The role of genes in causing dystonia

Association Analysis of NALCN Polymorphisms rs1338041 and rs61973742 in a Chinese Population with Isolated Cervical Dystonia

Background. A genome-wide association study (GWAS) demonstrated a possible association between cervical dystonia (CD) and a sodium leak channel, nonselective (NALCN) gene. However, the association between NALCN and CD was largely unknown in Asian population. The present study was carried out to examine the associations between the two single nucleotide polymorphisms (SNPs) rs1338041 and rs61973742 in the NALCN gene and CD in a Chinese population. Methods. In a cohort of 201 patients with isolated CD, we genotyped the two SNPs rs1338041 and rs61973742 using polymerase chain reaction restriction fragment length polymorphism (PCR-RFLP). We also included 289 unrelated, age- and sex-matched healthy controls (HCs) from the same region. Result. No significant differences were observed in either the genotype distributions or the minor allele frequencies (MAFs) of the two SNPs between the CD patients and the HCs. There were no significant differences between early-onset and late-onset CD patients, between patients with and without a positive family history of dystonia, or between patients with and without tremor or sensory tricks. Conclusion. Lack of association between the SNPs of NALCN and CD suggests that the SNPs of NALCN do not play a role in CD in a Chinese population.

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

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

TOR1A polymorphisms in a Russian cohort with primary focal/segmental dystonia

PURPOSE/AIM OF THE STUDY

To analyze contribution of rs3842225 and rs1182 single nucleotide polymorphisms (SNP) in TOR1A gene, the causative gene for the DYT1 form of hereditary early-onset generalized dystonia, to the development of focal and segmental dystonia in Russian patients.

MATERIALS AND METHODS

We analyzed associations between rs3842225 and rs1182 polymorphisms in TOR1A and focal/segmental dystonia in 254 patients from Russian population, including 218 Slavic patients and 36 patients of mixed ethnic background.

RESULTS

Stratification of patients based on age at the disease onset (≤ 30 years and > 30 years) showed statistically significant prevalence of the del-allele at the rs3842225 locus in Slavic patients with earlier age of onset of dystonia (36.96% vs. 21.39% in patients with late age of onset, p = 0.002) and an overrepresentation of the T-allele at the rs1182 locus (36.96% vs. 21.69%, p = 0.003). In Slavs, we also observed an overrepresentation of the homozygous genotypes, T/T (general sample of dystonia, 9.17% and focal dystonia, 10.28%) or G/G (general sample of dystonia, 60.55% and focal dystonia, 58.86%), compared to controls (T/T, 4.27% and G/G, 55.49%). In non-Slavic patients, we revealed neither significant associations, nor statistical tendencies regarding any of the clinical features.

CONCLUSIONS

Our data in an Eastern Slavic (Russian) population correspond well to results of other studies from different countries and confirm that certain TOR1A genotypes may be regarded as factors predisposing to focal and segmental dystonia.

[Focal dystonia in musicians: Phenomenology and musical triggering factors]

Dystonias are defined as a joint sustained and involuntary contraction of agonist and antagonist muscles, which can cause torsion, repetitive abnormal involuntary movements, and/or abnormal postures. One special group of dystonias are those known as occupational, which include dystonia disorders triggered by a repetitive motor activity associated with a specific professional activity or task. Musicians are a population particularly vulnerable to these types of dystonia, which are presented as a loss of coordination and voluntary motor control movements highly trained in musical interpretation. Our aim is to describe a clinical series of focal dystonias in musicians evaluated and treated in our centre.

PATIENTS AND METHODS

Data is presented on a clinical series of 12 musicians with occupational dystonia. Their history and phenomenology are described, as well as well as their outcome after therapy.

RESULTS

Demographic details: Mean age 34.8 ± 11.8 years, 10 males (83.3%) and 2 females (16.7%).

CLINICAL HISTORY

History of trauma in dystonic segment, 6 patients (50%); family history of neurological diseases in first-degree relatives, 6 patients (50%); occupational history according to music category, 8 patients (66.6%) were classical musicians and 4 patients (33.3%) were popular musicians.

PHENOMENOLOGY

The dystonia syndrome was characterised by having a mean age of onset of 28.2 ± 11.3 years (range 18-57 years). The segment affected was the hand (91.7%) in 11 patients. Of all the musicians seen in the clinic, 9 of them (75%) received therapy. The majority of patients appeared to have triggering factors specific to musical execution and linked to the requirement of fine motor control. It should be mentioned that 50% of the musicians treated maintained their professional activity or position in the orchestra to which they belonged.

CONCLUSIONS

The majority of our phenomenological findings are consistent with those reported in the current literature. However, it is worth mentioning the presence of triggering factors attributed to the specific requirements of performing music, linked to the participation of fine motor control.

Microvascular decompression surgery is effective for the laterocollis subtype of spasmodic torticollis: a long-term follow-up result

BACKGROUND

Spasmodic torticollis (ST) is characterized by sustained, involuntary, and painful spasms of specific muscle (s), which results into abnormal posture of the neck and head. Although various treatments for ST have been introduced, none of them shows absolute effectiveness. Earlier research from our department showed that microvascular decompression (MVD) surgery is effective in the short-term for ST patients with confirmed accessory nerve compression. However, the long-term outcome of MVD remains unknown.

METHOD

Twelve ST patients with confirmed accessory nerve compression received MVD surgery of their accessory nerves. We utilized the Toronto Western Spasmodic Torticollis Rating Scale (TWSTRS) to evaluate the long-term outcome (5.4 ± 0.87 years).

RESULTS

The MVD lowered total TWSTRS scores by 42.8 % in all ST patients. This result, however, only counted for moderate relief. Interestingly, we observed that the laterocollis (LC) subtypes of ST (n = 3) obtained a higher TWSTRS score improvement (86.9 ± 6.2 %), compared to that of the non-LC (28.1 ± 12 %) (P =0.0001). Additionally, the disability (92.7 ± 2 %) subscale score in the LC subtypes had the most prominent improvement compared to the pain (88.1 ± 5.1 %) and severity (81.3 ± 10.5 %).

CONCLUSIONS

In the cases of confirmed accessory nerve compression, the MVD could be considered as a treatment alternative for ST, especially for the LC subtypes.

Deep brain stimulation in DYT1 dystonia: a 10-year experience

BACKGROUND

Globus Pallidus Interna (GPi) deep brain stimulation (DBS) is an effective treatment for DYT1-associated dystonia, but long-term results are lacking.

OBJECTIVE

To evaluate the long-term effects of GPi DBS in patients with DYT1 dystonia.

METHODS

A retrospective chart review (cohort study) of 47 consecutive DYT1+ patients treated by a single surgical team over a 10-year period and followed for up to 96 months (mean, 46 months) was performed. Symptom severity was quantified with the Burke-Fahn-Marsden Dystonia Rating Scale (BFMDRS) motor (M) and disability (D) sub-scores.

RESULTS

As measured with the BFMDRS (M), symptom severity was reduced to less than 20% of baseline after 2 years of DBS therapy (P = .001). The disability scores were reduced to <30% of baseline (P = .001). Symptomatic improvement was durable throughout available follow-up. Sixty-one percent of patients had discontinued all dystonia-related medications at their last follow-up. Ninety-one percent had discontinued at least 1 class of medication. Infections requiring removal and later reimplantation of hardware occurred in 4 of 47 patients (8.5%). Hardware malfunction including lead fractures occurred in 4 of 47 cases (8.5%). Lead revision to address poor clinical response was performed in 2 of 92 implanted leads (2.2%).

CONCLUSION

GPi DBS is an effective therapy for DYT1-associated torsion dystonia. Statistically significant efficacy is maintained for up to 7 years. Neurologic complications are rare, but long-term hardware-related complications can be significant.

Brain activity related to phonation in young patients with adductor spasmodic dysphonia

OBJECTIVE

This study investigated the brain activities during phonation of young patients with adductor spasmodic dysphonia (ADSD) of relatively short disease duration (<10 years).

METHODS

Six subjects with ADSD of short duration (mean age: 24. 3 years; mean disease duration: 41 months) and six healthy controls (mean age: 30.8 years) underwent functional magnetic resonance imaging (fMRI) using a sparse sampling method to identify brain activity during vowel phonation (/i:/). Intragroup and intergroup analyses were performed using statistical parametric mapping software.

RESULTS

Areas of activation in the ADSD and control groups were similar to those reported previously for vowel phonation. All of the activated areas were observed bilaterally and symmetrically. Intergroup analysis revealed higher brain activities in the SD group in the auditory-related areas (Brodmann's areas [BA] 40, 41), motor speech areas (BA44, 45), bilateral insula (BA13), bilateral cerebellum, and middle frontal gyrus (BA46). Areas with lower activation were in the left primary sensory area (BA1-3) and bilateral subcortical nucleus (putamen and globus pallidus).

CONCLUSION

The auditory cortical responses observed may reflect that young ADSD patients control their voice by use of the motor speech area, insula, inferior parietal cortex, and cerebellum. Neural activity in the primary sensory area and basal ganglia may affect the voice symptoms of young ADSD patients with short disease duration.

Towards the classification of DYT6 dystonia mutants in the DNA-binding domain of THAP1

The transcription factor THAP1 (THanatos Associated Protein 1) has emerged recently as the cause of DYT6 primary dystonia, a type of rare, familial and mostly early-onset syndrome that leads to involuntary muscle contractions. Many of the mutations described in the DYT6 patients fall within the sequence-specific DNA-binding domain (THAP domain) of THAP1 and are believed to negatively affect DNA binding. Here, we have used an integrated approach combining spectroscopic (NMR, fluorescence, DSF) and calorimetric (ITC) methods to evaluate the effect of missense mutations, within the THAP domain, on the structure, stability and DNA binding. Our study demonstrates that none of the mutations investigated failed to bind DNA and some of them even bind DNA stronger than the wild-type protein. However, some mutations could alter DNA-binding specificity. Furthermore, the most striking effect is the decrease of stability observed for mutations at positions affecting the zinc coordination, the hydrophobic core or the C-terminal AVPTIF motif, with unfolding temperatures ranging from 46°C for the wild-type to below 37°C for two mutations. These findings suggest that reduction in population of folded protein under physiological conditions could also account for the disease.

Alternative approaches to modeling hereditary dystonias

Dystonia is a movement disorder characterized by involuntary muscle contractions resulting in abnormal postures. Although common in the clinic, the etiology of dystonia remains unclear. Most dystonias are idiopathic and are not associated with clear pathological brain abnormalities. Attempts to genetically model these dystonias in rodents have failed to replicate dystonic symptoms. This is at odds with the fact that rodents can exhibit dystonia. Because of this discrepancy, it is necessary to consider alternative approaches to generate phenotypically and genotypically faithful models of dystonia. Conditional knockout of dystonia-related genes is 1 technique that may prove useful for modeling genetic dystonias. Lentiviral-mediated small or short hairpin RNA (shRNA) knockdown of particular genes is another approach. Finally, in cases in which the function of a dystonia-related gene is well-known, pharmacological blockade of the protein product can be used. Such an approach was successfully implemented in the case of rapid-onset dystonia parkinsonism, DYT12. This (DYT12) is a hereditary dystonia caused by mutations in the α₃ isoform of the sodium potassium adenosine triphosphatase (ATPase) pump (sodium pump), which partially hampers its physiological function. It was found that partial selective pharmacological block of the sodium pumps in the cerebellum and basal ganglia of mice recapitulates all of the salient features of DYT12, including dystonia and parkinsonism induced by stress. This DYT12 model is unique in that it faithfully replicates human symptoms of DYT12, while targeting the genetic cause of this disorder. Acute disruption of proteins implicated in dystonia may prove a generally fruitful method to model dystonia in rodents.

Botulinum toxins in the treatment of primary focal dystonias

Focal dystonia, such as cervical dystonia, blepharospasm, oromandibular dystonia, laryngeal dystonia, and limb dystonia, is often observed in adult-onset primary dystonia syndromes that affect a specific area of the body and tend to have little or no spread. This review will examine the past, present, and future approaches to the treatment of focal dystonia. Botulinum toxin (BoNT) has emerged as the treatment of choice for the majority of focal dystonias. Currently four products are widely available commercially, three of BoNT/A type and one of BoNT/B type. Each has important pharmacological differences that give rise to markedly different dosing recommendations. The four approved BoNTs are safe and effective for treating focal dystonias, including long-term treatment. Adverse events are limited and transient and, for the most part, mild in severity. Potential problems with the use of BoNT agents are diffusion and neutralizing antibody formation; the latter can lead to treatment resistance. Because each BoNT product is developed from distinct purification and manufacturing procedures and has varying toxin complex size and structures, physicians need to be aware of these differences when choosing an agent.

Surgical treatment of dystonia

Dystonia is a neurological condition characterised by abnormal muscle contractions, often causing repetitive twisting movements or abnormal postures. Varying forms of surgical intervention, for dystonia unresponsive to medical therapy, have evolved over the years and have often been associated with poor outcomes and high morbidity. The advent of stereotactic neurosurgery and the success of Deep Brain Stimulation (DBS) in treating a number of movement disorders has revolutionized the surgical treatment for dystonia. This chapter reviews the literature concerning the surgical treatment dystonic conditions, from historical origins to the current use of modern functional neurosurgical techniques.

Assessment of D216H DYT1 polymorphism in a Chinese primary dystonia patient cohort

BACKGROUND

The D216H single-nucleotide polymorphism (SNP) (rs1801968) in DYT1 exon 4 has been suggested to be a genetic modifier in primary dystonia.

METHODS

To further explore this question, we assessed rs1801968 variations in a cohort of 210 Chinese patients with primary dystonia devoid of DYT1 mutations.

RESULTS

We found that focal dystonia, specifically cervical dystonia, was the most common form of dystonia, with 8.1% of all the patients having a positive family history of dystonia. No association of the D216H SNP with primary dystonia was identified. In a subsequent subgroup analysis, the 216H allele was found to occur more frequently in patients with writer's cramp, but no correlation was found between the allele and other forms of dystonia or age of onset.

CONCLUSIONS

Our findings do not confirm that the allele contributes to the risk of D216H SNP primary dystonia.