Mutations in GNAL cause primary torsion dystonia

ADCY5-related dyskinesia: Broader spectrum and genotype-phenotype correlations

OBJECTIVE

To investigate the clinical spectrum and distinguishing features of adenylate cyclase 5 (ADCY5)-related dyskinesia and genotype-phenotype relationship.

METHODS

We analyzed ADCY5 in patients with choreiform or dystonic movements by exome or targeted sequencing. Suspected mosaicism was confirmed by allele-specific amplification. We evaluated clinical features in our 50 new and previously reported cases.

RESULTS

We identified 3 new families and 12 new sporadic cases with ADCY5 mutations. These mutations cause a mixed hyperkinetic disorder that includes dystonia, chorea, and myoclonus, often with facial involvement. The movements are sometimes painful and show episodic worsening on a fluctuating background. Many patients have axial hypotonia. In 2 unrelated families, a p.A726T mutation in the first cytoplasmic domain (C1) causes a relatively mild disorder of prominent facial and hand dystonia and chorea. Mutations p.R418W or p.R418Q in C1, de novo in 13 individuals and inherited in 1, produce a moderate to severe disorder with axial hypotonia, limb hypertonia, paroxysmal nocturnal or diurnal dyskinesia, chorea, myoclonus, and intermittent facial dyskinesia. Somatic mosaicism is usually associated with a less severe phenotype. In one family, a p.M1029K mutation in the C2 domain causes severe dystonia, hypotonia, and chorea. The progenitor, whose childhood-onset episodic movement disorder almost disappeared in adulthood, was mosaic for the mutation.

CONCLUSIONS

ADCY5-related dyskinesia is a childhood-onset disorder with a wide range of hyperkinetic abnormal movements. Genotype-specific correlations and mosaicism play important roles in the phenotypic variability. Recurrent mutations suggest particular functional importance of residues 418 and 726 in disease pathogenesis.

Clinical and scientific perspectives on movement disorders: Stanley Fahn's contributions

Dr. Stanley Fahn, the H. Houston Merritt Professor of Neurology and Director Emeritus of the Center for Parkinson's Disease and Other Movement Disorders at Columbia University, one of the founders of the field of movement disorders, was the first president of the Movement Disorders Society (subsequently renamed as the International Parkinson and Movement Disorder Society). Together with his friend and colleague, Professor David Marsden, he also served as the first co-editor of the journal Movement Disorders. By emphasizing phenomenology as the key element in differentiating various hypokinetic and hyperkinetic movement disorders, Dr. Fahn drew attention to the clinical history and the power of observation in the diagnosis of movement disorders. Dr. Fahn had major influence on the development of classifications and assessments of various movement disorders and in organizing various research groups such as the Parkinson Study Group. As the founder and president of the World Parkinson Coalition and an organizer of the initial three World Parkinson Congresses, he has demonstrated his long-standing commitment to the cause of including patients as partners. The primary goal and objective of this invited review is to highlight some of Dr. Fahn's most impactful scientific and clinical contributions to the understanding and treatment of Parkinson's disease, dystonia, and other movement disorders.

A review of 18p deletions

Since 18p- was first described in 1963, much progress has been made in our understanding of this classic deletion condition. We have been able to establish a fairly complete picture of the phenotype when the deletion breakpoint occurs at the centromere, and we are working to establish the phenotypic effects when each gene on 18p is hemizygous. Our aim is to provide genotype-specific anticipatory guidance and recommendations to families with an 18p- diagnosis. In addition, establishing the molecular underpinnings of the condition will potentially suggest targets for molecular treatments. Thus, the next step is to establish the precise effects of specific gene deletions. As we look forward to deepening our understanding of 18p-, our focus will continue to be on the establishment of robust genotype-phenotype correlations and the penetrance of these phenotypes. We will continue to follow our 18p- cohort closely as they age to determine the presence or absence of some of these diagnoses, including spinocerebellar ataxia (SCA), facioscapulohumeral muscular dystrophy (FSHD), and dystonia. We will also continue to refine the critical regions for other phenotypes as we enroll additional (hopefully informative) participants into the research study and as the mechanisms of the genes in these regions are elucidated. Mouse models will also be developed to further our understanding of the effects of hemizygosity as well as to serve as models for treatment development.

A new knock-in mouse model of l-DOPA-responsive dystonia

Abnormal dopamine neurotransmission is associated with many different genetic and acquired dystonic disorders. For instance, mutations in genes critical for the synthesis of dopamine, including GCH1 and TH cause l-DOPA-responsive dystonia. Despite evidence that implicates abnormal dopamine neurotransmission in dystonia, the precise nature of the pre- and postsynaptic defects that result in dystonia are not known. To better understand these defects, we generated a knock-in mouse model of l-DOPA-responsive dystonia (DRD) mice that recapitulates the human p.381Q>K TH mutation (c.1141C>A). Mice homozygous for this mutation displayed the core features of the human disorder, including reduced TH activity, dystonia that worsened throughout the course of the active phase, and improvement in the dystonia in response to both l-DOPA and trihexyphenidyl. Although the gross anatomy of the nigrostriatal dopaminergic neurons was normal in DRD mice, the microstructure of striatal synapses was affected whereby the ratio of axo-spinous to axo-dendritic corticostriatal synaptic contacts was reduced. Microinjection of l-DOPA directly into the striatum ameliorated the dystonic movements but cerebellar microinjections of l-DOPA had no effect. Surprisingly, the striatal dopamine concentration was reduced to ∼1% of normal, a concentration more typically associated with akinesia, suggesting that (mal)adaptive postsynaptic responses may also play a role in the development of dystonia. Administration of D1- or D2-like dopamine receptor agonists to enhance dopamine signalling reduced the dystonic movements, whereas administration of D1- or D2-like dopamine receptor antagonists to further reduce dopamine signalling worsened the dystonia, suggesting that both receptors mediate the abnormal movements. Further, D1-dopamine receptors were supersensitive; adenylate cyclase activity, locomotor activity and stereotypy were exaggerated in DRD mice in response to the D1-dopamine receptor agonist SKF 81297. D2-dopamine receptors exhibited a change in the valence in DRD mice with an increase in adenylate cyclase activity and blunted behavioural responses after challenge with the D2-dopamine receptor agonist quinpirole. Together, our findings suggest that the development of dystonia may depend on a reduction in dopamine in combination with specific abnormal receptor responses.

Pain Relief in Cervical Dystonia with Botulinum Toxin Treatment

Dystonia is a neurological disorder characterized by intermittent or sustained muscle contractions that cause abnormal, usually repetitive, movements and postures. Dystonic movements can be tremulous and twisting and often follow a pattern. They are frequently associated with overflow muscle activation and may be triggered or worsened by voluntary action. Most voluntary muscles can be affected and, in the case of the neck muscles, the condition is referred to as cervical dystonia (CD), the most common form of dystonia. The high incidence of pain distinguishes CD from other focal dystonias and contributes significantly to patient disability and low quality of life. Different degrees of pain in the cervical region are reported by more than 60% of patients, and pain intensity is directly related to disease severity. Botulinum toxin (BoNT) is currently considered the treatment of choice for CD and can lead to an improvement in pain and dystonic symptoms in up to 90% of patients. The results for BoNT/A and BoNT/B are similar. The complex relationship between pain and dystonia has resulted in a large number of studies and more comprehensive assessments of dystonic patients. When planning the application of BoNT, pain should be a key factor in the choice of muscles and doses. In conclusion, BoNT is highly effective in controlling pain, and its analgesic effect is sustained for a long time in most CD patients.

Aberrant Purkinje cell activity is the cause of dystonia in a shRNA-based mouse model of Rapid Onset Dystonia-Parkinsonism

Loss-of-function mutations in the α3 isoform of the sodium pump are responsible for Rapid Onset Dystonia-Parkinsonism (RDP). A pharmacologic model of RDP replicates the most salient features of RDP, and implicates both the cerebellum and basal ganglia in the disorder; dystonia is associated with aberrant cerebellar output, and the parkinsonism-like features are attributable to the basal ganglia. The pharmacologic agent used to generate the model, ouabain, is selective for sodium pumps. However, close to the infusion sites in vivo it likely affects all sodium pump isoforms. Therefore, it remains to be established whether selective loss of α3-containing sodium pumps replicates the pharmacologic model. Moreover, while the pharmacologic model suggested that aberrant firing of Purkinje cells was the main cause of abnormal cerebellar output, it did not allow the scrutiny of this hypothesis. To address these questions RNA interference using small hairpin RNAs (shRNAs) delivered via adeno-associated viruses (AAV) was used to specifically knockdown α3-containing sodium pumps in different regions of the adult mouse brain. Knockdown of the α3-containing sodium pumps mimicked both the behavioral and electrophysiological changes seen in the pharmacologic model of RDP, recapitulating key aspects of the human disorder. Further, we found that knockdown of the α3 isoform altered the intrinsic pacemaking of Purkinje cells, but not the neurons of the deep cerebellar nuclei. Therefore, acute knockdown of proteins associated with inherited dystonias may be a good strategy for developing phenotypic genetic mouse models where traditional transgenic models have failed to produce symptomatic mice.

A missense mutation in KCTD17 causes autosomal dominant myoclonus-dystonia

Myoclonus-dystonia (M-D) is a rare movement disorder characterized by a combination of non-epileptic myoclonic jerks and dystonia. SGCE mutations represent a major cause for familial M-D being responsible for 30%-50% of cases. After excluding SGCE mutations, we identified through a combination of linkage analysis and whole-exome sequencing KCTD17 c.434 G>A p.(Arg145His) as the only segregating variant in a dominant British pedigree with seven subjects affected by M-D. A subsequent screening in a cohort of M-D cases without mutations in SGCE revealed the same KCTD17 variant in a German family. The clinical presentation of the KCTD17-mutated cases was distinct from the phenotype usually observed in M-D due to SGCE mutations. All cases initially presented with mild myoclonus affecting the upper limbs. Dystonia showed a progressive course, with increasing severity of symptoms and spreading from the cranio-cervical region to other sites. KCTD17 is abundantly expressed in all brain regions with the highest expression in the putamen. Weighted gene co-expression network analysis, based on mRNA expression profile of brain samples from neuropathologically healthy individuals, showed that KCTD17 is part of a putamen gene network, which is significantly enriched for dystonia genes. Functional annotation of the network showed an over-representation of genes involved in post-synaptic dopaminergic transmission. Functional studies in mutation bearing fibroblasts demonstrated abnormalities in endoplasmic reticulum-dependent calcium signaling. In conclusion, we demonstrate that the KCTD17 c.434 G>A p.(Arg145His) mutation causes autosomal dominant M-D. Further functional studies are warranted to further characterize the nature of KCTD17 contribution to the molecular pathogenesis of M-D.

Dopamine receptor and Gα(olf) expression in DYT1 dystonia mouse models during postnatal development

BACKGROUND

DYT1 dystonia is a heritable, early-onset generalized movement disorder caused by a GAG deletion (ΔGAG) in the DYT1 gene. Neuroimaging studies and studies using mouse models suggest that DYT1 dystonia is associated with dopamine imbalance. However, whether dopamine imbalance is key to DYT1 or other forms of dystonia continues to be debated.

METHODOLOGY/PRINCIPAL FINDINGS

We used Dyt1 knock out (Dyt1 KO), Dyt1 ΔGAG knock-in (Dyt1 KI), and transgenic mice carrying one copy of the human DYT1 wild type allele (DYT1 hWT) or human ΔGAG mutant allele (DYT1 hMT). D1R, D2R, and Gα(olf) protein expression was analyzed by western blot in the frontal cortex, caudate-putamen and ventral midbrain in young adult (postnatal day 60; P60) male mice from all four lines; and in the frontal cortex and caudate putamen in juvenile (postnatal day 14; P14) male mice from the Dyt1 KI and KO lines. Dopamine receptor and Gα(olf) protein expression were significantly decreased in multiple brain regions of Dyt1 KI and Dyt1 KO mice and not significantly altered in the DYT1 hMT or DYT1 hWT mice at P60. The only significant change at P14 was a decrease in D1R expression in the caudate-putamen of the Dyt1 KO mice.

CONCLUSION/SIGNIFICANCE

We found significant decreases in key proteins in the dopaminergic system in multiple brain regions of Dyt1 KO and Dyt1 KI mouse lines at P60. Deletion of one copy of the Dyt1 gene (KO mice) produced the most pronounced effects. These data offer evidence that impaired dopamine receptor signaling may be an early and significant contributor to DYT1 dystonia pathophysiology.

Mutations in HPCA cause autosomal-recessive primary isolated dystonia

Reports of primary isolated dystonia inherited in an autosomal-recessive (AR) manner, often lumped together as “DYT2 dystonia,” have appeared in the scientific literature for several decades, but no genetic cause has been identified to date. Using a combination of homozygosity mapping and whole-exome sequencing in a consanguineous kindred affected by AR isolated dystonia, we identified homozygous mutations in HPCA, a gene encoding a neuronal calcium sensor protein found almost exclusively in the brain and at particularly high levels in the striatum, as the cause of disease in this family. Subsequently, compound-heterozygous mutations in HPCA were also identified in a second independent kindred affected by AR isolated dystonia. Functional studies suggest that hippocalcin might play a role in regulating voltage-dependent calcium channels. The identification of mutations in HPCA as a cause of AR primary isolated dystonia paves the way for further studies to assess whether “DYT2 dystonia” is a genetically homogeneous condition or not.

The genetics of the dystonias--a review based on the new classification of the dystonias

The definition and classification of the dystonias was recently revisited. In the new 2013 classification, the dystonias are subdivided in terms of their etiology according to whether they are the result of pathological changes or structural damage, have acquired causes or are inherited. As hereditary dystonias are clinically and genetically heterogeneous, we sought to classify them according to the new recently defined criteria. We observed that although the new classification is still the subject of much debate and controversy, it is easy to use in a logical and objective manner with the inherited dystonias. With the discovery of new genes, however, it remains to be seen whether the new classification will continue to be effective.

Short- and long-term outcome of chronic pallidal neurostimulation in monogenic isolated dystonia

OBJECTIVES

Deep brain stimulation of the internal pallidum (GPi-DBS) is an established therapeutic option in treatment-refractory dystonia, and the identification of factors predicting surgical outcome is needed to optimize patient selection.

METHODS

In this retrospective multicenter study, GPi-DBS outcome of 8 patients with DYT6, 9 with DYT1, and 38 with isolated dystonia without known monogenic cause (non-DYT) was assessed at early (1-16 months) and late (22-92 months) follow-up using Burke-Fahn-Marsden Dystonia Rating Scale (BFMDRS) scores.

RESULTS

At early follow-up, mean reduction of dystonia severity was greater in patients with DYT1 (BFMDRS score: -60%) and non-DYT dystonia (-52%) than in patients with DYT6 dystonia (-32%; p = 0.046). Accordingly, the rate of responders was considerably lower in the latter group (57% vs >90%; p = 0.017). At late follow-up, however, GPi-DBS resulted in comparable improvement in all 3 groups (DYT6, -42%; DYT1, -44; non-DYT, -61%). Additional DBS of the same or another brain target was performed in 3 of 8 patients with DYT6 dystonia with varying results. Regardless of the genotype, patients with a shorter duration from onset of dystonia to surgery had better control of dystonia postoperatively.

CONCLUSIONS

Long-term GPi-DBS is effective in patients with DYT6, DYT1, and non-DYT dystonia. However, the effect of DBS appears to be less predictable in patients with DYT6, suggesting that pre-DBS genetic testing and counseling for known dystonia gene mutations may be indicated. GPi-DBS should probably be considered earlier in the disease course.

CLASSIFICATION OF EVIDENCE

This study provides Class IV evidence that long-term GPi-DBS improves dystonia in patients with DYT1, DYT6, and non-DYT dystonia.

Recent advances in the genetics of dystonia

Dystonia, a common and genetically heterogeneous neurological disorder, was recently defined as "a movement disorder characterized by sustained or intermittent muscle contractions causing abnormal, often repetitive, movements, postures, or both." Via the application of whole-exome sequencing, the genetic landscape of dystonia and closely related movement disorders is becoming exposed. In particular, several "novel" genetic causes have been causally associated with dystonia or dystonia-related disorders over the past 2 years. These genes include PRRT2 (DYT10), CIZ1 (DYT23), ANO3 (DYT24), GNAL (DYT25), and TUBB4A (DYT4). Despite these advances, major gaps remain in identifying the genetic origins for most cases of adult-onset isolated dystonia. Furthermore, model systems are needed to study the biology of PRRT2, CIZ1, ANO3, Gαolf, and TUBB4A in the context of dystonia. This review focuses on these recent additions to the family of dystonia genes, genotype-phenotype correlations, and possible cellular contributions of the encoded proteins to the development of dystonia.

Whole arm deletions of 18p: medical and developmental effects

Deletions of the short arm of chromosome 18 have been well-described in case reports. However, the utility of these descriptions in clinical practice is limited by varied and imprecise breakpoints. As we work to establish genotype-phenotype correlations for 18p-, it is critical to have accurate and complete clinical descriptions of individuals with differing breakpoints. In addition, the developmental profile of 18p- has not been well-delineated. We undertook a thorough review of the medical histories of 31 individuals with 18p- and a breakpoint in the centromeric region. We collected developmental data using mailed surveys and questionnaires. The most common findings included neonatal complications; cardiac anomalies; hypotonia; MRI abnormalities; endocrine dysfunction; strabismus; ptosis; and refractive errors. Less common features included holoprosencephaly and its microforms; hearing loss; and orthopedic anomalies. The developmental effects of the deletion appear to be less severe than reported in the literature, as average IQ scores were in the range of borderline intellectual functioning. Based on responses to standardized questionnaires, it appears this population has marked difficulty with activities of daily living, though several young adults were able to live independent of their parents. This manuscript represents the most comprehensive description of a cohort of 18p- individuals with identical breakpoints. Despite identical breakpoints, a great deal of phenotype variability remained among this population, suggesting that many of the genes on 18p- cause low-penetrance phenotypes when present in a hemizygous state. Future efforts will focus on the clinical description of individuals with more distal breakpoints and the identification of critical regions and candidate genes.

Dystonia--new advances in classification, genetics, pathophysiology and treatment

Dystonia is a heterogeneous movement disorder and has been defined as 'a syndrome of sustained muscle contractions, frequently causing twisted and repetitive movements, or abnormal postures'. The classification of dystonia has developed along with increasing knowledge, and different schemes have been suggested, including age at onset, body distribution, and etiology as the main differentiating factors. A revised definition and a new classification of dystonia have now been proposed by a group of leading dystonia experts and will be referred here. The discovery of the first two gene mutations causing primary generalized dystonia (DYT1-TOR1A and DYT6-THAP1) has facilitated studies on pathogenesis and pathophysiology of primary dystonias, by comparing neurophysiology between manifesting and non-manifesting carriers, and by studying the molecular biology of the mutant gene products. During recent years, several other gene mutations causing primary dystonia, dystonia-plus, and paroxysmal dystonia disorders have been discovered. Only during the last year, by the use of whole-exome sequencing techniques, mutations in three different genes in families with predominantly cervical dystonia were found, which may lead to improved insight into the pathogenesis also of the more frequent focal dystonias. Botulinum neurotoxin (BoNT) and deep brain stimulation (DBS) have revolutionized the symptomatic treatment for dystonia during the last two decades and continue to be refined to improve efficacy and expand their indications. Unfortunately, no progress has been made in the oral medication of dystonia. Current and future new insights into pathogenetic and pathophysiological mechanisms of dystonia will hopefully lead to improvement also in this area soon.

Decreased dopamine receptor 1 activity and impaired motor-skill transfer in Dyt1 ΔGAG heterozygous knock-in mice

DYT1 dystonia is a movement disorder caused by a trinucleotide deletion (ΔGAG) in DYT1 (TOR1A), corresponding to a glutamic acid loss in the C-terminal region of torsinA. Functional alterations in the basal ganglia circuits have been reported in both DYT1 dystonia patients and rodent models. Dyt1 ΔGAG heterozygous knock-in (KI) mice exhibit motor deficits and decreased striatal dopamine receptor 2 (D2R) binding activity, suggesting a malfunction of the indirect pathway. However, the role of the direct pathway in pathogenesis of dystonia is not yet clear. Here, we report that Dyt1 KI mice exhibit significantly decreased striatal dopamine receptor 1 (D1R) binding activity and D1R protein levels, suggesting the alteration of the direct pathway. The decreased D1R may be caused by translational or post-translational processes since Dyt1 KI mice had normal levels of striatal D1R mRNA and a normal number of striatal neurons expressing D1R. Levels of striatal ionotropic glutamate receptor subunits, dopamine transporter, acetylcholine muscarinic M4 receptor and adenosine A2A receptor were not altered suggesting a specificity of affected polytopic membrane-associated proteins. Contribution of the direct pathway to motor-skill learning has been suggested in another pharmacological rat model injected with a D1R antagonist. In the present study, we developed a novel motor skill transfer test for mice and found deficits in Dyt1 KI mice. Further characterization of both the direct and the indirect pathways in Dyt1 KI mice will aid the development of novel therapeutic drugs.

4-Phenylbutyrate attenuates the ER stress response and cyclic AMP accumulation in DYT1 dystonia cell models

Dystonia is a neurological disorder in which sustained muscle contractions induce twisting and repetitive movements or abnormal posturing. DYT1 early-onset primary dystonia is the most common form of hereditary dystonia and is caused by deletion of a glutamic acid residue (302/303) near the carboxyl-terminus of encoded torsinA. TorsinA is localized primarily within the contiguous lumen of the endoplasmic reticulum (ER) and nuclear envelope (NE), and is hypothesized to function as a molecular chaperone and an important regulator of the ER stress-signaling pathway, but how the mutation in torsinA causes disease remains unclear. Multiple lines of evidence suggest that the clinical symptoms of dystonia result from abnormalities in dopamine (DA) signaling, and possibly involving its down-stream effector adenylate cyclase that produces the second messenger cyclic adenosine-3', 5'-monophosphate (cAMP). Here we find that mutation in torsinA induces ER stress, and inhibits the cyclic adenosine-3', 5'-monophosphate (cAMP) response to the adenylate cyclase agonist forskolin. Both defective mechanins are corrected by the small molecule 4-phenylbutyrate (4-PBA) that alleviates ER stress. Our results link torsinA, the ER-stress-response, and cAMP-dependent signaling, and suggest 4-PBA could also be used in dystonia treatment. Other pharmacological agents known to modulate the cAMP cascade, and ER stress may also be therapeutic in dystonia patients and can be tested in the models described here, thus supplementing current efforts centered on the dopamine pathway.

Inherited isolated dystonia: clinical genetics and gene function

Isolated inherited dystonia-formerly referred to as primary dystonia-is characterized by abnormal motor functioning of a grossly normal appearing brain. The disease manifests as abnormal involuntary twisting movements. The absence of overt neuropathological lesions, while intriguing, has made it particularly difficult to unravel the pathogenesis of isolated inherited dystonia. The explosion of genetic techology enabling the identification of the causative gene mutations is transforming our understanding of dystonia pathogenesis, as the molecular, cellular and circuit level consequences of these mutations are identified in experimental systems. Here, I review the clinical genetics and cell biology of three forms of inherited dystonia for which the causative mutation is known: DYT1 (TOR1A), DYT6 (THAP1), DYT25 (GNAL).

Next generation sequencing and the future of genetic diagnosis

The introduction of next generation sequencing (NGS) has led to an exponential increase of elucidated genetic causes in both extremely rare diseases and common but heterogeneous disorders. It can be applied to the whole or to selected parts of the genome (genome or exome sequencing, gene panels). NGS is not only useful in large extended families with linkage information, but may also be applied to detect de novo mutations or mosaicism in sporadic patients without a prior hypothesis about the mutated gene. Currently, NGS is applied in both research and clinical settings, and there is a rapid transition of research findings to diagnostic applications. These developments may greatly help to minimize the "diagnostic odyssey" for patients as whole-genome analysis can be performed in a few days at reasonable costs compared with gene-by-gene analysis based on Sanger sequencing following diverse clinical tests. Despite the enthusiasm about NGS, one has to keep in mind its limitations, such as a coverage and accuracy of < 100%, resulting in missing variants and false positive findings. In addition, variant interpretation is challenging as there is usually more than one candidate variant found. Therefore, there is an urgent need to define standards for NGS with respect to run quality and variant interpretation, as well as mechanisms of quality control. Further, there are ethical challenges including incidental findings and how to guide unaffected probands seeking direct-to-customer testing. However, taken together, the application of NGS in research and diagnostics provides a tremendous opportunity to better serve our patients.

A headset method for measuring the visual temporal discrimination threshold in cervical dystonia

BACKGROUND

The visual temporal discrimination threshold (TDT) is the shortest time interval at which one can determine two stimuli to be asynchronous and meets criteria for a valid endophenotype in adult-onset idiopathic focal dystonia, a poorly penetrant disorder. Temporal discrimination is assessed in the hospital laboratory; in unaffected relatives of multiplex adult-onset dystonia patients distance from the hospital is a barrier to data acquisition. We devised a portable headset method for visual temporal discrimination determination and our aim was to validate this portable tool against the traditional laboratory-based method in a group of patients and in a large cohort of healthy controls.

METHODS

Visual TDTs were examined in two groups 1) in 96 healthy control participants divided by age and gender, and 2) in 33 cervical dystonia patients, using two methods of data acquisition, the traditional table-top laboratory-based system, and the novel portable headset method. The order of assessment was randomized in the control group. The results obtained by each technique were compared.

RESULTS

Visual temporal discrimination in healthy control participants demonstrated similar age and gender effects by the headset method as found by the table-top examination. There were no significant differences between visual TDTs obtained using the two methods, both for the control participants and for the cervical dystonia patients. Bland-Altman testing showed good concordance between the two methods in both patients and in controls.

DISCUSSION

The portable headset device is a reliable and accurate method for visual temporal discrimination testing for use outside the laboratory, and will facilitate increased TDT data collection outside of the hospital setting. This is of particular importance in multiplex families where data collection in all available members of the pedigree is important for exome sequencing studies.

Genetic animal models of dystonia: common features and diversities

Animal models are pivotal for studies of pathogenesis and treatment of disorders of the central nervous system which in its complexity cannot yet be modeled in vitro or using computer simulations. The choice of a specific model to test novel therapeutic strategies for a human disease should be based on validity of the model for the approach: does the model reflect symptoms, pathogenesis and treatment response present in human patients? In the movement disorder dystonia, prior to the availability of genetically engineered mice, spontaneous mutants were chosen based on expression of dystonic features, including abnormal muscle contraction, movements and postures. Recent discovery of a number of genes and gene products involved in dystonia initiated research on pathogenesis of the disorder, and the creation of novel models based on gene mutations. Here we present a review of current models of dystonia, with a focus on genetic rodent models, which will likely be first choice in the future either for pathophysiological or for preclinical drug testing or both. In order to help selection of a model depending on expression of a specific feature of dystonia, this review is organized by symptoms and current knowledge of pathogenesis of dystonia. We conclude that albeit there is increasing need for research on pathogenesis of the disease and development of improved models, current models do replicate features of dystonia and are useful tools to develop urgently demanded treatment for this debilitating disorder.

Negative allosteric modulation of mGlu5 receptor rescues striatal D2 dopamine receptor dysfunction in rodent models of DYT1 dystonia

Early onset torsion dystonia (DYT1) is an autosomal dominantly inherited disorder caused by deletion in TOR1A gene. Evidence suggests that TOR1A mutation produces dystonia through an aberrant neuronal signalling within the striatum, where D2 dopamine receptors (D2R) produce an abnormal excitatory response in cholinergic interneurons (ChIs) in different models of DYT1 dystonia. The excitability of ChIs may be modulated by group I metabotropic glutamate receptor subtypes (mGlu1 and 5). We performed electrophysiological and calcium imaging recordings from ChIs of both knock-in mice heterozygous for Δ-torsinA (Tor1a(+/Δgag) mice) and transgenic mice overexpressing human torsinA (hMT1). We demonstrate that the novel negative allosteric modulator (NAM) of metabotropic glutamate 5 (mGlu) receptor, dipraglurant (ADX48621) counteracts the abnormal membrane responses and calcium rise induced either by the D2R agonist quinpirole or by caged dopamine (NPEC-Dopamine) in both models. These inhibitory effects were mimicked by two other well-characterized mGlu5 receptor antagonists, SIB1757 and MPEP, but not by mGlu1 antagonism. D2R and mGlu5 post-receptor signalling may converge on PI3K/Akt pathway. Interestingly, we found that the abnormal D2R response was prevented by the selective PI3K inhibitor, LY294002, whereas PLC and PKC inhibitors were both ineffective. Currently, no satisfactory pharmacological treatment is available for DYT1 dystonia patients. Our data show that negative modulation of mGlu5 receptors may counteract abnormal D2R responses, normalizing cholinergic cell excitability, by modulating the PI3K/Akt post-receptor pathway, thereby representing a novel potential treatment of DYT1 dystonia.

Mutations in GNAL: a novel cause of craniocervical dystonia

IMPORTANCE

Mutations in the GNAL gene have recently been shown to cause primary torsion dystonia. The GNAL-encoded protein (Gαolf) is important for dopamine D1 receptor function and odorant signal transduction. We sequenced all 12 exons of GNAL in 461 patients from Germany, Serbia, and Japan, including 318 patients with dystonia (190 with cervical dystonia), 51 with hyposmia and Parkinson disease, and 92 with tardive dyskinesia or acute dystonic reactions.

OBSERVATIONS

We identified the following two novel heterozygous putative mutations in GNAL: p.Gly213Ser in a German patient and p.Ala353Thr in a Japanese patient. These variants were predicted to be pathogenic in silico, were absent in ethnically matched control individuals, and impaired Gαolf coupling to D1 receptors in a bioluminescence energy transfer (BRET) assay. Two additional variants appeared to be benign because they behaved like wild-type samples in the BRET assay (p.Ala311Thr) or were detected in ethnically matched controls (p.Thr92Ala). Both patients with likely pathogenic mutations had craniocervical dystonia with onset in the fifth decade of life. No pathogenic mutations were detected in the patients with hyposmia and Parkinson disease, tardive dyskinesias, or acute dystonic reactions.

CONCLUSIONS AND RELEVANCE

Mutations in GNAL can cause craniocervical dystonia in different ethnicities. The BRET assay may be a useful tool to support the pathogenicity of identified variants in the GNAL gene.

Genetics in dystonia: an update

The past year has been extremely successful with regard to the genetics of dystonia, with the identification of four new dystonia genes (CIZ1, ANO3, GNAL, and TUBB4A). This progress was primarily achieved because of the application of a new technology, next-generation DNA sequencing, which allows rapid and comprehensive assessment of a patient's genome. In addition, a combination of next-generation and traditional Sanger sequencing has expanded the phenotypic spectrum associated with some of the dystonia plus (ATP1A3) and paroxysmal (PRRT2) loci. This article reviews the newly identified genes and phenotypes and discusses the future applications of next-generation sequencing to dystonia research.

Combined occurrence of a novel TOR1A and a THAP1 mutation in primary dystonia

BACKGROUND

The ΔGAG deletion of the TOR1A gene (DYT1) is responsible for DYT1 dystonia. However, no other TOR1A mutation has been reported in the Chinese population.

METHODS

Two hundred one dystonia patients without the ΔGAG deletion were screened for other mutations in TOR1A. Gene function changes were analyzed by subcellular distribution and luciferase reporter assay.

RESULTS

A novel TOR1A mutation (c.581A>T, p.Asp194Val) was found in a patient with early-onset segmental dystonia harboring a THAP1 mutation (c.539T>C, p.Leu180Ser). Overexpression of mutant TOR1A Asp194Val protein induces inclusion formation in SK-N-AS cell lines, and the repressive activity of the mutant THAP1 Leu180Ser protein on TOR1A gene expression is decreased compared with wild-type THAP1.

CONCLUSIONS

This is the first report about a dystonia patient harboring two distinct dystonia gene mutations. Functional analysis indicated a potential additive effect of these two mutations, which might provoke the occurrence of dystonic symptoms in this patient.

Dystonia

PURPOSE OF REVIEW

The purpose of this review is to provide an update on the classification, phenomenology, pathophysiology, and treatment of dystonia.

RECENT FINDINGS

A revised definition based on the main phenomenologic features of dystonia has recently been developed in an expert consensus approach. Classification is based on two main axes: clinical features and etiology. Currently, genes have been reported for 14 types of monogenic isolated and combined dystonia. Isolated dystonia (with dystonic tremor) can be caused by mutations in TOR1A (DYT1), TUBB4 (DYT4), THAP1 (DYT6), PRKRA (DYT16), CIZ1 (DYT23), ANO3 (DYT24), and GNAL (DYT25). Combined dystonias (with parkinsonism or myoclonus) are further subdivided into persistent (GCHI [DYT5], SGCE [DYT11], and ATP1A3 [DYT12], with TAF1 most likely but not yet proven to be linked to DYT3) and paroxysmal (PNKD [DYT8], PRRT2 [DYT10], and SLC2A1 [DYT18]). Recent insights from neurophysiologic studies identified functional abnormalities in two networks in dystonia: the basal ganglia-sensorimotor network and, more recently, the cerebellothalamocortical pathway. Besides the well-known lack of inhibition at different CNS levels, dystonia is specifically characterized by maladaptive plasticity in the sensorimotor cortex and loss of cortical surround inhibition. The exact role (modulatory or compensatory) of the cerebellar-cortical pathways still has to be further elucidated. In addition to botulinum toxin for focal forms, deep brain stimulation of the globus pallidus internus is increasingly recognized as an effective treatment for generalized and segmental dystonia.

SUMMARY

The revised classification and identification of new genes for different forms of dystonia, including adult-onset segmental dystonia, enable an improved diagnostic approach. Recent pathophysiologic insights have fundamentally contributed to a better understanding of the disease mechanisms and impact on treatment, such as functional neurosurgery and nonpharmacologic treatment options.

DRD1 rare variants associated with tardive-like dystonia: a pilot pathway sequencing study in dystonia

The dystonias are a clinical heterogeneous group with a complex genetic background. To gain more insight in genetic risk factors in dystonia we used a pathway sequence approach in patients with an extreme dystonia phenotype (n = 26). We assessed all coding and non-coding variants in candidate genes in D1-like subclass of dopamine receptor genes (DRD1, DRD5) and the synaptic vesicle pathway linked to torsinA (TOR1A, STON2, SNAPIN, KLC1 and THAP1), spanning 96 Kb. Two rare missense variants in DRD1 were found: c.68G>A(p.Arg23His) in the screening group and c.776C>A(p.Ser259Tyr) in an additional screen of 15 selected dystonia patients. Genetic burden analysis of DRD1 rare variants in patients (4.8%) versus European American controls from ESP (0.72%) reveals an OR 5.35 (95% CI 1.29-23.1). No rare missense SNVs in the synaptic vesicle pathway were found. Sequencing of TOR1A showed variant enrichment in haplotype 2, possibly accountable for contradictive results in previous association studies. Two new rare SNVs were detected in THAP1, including a nonsense mutation (p.Gln167Ter) and a splice site variant (c.72-1G>A). Screening for rare SNV of candidate pathways in a phenotype extreme population appears to be a promising alternative method to identify genetic risk factors in complex disorders like primary torsion dystonia. These findings indicate a role for rare genetic variation in dopamine processing genes in dystonia pathophysiology.

Emerging common molecular pathways for primary dystonia

The dystonias are a group of hyperkinetic movement disorders whose principal cause is neuron dysfunction at 1 or more interconnected nodes of the motor system. The study of genes and proteins that cause familial dystonia provides critical information about the cellular pathways involved in this dysfunction, which disrupts the motor pathways at the systems level. In recent years study of the increasing number of DYT genes has implicated a number of cell functions that appear to be involved in the pathogenesis of dystonia. A review of the literature published in English-language publications available on PubMed relating to the genetics and cellular pathology of dystonia was performed. Numerous potential pathogenetic mechanisms have been identified. We describe those that fall into 3 emerging thematic groups: cell-cycle and transcriptional regulation in the nucleus, endoplasmic reticulum and nuclear envelope function, and control of synaptic function. © 2013 Movement Disorder Society.

Genetics of dystonia: what's known? What's new? What's next?

Although all forms of dystonia share the core clinical features of involuntary dystonic dyskinesia, there is not only marked phenotypic but also etiologic heterogeneity. Isolated dystonia can be caused by mutations in TOR1A (DYT1), TUBB4 (DYT4), THAP1 (DYT6), CIZ1 (DYT23), ANO3 (DYT24), and GNAL (DYT25). Combined dystonias (with parkinsonism or myoclonus) are further subdivided into persistent (TAF1 [DYT3], GCHI [DYT5], SGCE [DYT11], ATP1A3 [DYT12]), PRKRA (DYT16), and paroxysmal (MR-1 [DYT8], PRRT2 [DYT10], SLC2A1 [DYT18]. With the advent of next-generation sequencing, an unprecedented number of new dystonia genes have recently been described, including 4 in the past 12 months. Despite the need for independent confirmation, these recent findings raise 2 important questions regarding (1) the role of genetics in dystonia overall and (2) the role of different molecular mechanisms in dystonia pathogenesis. The genetic contribution to dystonia represents a continuum ranging from genetic susceptibility factors of small effect to causative genes with markedly reduced penetrance to those with full penetrance. Equally diverse and complex are the pathways and neuronal function(s) putatively involved in dystonia pathogenesis including dopamine signaling, intracellular transport, cytoskeletal dynamics, transcriptional regulation, cell-cycle control, ion channel function, energy metabolism, signal transduction, and detoxification mechanisms. In the next decade of dystonia research, we expect to see the discovery of additional dystonia genes and susceptibility factors. In this context, it will be of great interest to explore whether the diverse cellular functions of the known dystonia proteins may be linked to shared pathways and thus complete the complex puzzle of dystonia pathogenesis. © 2013 Movement Disorder Society.

Primary and secondary dystonic syndromes: an update

PURPOSE OF REVIEW

The dystonias are a common but complex group of disorders that show considerable variation in cause and clinical presentation. The purpose of this review is to highlight the most important discoveries and insights from across the field over the period of the past 18 months.

RECENT FINDINGS

Five new genes for primary dystonia (PRRT2, CIZ1, ANO3, TUBB4A and GNAL) have made their appearance in the literature. New subtypes of neuronal brain iron accumulation have been delineated and linked to mutations in C19orf12 and WDR45, while a new treatable form of dystonia with brain manganese deposition related to mutations in SLC30A10 has been described. At the same time, the phenotypes of other forms of dystonic syndromes have been expanded or linked together. Finally, there has been increasing recognition of both the extramotor phenotype in dystonia and the part played by the cerebellum in its pathophysiology.

SUMMARY

Recently, there has been unprecedented change in the scientific landscape with respect to the cause of various dystonic syndromes that is likely to make a direct impact on clinical practice in the near future. Understanding the genetic cause of these syndromes and the often wide phenotypic variation in their presentations will improve diagnosis and treatment. With time, these discoveries may also lead to much-needed progress in elucidating the underlying pathophysiology of dystonia.

A rare sequence variant in intron 1 of THAP1 is associated with primary dystonia

Although coding variants in THAP1 have been causally associated with primary dystonia, the contribution of noncoding variants remains uncertain. Herein, we examine a previously identified Intron 1 variant (c.71+9C>A, rs200209986). Among 1672 subjects with mainly adult-onset primary dystonia, 12 harbored the variant in contrast to 1/1574 controls (P < 0.01). Dystonia classification included cervical dystonia (N = 3), laryngeal dystonia (adductor subtype, N = 3), jaw-opening oromandibular dystonia (N = 1), blepharospasm (N = 2), and unclassified (N = 3). Age of dystonia onset ranged from 25 to 69 years (mean = 54 years). In comparison to controls with no identified THAP1 sequence variants, the c.71+9C>A variant was associated with an elevated ratio of Isoform 1 (NM_018105) to Isoform 2 (NM_199003) in leukocytes. In silico and minigene analyses indicated that c.71+9C>A alters THAP1 splicing. Lymphoblastoid cells harboring the c.71+9C>A variant showed extensive apoptosis with relatively fewer cells in the G2 phase of the cell cycle. Differentially expressed genes from lymphoblastoid cells revealed that the c.71+9C>A variant exerts effects on DNA synthesis, cell growth and proliferation, cell survival, and cytotoxicity. In aggregate, these data indicate that THAP1 c.71+9C>A is a risk factor for adult-onset primary dystonia.

Heterogeneity in primary dystonia: lessons from THAP1, GNAL, and TOR1A in Amish-Mennonites

A founder mutation in the Thanatos-associated (THAP) domain containing, apoptosis associated protein 1 (THAP1) gene causing primary dystonia was originally described in the Amish-Mennonites. However, there may be both genotypic and phenotypic heterogeneity of dystonia in this population that may also inform studies in other ethnic groups. Genotyping for THAP1 and for guanine nucleotide binding protein (G protein), α-activating activity polypeptide, olfactory type (GNAL) mutations and genotype-phenotype comparisons were performed for 76 individuals of Amish-Mennonites heritage with primary dystonia. Twenty-seven individuals had mutations in THAP1-most with the founder indel mutation-but two had different THAP1 mutations, 8 had mutations in GNAL, and 1 had a de novo GAG deletion in torsin 1A (TOR1A) (dystonia 1 [DYT1]). In the primary analysis comparing THAP1 carriers versus all non-THAP1, non-GNAL, non-TOR1A individuals, age at onset was lower in THAP1 carriers (mean age ± standard deviation, 15.5 ± 9.2 years [range, 5-38 years] vs. 39.2 ± 17.7 years [range, 1-70 years]; P < 0.001), and THAP1 carriers were more likely to have onset of dystonia in an arm (44.4% vs. 15.0%; P = 0.02) and to have arm involvement (88.9% vs. 22.5%; P < 0.01), leg involvement (51.9% vs. 10.0%; P = 0.01), and jaw/tongue involvement (33.3% vs. 7.5%; P = 0.02) involvement at their final examination. Carriers were less likely to have dystonia restricted to a single site (11.11% in carriers vs. 65.9% in noncarriers; P < 0.01) and were less likely to have dystonia onset in cervical regions (25.9% of THAP1 carriers vs. 52.5% of noncarriers; P = 0.04). Primary dystonia in the Amish-Mennonites is genetically diverse and includes not only the THAP1 indel founder mutation but also different mutations in THAP1 and GNAL as well as the TOR1A GAG deletion. Phenotype, particularly age at onset combined with final distribution, may be highly specific for the genetic etiology.

Regional specificity of synaptic plasticity deficits in a knock-in mouse model of DYT1 dystonia

DYT1 dystonia is a movement disorder caused by a deletion in the C-terminal of the protein torsinA. It is unclear how torsinA mutation might disrupt cellular processes encoding motor activity, and whether this impairment occurs in specific brain regions. Here, we report a selective impairment of corticostriatal synaptic plasticity in knock-in mice heterozygous for Δ-torsinA (Tor1a(+/Δgag) mice) as compared to controls (Tor1a(+/+) mice). In striatal spiny neurons from Tor1a(+/Δgag) mice, high-frequency stimulation failed to induce long-term depression (LTD), whereas long-term potentiation (LTP) exhibited increased amplitude. Of interest, blockade of D2 dopamine receptors (D2Rs) increased LTP in Tor1a(+/+) mice to a level comparable to that measured in Tor1a(+/Δgag) mice and normalized the levels of potentiation across mouse groups. A low-frequency stimulation (LFS) protocol was unable to depotentiate corticostriatal synapses in Tor1a(+/Δgag) mice. Muscarinic M1 acetylcholine receptor (mAChR) blockade rescued plasticity deficits. Additionally, we found an abnormal responsiveness of cholinergic interneurons to D2R activation, consisting in an excitatory response rather than the expected inhibition, further confirming an imbalance between dopaminergic and cholinergic signaling in the striatum. Conversely, synaptic activity and plasticity in the CA1 hippocampal region were unaltered in Tor1a(+/Δgag) mice. Importantly, the M1 mAChR-dependent enhancement of hippocampal LTP was unaffected in both genotypes. Similarly, both basic properties of dopaminergic nigral neurons and their responses to D2R activation were normal. These results provide evidence for a regional specificity of the electrophysiological abnormalities observed and demonstrate the reproducibility of such alterations in distinct models of DYT1 dystonia.

Cervical dystonia: about familial and sporadic cases in 88 patients

Cervical dystonia (CD) affects the musculature of the neck in a focal way or associated to other parts of the body. The aim of this study was to identify clinical differences between patients with dystonia patients without family history and with family history (sporadic). Eighty-eight patients with CD were recruited in a Movement Disorders Clinic between June of 2008 and June of 2009. Only patients with no etiological diagnosis were accepted for analysis. The age of onset of symptoms was later in patients with focal and segmental dystonia than in patients with generalized dystonia (p<0.001). The severity of symptoms was higher in patients with sporadic dystonia than in familial patients (p<0.01). Generalized cases were more severe in patients with a family history (p<0.01). Sporadic patients had higher levels of pain than familial cases (p<0.05). We expect soon to present the results of genetic analyzes of these patients.

The phenotypic spectrum of DYT24 due to ANO3 mutations

Genes causing primary dystonia are rare. Recently, pathogenic mutations in the anoctamin 3 gene (ANO3) have been identified to cause autosomal dominant craniocervical dystonia and have been assigned to the dystonia locus dystonia-24 (DYT24). Here, we expand on the phenotypic spectrum of DYT24 and provide demonstrative videos. Moreover, tremor recordings were performed, and back-averaged electroencephalography, sensory evoked potentials, and C-reflex studies were carried out in two individuals who carried two different mutations in ANO3. Ten patients from three families are described. The age at onset ranged from early childhood to the forties. Cervical dystonia was the most common site of onset followed by laryngeal dystonia. The characteristic feature in all affected individuals was the presence of tremor, which contrasts DYT24 from the typical DYT6 phenotype. Tremor was the sole initial manifestation in some individuals with ANO3 mutations, leading to misdiagnosis as essential tremor. Electrophysiology in two patients with two different mutations showed co-contraction of antagonist muscles, confirming dystonia, and a 6-Hz arm tremor at rest, which increased in amplitude during action. In one of the studied patients, clinically superimposed myoclonus was observed. The duration of the myoclonus was in the range of 250 msec at about 3 Hz, which is more consistent with subcortical myoclonus. In summary, ANO3 causes a varied phenotype of young-onset or adult-onset craniocervical dystonia with tremor and/or myoclonic jerks. Patients with familial cervical dystonia who also have myoclonus-dystonia as well as patients with prominent tremor and mild dystonia should be tested for ANO3 mutations. © 2014 The Authors. Movement Disorders published by International Parkinson and Movement Disorder Society