Clinical and genetic evaluation of DYT1 and DYT6 primary dystonia in China

Research progress in spasmodic torticollis rehabilitation treatment

Spasmodic torticollis (ST) is a focal dystonia that affects adults, causing limited muscle control and impacting daily activities and quality of life. The etiology and curative methods for ST remain unclear. Botulinum toxin is widely used as a first-line treatment, but long-term usage can result in reduced tolerance and adverse effects. Rehabilitation therapy, with its minimal side effects and low potential for harm, holds significant clinical value. This article explores the effectiveness of adjunctive therapies, including exercise therapy, transcranial magnetic stimulation, shockwave therapy, neuromuscular electrical stimulation, vibration therapy, electromyographic biofeedback, and acupuncture, in the treatment of ST. The aim is to provide clinicians with additional treatment options and to discuss the efficacy of rehabilitation therapy for ST.

Movement disorders of the mouth: a review of the common phenomenologies

Movement disorders of the mouth encompass a spectrum of hyperactive movements involving the muscles of the orofacial complex. They are rare conditions and are described in the literature primarily in case reports originating from neurologists, psychiatrists, and the dental community. The focus of this review is to provide a phenomenological description of different oral motor disorders including oromandibular dystonia, orofacial dyskinesia and orolingual tremor, and to offer management strategies for optimal treatment based on the current literature. A literature search of full text studies using PubMed/Medline and Cochrane library combined with a manual search of the reference lists was conducted until June 2021. Results from this search included meta-analyses, systematic reviews, reviews, clinical studies, case series, and case reports published by neurologists, psychiatrists, dentists and oral and maxillofacial surgeons. Data garnered from these sources were used to provide an overview of most commonly encountered movement disorders of the mouth, aiding physicians in recognizing these rare conditions and in initiating appropriate therapy.

Investigating DYT1 in a Taiwanese dystonia cohort

BACKGROUND/PURPOSE

A heterozygous three-nucleotide (GAG) in-frame deletion in the TOR1A gene causes the rare disease, dystonia (DYT1), which typically presents as focal limb dystonia during adolescence, then spreads to other limbs. This study investigated the frequency and clinical features of DYT1 in a Taiwanese dystonia cohort.

METHODS

We performed targeted next generation sequencing in 318 patients with primary dystonia. We identified one DYT1 family with various types of dystonia, and we described the clinical presentations observed in this family during a 30-year follow-up. We compared the clinical characteristics to those reported in previous studies on DYT1 from 2000 to 2020.

RESULTS

Among 318 patients, we identified only one DYT1 patient (0.3%) with an autosomal dominant family history of dystonia. The proband was a 43-year-old man that experienced progressive onset of focal lower limb dystonia from age 11 years. The disease spread caudal-rostrally to the upper limbs and cervical muscles. Prominent cervical dystonia was noted during follow-up, which was an atypical presentation of DYT1. Clinical assessments of other family members showed intrafamily variability. The proband's father and an affected sibling demonstrated only mild right-hand writer's cramp. A systematic review of previously reported DTY1 cases showed that Asian patients had a higher frequency of cervical dystonia (44.8%) than groups of Ashkenazi Jews (35%) and Non-Jewish Caucasians (30.5%) (P = 0.04).

CONCLUSION

Our findings revealed that DYT1 is rare in a Taiwanese dystonia cohort. The presentation of marked cervical dystonia could be the main feature of Asian patients with DYT1.

Unraveling Molecular Mechanisms of THAP1 Missense Mutations in DYT6 Dystonia

Mutations in THAP1 (THAP domain-containing apoptosis-associated protein 1) are responsible for DYT6 dystonia. Until now, more than eighty different mutations in THAP1 gene have been found in patients with primary dystonia, and two third of them are missense mutations. The potential pathogeneses of these missense mutations in human are largely elusive. In the present study, we generated stable transfected human neuronal cell lines expressing wild-type or mutated THAP1 proteins found in DYT6 patients. Transcriptional profiling using microarrays revealed a set of 28 common genes dysregulated in two mutated THAP1 (S21T and F81L) overexpression cell lines suggesting a common mechanism of these mutations. ChIP-seq showed that THAP1 can bind to the promoter of one of these genes, superoxide dismutase 2 (SOD2). Overexpression of THAP1 in SK-N-AS cells resulted in increased SOD2 protein expression, whereas fibroblasts from THAP1 patients have less SOD2 expression, which indicates that SOD2 is a direct target gene of THAP1. In addition, we show that some THAP1 mutations (C54Y and F81L) decrease the protein stability which might also be responsible for altered transcription regulation due to dosage insufficiency. Taking together, the current study showed different potential pathogenic mechanisms of THAP1 mutations which lead to the same consequence of DYT6 dystonia.

New THAP1 mutation and role of putative modifier in TOR1A

OBJECTIVES

The prevalence of DYT1 (mutation in TOR1A) and DYT6 (mutation in THAP1) may vary in different populations, which can have important implications in clinical investigation. Our goal was to characterize patients with inherited and isolated dystonia and determine the frequency of mutations responsible for DYT1 and DYT6 in Brazilian patients.

METHODS

Two movement disorder specialists examined 78 patients with idiopathic isolated dystonia using a standardized questionnaire, before sequencing TOR1A and THAP1 genes.

RESULTS

Clinically, our cohort was similar to those described in the international literature. Molecular studies of 68 subjects revealed only one potentially deleterious variant in THAP1 (1/68 patients, 1.47%). This was a novel 10-bp deletion at the end of exon 1, g.5308_5317del (ng_011837.1), which is predicted to create an alternative splicing and the insertion of a premature stop codon. Although we did not observe any potentially deleterious mutations in TOR1A, we found the missense variant rs1801968 (TOR1A p.D216H), previously reported as either a modifier of dystonia phenotype or a predisposing factor for dystonia. However, we did not identify any phenotypic impact related to the missense variant rs1801968 (P = 0.3387).

CONCLUSIONS

Although clinically similar to most cohorts with dystonia worldwide, the classical mutation (c.907_909delGAG) in TOR1A (causing DYT1) is absent in our patients. However, we found a potentially deleterious THAP1 mutation not previously reported. In addition, we found no association of rs1801968 with dystonia.

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.

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.

The focal dystonias: current views and challenges for future research

The most common forms of dystonia are those that develop in adults and affect a relatively isolated region of the body. Although these adult-onset focal dystonias are most prevalent, knowledge of their etiologies and pathogenesis has lagged behind some of the rarer generalized dystonias, in which the identification of genetic defects has facilitated both basic and clinical research. This summary provides a brief review of the clinical manifestations of the adult-onset focal dystonias, focusing attention on less well understood clinical manifestations that need further study. It also provides a simple conceptual model for the similarities and differences among the different adult-onset focal dystonias as a rationale for lumping them together as a class of disorders while at the same time splitting them into subtypes. The concluding section outlines some of the most important research questions for the future. Answers to these questions are critical for advancing our understanding of this group of disorders and for developing novel therapeutics.

Mutation screening of the DYT6/THAP1 gene in Serbian patients with primary dystonia

Primary dystonia (PrD) is characterized by sustained muscle contractions, causing twisting and repetitive movements and abnormal postures. Besides DYT1/TOR1A gene, DYT6/THAP1 gene is the second gene known to cause primary pure dystonia. We screened 281 Serbian primary dystonia patients and 106 neurologically healthy control individuals for the GAG deletion in TOR1A gene and for mutations in THAP1 gene by direct sequencing. Nine subjects were found to have the GAG deletion in TOR1A gene. Four coding mutations, including two novel mutations, were identified in the THAP1 gene in five unrelated patients. Two mutations were missense, one was nonsense, and one was 24 bp duplication. None of the coding mutations were seen in 106 control individuals. In addition, one novel nucleotide change in the 5'UTR region of THAP1 gene was detected in two unrelated patients. The mutation frequency of THAP1 gene in Serbian patients with primary dystonia was 1.8 %, similar to the mutation frequency in other populations. Most of the patients reported here with THAP1 mutations had the clinical features of predominantly laryngeal or oromandibular dystonia. Our data expand the genotypic spectrum of THAP1 and strengthen the association with upper body involvement, including the cranial and cervical regions that are usually spared in DYT1-PrD.

THAP1 mutations and dystonia phenotypes: genotype phenotype correlations

THAP1 mutations have been shown to be the cause of DYT6. A number of different mutation types and locations in the THAP1 gene have been associated with a range of severity and dystonia phenotypes, but, as yet, it has been difficult to identify clear genotype phenotype patterns. Here, we screened the THAP1 gene in a further series of dystonia cases and evaluated the mutation pathogenicity in this series as well as previously reported mutations to investigate possible phenotype-genotype correlations. THAP1 mutations have been identified throughout the coding region of the gene, with the greatest concentration of variants localized to the THAP1 domain. In the additional cases analyzed here, a further two mutations were found. No obvious, indisputable genotype-phenotype correlation emerged from these data. However, we managed to find a correlation between the pathogenicity of mutations, distribution, and age of onset of dystonia. THAP1 mutations are an important cause of dystonia, but, as yet, no clear genotype-phenotype correlations have been identified. Greater mutation numbers in different populations will be important and mutation-specific functional studies will be essential to identify the pathogenicity of the various THAP1 mutations. © 2012 Movement Disorder Society

Subcellular distribution of THAP1 and alterations in the microstructure of brain white matter in DYT6 dystonia

BACKGROUND

Mutations in the THAP1 gene have recently been identified as the cause of DYT6 primary dystonia. However, the changes in THAP1 gene function and in the microstructure of brain white matter have not been well-characterized.

METHODS

Four different mutations of THAP1 expression (clones F22fs71X, C54F, F25fs53X, and L180S) were transfected into HEK-293T cells. The subcellular distribution of THAP1 in each clone was identified using immunofluorescence microscopy and Western blot. Six patients who harbored these THAP1 mutations underwent diffusion tensor magnetic resonance imaging (DTI) of the brain. The fractional anisotropy (FA) and mean diffusivity (MD) were measured in twenty-four regions of interest (ROI).

RESULTS

In two truncated mutations (F22fs71X and F25fs53X), the subcellular distribution of THAP1 were both in the cytoplasm and nucleus. However, the subcellular distribution was detected almost in the nucleus in two missense mutations (C54F and L180S). In the DTI maps, the average values of fractional anisotropy (FA), a measure of axonal integrity and coherence, was reduced (p < 0.005) in the subgyral white matter of the sensorimotor cortex of the DYT1 carriers, comparing with controls.

CONCLUSIONS

Truncated THAP1 mutations (F22fs71X and F25fs53X) can alter the subcellular distributions, while some missense mutation (C54F and L180S) can not. The axonal integrity and coherence in the region of sensorimotor area of the brain was damaged in DYT6 dystonia.

Genotype-phenotype correlations in THAP1 dystonia: molecular foundations and description of new cases

An extensive variety of THAP1 sequence variants have been associated with focal, segmental and generalized dystonia with age of onset ranging from 3 to over 60 years. In previous work, we screened 1114 subjects with mainly adult-onset primary dystonia (Neurology 2010; 74:229-238) and identified 6 missense mutations in THAP1. For this report, we screened 750 additional subjects for mutations in coding regions of THAP1 and interrogated all published descriptions of THAP1 phenotypes (gender, age of onset, anatomical distribution of dystonia, family history and site of onset) to explore the possibility of THAP1 genotype-phenotype correlations and facilitate a deeper understanding of THAP1 pathobiology. We identified 5 additional missense mutations in THAP1 (p.A7D, p.K16E, p.S21C, p.R29Q, and p.I80V). Three of these variants are associated with appendicular tremors, which were an isolated or presenting sign in some of the affected subjects. Abductor laryngeal dystonia and mild blepharospasm can be manifestations of THAP1 mutations in some individuals. Overall, mean age of onset for THAP1 dystonia is 16.8 years and the most common sites of onset are the arm and neck, and the most frequently affected anatomical site is the neck. In addition, over half of patients exhibit either cranial or laryngeal involvement. Protein truncating mutations and missense mutations within the THAP domain of THAP1 tend to manifest at an earlier age and exhibit more extensive anatomical distributions than mutations localized to other regions of THAP1.

Milestones in dystonia

The last 25 years have seen remarkable advances in our understanding of the genetic etiologies of dystonia, new approaches into dissecting underlying pathophysiology, and independent progress in identifying effective treatments. In this review we highlight some of these advances, especially the genetic findings that have taken us from phenomenological to molecular-based diagnoses. Twenty DYT loci have been designated and 10 genes identified, all based on linkage analyses in families. Hand in hand with these genetic findings, neurophysiological and imaging techniques have been employed that have helped illuminate the similarities and differences among the various etiological dystonia subtypes. This knowledge is just beginning to yield new approaches to treatment including those based on DYT1 animal models. Despite the lag in identifying genetically based therapies, effective treatments, including impressive benefits from deep brain stimulation and botulinum toxin chemodenervation, have marked the last 25 years. The challenge ahead includes continued advancement into understanding dystonia's many underlying causes and associated pathology and using this knowledge to advance treatment including preventing genetic disease expression.

Identification and functional analysis of novel THAP1 mutations

Mutations in THAP1 have been associated with dystonia 6 (DYT6). THAP1 encodes a transcription factor that represses the expression of DYT1. To further evaluate the mutational spectrum of THAP1 and its associated phenotype, we sequenced THAP1 in 567 patients with focal (n = 461), segmental (n = 68), or generalized dystonia (n = 38). We identified 10 novel variants, including six missense substitutions within the DNA-binding Thanatos-associated protein domain (Arg13His, Lys16Glu, His23Pro, Lys24Glu, Pro26Leu, Ile80Val), a 1bp-deletion downstream of the nuclear localization signal (Asp191Thrfs*9), and three alterations in the untranslated regions. The effect of the missense variants was assessed using prediction tools and luciferase reporter gene assays. This indicated the Ile80Val substitution as a benign variant. The subcellular localization of Asp191Thrfs*9 suggests a disturbed nuclear import for this mutation. Thus, we consider six of the 10 novel variants as pathogenic mutations accounting for a mutation frequency of 1.1%. Mutation carriers presented mainly with early onset dystonia (<12 years in five of six patients). Symptoms started in an arm or neck and spread to become generalized in three patients or segmental in two patients. Speech was affected in four mutation carriers. In conclusion, THAP1 mutations are rare in unselected dystonia patients and functional analysis is necessary to distinguish between benign variants and pathogenic mutations.

Novel THAP1 gene mutations in patients with primary dystonia from southwest China

BACKGROUND

Clinical presentation and DYT6/THAP1 mutations among Chinese patients with primary dystonia have not been well studied.

METHODS

Patients with primary pure dystonia from Southwest China who did not have a mutation in DYT1 exon 5 were included in the present study. Mutations of the THAP1 gene were screened by direct sequencing.

RESULTS

A total of 231 patients were examined. Cervical dystonia (58.47%) was found to be the most frequent form of focal dystonia. Novel heterozygous missense mutation [c.521A>G (p.E174G)] was found in exon 3 of the THAP1 gene in one patient and one insertion mutation [c.214_215InsA (p.L72fsX86)] in exon 2 in another. Initial symptoms of patients with these mutations were early-onset cervical dystonia. Both patients had no dysarthria. A silent change [c.489C>G (p.L63L)] in exon 3 was identified in three patients with Meige syndrome.

CONCLUSION

The mutation frequency of the THAP1 gene was 0.87% in Chinese patients with primary pure dystonia, similar to the mutation frequency found in other ethnic groups. Patients presenting with early-onset cervical dystonia should be screened for THAP1 gene mutations to fully assess all the possible etiologies of dystonia. Further studies are needed for p.L63L in THAP1 in Meige syndrome.

Dimerization of the DYT6 dystonia protein, THAP1, requires residues within the coiled-coil domain

Thanatos-associated [THAP] domain-containing apoptosis-associated protein 1 (THAP1) is a DNA-binding protein that has been recently associated with DYT6 dystonia, a hereditary movement disorder involving sustained, involuntary muscle contractions. A large number of dystonia-related mutations have been identified in THAP1 in diverse patient populations worldwide. Previous reports have suggested that THAP1 oligomerizes with itself via a C-terminal coiled-coil domain, raising the possibility that DYT6 mutations in this region might affect this interaction. In this study, we examined the ability of wild-type THAP1 to bind itself and the effects on this interaction of the following disease mutations: C54Y, F81L, ΔF132, T142A, I149T, Q154fs180X, and A166T. The results confirmed that wild-type THAP1 associated with itself and most of the DYT6 mutants tested, except for the Q154fs180X variant, which loses most of the coiled-coil domain because of a frameshift at position 154. However, deletion of C-terminal residues after position 166 produced a truncated variant of THAP1 that was able to bind the wild-type protein. The interaction of THAP1 with itself therefore required residues within a 13-amino acid region (aa 154-166) of the coiled-coil domain. Further inspection of this sequence revealed elements highly consistent with previous descriptions of leucine zippers, which serve as dimerization domains in other transcription factor families. Based on this similarity, a structural model was generated to predict how hydrophobic residues in this region may mediate dimerization. These observations offer additional insight into the role of the coiled-coil domain in THAP1, which may facilitate future analyses of DYT6 mutations in this region.

THAP1/DYT6 sequence variants in non-DYT1 early-onset primary dystonia in China and their effects on RNA expression

Mutations in the THAP1 gene were recently identified as the cause of DYT6 primary dystonia. More than 40 mutations in this gene have been described in different populations. However, no previous report has identified sequence variations that affect the transcript process of the THAP1 gene. In addition, the mutation frequency in Chinese early-onset primary dystonia has not been well characterized. One hundred and two unrelated patients with non-DYT1 early-onset primary dystonia (age at onset <26 years), family members of participants with mutations, and 200 neurologically normal controls were screened for THAP1 gene mutations. The effects of the identified mutations on RNA expression were analyzed using semi-quantitative real-time PCR. Seven sequence variants (c.63_66del TTTC, c.161G>T, c.224A>T, c.267G>A, c.339T>C, c.449A>C, and c.539T>C) were identified in this group of patients (6.9%). In this cohort, 15 subjects (seven unrelated patients and eight family members) were detected to have THAP1 sequence variants. Among these 15 subjects, 11 were manifested (penetrance of DYT6 was 73.3%) and seven presented with craniocervical involvement (63.6%). However, one patient manifested paroxysmal headshake, and one presented with essential hand tremor. Semi-quantitative real-time PCR indicated that a novel silent mutation (c.267G>A) decreased the expression of THAP1 in human lymphocytes. Our findings indicated that THAP1 sequence variants are not common in non-DYT1 early-onset primary dystonia in China and that the clinical manifestation may vary. One silent mutation (c.267G>A) was shown to affect THAP1 expression.

Consideration of genetic contributions to the risk for spasmodic dysphonia

Spasmodic dysphonia, a form of the neurologic condition known as dystonia, results from involuntary spasms of the larynx, producing interruptions of speech and changes in voice quality. The pathogenesis of spasmodic dysphonia is not well understood. However, several genetic mutations have been identified that cause different forms of dystonia. In some individuals, these genetic mutations result in spasmodic dysphonia, either with no other signs of dystonia or as part of a broader dystonia phenotype. Thus, research in the growing field of dystonia genetics may help to inform our understanding of the pathogenesis of spasmodic dysphonia.

Identifying the genetic components underlying the pathophysiology of movement disorders

Movement disorders are a heterogeneous group of neurological conditions, few of which have been classically described as bona fide hereditary illnesses (Huntington’s chorea, for instance). Most are considered to be either sporadic or to feature varying degrees of familial aggregation (parkinsonism and dystonia). In the late twentieth century, Mendelian monogenic mutations were found for movement disorders with a clear and consistent family history. Although important, these findings apply only to very rare forms of movement disorders. Already in the twenty-first century, and taking advantage of the modern developments in genetics and molecular biology, growing attention is being paid to the complex genetics of movement disorders. The search for risk genetic variants (polymorphisms) in large cohorts and the identification of different risk variants across different populations and ethnic groups are under way, with the most relevant findings to date corresponding to recent genome wide association studies in Parkinson’s disease. These new approaches focusing on risk variants may enable the design of screening tests for early or even preclinical disease, and the identification of likely therapeutic targets.

Genetic and clinical features of primary torsion dystonia

Primary torsion dystonia (PTD) is defined as a syndrome in which dystonia is the only clinical sign (except for tremor), and there is no evidence of neuronal degeneration or an acquired cause by history or routine laboratory assessment. Seven different loci have been recognized for PTD but only two of the genes have been identified. In this review we will describe the phenotypes associated with these loci and discuss the responsible gene. This article is part of a Special Issue entitled "Advances in dystonia".