Sporadic rapid-onset dystonia-parkinsonism syndrome: failure of bilateral pallidal stimulation

Rapid-Onset Dystonia and Parkinsonism in a Patient With Gaucher Disease

Biallelic mutations in GBA1 cause the lysosomal storage disorder Gaucher disease, and carriers of GBA1 variants have an increased risk of Parkinson's disease (PD). It is still unknown whether GBA1 variants are also associated with other movement disorders. We present the case of a woman with type 1 Gaucher disease who developed acute dystonia and parkinsonism at 35 years of age during a recombinant enzyme infusion treatment. She developed severe dystonia in all extremities and a bilateral pill-rolling tremor that did not respond to levodopa treatment. Despite the abrupt onset of symptoms, neither Sanger nor whole genome sequencing revealed pathogenic variants in ATP1A3 associated with rapid-onset dystonia-parkinsonism (RDP). Further examination showed hyposmia and presynaptic dopaminergic deficits in [18F]-DOPA PET, which are commonly seen in PD but not in RDP. This case extends the spectrum of movement disorders reported in patients with GBA1 mutations, suggesting an intertwined phenotype.

ATP1A3 mutation in rapid-onset dystonia parkinsonism: New data and genotype-phenotype correlation analysis

Background

Rapid-onset dystonia parkinsonism (RDP) is a rare disease caused by ATP1A3 mutation with considerable clinical heterogeneity. Increased knowledge of RDP could be beneficial in its early diagnosis and treatment.

Objective

This study aimed to summarize the gene mutation spectrum of ATP1A3 associated with RDP, and to explore the correlation of ATP1A3 variants with RDP clinical phenotypes.

Methods

In this study, we reported two RDP patients from a family with a novel inherited ATP1A3 variant. Then, we reviewed and analyzed the available literature in English focused on ATP1A3-causative RDP. A total of 35 articles covering 15 families (59 patients) and 36 sporadic RDP cases were included in our analysis.

Results

The variant A813V (2438C>T) in ATP1A3 found in our cases was a novel mutant. Delays in diagnosis were common, with a mean delay time of 14 years. ATP1A3 had distinct RDP-related mutation hotspots, which consisted of exon8, 14, 17, and 18, and the most frequently occurring variants were T613M and I578S. Approximately 74.5% of patients have specific triggers before disease onset, and 82.1% of RDPs have stable symptoms within 1 month. The incidence rates of dystonia and bradykinesia are 100 and 88.1%, respectively. The onset site varied and exhibited a rostrocaudal gradient distribution pattern in 45% of patients with RDP. Approximately 63.6% of patients had mild improvement after receiving comprehensive interventions, especially in gait disturbance amelioration.

Conclusion

In patients with acute and unexplained dystonia or bradykinesia, gene screening on ATP1A3 should be timely performed. When a diagnosis has been made, treatments that may be effective are to be attempted. Our study would be helpful for the early diagnosis and treatment of ATP1T3-related RDP.

Deep Brain Stimulation of the Globus Pallidus Internus for Secondary Dystonia: Clinical Cases and Systematic Review of the Literature Regarding the Effectiveness of Globus Pallidus Internus versus Subthalamic Nucleus

OBJECTIVE

Deep brain stimulation (DBS) is a frequently applied therapy in primary dystonia. For secondary dystonia, the effects can be less favorable. We share our long-term findings in 9 patients with severe secondary dystonia and discuss these findings in the light of the literature.

METHODS

Patients who had undergone globus pallidus internus (GPi)-DBS for secondary dystonia were included. Burke-Fahn-Marsden Dystonia Rating Scale (BFMDRS) scores, clinical improvement rates, follow-up periods, stimulation parameters and the need for internal pulse generator replacements were analyzed. The PubMed and Google Scholar databases were searched for articles describing GPi-DBS and subthalamic nucleus (STN)-DBS only for secondary dystonia cases. Keywords were "dystonia," "deep brain stimulation," "GPi," "dystonia," "deep brain stimulation," and "STN."

RESULTS

A total of 9 secondary dystonia patients (5 male, 4 female) had undergone GPi-DBS with microelectrode recording in our units. The mean follow-up period was 29 months. The average BFMDRS score was 58.2 before the surgery, whereas the mean value was 36.5 at the last follow-up of the patients (mean improvement, 39%; minimum, 9%; maximum, 63%). In the literature review, we identified 264 GPi-DBS cases (mean follow-up, 19 months) in 72 different articles about secondary dystonia. The mean BFMDRS improvement rate was 52%. In 146 secondary dystonia cases, reported in 19 articles, STN-DBS was performed. The average follow-up period was 20 months and the improvement in BFMDRS score was 66%.

CONCLUSIONS

Although GPi-DBS has favorable long-term efficacy and safety in the treatment of patients with secondary dystonia, STN seems a promising target for stimulation in patients with secondary dystonia. Further studies including a large number of patients, longer follow-up periods, and more homogenous patients are necessary to establish the optimal target for DBS in the management of secondary dystonias.

Arching deep brain stimulation in dystonia types

Although medical treatment including botulinum toxic injection is the first-line treatment for dystonia, response is insufficient in many patients. In these patients, deep brain stimulation (DBS) can provide significant clinical improvement. Mounting evidence indicates that DBS is an effective and safe treatment for dystonia, especially for idiopathic and inherited isolated generalized/segmental dystonia, including DYT-TOR1A. Other inherited dystonia and acquired dystonia also respond to DBS to varying degrees. For Meige syndrome (craniofacial dystonia), other focal dystonia, and some rare inherited dystonia, further evidences are still needed to evaluate the role of DBS. Because short disease duration at DBS surgery and absence of fixed musculoskeletal deformity are associated with better outcome, DBS should be considered as early as possible when indicated after careful evaluation including genetic work-up. This review will focus on the factors to be considered in DBS for patients with dystonia and the outcome of DBS in the different types of dystonia.

Pallidal Deep Brain Stimulation for Monogenic Dystonia: The Effect of Gene on Outcome

Globus pallidus internus deep brain stimulation (GPi DBS) is the most effective intervention for medically refractory segmental and generalized dystonia in both children and adults. Predictive factors for the degree of improvement after GPi DBS include shorter disease duration and dystonia subtype with idiopathic isolated dystonia usually responding better than acquired combined dystonias. Other factors contributing to variability in outcome may include body distribution, pattern of dystonia and DBS related factors such as lead placement and stimulation parameters. The responsiveness to DBS appears to vary between different monogenic forms of dystonia, with some improving more than others. The first observation in this regard was reports of superior DBS outcomes in DYT-TOR1A (DYT1) dystonia, although other studies have found no difference. Recently a subgroup with young onset DYT-TOR1A, more rapid progression and secondary worsening after effective GPi DBS, has been described. Myoclonus dystonia due to DYT-SCGE (DYT11) usually responds well to GPi DBS. Good outcomes following GPi DBS have also been documented in X-linked dystonia Parkinsonism (DYT3). In contrast, poorer, more variable DBS outcomes have been reported in DYT-THAP1 (DYT6) including a recent larger series. The outcome of GPi DBS in other monogenic isolated and combined dystonias including DYT-GNAL (DYT25), DYT-KMT2B (DYT28), DYT-ATP1A3 (DYT12), and DYT-ANO3 (DYT24) have been reported with varying results in smaller numbers of patients. In this article the available evidence for long term GPi DBS outcome between different genetic dystonias is reviewed to reappraise popular perceptions of expected outcomes and revisit whether genetic diagnosis may assist in predicting DBS outcome.

Mutational and phenotypic expansion of ATP1A3-related disorders: Report of nine cases

BACKGROUND

Mutations in the ATP1A3 gene are known to be the cause of three distinct neurological syndromes including alternating hemiplegia of childhood (AHC), rapid-onset dystonia parkinsonism (RDP) and cerebellar ataxia, arefexia, pes cavus, optic atrophy and sensorineural hearing impairment (CAPOS). Recent studies have suggested the broader diversity of ATP1A3-related disorders. This study aimed to investigate the clinical spectrum in patients carrying causative mutations within the ATP1A3 gene.

METHOD

The medical histories of nine unrelated patients with diverse phenotypes harboring variants in ATP1A3 were retrospectively analyzed after they were referred to a tertiary epilepsy center in one of the two different health care systems (Germany or Thailand). Clinical features, neurophysiological data, imaging results, genetic characteristics and treatments were reviewed.

RESULTS

Three patients harbor novel mutations in the ATP1A3 gene. Atypical clinical features and imaging findings were observed in two cases, one with hemiplegia-hemiconvulsion-epilepsy syndrome, and the other with neurodegeneration with brain iron accumulation. All nine patients presented with intellectual impairment. Alternating hemiplegia of childhood (AHC) was the most common phenotype (67%). Flunarizine and topiramate led to symptom reduction in 83% and 25% of AHC cases administered, respectively.

CONCLUSION

The present case series expands the clinical and genetic spectrum of ATP1A3-related disorders.

Pallidal Deep Brain Stimulation in DYT6 Dystonia: Clinical Outcome and Predictive Factors for Motor Improvement

Pallidal deep brain stimulation is an established treatment in dystonia. Available data on the effect in DYT-THAP1 dystonia (also known as DYT6 dystonia) are scarce and long-term follow-up studies are lacking. In this retrospective, multicenter follow-up case series of medical records of such patients, the clinical outcome of pallidal deep brain stimulation in DYT-THAP1 dystonia, was evaluated. The Burke Fahn Marsden Dystonia Rating Scale served as an outcome measure. Nine females and 5 males were enrolled, with a median follow-up of 4 years and 10 months after implant. All benefited from surgery: dystonia severity was reduced by a median of 58% (IQR 31-62, p = 0.001) at last follow-up, as assessed by the Burke Fahn Marsden movement subscale. In the majority of individuals, there was no improvement of speech or swallowing, and overall, the effect was greater in the trunk and limbs as compared to the cranio-cervical and orolaryngeal regions. No correlation was found between disease duration before surgery, age at surgery, or preoperative disease burden and the outcome of deep brain stimulation. Device- and therapy-related side-effects were few. Accordingly, pallidal deep brain stimulation should be considered in clinically impairing and pharmaco-resistant DYT-THAP1 dystonia. The method is safe and effective, both short- and long-term.

Revising rapid-onset dystonia-parkinsonism: Broadening indications for ATP1A3 testing

BACKGROUND AND OBJECTIVES

Rapid-onset dystonia-parkinsonism (RDP) is caused by mutations in the ATP1A3 gene, which codes for the α-3 subunit of the Na⁺ /K⁺ ATPase. It has been characterized by rapid-onset bulbar dysfunction, limb dystonia, bradykinesia, and a rostrocaudal spatial gradient of expression, usually after a physiologic trigger. We reexamined whether these features were in fact characteristic.

METHODS

We characterized phenotypic variation within a cohort of 50 ATP1A3 mutation-positive individuals (carriers) and 44 mutation-negative family members (noncarriers). Potential participants were gathered through referral for clinical suspicion of RDP or alternating hemiplegia of childhood. Inclusion criteria were having a ATP1A3 mutation or being a family member of such an individual.

RESULTS

We found RDP is underdiagnosed if only "characteristic" patients are tested. Rapid onset and bulbar predominance were not universally present in carriers. Among those with at least mild symptoms of dystonia, rostrocaudal severity gradient was rare (7%). Symptoms began focally but progressed to be generalized (51%) or multifocal (49%). Arm (41%) onset was most common. Arms and voice were typically most severely affected (48% and 44%, respectively). Triggers preceded onset in 77% of the participants. Rapid onset, dystonia, parkinsonism, bulbar symptoms, headaches, seizures, frontal impairment, and a history of mood disorder and a history of psychosis were more common in carriers. Approximately half of the proband mutations occurred de novo (56%).

CONCLUSIONS

Our findings suggest that patients should not be excluded from ATP1A3 testing because of slow onset, limb onset, absent family history, or onset in middle adulthood. RDP should be strongly considered in the differential for any bulbar dystonia. © 2019 International Parkinson and Movement Disorder Society.

Current therapies and therapeutic decision making for childhood-onset movement disorders

Movement disorders differ in children to adults. First, neurodevelopmental movement disorders such as tics and stereotypies are more prevalent than parkinsonism, and second, there is a genomic revolution which is now explaining many early-onset dystonic syndromes. We outline an approach to children with movement disorders starting with defining the movement phenomenology, determining the level of functional impairment due to abnormal movements, and screening for comorbid psychiatric conditions and cognitive impairments which often contribute more to disability than the movements themselves. The rapid improvement in our understanding of the etiology of movement disorders has resulted in an increasing focus on precision medicine, targeting treatable conditions and defining modifiable disease processes. We profile some of the key disease-modifying therapies in metabolic, neurotransmitter, inflammatory, and autoimmune conditions and the increasing focus on gene or cellular therapies. When no disease-modifying therapies are possible, symptomatic therapies are often all that is available. These classically target dopaminergic, cholinergic, alpha-adrenergic, or GABAergic neurochemistry. Increasing interest in neuromodulation has highlighted that some clinical syndromes respond better to DBS, and further highlights the importance of "disease-specific" therapies with a future focus on individualized therapies according to the genomic findings or disease pathways that are disrupted. We summarize some pragmatic applications of symptomatic therapies, neuromodulation techniques, and some rehabilitative interventions and provide a contemporary overview of treatment in childhood-onset movement disorders. © 2019 International Parkinson and Movement Disorder Society.

Deep brain stimulation for early-onset dystonia

Deep brain stimulation (DBS) is considered as a treatment option for many neurological diseases. Many patients with movement disorders exhibit remarkable improvement after DBS. Owing to its minimally invasive nature, reversibility, and adjustability, DBS has been increasingly used over the past several decades. Dystonia is one of the most common movement disorders among children, and there is no effective treatment. Recently, some surgeon groups have performed DBS surgery for children. However, the outcomes of DBS in children are not well characterized. Here we mainly discuss the efficacy of DBS against childhood-onset dystonia and introduce the main procedure of pediatric DBS based on our own experience.

Atypical Presentation of Rapid-onset Dystonia-parkinsonism (DYT12) Unresponsive to Deep Brain Stimulation of the Subthalamic Nucleus

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ATP1A3-related disorders: An update

Alternating Hemiplegia of Childhood (AHC), Rapid-onset Dystonia Parkinsonism (RDP) and CAPOS syndrome (cerebellar ataxia, areflexia, pes cavus, optic atrophy, and sensorineural hearing loss) are three distinct, yet partially overlapping clinical syndromes that have long been thought to be allelic disorders. From 2004 to 2012, both autosomal dominant and de novo mutations in ATP1A3 have been detected in patients affected by these three conditions. Growing evidence suggests that AHC, RDP and CAPOS syndrome are part of a large and continuously expanding clinical spectrum and share some recurrent clinical features, such as abrupt-onset, asymmetric anatomical distribution and the presence of triggering factors, which are highly suggestive of ATP1A3 mutations. In this review, we will highlight the main clinical and genetic features of ATP1A3-related disorders focussing on shared and distinct features that can be helpful in clinical practice to individuate mutation carriers.

Deep brain stimulation for monogenic dystonia

PURPOSE OF REVIEW

Deep brain stimulation (DBS) has recently emerged as an important management option in children with medically refractory dystonia. DBS is most commonly used, best studied, and thought to be most efficacious for a select group of childhood or adolescent onset monogenic dystonias (designated with a standard 'DYT' prefix). We review how to clinically recognize these types of dystonia and the relative efficacy of DBS for key monogenic dystonias.

RECENT FINDINGS

Though used for dystonia in adults for several years, DBS has only lately been used in children. Recent evidence shows that patients with shorter duration of dystonia often experience greater benefit following DBS. This suggests that early recognition of the appropriate dystonic phenotypes and consideration of DBS in these patients may improve the management of dystonia.

SUMMARY

DBS should be considered early in patients who have medically refractory dystonia, especially for the monogenic dystonias that have a high response rate to DBS. It is important to differentiate between these monogenic dystonias and dystonias of other causes to properly prognosticate for these patients and to determine whether DBS is an appropriate management option.

Emerging Monogenic Complex Hyperkinetic Disorders

Purpose of Review

Hyperkinetic movement disorders can manifest alone or as part of complex phenotypes. In the era of next-generation sequencing (NGS), the list of monogenic complex movement disorders is rapidly growing. This review will explore the main features of these newly identified conditions.

Recent Findings

Mutations in ADCY5 and PDE10A have been identified as important causes of childhood-onset dyskinesias and KMT2B mutations as one of the most frequent causes of complex dystonia in children. The delineation of the phenotypic spectrum associated with mutations in ATP1A3, FOXG1, GNAO1, GRIN1, FRRS1L, and TBC1D24 is revealing an expanding genetic overlap between epileptic encephalopathies, developmental delay/intellectual disability, and hyperkinetic movement disorders,.

Summary

Thanks to NGS, the etiology of several complex hyperkinetic movement disorders has been elucidated. Importantly, NGS is changing the way clinicians diagnose these complex conditions. Shared molecular pathways, involved in early stages of brain development and normal synaptic transmission, underlie basal ganglia dysfunction, epilepsy, and other neurodevelopmental disorders.

Deep Brain Stimulation in Rare Inherited Dystonias

BACKGROUND

Rare causes of inherited movement disorders often present with a debilitating phenotype of dystonia, sometimes combined with parkinsonism and other neurological signs. Since these disorders are often resistant to medications, DBS may be considered as a possible treatment.

METHODS

Patients with identified genetic diseases (ataxia-telangiectasia, chorea-achantocytosis, dopa-responsive dystonia, congenital nemaline myopathy, methylmalonic aciduria, neuronal ceroid lipofuscinosis, spinocerebellar ataxia types 2 and 3, Wilson's disease, Woodhouse-Sakati syndrome, methylmalonic aciduria, and X trisomy) and disabling dystonia underwent bilateral GPi DBS (bilateral thalamic Vim nucleus in 1 case). The primary outcome was the difference in the Burke-Fahn-Marsden Dystonia Rating Scale (BFMDRS) between baseline, 1 year and last available follow-up. Preoperative factors such as age at surgery, disease duration at surgery, proportion of life lived with dystonia and severity of dystonia were correlated to the primary outcome.

RESULTS

Eleven patients were operated between February 2003 and December 2013. Age and duration of disease at time of surgery were 30 ± 19 and 12.5 ± 15.7 years, respectively. DBS effects on dystonia severity were variable but overall marginally effective, with a mean improvement of 7.9% (p = 0.39) at 1-year follow-up and 16.7% (p = 0.46) at last follow-up (mean 47.3 ± 19.9 months after surgery). No preoperative factors were identified to predict the surgical outcome.

CONCLUSION

Our findings support the current knowledge that DBS is modestly effective in treating rare inherited dystonias with a combined phenotype. However, the BFMDRS might not be the best tool to measure outcome in these severely affected patients.

Childhood dystonias

OPINION STATEMENT

Dystonia is a movement disorder caused by diverse etiologies. Its treatment in children is particularly challenging due to the complexity of the development of the nervous system from birth to young adulthood. The treatment options of childhood dystonia include several oral pharmaceutical agents, botulinum toxin injections, and deep brain stimulation (DBS) therapy. The choice of drug therapy relies on the suspected etiology of the dystonia and the adverse effect profile of the drugs. Dystonic syndromes with known etiologies may require specific interventions, but most dystonias are treated by trying serially a handful of medications starting with those with the best risk/benefit profile. In conjunction to drug therapy, botulinum toxin injections may be used to target a problematic group dystonic muscles. The maximal botulinum toxin dose is limited by the weight of the child, therefore limiting the number of the muscles amenable to such treatment. When drugs and botulinum toxin injections fail to control the child's disabling dystonia, DBS therapy may be offered as a last remedy. Delivering optimal DBS therapy to children with dystonia requires a multidisciplinary team of experienced pediatric neurosurgeons, neurologists, and nurses to select adequate candidates, perform this delicate stereotactic procedure, and optimize DBS delivery. Even in the best hands, the response of childhood dystonia to DBS therapy varies greatly. Future therapy of childhood dystonia will parallel the advancement of knowledge of the pathophysiology of dystonic syndromes and the development of clinical and research tools for their study.

The expanding spectrum of neurological phenotypes in children with ATP1A3 mutations, Alternating Hemiplegia of Childhood, Rapid-onset Dystonia-Parkinsonism, CAPOS and beyond

BACKGROUND

ATP1A3 mutations have now been recognized in infants and children presenting with a diverse group of neurological phenotypes, including Rapid-onset Dystonia-Parkinsonism (RDP), Alternating Hemiplegia of Childhood (AHC), and most recently, Cerebellar ataxia, Areflexia, Pes cavus, Optic atrophy, and Sensorineural hearing loss (CAPOS) syndrome.

METHODS

Existing literature on ATP1A3-related disorders in the pediatric population were reviewed, with attention to clinical features and associated genotypes among those with RDP, AHC, or CAPOS syndrome phenotypes.

RESULTS

While classically defined phenotypes associated with AHC, RDP, and CAPOS syndromes are distinct, common elements among ATP1A3-related neurological disorders include characteristic episodic neurological symptoms and signs that vary in severity, duration, and frequency of occurrence. Affected children typically present in the context of an acute onset of paroxysmal, episodic neurological symptoms ranging from oculomotor abnormalities, hypotonia, paralysis, dystonia, ataxia, seizure-like episodes, or encephalopathy. Neurodevelopmental delays or persistence of dystonia, chorea, or ataxia after resolution of an initial episode are common, providing important clues for diagnosis.

CONCLUSIONS

The phenotypic spectrum of ATP1A3-related neurological disorders continues to expand beyond the distinct yet overlapping phenotypes in patients with AHC, RDP, and CAPOS syndromes. ATP1A3 mutation analysis is appropriate to consider in the diagnostic algorithm for any child presenting with episodic or fluctuating ataxia, weakness or dystonia whether they manifest persistence of neurological symptoms between episodes. Additional work is needed to better identify and classify affected patients and develop targeted treatment approaches.

Deep brain stimulation for dystonia

The few controlled studies that have been carried out have shown that bilateral internal globus pallidum stimulation is a safe and long-term effective treatment for hyperkinetic disorders. However, most recent published data on deep brain stimulation (DBS) for dystonia, applied to different targets and patients, are still mainly from uncontrolled case reports (especially for secondary dystonia). This precludes clear determination of the efficacy of this procedure and the choice of the 'good' target for the 'good' patient. We performed a literature analysis on DBS for dystonia according to the expected outcome. We separated those with good evidence of favourable outcome from those with less predictable outcome. In the former group, we review the main results for primary dystonia (generalised/focal) and highlight recent data on myoclonus-dystonia and tardive dystonia (as they share, with primary dystonia, a marked beneficial effect from pallidal stimulation with good risk/benefit ratio). In the latter group, poor or variable results have been obtained for secondary dystonia (with a focus on heredodegenerative and metabolic disorders). From this overview, the main results and limits for each subgroup of patients that may help in the selection of dystonic patients who will benefit from DBS are discussed.

Na+/K+ ATPase α1 and α3 isoforms are differentially expressed in α- and γ-motoneurons

The Na(+)/K(+) ATPase (NKA) is an essential membrane protein underlying the membrane potential in excitable cells. Transmembrane ion transport is performed by the catalytic α subunits (α1-4). The predominant subunits in neurons are α1 and α3, which have different affinities for Na(+) and K(+), impacting on transport kinetics. The exchange rate of Na(+)/K(+) markedly influences the activity of the neurons expressing them. We have investigated the distribution and function of the main isoforms of the α subunit expressed in the mouse spinal cord. NKAα1 immunoreactivity (IR) displayed restricted labeling, mainly confined to large ventral horn neurons and ependymal cells. NKAα3 IR was more widespread in the spinal cord, again being observed in large ventral horn neurons, but also in smaller interneurons throughout the dorsal and ventral horns. Within the ventral horn, the α1 and α3 isoforms were mutually exclusive, with the α3 isoform in smaller neurons displaying markers of γ-motoneurons and α1 in α-motoneurons. The α3 isoform was also observed within muscle spindle afferent neurons in dorsal root ganglia with a higher proportion at cervical versus lumbar regions. We confirmed the differential expression of α subunits in motoneurons electrophysiologically in neonatal slices of mouse spinal cord. γ-Motoneurons were excited by bath application of low concentrations of ouabain that selectively inhibit NKAα3 while α-motoneurons were insensitive to these low concentrations. The selective expression of NKAα3 in γ-motoneurons and muscle spindle afferents, which may affect excitability of these neurons, has implications in motor control and disease states associated with NKAα3 dysfunction.

The genetics of dystonia: new twists in an old tale

Dystonia is a common movement disorder seen by neurologists in clinic. Genetic forms of the disease are important to recognize clinically and also provide valuable information about possible pathogenic mechanisms within the wider disorder. In the past few years, with the advent of new sequencing technologies, there has been a step change in the pace of discovery in the field of dystonia genetics. In just over a year, four new genes have been shown to cause primary dystonia (CIZ1, ANO3, TUBB4A and GNAL), PRRT2 has been identified as the cause of paroxysmal kinesigenic dystonia and other genes, such as SLC30A10 and ATP1A3, have been linked to more complicated forms of dystonia or new phenotypes. In this review, we provide an overview of the current state of knowledge regarding genetic forms of dystonia—related to both new and well-known genes alike—and incorporating genetic, clinical and molecular information. We discuss the mechanistic insights provided by the study of the genetic causes of dystonia and provide a helpful clinical algorithm to aid clinicians in correctly predicting the genetic basis of various forms of dystonia.

Deep brain stimulation for dystonia

The few reported controlled studies show that bilateral stimulation of the globus pallidus interna (GPi) is a safe and effective long-term treatment for hyperkinetic disorders. However, the recently published data on deep brain stimulation (DBS) applied to different targets or patients (especially those with secondary dystonia) are mainly uncontrolled case reports, precluding a clear determination of its efficacy, and providing little guidance as to the choice of a "good" target in a "good" patient. This chapter reviews the literature on DBS in primary dystonia, paying particular attention to the risk:benefit ratio in focal and segmental dystonias (cervical dystonia, cranial dystonia) and to the predictive factors for a good outcome. The chapter also highlights recent data on the marked benefits of the technique in myoclonus dystonia (in which pallidal, as opposed to thalamic, stimulation is more effective) and in tardive dystonia-dyskinesia. Although, the decision to treat appears relatively straightforward in patients with primary dystonia, myoclonus-dystonia, and tardive dystonia who have a normal findings on magnetic resonance imaging and normal cognitive function, there are still no reliable tools to help predict the timescale of postoperative benefit. This chapter provides a comprehensive analysis of the use of the treatment in various types of secondary dystonia, with little to moderate benefit in most cases, based on single cases or small series. Beyond the reduction in the severity of dystonia, the global motor and functional outcome is difficult to determine owing to the paucity of adequate evaluation tools. Because of the large interpatient variability, different targets may be effective depending on the symptoms in each individual.

Combined pallidal and subthalamic nucleus stimulation in sporadic dystonia-parkinsonism

Multifocal deep brain stimulation (DBS) is a new technique that has been introduced recently. A 39-year-old man with dystonia-parkinsonism underwent the simultaneous implantation of subthalamic nucleus (STN) and globus pallidus internus (GPi) DBS electrodes.

While bilateral STN DBS controlled the parkinsonian symptoms well and allowed for a reduction in levodopa, the improvement of dystonia was only temporary. Additional GPi DBS also alleviated dystonic symptoms. Formal assessment at the 1-year follow-up showed that both the parkinsonian symptoms and the dystonia were markedly improved via continuous bilateral combined STN and GPi stimulation. Sustained benefit was achieved at 3 years postoperatively.

Pattern of local field potential activity in the globus pallidus internum of dystonic patients during walking on a treadmill

The basal ganglia (BG) are involved in gait. This notion is exemplified by observations that gait is disturbed by most diseases that affect the BG. However, it is unclear in what way the BG are activated during gait. One method to investigate the activity of the BG is to record local field potentials (LFPs) from electrodes placed in the BG for therapeutic purposes. Nowadays, the globus pallidus internum (GPi) represents the target for deep brain stimulation (DBS) in dystonia. LFPs recorded from this area have been shown to delineate activity associated with dystonic cramps but also activity that may be relevant for certain types of movement. In this study we recorded LFPs from DBS electrodes implanted into the GPi of eight patients with dystonia during walking on a treadmill machine and compared these data with data acquired during rest (sitting and standing). There was no difference in the power of frequency bands during the sitting and standing conditions. LFP power in the theta (4-8 Hz), alpha (8-12 Hz) and gamma (60-90 Hz) frequency bands was higher during walking than during the resting conditions. Beta (15-25 Hz) frequencies were the only frequencies that were down-regulated during walking. The amplitude of the theta and alpha frequency bands was modulated during the gait cycle. These data shed light on the function of the BG in patients with dystonia and demonstrate that, during gait, their overall activity increases in a specific way without showing increases of narrow frequency bands.

Dystonia-plus syndromes

Dystonia-plus syndromes represent a heterogeneous group of diseases, where dystonia is accompanied by other neurological features and gene mutations can be detected frequently. Symptomatic dystonias and complex neurodegenerative diseases with dystonia as part of the clinical presentation are excluded from this category. At present, the following disorders are categorized as dystonia-plus syndromes: Dopa-responsive dystonia (DRD) is a mostly pediatric-onset, neurometabolic disorder with two different modes of inheritance: in its autosomal-dominant form, heterozygous mutations of GTP-cyclohydrolase I (GCH1, DYT5) cause DRD with reduced penetrance and excellent and lasting response to levodopa. Autosomal-recessive (AR) forms of DRD are caused by homozygous or compound heterozygous mutations of the tyrosine hydroxylase (TH) or the sepiapterin reductase (SPR) gene. In AR-DRD, the phenotype is generally more severe including cognitive deficits and developmental delay. Diagnosis can be confirmed by analysis of CSF pterine metabolites. Alternatively, comprehensive genetic testing yields causative mutations in up to 80% of patients. Myoclonus-dystonia (M-D) is caused by heterozygous mutations of the epsilon-sarcoglycan gene (SGCE). Dystonia is generally only mild to moderate, and 'lightning-like' myoclonic jerks occur rarely at rest and can be triggered by complex motor tasks like writing and drawing. Both features together with an age at onset below 25 years strongly predict SGCE mutation in M-D and differentiate this genetic disease from other 'jerky' dystonias. The combination of dystonia and parkinsonism can only be rarely observed in non-degenerative syndromes. Besides DRD, two additional syndromes have been classified. Rapid-onset dystonia-parkinsonism (RPD, DYT12) is a rare disorder with an abrupt onset of symptoms over minutes to days, prominent bulbar involvement and parkinsonism with a lack of response to levodopa. Patients with this rare phenotype should be screened for mutation in the Na(+)/K(+) ATPase alpha3-subunit (ATP1A3) gene, even if family history is negative. Recently, a novel form of dystonia-parkinsonism (DYT16) has been found to be linked to mutations in the PRKRA gene, whose relation to basal ganglia disorders is yet unknown .

[123I]-FP-CIT and [99mTc]-HMPAO single photon emission computed tomography in a new sporadic case of rapid-onset dystonia-parkinsonism

Rapid-onset dystonia-parkinsonism (RDP) is a rare, autosomal-dominantly inherited syndrome characterized by abrupt onset, over hours to days, of dystonic and parkinsonian symptoms. To date, RDP has been described in a small number of families, and in only four sporadic cases.

METHODS

We here report a new sporadic case of RDP who has a novel de novo mutation in the ATP1A3 gene. Striatal dopamine transporters have been assessed quantitatively using [123I]-FP-CIT SPECT. A volume of interest (VOI) was drawn within the occipital cortex to obtain non-specific activity and specific to non-specific binding ratios (BR) were calculated. A single template of predefined VOI 3D-drawn on right and left caudate nucleus and putamen was applied to the spatially normalized BR images. BR values were compared to those obtained from an age-matched control group and from a group of patients suffering from Parkinson's disease (Hoehn and Yahr score 2 or 3). A [99mTc]-HMPAO cerebral blood flow study was also performed.

RESULTS

In the control group, BR values (mean+/-Standard Deviation) were 3.5+/-0.4 for the left striatum and 3.3+/-0.3 for the right one. RDP patient's values were 3 and 2.7, respectively. In the Parkinson group, values were 1.6+/-0.3 and 1.7+/-0.4, respectively. [99mTc]-HMPAO scan showed homogeneous cortical and sub-cortical perfusion.

CONCLUSION

Quantification of striatal [123I]-FP-CIT uptake in a new sporadic case of RDP with a novel mutation in the ATP1A3 gene showed values just within the range of normality. [99mTc]-HMPAO scan was normal.

Treatment of dystonia with deep brain stimulation

Pallidal deep brain stimulation (DBS) is an established treatment option for medically refractive dystonia. The mechanism by which globus pallidus pars interna (GPi) DBS improves dystonia is still unclear. Primary generalized dystonia usually responds well to this therapy, as recently confirmed in two well-designed, double-blind, controlled trials; however, predictors of outcome within this population are not well known. The role of GPi DBS in idiopathic cervical dystonia resistant to treatment with botulinum toxin, in tardive dystonia, and in some types of secondary dystonia are emerging as populations of patients who may also benefit, but outcomes are not well documented. Serious complications from this therapy are rare. Future research will likely continue to address the most appropriate programming settings for various populations of dystonia, the mechanism by which DBS affects dystonia, and the possibility of alternative brain targets that might have less associated side effects or greater efficacy than the GPi.

Surgery for other movement disorders: dystonia, tics

PURPOSE OF REVIEW

Various movement disorders are now treated with stereotactic procedures, particularly deep brain stimulation. We review the neurosurgical treatment of dystonias and tics, focusing mainly on the surgical aspects and outcome of deep brain stimulation.

RECENT FINDINGS

Pallidal stimulation is nowadays the mainstay surgical treatment for patients with dystonia, particularly generalized dystonia. Various well designed recent clinical trials support the efficacy of the procedure. Improvements of 40-80% have been reported in primary generalized, segmental and cervical dystonia. For secondary dystonia, a similar outcome has been described in patients with tardive dystonia and pantothenate kinase-associated neurodegeneration. In patients with Tourette's syndrome, the results of the first trials with thalamic and pallidal deep brain stimulation have been very promising. Improvements of 70-90% in the frequency of tics have been reported with surgery in both targets.

SUMMARY

Deep brain stimulation has become an established therapy for dystonia and is currently being used to treat Tourette's syndrome. With accumulation of experience, clinical features that are more responsive to surgery and the best surgical candidates will be revealed. This will likely improve even further the outcome of surgery for the treatment of these disorders.

Heterogeneity of presentation and outcome in the Irish rapid-onset dystonia–Parkinsonism kindred

The authors report a 7-year follow-up video study and molecular data on the Irish rapid-onset dystonia-Parkinsonism kindred. All affected patients tested had a missense mutation in the Na(+)/K(+) -ATPase alpha3 subunit (ATP1A3), twice previously identified, suggestive of a mutation hotspot. Clinical presentation, progression, and outcome in this kindred is varied. Some patients remain stable over many years, others worsen, have a fluctuating course, or improve over time. To date there have been no effective treatments for this disorder, although Na(+)/K(+) ATPase may be a future therapeutic target. The broad phenotypic spectrum of RDP described in the text and detailed in the video, should be considered when evaluating patients with dystonia.