remains unknown. Mouse models which have embryonically targeted torsinA have failed to recapitulate the dystonia seen in patients, possibly due to differential developmental compensation between rodents and humans. To address this issue, torsinA was acutely knocked down in select brain regions of adult mice using shRNAs. TorsinA knockdown in the cerebellum, but not in the basal ganglia, was sufficient to induce dystonia. In agreement with a potential developmental compensation for loss of torsinA in rodents, torsinA knockdown in the immature cerebellum failed to produce dystonia. Abnormal motor symptoms in knockdown animals were associated with irregular cerebellar output caused by changes in the intrinsic activity of both Purkinje cells and neurons of the deep cerebellar nuclei. These data identify the cerebellum as the main site of dysfunction in DYT1, and offer new therapeutic targets.

DOI:http://dx.doi.org/10.7554/eLife.22775.001

Dystonia is the third most common type of movement disorder after Parkinson’s disease and tremor. Patients with dystonia experience prolonged involuntary contractions of their muscles, often causing uncontrollable postures or repetitive movements. Almost thirty years ago, genetic studies revealed that a mutation in the gene that encodes a protein called torsinA causes the most common type of dystonia, called DYT1.

Exactly how mutations that affect the torsinA protein give rise to DYT1 remains unclear, and there are still no effective treatments for the disorder. Part of the problem is that we do not fully understand how torsinA works, or which of its many proposed functions is relevant to dystonia. Moreover, attempts to study DYT1 using genetically modified mice have proved largely unsuccessful. This is because mice that simply express the same genetic mutations that cause dystonia in humans do not show the overt symptoms of dystonia.

Fremont, Tewari et al. have now generated a mouse ‘model’ that does show symptoms of dystonia, and used these model mice to investigate the role of torsinA in the disorder. Acutely reducing the amount of torsinA protein in a region of the brain called the cerebellum induced the symptoms of dystonia in the mice. Conversely, reducing the amount of torsinA in a different brain area known as the basal ganglia had no such effect, even though both the cerebellum and the basal ganglia contribute to movement. Furthermore, neither manipulation had any effect in juvenile mice, which suggests that, in contrast to humans, young mice can compensate for the loss of torsinA.

Fremont, Tewari et al. also found that the loss of torsinA causes the cerebellum to generate incorrect output signals, which in turn trigger the abnormal movements seen in dystonia. In the future, further studies of the model mice could identify the exact changes that occur in neurons following the loss of torsinA from the cerebellum. Understanding these changes could potentially pave the way for developing effective treatments for DYT1 and other dystonias.

DOI:http://dx.doi.org/10.7554/eLife.22775.002

SCA 6 with Writer's Cramp: The Phenotype Expanded

Spinocerebellar ataxia type 6 (SCA6) presents typically with a pure cerebellar syndrome. Only 1 SCA 6 patient with writer's cramp has been reported on and a family history of ataxia and writer's cramp has never been reported on. Two other SCA6 patients with a shoulder girdle/hand dystonia and unspecified upper-limb dystonia with a family history of ataxia have been reported on. We report on the largest family with SCA6 and writer's cramp. The proband developed dysarthria, ataxia, and writer's cramp by age 37. His father presented with ataxia at 55, followed by writer's cramp and dysarthria. The proband's brother developed ataxia at 41, followed by dysarthria and writer's cramp. A paternal uncle (deceased; not examined) and 58-yr-old brother both developed pure ataxia (genetic testing is pending). This large family with complex movement disorder demonstrates that it is important to consider SCA6 in a patient presenting with an ataxia and writer's cramp and supports cerebellum involvement in dystonia.

Paroxysmal tonic upward gaze as a presentation of de-novo mutations in CACNA1A

OBJECTIVE

Paroxysmal tonic upward gaze was initially described as a benign phenomenon with negative investigations and eventual complete resolution of symptoms. Later publications demonstrated that a similar clinical picture may arise from structural brain lesions, channelopathies, neurotransmitter disorders, and epileptic seizures. CACNA1A related disorders manifest as a wide spectrum of paroxysmal neurological disorders: episodic ataxia 2, hemiplegic migraine, benign paroxysmal torticollis of infancy, and paroxysmal vertigo. Paroxysmal tonic upward gaze as a phenomenon in patients with mutations in the CACNA1A gene has only been reported once.

METHODS

We describe three patients with multiple episodes of paroxysmal tonic upward gaze that appeared during the first months of life. In addition the patients demonstrated motor and language delay and cerebellar ataxia. A sequence analysis of the CACNA1A gene in one patient and whole exome sequencing in the other patients were performed.

RESULTS

Sequence analysis of the CACNA1A gene in one patient and whole exome sequencing in the two other patients revealed 3 different de-novo mutations in the CACNA1A gene.

CONCLUSION

CACNA1A mutations should be evaluated in infants and young children with paroxysmal tonic upgaze especially if associated with developmental delay, cerebellar signs, and other types of paroxysmal event.

Dystonia and cerebellar degeneration in the leaner mouse mutant

Cerebellar degeneration is traditionally associated with ataxia. Yet, there are examples of both ataxia and dystonia occurring in individuals with cerebellar degeneration. There is also substantial evidence suggesting that cerebellar dysfunction alone may cause dystonia. The types of cerebellar defects that may cause ataxia, dystonia, or both have not been delineated. In the current study, we explored the relationship between cerebellar degeneration and dystonia using the leaner mouse mutant. Leaner mice have severe dystonia that is associated with dysfunctional and degenerating cerebellar Purkinje cells. Whereas the density of Purkinje cells was not significantly reduced in 4 week-old leaner mice, approximately 50% of the neurons was lost by 34 weeks of age. On the other hand, the dystonia and associated functional disability became significantly less severe during this same interval. In other words, dystonia improved as Purkinje cells were lost, suggesting that dysfunctional Purkinje cells, rather than Purkinje cell loss, contribute to the dystonia. These results provide evidence that distorted cerebellar function may cause dystonia and support the concept that different types of cerebellar defects can have different functional consequences.

Abnormal high-frequency burst firing of cerebellar neurons in rapid-onset dystonia-parkinsonism

Loss-of-function mutations in the α3 isoform of the Na(+)/K(+) ATPase (sodium pump) are responsible for rapid-onset dystonia parkinsonism (DYT12). Recently, a pharmacological model of DYT12 was generated implicating both the cerebellum and basal ganglia in the disorder. Notably, partially blocking sodium pumps in the cerebellum was necessary and sufficient for induction of dystonia. Thus, a key question that remains is how partially blocking sodium pumps in the cerebellum induces dystonia. In vivo recordings from dystonic mice revealed abnormal high-frequency bursting activity in neurons of the deep cerebellar nuclei (DCN), which comprise the bulk of cerebellar output. In the same mice, Purkinje cells, which provide strong inhibitory drive to DCN cells, also fired in a similarly erratic manner. In vitro studies demonstrated that Purkinje cells are highly sensitive to sodium pump dysfunction that alters the intrinsic pacemaking of these neurons, resulting in erratic burst firing similar to that identified in vivo. This abnormal firing abates when sodium pump function is restored and dystonia caused by partial block of sodium pumps can be similarly alleviated. These findings suggest that persistent high-frequency burst firing of cerebellar neurons caused by sodium pump dysfunction underlies dystonia in this model of DYT12.

[A case of 77-year-old male with spinocerebellar ataxia type 31 with left dominant dystonia]

We report on the case of a 77-year-old male with genetically proven spinocerebellar ataxia type 31 (SCA31) who had dystonia. He was referred to our hospital for evaluation following a 6-year history of slowly progressive unsteadiness of his left leg during walking and dysarthria at the age of 62 years old. On the basis of his symptoms, we diagnosed him as spinocerebellar degeneration (SCD), and prescribed taltirelin hydrate. However, his symptoms continued to worsen. He required a cane for walking at the age of 63 years, and a wheelchair at the age of 66 years. He was admitted to our hospital following acute cerebral infarction at the age of 77 years. On examination at admission, right hemiparesis and cerebellar ataxia were detected. And left hallux moved involuntarily toward the top surface of the foot at rest, that is dystonia. The dystonia was not associated with cerebral infarction, because it had been several years with dystonia that he got cerebral infarction. Genetic analysis revealed that this patient harbored a heterozygous SCA31 mutation. Previously there have been no reports of SCA31 associated with dystonia. Our case report support clinical heterogeneity of SCA31, and highlight the importance of considering this type in patients with dystonia and ataxia. Patients with the combination of dystonia and ataxia and a family history of a neurodegenerative disorder should be tested for SCA31.

Assessment of patients with isolated or combined dystonia: an update on dystonia syndromes

The clinical evaluation of a patient with dystonia is a stepwise process, beginning with classification of the phenomenology of the movement disorder(s), then formulation of the dystonia syndrome, which, in turn, leads to a targeted etiological differential diagnosis. In recent years, there have been significant advances in our understanding of the etiological basis of dystonia, aided especially by discoveries in imaging and genetics. In this review, we provide an update on the assessment of a patient with dystonia, including the phenomenology of dystonia and highlighting how to integrate clinical, imaging, blood, and neurophysiological investigations in order to formulate a dystonia syndrome. Evolving or emerging dystonia syndromes are reviewed, and potential etiologies of these as well as established dystonia syndromes listed to guide diagnostic testing. © 2013 Movement Disorder Society.

Magnetic resonance imaging biomarkers in patients with progressive ataxia: current status and future direction

A diagnostic challenge commonly encountered in neurology is that of an adult patient presenting with ataxia. The differential is vast and clinical assessment alone may not be sufficient due to considerable overlap between different causes of ataxia. Magnetic resonance (MR)-based biomarkers such as voxel-based morphometry, MR spectroscopy, diffusion-weighted and diffusion-tensor imaging and functional MR imaging are gaining great attention for their potential as indicators of disease. A number of studies have reported correlation with clinical severity and underlying pathophysiology, and in some cases, MR imaging has been shown to allow differentiation of conditions causing ataxia. However, despite recent advances, their sensitivity and specificity vary. In addition, questions remain over their validity and reproducibility, especially when applied in routine clinical practice. This article extensively reviews the current literature regarding MR-based biomarkers for the patient with predominantly adult-onset ataxia. Imaging features characteristic of a particular ataxia are provided and features differentiating ataxia groups and subgroups are discussed. Finally, discussion will turn to the feasibility of applying these biomarkers in routine clinical practice.

The genetics of dystonias

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

Limited regional cerebellar dysfunction induces focal dystonia in mice

Dystonia is a complex neurological syndrome broadly characterized by involuntary twisting movements and abnormal postures. The anatomical distribution of the motor symptoms varies among dystonic patients and can range from focal, involving an isolated part of the body, to generalized, involving many body parts. Functional imaging studies of both focal and generalized dystonias in humans often implicate the cerebellum suggesting that similar pathological processes may underlie both. To test this, we exploited tools developed in mice to generate animals with gradients of cerebellar dysfunction. By using conditional genetics to regionally limit cerebellar dysfunction, we found that abnormalities restricted to Purkinje cells were sufficient to cause dystonia. In fact, the extent of cerebellar dysfunction determined the extent of abnormal movements. Dysfunction of the entire cerebellum caused abnormal postures of many body parts, resembling generalized dystonia. More limited regions of dysfunction that were created by electrical stimulation or conditional genetic manipulations produced abnormal movements in an isolated body part, resembling focal dystonia. Overall, these results suggest that focal and generalized dystonias may arise through similar mechanisms and therefore may be approached with similar therapeutic strategies.

Spinocerebellar ataxia type 6

The autosomal dominant spinocerebellar ataxias (SCA) are a genetically heterogeneous group of neurodegenerative disorders characterized by progressive motor incoordination, in some cases with ataxia alone and in others in association with additional progressive neurological deficits. Spinocerebellar ataxia type 6 (SCA6) is the prototype of a pure cerebellar ataxia, associated with a severe form of progressive ataxia and cerebellar dysfunction. SCA6, originally classified as such by Zhuchenko et al. (1997), is caused by a CAG repeat expansion in the CACNA1A gene which encodes the α1A subunit of the P/Q-type voltage-gated calcium channel. SCA6 is one of ten polyglutamine-encoding CAG nucleotide repeat expansion disorders comprising other neurodegenerative disorders such as Huntington's disease. The present review describes clinical, genetic, and pathological manifestations associated with this illness. Currently, there is no treatment for this neurodegenerative disease. Successful therapeutic strategies must target a valid pathological mechanism; thus, understanding the underlying mechanisms of disease is crucial to finding a proper treatment. Hence, this chapter will discuss as well the molecular mechanisms possibly associated with SCA6 pathology and their implication for the development of future treatment.

Movement disorders in spinocerebellar ataxias

Autosomal dominant spinocerebellar ataxias (SCAs) can present with a large variety of noncerebellar symptoms, including movement disorders. In fact, movement disorders are frequent in many of the various SCA subtypes, and they can be the presenting, dominant, or even isolated disease feature. When combined with cerebellar ataxia, the occurrence of a specific movement disorder can provide a clue toward the underlying genotype. There are reasons to believe that for some coexisting movement disorders, the cerebellar pathology itself is the culprit, for example, in the case of cortical myoclonus and perhaps dystonia. However, movement disorders in SCAs are more likely related to extracerebellar pathology, and imaging and neuropathological data indeed show involvement of other parts of the motor system (substantia nigra, striatum, pallidum, motor cortex) in some SCA subtypes. When confronted with a patient with an isolated movement disorder, that is, without ataxia, there is currently no reason to routinely screen for SCA gene mutations, the only exceptions being SCA2 in autosomal dominant parkinsonism (particularly in Asian patients) and SCA17 in the case of a Huntington's disease-like presentation without an HTT mutation.

The functional neuroanatomy of dystonia

Dystonia is a neurological disorder characterized by involuntary twisting movements and postures. There are many different clinical manifestations, and many different causes. The neuroanatomical substrates for dystonia are only partly understood. Although the traditional view localizes dystonia to basal ganglia circuits, there is increasing recognition that this view is inadequate for accommodating a substantial portion of available clinical and experimental evidence. A model in which several brain regions play a role in a network better accommodates the evidence. This network model accommodates neuropathological and neuroimaging evidence that dystonia may be associated with abnormalities in multiple different brain regions. It also accommodates animal studies showing that dystonic movements arise with manipulations of different brain regions. It is consistent with neurophysiological evidence suggesting defects in neural inhibitory processes, sensorimotor integration, and maladaptive plasticity. Finally, it may explain neurosurgical experience showing that targeting the basal ganglia is effective only for certain subpopulations of dystonia. Most importantly, the network model provides many new and testable hypotheses with direct relevance for new treatment strategies that go beyond the basal ganglia. This article is part of a Special Issue entitled "Advances in dystonia".

Nonprimary dystonias

Dystonias can be classified as primary or secondary, as dystonia-plus syndromes, and as heredodegenerative dystonias. Their prevalence is difficult to determine. In our experience 80-90% of all dystonias are primary. About 20-30% of those have a genetic background; 10-20% are secondary, with tardive dystonia and dystonia in cerebral palsy being the most common forms. If dystonia in spastic conditions is accepted as secondary dystonia, this is the most common form of all dystonia. In primary dystonias, the dystonic movements are the only symptoms. In secondary dystonias, dystonic movements result from exogenous processes directly or indirectly affecting brain parenchyma. They may be caused by focal and diffuse brain damage, drugs, chemical agents, physical interactions with the central nervous system, and indirect central nervous system effects. Dystonia-plus syndromes describe brain parenchyma processes producing predominantly dystonia together with other movement disorders. They include dopa-responsive dystonia and myoclonus-dystonia. Heredodegenerative dystonias are dystonic movements occurring in the context of other heredodegenerative disorders. They may be caused by impaired energy metabolism, impaired systemic metabolism, storage of noxious substances, oligonucleotid repeats and other processes. Pseudodystonias mimic dystonia and include psychogenic dystonia and various orthopedic, ophthalmologic, vestibular, and traumatic conditions. Unusual manifestations, unusual age of onset, suspect family history, suspect medical history, and additional signs may indicate nonprimary dystonia. If they are suspected, etiological clarification becomes necessary. Unfortunately, potential etiologies are legion. Diagnostic algorithms can be helpful. Treatment of nonprimary dystonias, with few exceptions, does not differ from treatment of primary dystonias. The most effective treatment for focal and segmental dystonias is local botulinum toxin injections. Deep brain stimulation of the globus pallidus internus is effective for generalized dystonia. Antidystonic drugs, including anticholinergics, tetrabenazine, clozapine, and gamma-aminobutyric acid receptor agonists, are less effective and often produce adverse effects. Dopamine is extremely effective in dopa-responsive dystonia. The Bertrand procedure can be effective in cervical dystonia. Other peripheral surgery, including myotomy, myectomy, neurotomy, rhizotomy, ramizectomy, and accessory nerve neurolysis, has largely been abandoned. Central surgery other than deep brain stimulation is obsolete. Adjuvant therapies, including orthoses, physiotherapy, ergotherapy, behavioral therapy, social support, and support groups, may be helpful. Analgesics should also be considered where appropriate.

Expansion of the phenotypic spectrum of SCA14 caused by the Gly128Asp mutation in PRKCG

Two cases of spinocerebellar ataxia type 14 (SCA14) with a G128D mutation in the protein kinase C gamma gene (PRKCG) without a definite family history have been reported previously. Here, we describe the first familial cases of SCA14 with a G128D mutation in PRKCG. Among three family members, the chief complaints varied and included ataxic gait, cervical dystonia, and positional vertigo. Moreover, retinal degeneration and facial muscle weakness were observed, although these are not expected to be present in SCA14. Cerebral blood flow evaluation using single photon emission computed tomography (SPECT) also differed among family members. It is possible that patients with the G128D mutation suffering from SCA14 may sometimes be classified as unaffected due to the varying clinical signs among family members.

Neuronal firing rates and patterns in the globus pallidus internus of patients with cervical dystonia differ from those with Parkinson's disease

Cervical dystonia (CD) is a movement disorder that involves involuntary turning and twisting of the neck caused by abnormal muscle contraction. Deep brain stimulation (DBS) in the globus pallidus internus (GPi) is used to treat both CD and the motor symptoms of Parkinson's disease (PD). It has been suggested that the differing motor symptoms in CD and PD may arise from a decreased GPi output in CD and elevation of output in PD. To test this hypothesis, extracellular recordings of GPi neuronal activity were obtained during stereotactic surgery for the implantation of DBS electrodes in seven idiopathic CD and 14 PD patients. The mean GPi neuronal firing rate recorded from CD patients was lower than that in PD patients (P < 0.001; means +/- SE: 71.4 +/- 2.2 and 91.7 +/- 3.0 Hz, respectively). Furthermore, GPi neurons fired in a more irregular pattern consisting of more frequent and longer pauses in CD compared with PD patients. When comparisons were done based on locations of recordings, these differences in firing rates and patterns were limited to the ventral portion of the GPi. In contrast, no difference in firing rate or pattern was observed in the globus pallidus externus between the two groups. These findings suggest that alterations in both firing rate and firing pattern may underlie the differing motor symptoms associated with these two movement disorders.

Une crampe de l’écrivain associée à une ataxie spinocérébelleuse de type 7

Spinocerebellar ataxia type 7 (SCA 7) is a rare autosomal dominant neurodegenerative disorder (ADCA) caused by expansion of a highly unstable CAG repeat. Clinical features including progressive cerebellar, retinal degeneration and pyramidal signs. We report a patient with SCA 7 diagnosis revealed by progressive cerebellar ataxia and writer's cramp.

Cervical dystonia in spinocerebellar ataxia type 2: clinical and polymyographic findings

Eighteen patients from three large multigenerational families with genetically established spinocerebellar ataxia type 2 (SCA2) were examined, with special attention to the presence of dystonic features. Cervical dystonia (CD) was diagnosed according to standardised clinical criteria. CD was scored using the Tsui score. Polymyography was performed in six cases using bilateral surface electrode recordings of the sternocleidomastoid and trapezius muscles together with needle electrode recordings of the splenius capitis muscles bilaterally. CD was found in 11 of 18 patients (61%), and was the presenting symptom in one case. Severity of CD was mild to moderate, with Tsui scores ranging from 5 to 12 points. Polymyography in 6 of 11 SCA2 patients with CD showed the typical pattern of dystonia with spontaneous, involuntary muscle activation at rest in at least one neck muscle with disturbed reciprocal inhibition of antagonistic neck muscles. CD appears to be a common clinical feature in SCA2 and may precede ataxia and gait disturbance. By contrast, none of the 18 patients had dystonic features in other body regions. CD has probably been underreported in patients with the ataxic SCA2 phenotype and should be considered as an additional clinical manifestation in patients with hereditary ataxia.

Parkinsonism and nigrostriatal dysfunction are associated with spinocerebellar ataxia type 6 (SCA6)

SCA6 is a slowly progressive, late-onset cerebellar ataxia due to a trinucleotide expansion in the CACNA1A gene. We describe two unrelated cases that presented with Parkinsonism and cerebellar ataxia. One case was L-dopa-responsive with a pattern of (18)F-dopa uptake similar to Parkinson's disease, and the second case was not L-dopa-responsive and had an atypical pattern of nigrostriatal dysfunction. We suggest that SCA6, in common with SCA2 and SCA3, may be associated with Parkinsonism attributable to nigral loss and dopaminergic dysfunction. Moreover, isolated cases may be confused with multiple system atrophy.

Caytaxin deficiency causes generalized dystonia in rats

The genetically dystonic rat (SD-dt:JFL) is an autosomal recessive model of generalized dystonia. Without cerebellectomy, the dt rat dies prior to Postnatal Day 40. The dt locus was mapped to a 4.2 Mb region on Chr 7q11 and candidate genes were screened with semi-quantitative RT-PCR. Then, Southern blotting and genomic DNA sequencing identified the 3'-long terminal repeat portion of an intracisternal A particle element inserted into Intron 1 of Atcay, the gene which encodes caytaxin. Northern and Western blotting and quantitative real-time RT-PCR defined the Atcay allele in dt rats (Atcay(dt)) as hypomorphic. To establish a framework for functional studies of caytaxin, the developmental expression of rat Atcay transcript was analyzed with Northern blotting, relative quantitative multiplex real-time RT-PCR (QRT-PCR) and in situ hybridization. With a multiple tissue Northern blot, three Atcay transcripts were identified in brain but none were present in heart, spleen, lung, liver, muscle, kidney or testis. With a multiple time-point Northern blot, the same three transcripts were present in cerebellum at Embryonic Day (E15), Postnatal Day 1 (P1), P7, P14, P36 and 8 months. During early development (E15 to P14), the relative proportion of the smallest transcript was increased. QRT-PCR was performed with total RNA from cerebral cortex, striatum, thalamus, hippocampus and cerebellum. Transcript levels peaked at P7 in hippocampus, increased linearly from P1 to P36 in cerebellum, and showed minimal developmental regulation in cerebral cortex. Radioactive in situ hybridization localized Atcay transcript to seemingly all neuronal populations in brain. In cerebellum, Atcay transcript was present in the molecular, Purkinje and granular layers; transcript density in the molecular layer peaked at P14. In the background of previous biochemical, behavioral and electrophysiological studies in the dt rat, our data are compatible with a vital role for caytaxin in the development and neurophysiology of cerebellar cortex.

Animal models of generalized dystonia

Dystonia is a prevalent neurological disorder characterized by abnormal co-contractions of antagonistic muscle groups that produce twisting movements and abnormal postures. The disorder may be inherited, arise sporadically, or result from brain insult. Dystonia is a heterogeneous disorder because patients may exhibit focal or generalized symptoms associated with abnormalities in many brain regions including basal ganglia and cerebellum. Elucidating the pathogenic mechanisms underlying dystonia has therefore been challenging. Animal models of dystonia exhibit similar heterogeneity and are useful for understanding pathogenesis. The neurochemical and neurophysiological abnormalities in rodents with idiopathic generalized dystonia suggest that dysfunctional output from basal ganglia, cerebellum, or from multiple systems is the cause of motor dysfunction. Findings from drug- or toxin-induced dystonia in rodents and nonhuman primates mirror the genetic models. The parallels between dystonia in humans and animals suggest that the models will continue to prove useful in determining pathogenesis. Furthermore, detailed characterization of the existing models of dystonia and the development of new models hold promise for the identification of novel therapeutics.

Rodent models for dystonia research: Characteristics, evaluation, and utility

A large number of different genetic and acquired disorders of the nervous system may be associated with dystonia. To elucidate its pathogenesis and to facilitate the discovery of potential novel treatments, there has been a growing interest in the development of animal models and particularly rodent models. Multiple animal models for dystonia have now been developed and partially characterized. The results obtained from studies of these models often lead in very different directions, in part because the different models target different aspects of a very heterogeneous disorder. A recent workshop addressed four main issues affecting those who conduct dystonia research with animal models, including the different ways in which dystonic disorders can be modeled in rodents, key features that constitute a useful model, methods used in the evaluation of these models, and recommendations for future research. This review summarizes the main outcomes of this conference. 2005 Movement Disorder Society.

Dystonia as a presenting sign of spinocerebellar ataxia type 1

We report on a 39-year-old man who presented initially with marked blepharospasm, oromandibular dystonia and retrocollis and one year later developed mild ataxia. Our findings suggest that dystonia can be a disabling presenting sign of SCA1 and support the clinical heterogeneity of SCA1, highlighting the importance of considering this entity in patients combining dystonia and cerebellar ataxia.

Characterization of ataxias with magnetic resonance imaging and spectroscopy

A wide variety of autosomal transmitted ataxias exist and their ultimate characterization requires genetic testing. Common clinical characteristics among different ataxia types complicate the choice of the appropriate genetic test. Magnetic resonance imaging (MRI) and magnetic resonance spectroscopy (MRS) generally show cerebellar or cerebral atrophy and perturbed metabolite levels which differ between ataxias. In order to help the clinician accurately identify the ataxia type, reported MRI and MRS data in different brain regions are summarized for more than 60 different types of autosomal inherited and sporadic ataxias.

Focal dystonia as a presenting sign of spinocerebellar ataxia 17

We report on the clinical manifestation of spinocerebellar ataxia 17 (SCA17) in 3 members of a German family, in whom the pathological repeat expansion in the TATA-binding protein gene ranged from 53 to 55 repeats (normal: 29-42). The main clinical features were focal dystonia as presenting sign, followed by cerebellar ataxia, and, in the later course of one case, dementia and marked spasticity with signs of cerebellar and cerebral atrophy on brain computed tomography (CT) scan. In conclusion, SCA17 mutations should be considered in the differential diagnosis of focal dystonia.

Slowly progressive cerebellar ataxia and cervical dystonia: clinical presentation of a new form of spinocerebellar ataxia?

We describe 5 cases with a rare combination of young-onset, slowly progressive cerebellar ataxia and cervical dystonia. Two were sporadic, whereas the other 3 were familial, including 2 from one family. The age of onset of these cases was between 16 and 37 years. The presenting symptom was cervical dystonia and/or dystonic head tremor in 3 patients and hand or lower limb tremor in 2. In 2 cases, cervical dystonia and/or dystonic head tremor developed approximately 6 to 10 years before cerebellar dysfunction, and in three they developed at the same time. Apart from cervical dystonia, there was mild dystonic limb involvement in 2 cases, but generalized dystonia was not seen. Cerebellar ataxia was slowly progressive. A literature search showed 10 cases of cervical dystonia associated with genetically undetermined (n = 5) or genetically proven (n = 5) spinocerebellar ataxia (SCA). When the genotype was known, these patients had either SCA3, 6, 7, or 12. However, our 5 cases (or their first-degree relatives) tested negative for SCA1, 2, 3, 6, and 7, and in the 4 cases (or their first-degree relatives) tested for SCA12, the result was negative. We propose that this rare phenotype manifesting as a combination of cerebellar ataxia and cervical dystonia may represent one or more new, as yet uncharacterized, genotypes of inherited young-onset spinocerebellar ataxia.

Movement disorders in Friedreich's ataxia

Since the discovery of the gene mutation causing Friedreich's ataxia (FA), the rich spectrum of clinical manifestations of this autosomal recessive disorder is being increasingly recognized. Movement disorders besides ataxia, however, have not been fully characterized in patients with FA. We describe here two young male patients who, in addition to progressive ataxia, kinetic tremor and other typical features of FA, also manifest axial and limb dystonia. The primary purpose of this report is to draw attention to the broad spectrum of hyperkinetic movement disorders that can present as or be associated with FA.