Identification and functional analysis of novel THAP1 mutations

Large-Scale Screening: Phenotypic and Mutational Spectrum in Isolated and Combined Dystonia Genes

BACKGROUND

Pathogenic variants in several genes have been linked to genetic forms of isolated or combined dystonia. The phenotypic and genetic spectrum and the frequency of pathogenic variants in these genes have not yet been fully elucidated, neither in patients with dystonia nor with other, sometimes co-occurring movement disorders such as Parkinson's disease (PD).

OBJECTIVES

To screen >2000 patients with dystonia or PD for rare variants in known dystonia-causing genes.

METHODS

We screened 1207 dystonia patients from Germany (DysTract consortium), Spain, and South Korea, and 1036 PD patients from Germany for pathogenic variants using a next-generation sequencing gene panel. The impact on DNA methylation of KMT2B variants was evaluated by analyzing the gene's characteristic episignature.

RESULTS

We identified 171 carriers (109 with dystonia [9.0%]; 62 with PD [6.0%]) of 131 rare variants (minor allele frequency <0.005). A total of 52 patients (48 dystonia [4.0%]; four PD [0.4%, all with GCH1 variants]) carried 33 different (likely) pathogenic variants, of which 17 were not previously reported. Pathogenic biallelic variants in PRKRA were not found. Episignature analysis of 48 KMT2B variants revealed that only two of these should be considered (likely) pathogenic.

CONCLUSION

This study confirms pathogenic variants in GCH1, GNAL, KMT2B, SGCE, THAP1, and TOR1A as relevant causes in dystonia and expands the mutational spectrum. Of note, likely pathogenic variants only in GCH1 were also found among PD patients. For DYT-KMT2B, the recently described episignature served as a reliable readout to determine the functional effect of newly identified variants. © 2024 The Authors. Movement Disorders published by Wiley Periodicals LLC on behalf of International Parkinson and Movement Disorder Society.

Genetics and Pathogenesis of Dystonia

Dystonia is a clinically and genetically highly heterogeneous neurological disorder characterized by abnormal movements and postures caused by involuntary sustained or intermittent muscle contractions. A number of groundbreaking genetic and molecular insights have recently been gained. While they enable genetic testing and counseling, their translation into new therapies is still limited. However, we are beginning to understand shared pathophysiological pathways and molecular mechanisms. It has become clear that dystonia results from a dysfunctional network involving the basal ganglia, cerebellum, thalamus, and cortex. On the molecular level, more than a handful of, often intertwined, pathways have been linked to pathogenic variants in dystonia genes, including gene transcription during neurodevelopment (e.g., KMT2B, THAP1), calcium homeostasis (e.g., ANO3, HPCA), striatal dopamine signaling (e.g., GNAL), endoplasmic reticulum stress response (e.g., EIF2AK2, PRKRA, TOR1A), autophagy (e.g., VPS16), and others. Thus, different forms of dystonia can be molecularly grouped, which may facilitate treatment development in the future.

Transcriptional regulatory network for neuron-glia interactions and its implication for DYT6 dystonia

Advances in sequencing technologies have identified novel genes associated with inherited forms of dystonia, providing valuable insights into its genetic basis and revealing diverse genetic pathways and mechanisms involved in its pathophysiology. Since identifying genetic variation in the transcription factor coding THAP1 gene linked to isolated dystonia, numerous investigations have employed transcriptomic studies in DYT-THAP1 models to uncover pathogenic molecular mechanisms underlying dystonia. This review examines key findings from transcriptomic studies conducted on in vivo and in vitro DYT-THAP1 models, which demonstrate that the THAP1-regulated transcriptome is diverse and cell-specific, yet it is bound and co-regulated by a common set of proteins. Prominent among its functions, THAP1 and its co-regulatory network target molecular pathways critical for generating myelinating oligodendrocytes that ensheath axons and generate white matter in the central nervous system. Several lines of investigation have demonstrated the importance of myelination and oligodendrogenesis in motor function during development and in adults, emphasizing the non-cell autonomous contributions of glial cells to neural circuits involved in motor function. Further research on the role of myelin abnormalities in motor deficits in DYT6 models will enhance our understanding of axon-glia interactions in dystonia pathophysiology and provide potential therapeutic interventions targeting these pathways.

Emerging role of a systems biology approach to elucidate factors of reduced penetrance: transcriptional changes in THAP1-linked dystonia as an example

Pathogenic variants in THAP1 can cause dystonia with a penetrance of about 50 %. The underlying mechanisms are unknown and can be considered as means of endogenous disease protection. Since THAP1 encodes a transcription factor, drivers of this variability putatively act at the transcriptome level. Several transcriptome studies tried to elucidate THAP1 function in diverse cellular and mouse models, including mutation carrier-derived cells and iPSC-derived neurons, unveiling various differentially expressed genes and affected pathways. These include nervous system development, dopamine signalling, myelination, or cell-cell adhesion. A network diffusion analysis revealed mRNA splicing, mitochondria, DNA repair, and metabolism as significant pathways that may represent potential targets for therapeutic interventions.

Genetic screening in patients of Meige syndrome and blepharospasm

OBJECTIVE

Meige syndrome (MS) is cranial dystonia, including bilateral eyelid spasms (blepharospasm; BSP) and involuntary movements of the jaw muscles (oromandibular dystonia; OMD). Up to now, the pathogenic genes of MS and BSP are still unclear.

METHODS

We performed Sanger sequencing of GNAL, TOR1A, TOR2A, THAP1, and REEP4 exons on 78 patients, including 53 BSP and 25 MS and 96 healthy controls.

RESULTS

c.845G > C[R282P] of TOR1A, c.629delC[p.Gly210AlafsTer60] of TOR2A, c.1322A > G[N441S] of GNAL, c.446G > A[R149Q], and c.649C > T[R217C] of REEP4 were identified and predicated as deleterious probably damaging variants. Three potential alterations of splicing variants of TOR1A and TOR2A were identified in patients. The frequencies of TOR1A rs1435566780 and THAP1 rs545930392 were higher in patients than in controls.

CONCLUSIONS

TOR1A rs1435566780 (c.*16G > C(G > A)) and THAP1 rs545930392 (c.192G > A[K64K]) may contribute to the etiology of MS and BSP. Other identified rare mutations predicted as deleterious probably damaging need further confirmation. Larger MS and BSP cohorts and functional studies will need to be performed further to elucidate the association between these genes and the diseases.

Pathophysiological mechanisms of oromandibular dystonia

Oromandibular dystonia (OMD) is a rare form of focal idiopathic dystonia. OMD was clinically identified at the beginning of the 20th century, and the main clinical features have been progressively described over the years. However, OMD has several peculiarities that still remain unexplained, including the high rate of oral trauma, which is often related to the onset of motor symptoms. The purpose of this paper was to formulate a hypothesis regarding the pathophysiology of OMD, starting from the neuroanatomical basis of the masticatory and facial systems and highlighting the features that differentiate this condition from other forms of focal idiopathic dystonia. We provide a brief review of the clinical and etiological features of OMD as well as neurophysiological and neuroimaging findings obtained from studies in patients with OMD. We discuss possible pathophysiological mechanisms underlying OMD and suggest that abnormalities in sensory input processing may play a prominent role in OMD pathophysiology, possibly triggering a cascade of events that results in sensorimotor cortex network dysfunction. Finally, we identify open questions that future studies should address, including the effect of abnormal sensory input processing and oral trauma on the peculiar neurophysiological abnormalities observed in OMD.

Tremor in Primary Monogenic Dystonia

PURPOSE OF REVIEW

Tremor is an important phenotypic feature of dystonia with wide variability in the reported prevalence ranging from 14 to 86.67%. This variability may be due to the types of dystonia patients reported in different studies. This article reviews research articles reporting tremor in primary monogenic dystonia.

RECENT FINDINGS

We searched the MDS gene data and selected all research articles reporting tremor in primary monogenic dystonia. Tremor was reported in nine dystonia genes, namely DYT-HPCA, DYT-ANO3, DYT-KCTD17, DYT-THAP1, DYT-PRKRA, DYT-GNAL, DYT-TOR1A, DYT-KMT2B, and DYT-SGCE in the descending order of its frequency. HPCA gene mutation is rare, but all reported patients had tremor. Similarly, tremor was reported in eight genes associated with dystonia parkinsonism, namely DYT-SLC6A3, DYT-TH, DYT-SPR, DYT-PTS, DYT-GCH1, DYT-TAF1, DYT-QDPR, and DYT-SCL30A10 in the descending order of its prevalence. DYT-HPCA and DYT-ANO3 gene showed the highest prevalence of tremor in isolated dystonia, and DYT-SLC6A3 has the highest prevalence of tremor in combined dystonia.

Reduced Expression of GABA A Receptor Alpha2 Subunit Is Associated With Disinhibition of DYT-THAP1 Dystonia Patient-Derived Striatal Medium Spiny Neurons

DYT-THAP1 dystonia (formerly DYT6) is an adolescent-onset dystonia characterized by involuntary muscle contractions usually involving the upper body. It is caused by mutations in the gene THAP1 encoding for the transcription factor Thanatos-associated protein (THAP) domain containing apoptosis-associated protein 1 and inherited in an autosomal-dominant manner with reduced penetrance. Alterations in the development of striatal neuronal projections and synaptic function are known from transgenic mice models. To investigate pathogenetic mechanisms, human induced pluripotent stem cell (iPSC)-derived medium spiny neurons (MSNs) from two patients and one family member with reduced penetrance carrying a mutation in the gene THAP1 (c.474delA and c.38G > A) were functionally characterized in comparison to healthy controls. Calcium imaging and quantitative PCR analysis revealed significantly lower Ca²⁺ amplitudes upon GABA applications and a marked downregulation of the gene encoding the GABA_A receptor alpha2 subunit in THAP1 MSNs indicating a decreased GABAergic transmission. Whole-cell patch-clamp recordings showed a significantly lower frequency of miniature postsynaptic currents (mPSCs), whereas the frequency of spontaneous action potentials (APs) was elevated in THAP1 MSNs suggesting that decreased synaptic activity might have resulted in enhanced generation of APs. Our molecular and functional data indicate that a reduced expression of GABA_A receptor alpha2 subunit could eventually lead to limited GABAergic synaptic transmission, neuronal disinhibition, and hyperexcitability of THAP1 MSNs. These data give pathophysiological insight and may contribute to the development of novel treatment strategies for DYT-THAP1 dystonia.

Genotype-Phenotype Relations for Isolated Dystonia Genes: MDSGene Systematic Review

This comprehensive MDSGene review is devoted to 7 genes - TOR1A, THAP1, GNAL, ANO3, PRKRA, KMT2B, and HPCA - mutations in which may cause isolated dystonia. It followed MDSGene's standardized data extraction protocol and screened a total of ~1200 citations. Phenotypic and genotypic data on ~1200 patients with 254 different mutations were curated and analyzed. There were differences regarding age at onset, site of onset, and distribution of symptoms across mutation carriers in all 7 genes. Although carriers of TOR1A, THAP1, PRKRA, KMT2B, or HPCA mutations mostly showed childhood and adolescent onset, patients with GNAL and ANO3 mutations often developed first symptoms in adulthood. GNAL and KMT2B mutation carriers frequently have 1 predominant site of onset, that is, the neck (GNAL) or the lower limbs (KMT2B), whereas site of onset in DYT-TOR1A, DYT-THAP1, DYT-ANO3, DYT-PRKRA, and DYT-HPCA was broader. However, in most DYT-THAP1 and DYT-ANO3 patients, dystonia first manifested in the upper half of the body (upper limb, neck, and craniofacial/laryngeal), whereas onset in DYT-TOR1A, DYT-PRKRA and DYT-HPCA was frequently observed in an extremity, including both upper and lower ones. For ANO3, a segmental/multifocal distribution was typical, whereas TOR1A, PRKRA, KMT2B, and HPCA mutation carriers commonly developed generalized dystonia. THAP1 mutation carriers presented with focal, segmental/multifocal, or generalized dystonia in almost equal proportions. GNAL mutation carriers rarely showed generalization. This review provides a comprehensive overview of the current knowledge of hereditary isolated dystonia. The data are also available in an online database (http://www.mdsgene.org), which additionally offers descriptive summary statistics. © 2021 The Authors. Movement Disorders published by Wiley Periodicals LLC on behalf of International Parkinson and Movement Disorder Society.

Blepharospasm, Oromandibular Dystonia, and Meige Syndrome: Clinical and Genetic Update

Meige syndrome (MS) is cranial dystonia characterized by the combination of upper and lower cranial involvement and including binocular eyelid spasms (blepharospasm; BSP) and involuntary movements of the jaw muscles (oromandibular dystonia; OMD). The etiology and pathogenesis of this disorder of the extrapyramidal system are not well-understood. Neurologic and ophthalmic examinations often reveal no abnormalities, making diagnosis difficult and often resulting in misdiagnosis. A small proportion of patients have a family history of the disease, but to date no causative genes have been identified to date and no cure is available, although botulinum toxin A therapy effectively mitigates the symptoms and deep brain stimulation is gaining increasing attention as a viable alternative treatment option. Here we review the history and progress of research on MS, BSP, and OMD, as well as the etiology, pathology, diagnosis, and treatment.

Isolated dystonia: clinical and genetic updates

Four genes associated with isolated dystonia are currently well replicated and validated. DYT-THAP1 manifests as young-onset generalized dystonia with predominant craniocervical symptoms; and is associated with mostly deleterious missense variation in the THAP1 gene. De novo and inherited missense and protein truncating variation in GNAL as well as primarily missense variation in ANO3 cause isolated focal and/or segmental dystonia with preference for the upper half of the body and older ages at onset. The GAG deletion in TOR1A is associated with generalized dystonia with onset in childhood in the lower limbs. Rare variation in these genes causes monogenic sporadic and inherited forms of isolated dystonia; common variation may confer risk and imply that dystonia is a polygenic trait in a subset of cases. Although candidate gene screens have been successful in the past in detecting gene-disease associations, recent application of whole-genome and whole-exome sequencing methods enable unbiased capture of all genetic variation that may explain the phenotype. However, careful variant-level evaluation is necessary in every case, even in genes that have previously been associated with disease. We review the genetic architecture and phenotype of DYT-THAP1, DYT-GNAL, DYT-ANO3, and DYT-TOR1A by collecting case reports from the literature and performing variant classification using pathogenicity criteria.

Diverse Mechanisms Lead to Common Dysfunction of Striatal Cholinergic Interneurons in Distinct Genetic Mouse Models of Dystonia

Clinical and experimental data indicate striatal cholinergic dysfunction in dystonia, a movement disorder typically resulting in twisted postures via abnormal muscle contraction. Three forms of isolated human dystonia result from mutations in the TOR1A (DYT1), THAP1 (DYT6), and GNAL (DYT25) genes. Experimental models carrying these mutations facilitate identification of possible shared cellular mechanisms. Recently, we reported elevated extracellular striatal acetylcholine by in vivo microdialysis and paradoxical excitation of cholinergic interneurons (ChIs) by dopamine D2 receptor (D2R) agonism using ex vivo slice electrophysiology in Dyt1 ^ΔGAG/+ mice. The paradoxical excitation was caused by overactive muscarinic receptors (mAChRs), leading to a switch in D2R coupling from canonical G_i/o to noncanonical β-arrestin signaling. We sought to determine whether these mechanisms in Dyt1 ^ΔGAG/+ mice are shared with Thap1 ^C54Y/+ knock-in and Gnal ^+/- knock-out dystonia models and to determine the impact of sex. We found Thap1 ^C54Y/+ mice of both sexes have elevated extracellular striatal acetylcholine and D2R-induced paradoxical ChI excitation, which was reversed by mAChR inhibition. Elevated extracellular acetylcholine was absent in male and female Gnal ^+/- mice, but the paradoxical D2R-mediated ChI excitation was retained and only reversed by inhibition of adenosine A2ARs. The G_i/o-preferring D2R agonist failed to increase ChI excitability, suggesting a possible switch in coupling of D2Rs to β-arrestin, as seen previously in a DYT1 model. These data show that, whereas elevated extracellular acetylcholine levels are not always detected across these genetic models of human dystonia, the D2R-mediated paradoxical excitation of ChIs is shared and is caused by altered function of distinct G-protein-coupled receptors.SIGNIFICANCE STATEMENT Dystonia is a common and often disabling movement disorder. The usual medical treatment of dystonia is pharmacotherapy with nonselective antagonists of muscarinic acetylcholine receptors, which have many undesirable side effects. Development of new therapeutics is a top priority for dystonia research. The current findings, considered in context with our previous investigations, establish a role for cholinergic dysfunction across three mouse models of human genetic dystonia: DYT1, DYT6, and DYT25. The commonality of cholinergic dysfunction in these models arising from diverse molecular etiologies points the way to new approaches for cholinergic modulation that may be broadly applicable in dystonia.

The Twists of Pediatric Dystonia: Phenomenology, Classification, and Genetics

This article aims to provide a practical review of pediatric dystonia from a clinician's perspective. The focus is on the underlying genetic causes, recent findings, and treatable conditions. Dystonia can occur in an isolated fashion or accompanied by other neurological or systemic features. The clinical presentation is often a complex overlap of neurological findings with a large differential diagnosis. We recommend an approach guided by thorough clinical evaluation, brain magnetic resonance imaging (MRI), biochemical analysis, and genetic testing to hone in on the diagnosis. This article highlights the clinical and genetic complexity of pediatric dystonia and underlines the importance of a genetic diagnosis for therapeutic considerations.

Inherited dystonias: clinical features and molecular pathways

Recent decades have witnessed dramatic increases in understanding of the genetics of dystonia - a movement disorder characterized by involuntary twisting and abnormal posture. Hampered by a lack of overt neuropathology, researchers are investigating isolated monogenic causes to pinpoint common molecular mechanisms in this heterogeneous disease. Evidence from imaging, cellular, and murine work implicates deficiencies in dopamine neurotransmission, transcriptional dysregulation, and selective vulnerability of distinct neuronal populations to disease mutations. Studies of genetic forms of dystonia are also illuminating the developmental dependence of disease symptoms that is typical of many forms of the disease. As understanding of monogenic forms of dystonia grows, a clearer picture will develop of the abnormal motor circuitry behind this relatively common phenomenology. This chapter focuses on the current data covering the etiology and epidemiology, clinical presentation, and pathogenesis of four monogenic forms of isolated dystonia: DYT-TOR1A, DYT-THAP1, DYT-GCH1, and DYT-GNAL.

Update on the Genetics of Dystonia

Mainly due to the advent of next-generation sequencing (NGS), the field of genetics of dystonia has rapidly grown in recent years, which led to the discovery of a number of novel dystonia genes and the development of a new classification and nomenclature for inherited dystonias. In addition, new findings from both in vivo and in vitro studies have been published on the role of previously known dystonia genes, extending our understanding of the pathophysiology of dystonia. We here review the current knowledge and recent findings in the known genes for isolated dystonia TOR1A, THAP1, and GNAL as well as for the combined dystonias due to mutations in GCH1, ATP1A3, and SGCE. We present confirmatory evidence for a role of dystonia genes that had not yet been unequivocally established including PRKRA, TUBB4A, ANO3, and TAF1. We finally discuss selected novel genes for dystonia such as KMT2B and VAC14 along with the challenges for gene identification in the NGS era and the translational importance of dystonia genetics in clinical practice.

Novel GNB1 mutations disrupt assembly and function of G protein heterotrimers and cause global developmental delay in humans

Global developmental delay (GDD), often accompanied by intellectual disability, seizures and other features is a severe, clinically and genetically highly heterogeneous childhood-onset disorder. In cases where genetic causes have been identified, de novo mutations in neuronally expressed genes are a common scenario. These mutations can be best identified by exome sequencing of parent-offspring trios. De novo mutations in the guanine nucleotide-binding protein, beta 1 (GNB1) gene, encoding the Gβ1 subunit of heterotrimeric G proteins, have recently been identified as a novel genetic cause of GDD. Using exome sequencing, we identified 14 different novel variants (2 splice site, 2 frameshift and 10 missense changes) in GNB1 in 16 pediatric patients. One mutation (R96L) was recurrently found in three ethnically diverse families with an autosomal dominant mode of inheritance. Ten variants occurred de novo in the patients. Missense changes were functionally tested for their pathogenicity by assaying the impact on complex formation with Gγ and resultant mutant Gβγ with Gα. Signaling properties of G protein complexes carrying mutant Gβ1 subunits were further analyzed by their ability to couple to dopamine D1R receptors by real-time bioluminescence resonance energy transfer (BRET) assays. These studies revealed altered functionality of the missense mutations R52G, G64V, A92T, P94S, P96L, A106T and D118G but not for L30F, H91R and K337Q. In conclusion, we demonstrate a pathogenic role of de novo and autosomal dominant mutations in GNB1 as a cause of GDD and provide insights how perturbation in heterotrimeric G protein function contributes to the disease.

Mouse model of rare TOR1A variant found in sporadic focal dystonia impairs domains affected in DYT1 dystonia patients and animal models

Rare de novo mutations in genes associated with inherited Mendelian disorders are potential contributors to sporadic disease. DYT1 dystonia is an autosomal dominant, early-onset, generalized dystonia associated with an in-frame, trinucleotide deletion (n. delGAG, p. ΔE 302/303) in the Tor1a gene. Here we examine the significance of a rare missense variant in the Tor1a gene (c. 613T>A, p. F205I), previously identified in a patient with sporadic late-onset focal dystonia, by modeling it in mice. Homozygous F205I mice have motor impairment, reduced steady-state levels of TorsinA, altered corticostriatal synaptic plasticity, and prominent brain imaging abnormalities in areas associated with motor function. Thus, the F205I variant causes abnormalities in domains affected in people and/or mouse models with the DYT1 Tor1a mutation (ΔE). Our findings establish the pathological significance of the F205I Tor1a variant and provide a model with both etiological and phenotypic relevance to further investigate dystonia mechanisms.

DYT6 Dystonia: A Neuropathological Study

BACKGROUND

Mutations in the thanatos-associated protein domain containing apoptosis-associated protein 1 gene (THAP1) are responsible for adult-onset isolated dystonia (DYT6). However, no neuropathological studies of genetically proven DYT6 cases have been previously reported.

OBJECTIVE

We report the first detailed neuropathological investigation carried out on two DYT6 brains.

METHODS

Genetic screening for THAP1 gene mutations using standard Sanger polymerase chain reaction sequencing identified 2 cases, 1 with a known pathogenic mutation and the other with a novel mutation. A detailed neuropathological assessment of the cases was performed.

RESULTS

Both DYT6 cases showed no significant neurodegeneration and no specific disease-related pathology.

CONCLUSIONS

No neuropathological features that could be defined as hallmark features of DYT6 dystonia were identified. Our study supports the notion that in isolated dystonia, there is no significant neurodegeneration or morphological lesions that can be identified using routine methods.

Screening for THAP1 Mutations in Polish Patients with Dystonia Shows Known and Novel Substitutions

The aim of this study was to assess the presence of DYT6 mutations in Polish patients with isolated dystonia and to characterize their phenotype. We sequenced THAP1 exons 1, 2 and 3 including exon-intron boundaries and 5'UTR fragment in 96 non-DYT1 dystonia patients. In four individuals single nucleotide variations were identified. The coding substitutions were: c. 238A>G (p.Ile80Val), found in two patients, and c.167A>G (p.Glu56Gly), found in one patient. The same variations were present also in the patients' symptomatic as well as asymptomatic relatives. Mutation penetration in the analyzed families was 50-66.7%. In the fourth patient, a novel c.-249C>A substitution in the promoter region was identified. The patient, initially suspected of idiopathic isolated dystonia, finally presented with pantothenate kinase 2-associated neurodegeneration phenotype and was a carrier of two PANK2 mutations. This is the first identified NBIA1 case carrying mutations in both PANK2 and THAP1 genes. In all symptomatic THAP1 mutation carriers (four probands and their three affected relatives) the first signs of dystonia occurred before the age of 23. A primary localization typical for DYT6 dystonia was observed in six individuals. Five subjects developed the first signs of dystonia in the upper limb. In one patient the disease began from laryngeal involvement. An uncommon primary involvement of lower limb was noted in the THAP1 and PANK2 mutations carrier. Neither of these THAP1 substitutions were found in 150 unrelated healthy controls. To the contrary, we identified a heterozygous C/T genotype of c.57C>T single nucleotide variation (p.Pro19Pro, rs146087734) in one healthy control, but in none of the patients. Therefore, a previously proposed association between this substitution and DYT6 dystonia seems unlikely. We found also no significant difference between cases and controls in genotypes distribution of the two-nucleotide -237-236 GA>TT (rs370983900 & rs1844977763) polymorphism.

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.

Dystonia type 6 gene product Thap1: identification of a 50 kDa DNA-binding species in neuronal nuclear fractions

Mutations in THAP1 result in dystonia type 6, with partial penetrance and variable phenotype. The goal of this study was to examine the nature and expression pattern of the protein product(s) of the Thap1 transcription factor (DYT6 gene) in mouse neurons, and to study the regional and developmental distribution, and subcellular localization of Thap1 protein. The goal was accomplished via overexpression and knock-down of Thap1 in the HEK293T cell line and in mouse striatal primary cultures and western blotting of embryonic Thap1-null tissue. The endogenous and transduced Thap1 isoforms were characterized using three different commercially available anti-Thap1 antibodies and validated by immunoprecipitation and DNA oligonucleotide affinity chromatography. We identified multiple, novel Thap1 species of apparent M_r 32 kDa, 47 kDa, and 50–52 kDa in vitro and in vivo, and verified the previously identified species at 29–30 kDa in neurons. The Thap1 species at the 50 kDa size range was exclusively detected in murine brain and testes and were located in the nuclear compartment. Thus, in addition to the predicted 25 kDa apparent M_r, we identified Thap1 species with greater apparent M_r that we speculate may be a result of posttranslational modifications. The neural localization of the 50 kDa species and its nuclear compartmentalization suggests that these may be key Thap1 species controlling neuronal gene transcription. Dysfunction of the neuronal 50 kDa species may therefore be implicated in the pathogenesis of DYT6.

THAP1, the gene mutated in DYT6 dystonia, autoregulates its own expression

THAP1 encodes a transcription factor but its regulation is largely elusive. TOR1A was shown to be repressed by THAP1 in vitro. Notably, mutations in both of these genes lead to dystonia (DYT6 or DYT1). Surprisingly, expressional changes of TOR1A in THAP1 mutation carriers have not been detected indicating additional levels of regulation. Here, we investigated whether THAP1 is able to autoregulate its own expression. Using in-silico prediction, luciferase reporter gene assays, and (quantitative) chromatin immunoprecipitation (ChIP), we defined the THAP1 minimal promoter to a 480bp-fragment and demonstrated specific binding of THAP1 to this region which resulted in repression of the THAP1 promoter. This autoregulation was disturbed by different DYT6-causing mutations. Two mutants (Ser6Phe, Arg13His) were shown to be less stable than wildtype THAP1 adding to the effect of reduced binding to the THAP1 promoter. Overexpressed THAP1 is preferably degraded through the proteasome. Notably, endogenous THAP1 expression was significantly reduced in cells overexpressing wildtype THAP1 as demonstrated by quantitative PCR. In contrast, higher THAP1 levels were detected in induced pluripotent stem cell (iPS)-derived neurons from THAP1 mutation carriers. Thus, we identified a feedback-loop in the regulation of THAP1 expression and demonstrated that mutant THAP1 leads to higher THAP1 expression levels. This compensatory autoregulation may contribute to the mean age at onset in the late teen years or even reduced penetrance in some THAP1 mutation carriers.

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.

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.

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.

NMR studies of a new family of DNA binding proteins: the THAP proteins

The THAP (THanatos-Associated Protein) domain is an evolutionary conserved C2CH zinc-coordinating domain shared with a large family of cellular factors (THAP proteins). Many members of the THAP family act as transcription factors that control cell proliferation, cell cycle progression, angiogenesis, apoptosis and epigenetic gene silencing. They recognize specific DNA sequences in the promoters of target genes and subsequently recruit effector proteins. Recent structural and functional studies have allowed getting better insight into the nuclear and cellular functions of some THAP members and the molecular mechanisms by which they recognize DNA. The present article reviews recent advances in the knowledge of the THAP domains structures and their interaction with DNA, with a particular focus on NMR. It provides the solution structure of the THAP domain of THAP11, a recently characterized human THAP protein with important functions in transcription and cell growth in colon cancer.

Neuropathology of cervical dystonia

The aim of this study was to search for neuropathological changes in postmortem brain tissue of individuals with cervical dystonia (CD). Multiple regions of formalin-preserved brains were collected from patients with CD and controls and examined with an extensive battery of histopathological stains in a two-stage study design. In stage one, 4 CD brains underwent a broad screening neuropathological examination. In stage two, these 4 CD brains were combined with 2 additional CD brains, and the subjective findings were quantified and compared to 16 age-matched controls. The initial subjective neuropathological assessment revealed only two regions with relatively consistent changes. The substantia nigra had frequent ubiquitin-positive intranuclear inclusions known as Marinesco bodies. Additionally, the cerebellum showed patchy loss of Purkinje cells, areas of focal gliosis and torpedo bodies. Other brain regions showed minor or inconsistent changes. In the second stage of the analysis, quantitative studies failed to reveal significant differences in the numbers of Marinesco bodies in CD versus controls, but confirmed a significantly lower Purkinje cell density in CD. Molecular investigations revealed 4 of the CD cases and 2 controls to harbor sequence variants in non-coding regions of THAP1, and these cases had lower Purkinje cell densities regardless of whether they had CD. The findings suggest that subtle neuropathological changes such as lower Purkinje cell density may be found in primary CD when relevant brain regions are investigated with appropriate methods.

The genetics of dystonias

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

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

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.

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.

Improved motor performance in Dyt1 ΔGAG heterozygous knock-in mice by cerebellar Purkinje-cell specific Dyt1 conditional knocking-out

Early-onset generalized torsion dystonia (dystonia 1) is an inherited movement disorder caused by mutations in DYT1 (TOR1A), which codes for torsinA. Most patients have a 3-base pair deletion (ΔGAG) in one allele of DYT1, corresponding to a loss of a glutamic acid residue (ΔE) in the C-terminal region of the protein. Functional alterations in basal ganglia circuits and the cerebellum have been reported in dystonia. Pharmacological manipulations or mutations in genes that result in functional alterations of the cerebellum have been reported to have dystonic symptoms and have been used as phenotypic rodent models. Additionally, structural lesions in the abnormal cerebellar circuits, such as cerebellectomy, have therapeutic effects in these models. A previous study has shown that the Dyt1 ΔGAG heterozygous knock-in (KI) mice exhibit motor deficits in the beam-walking test. Both Dyt1 ΔGAG heterozygous knock-in (KI) and Dyt1 Purkinje cell-specific knockout (Dyt1 pKO) mice exhibit dendritic alterations of cerebellar Purkinje cells. Here, Dyt1 pKO mice exhibited significantly less slip numbers in the beam-walking test, suggesting better motor performance than control littermates, and normal gait. Furthermore, Dyt1 ΔGAG KI/Dyt1 pKO double mutant mice exhibited significantly lower numbers of slips than Dyt1 ΔGAG heterozygous KI mice, suggesting Purkinje-cell specific knockout of Dyt1 wild-type (WT) allele in Dyt1 ΔGAG heterozygous KI mice rescued the motor deficits. The results suggest that molecular lesions of torsinA in Purkinje cells by gene therapy or intervening in the signaling pathway downstream of the cerebellar Purkinje cells may rescue motor symptoms in dystonia 1.

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.