Clinicopathological Phenotype and Genetics of X-Linked Dystonia-Parkinsonism (XDP; DYT3; Lubag)

Striatal parvalbumin interneurons are activated in a mouse model of cerebellar dystonia

Dystonia is thought to arise from abnormalities in the motor loop of the basal ganglia; however, there is an ongoing debate regarding cerebellar involvement. We adopted an established cerebellar dystonia mouse model by injecting ouabain to examine the contribution of the cerebellum. Initially, we examined whether the entopeduncular nucleus (EPN), substantia nigra pars reticulata (SNr), globus pallidus externus (GPe) and striatal neurons were activated in the model. Next, we examined whether administration of a dopamine D1 receptor agonist and dopamine D2 receptor antagonist or selective ablation of striatal parvalbumin (PV, encoded by Pvalb)-expressing interneurons could modulate the involuntary movements of the mice. The cerebellar dystonia mice had a higher number of cells positive for c-fos (encoded by Fos) in the EPN, SNr and GPe, as well as a higher positive ratio of c-fos in striatal PV interneurons, than those in control mice. Furthermore, systemic administration of combined D1 receptor agonist and D2 receptor antagonist and selective ablation of striatal PV interneurons relieved the involuntary movements of the mice. Abnormalities in the motor loop of the basal ganglia could be crucially involved in cerebellar dystonia, and modulating PV interneurons might provide a novel treatment strategy.

SAK3 confers neuroprotection in the neurodegeneration model of X-linked Dystonia-Parkinsonism

Background X-linked Dystonia-Parkinsonism(XDP) is an adult-onset neurodegenerative disorder that results in the loss of striatal medium spiny neurons (MSNs). XDP is associated with disease-specific mutations in and around the TAF1 gene. This study highlights the utility of directly reprogrammed MSNs from fibroblasts of affected XDP individuals as a platform that captures cellular and epigenetic phenotypes associated with XDP-related neurodegeneration. In addition, the current study demonstrates the neuroprotective effect of SAK3 currently tested in other neurodegenerative diseases. Methods XDP fibroblasts from three independent patients as well as age- and sex-matched control fibroblasts were used to generate MSNs by direct neuronal reprogramming using miRNA-9/9*-124 and thetranscription factors CTIP2 , DLX1 -P2A- DLX2 , and MYT1L . Neuronal death, DNA damage, and mitochondrial health assays were carried out to assess the neurodegenerative state of directly reprogrammed MSNs from XDP patients (XDP-MSNs). RNA sequencing and ATAC sequencing were performed to infer changes in the transcriptomic and chromatin landscapesof XDP-MSNs compared to those of control MSNs (Ctrl-MSNs). Results Our results show that XDP patient fibroblasts can be successfully reprogrammed into MSNs and XDP-MSNs display several degenerative phenotypes, including neuronal death, DNA damage, and mitochondrial dysfunction, compared to Ctrl-MSNs reprogrammed from age- and sex-matched control individuals' fibroblasts. In addition, XDP-MSNs showed increased vulnerability to TNFα -toxicity compared to Ctrl-MSNs. To dissect the altered cellular state in XDP-MSNs, we conducted transcriptomic and chromatin accessibility analyses using RNA- and ATAC-seq. Our results indicate that pathways related to neuronal function, calcium signaling, and genes related to other neurodegenerative diseases are commonly altered in XDP-MSNs from multiple patients. Interestingly, we found that SAK3, a T-type calcium channel activator, that may have therapeutic values in other neurodegenerative disorders, protected XDP-MSNs from neuronal death. Notably, we found that SAK3-mediated alleviation of neurodegeneration in XDP-MSNs was accompanied by gene expression changes toward Ctrl-MSNs.

A scoping review on the diagnosis and treatment of X-linked dystonia-parkinsonism

INTRODUCTION

X-linked dystonia-parkinsonism (XDP) is a progressive neurodegenerative disorder that has been studied well in recent years.

OBJECTIVES

This scoping review aimed to describe the current state of knowledge about the diagnosis and treatment of XDP, to provide clinicians with a concise and up-to-date overview.

METHODS

We conducted a scoping review of pertinent literature on the diagnosis and treatment of XDP using Preferred Reporting Items for Systematic Reviews and Meta-Analyses extension for Scoping Reviews guidelines.

RESULTS

There were 24 articles on diagnostic methods and 20 articles on therapeutic interventions for XDP, with 7 review articles describing both. The detection of the SVA retrotransposon insertion within the TAF1 gene is confirmatory for XDP. Oral medications are marginally effective. Chemodenervation with botulinum toxin is an effective treatment. Pallidal deep brain stimulation (DBS) has been shown to provide significant improvement in the dystonia and quality of life of patients with XDP for a longer time. A less invasive surgical option is the transcranial magnetic resonance-guided focused ultrasound (tcMRgFUS), which has shown promising effects with the limited number of case reports available.

CONCLUSION

XDP is a geneti disorder characterized by striatal symptoms and pathology on neuroimaging. No effective oral medications are available for the management of XDP. The use of botulinum toxin is limited by its cost and duration of effects. As of now, pallidal DBS is deemed to be the best option. Another promising option is the tcMRgFUS but still has limited studies on its safety and efficacy in XDP.

Endemic parkinsonism: clusters, biology and clinical features

The term 'endemic parkinsonism' refers to diseases that manifest with a dominant parkinsonian syndrome, which can be typical or atypical, and are present only in a particular geographically defined location or population. Ten phenotypes of endemic parkinsonism are currently known: three in the Western Pacific region; two in the Asian-Oceanic region; one in the Caribbean islands of Guadeloupe and Martinique; and four in Europe. Some of these disease entities seem to be disappearing over time and therefore are probably triggered by unique environmental factors. By contrast, other types persist because they are exclusively genetically determined. Given the geographical clustering and potential overlap in biological and clinical features of these exceptionally interesting diseases, this Review provides a historical reference text and offers current perspectives on each of the 10 phenotypes of endemic parkinsonism. Knowledge obtained from the study of these disease entities supports the hypothesis that both genetic and environmental factors contribute to the development of neurodegenerative diseases, not only in endemic parkinsonism but also in general. At the same time, this understanding suggests useful directions for further research in this area.

X-linked dystonia parkinsonism: epidemiology, genetics, clinical features, diagnosis, and treatment

X-linked dystonia parkinsonism (XDP) is a rare X-linked recessive degenerative movement disorder that only affects Filipino descent, predominantly males. Its underlying cause is associated with the genetic alterations in the TAF1/DYT3 multiple transcription system. SINE-VNTR-Alu (SVA) retrotransposon insertion was suggested to be the responsible genetic mutation. Clinically, it initially presents as focal dystonia and generalizes within years. Parkinsonism arises years later and coexists with dystonia. Nonmotor symptoms like cognitive impairment and mood disorders are also common among XDP patients. XDP diagnosis relies on clinical history and physical examination. On imaging, abnormalities of the striatum, such as atrophy, are widely seen and can explain the clinical presentations with a three-model pathway of the striatum. Treatments aim for symptomatic relief of dystonia and parkinsonism and to prevent complications. Oral medications, chemo-denervation, and surgery are used in XDP patients. This review summarizes the currently important information regarding XDP, providing a synoptic overview and understanding of XDP for future studies.

Isolated and combined dystonias: Update

Dystonia is a hyperkinetic movement disorder with a unique motor phenomenology that can manifest as an isolated clinical syndrome or combined with other neurological features. This chapter reviews the characteristic features of dystonia phenomenology and the syndromic approach to evaluating the disorders that may allow us to differentiate the isolated and combined syndromes. We also present the most common types of isolated and combined dystonia syndromes. Since accelerated gene discoveries have increased our understanding of the molecular mechanisms of dystonia pathogenesis, we also present isolated and combined dystonia syndromes by shared biological pathways. Examples of these converging mechanisms of the isolated and combined dystonia syndromes include (1) disruption of the integrated response pathway through eukaryotic initiation factor 2 alpha signaling, (2) disease of dopaminergic signaling, (3) alterations in the cerebello-thalamic pathway, and (4) disease of protein mislocalization and stability. The discoveries that isolated and combined dystonia syndromes converge in shared biological pathways will aid in the development of clinical trials and therapeutic strategies targeting these convergent molecular pathways.

Transcriptional Alterations in X-Linked Dystonia–Parkinsonism Caused by the SVA Retrotransposon

X-linked dystonia–parkinsonism (XDP) is a severe neurodegenerative disorder that manifests as adult-onset dystonia combined with parkinsonism. A SINE-VNTR-Alu (SVA) retrotransposon inserted in an intron of the TAF1 gene reduces its expression and alters splicing in XDP patient-derived cells. As a consequence, increased levels of the TAF1 intron retention transcript TAF1-32i can be found in XDP cells as compared to healthy controls. Here, we investigate the sequence of the deep intronic region included in this transcript and show that it is also present in cells from healthy individuals, albeit in lower amounts than in XDP cells, and that it undergoes degradation by nonsense-mediated mRNA decay. Furthermore, we investigate epigenetic marks (e.g., DNA methylation and histone modifications) present in this intronic region and the spanning sequence. Finally, we show that the SVA evinces regulatory potential, as demonstrated by its ability to repress the TAF1 promoter in vitro. Our results enable a better understanding of the disease mechanisms underlying XDP and transcriptional alterations caused by SVA retrotransposons.

A Cross-Cultural Validation of the Filipino and Hiligaynon Versions of the Parts IIIB (Non-Motor Features) and IV (Activities of Daily Living) of the X-Linked Dystonia-Parkinsonism- MDSP Rating Scale

Introduction

X-linked dystonia-parkinsonism (XDP) is a progressive movement disorder which also encompasses non-motor features and alterations in activities of daily living. The study aims to translate the Parts IIIB (Non-Motor Features) and IV (Activities of Daily Living) of the XDP-Movement Disorder Society of Philippines Rating Scale to Filipino and Hiligaynon and subsequently validate these versions, which are more understandable to the natives given that XDP originated from the Panay Islands in the Philippines.

Methods

This is a cross-cultural, cross-sectional validation study, composed of the following steps: forward translation, backward translation, panel reconciliation, pretesting, and field testing. Two sets of 10 XDP patients were recruited to the Filipino and Hiligaynon groups for pretesting and cognitive debriefing while another 2 sets of 50 XDP patients were assigned for field testing.

Results

The Filipino version had a good internal consistency with a Cronbach's alpha of 0.951 during the pretesting and 0.886 during the field testing. Similar results were seen in the Hiligaynon version (0.837; 0.900). Both also had good conceptual equivalence as demonstrated by significant Pearson r values of 0.384 to 0.814 for the Filipino and 0.355 to 0.800 for the Hiligaynon versions.

Conclusion

The Filipino and Hiligaynon versions of the Parts IIIB and IV of the XDP-MDSP scale are internally valid and reliable. These scales are considered acceptable to assess the severity of the non-motor features and difficulties in activities of daily living among XDP patients.

Ataxia with vitamin E deficiency in the Philippines : A case report of two siblings

Here we report two siblings with ataxia and peripheral neuropathy. One patient showed head tremors. Genetic analysis revealed a mutation in the hepatic α-tocopherol transfer protein (α-TTP) gene (TTPA) on chromosome 8q13. They were diagnosed with ataxia with vitamin E deficiency which is firstly reported in the Philippines. As the symptoms of ataxia with vitamin E deficiency can be alleviated with lifelong vitamin E administration, differential diagnosis from similar syndromes is important. In addition, ataxia with vitamin E deficiency causes movement disorders. Therefore, a common hereditary disease in the Philippines, X-linked dystonia-parkinsonism, could be another differential diagnosis. The Philippines is an archipelago comprising 7,107 islands, and the prevalence of rare hereditary diseases among the populations of small islands is still unclear. For neurologists, establishing a system of genetic diagnosis and counseling in rural areas remains challenging. These unresolved problems should be addressed in the near future. J. Med. Invest. 68 : 400-403, August, 2021.

Dystonia and Cerebellum: From Bench to Bedside

Dystonia pathogenesis remains unclear; however, findings from basic and clinical research suggest the importance of the interaction between the basal ganglia and cerebellum. After the discovery of disynaptic pathways between the two, much attention has been paid to the cerebellum. Basic research using various dystonia rodent models and clinical studies in dystonia patients continues to provide new pieces of knowledge regarding the role of the cerebellum in dystonia genesis. Herein, we review basic and clinical articles related to dystonia focusing on the cerebellum, and clarify the current understanding of the role of the cerebellum in dystonia pathogenesis. Given the recent evidence providing new hypotheses regarding dystonia pathogenesis, we discuss how the current evidence answers the unsolved clinical questions.

Neurocognitive profile of patients with X-linked dystonia-parkinsonism

X-linked dystonia-parkinsonism (XDP) is a debilitating movement disorder endemic to the Panay Island, Philippines. Most studies focus on motor symptoms, hence we reviewed the neurocognitive profile of XDP patients. Neurocognitive testing of XDP patients focused on five domains: general intellectual functioning, episodic memory, language, attention and executive function, and affect. Twenty-nine genetically confirmed patients were included. Twenty-six (89.6%) had impairments in one or more domains, while only three had no impairment in any domain. Attention and executive function was the most commonly affected domain (n = 23, 79.3%). Deficits in general intellect, episodic memory, attention and executive function and affect were seen in our subset of XDP patients. The striatal pathology affecting the frontostriatal circuitry mandating these cognitive processes is mainly implicated in these impairments. The results of our study provided further evidence on the extent of cognitive impairment in XDP using a select battery of neurocognitive tests.

TAF1 Transcripts and Neurofilament Light Chain as Biomarkers for X-linked Dystonia-Parkinsonism

Background

X‐linked dystonia‐parkinsonism is a rare neurological disease endemic to the Philippines. Dystonic symptoms appear in males at the mean age of 40 years and progress to parkinsonism with degenerative pathology in the striatum. A retrotransposon inserted in intron 32 of the TAF1 gene leads to alternative splicing in the region and a reduction of the full‐length mRNA transcript.

Objectives

The objective of this study was to discover cell‐based and biofluid‐based biomarkers for X‐linked dystonia‐parkinsonism.

Methods

RNA from patient‐derived neural progenitor cells and their secreted extracellular vesicles were used to screen for dysregulation of TAF1 expression. Droplet‐digital polymerase chain reaction was used to quantify the expression of TAF1 mRNA fragments 5′ and 3′ to the retrotransposon insertion and the disease‐specific splice variant TAF1‐32i in whole‐blood RNA. Plasma levels of neurofilament light chain were measured using single‐molecule array.

Results

In neural progenitor cells and their extracellular vesicles, we confirmed that the TAF1‐3′/5′ ratio was lower in patient samples, whereas TAF1‐32i expression is higher relative to controls. In whole‐blood RNA, both TAF1‐3′/5′ ratio and TAF1‐32i expression can differentiate patient (n = 44) from control samples (n = 18) with high accuracy. Neurofilament light chain plasma levels were significantly elevated in patients (n = 43) compared with both carriers (n = 16) and controls (n = 21), with area under the curve of 0.79.

Conclusions

TAF1 dysregulation in blood serves as a disease‐specific biomarker that could be used as a readout for monitoring therapies targeting TAF1 splicing. Neurofilament light chain could be used in monitoring neurodegeneration and disease progression in patients. © 2020 The Authors. Movement Disorders published by Wiley Periodicals LLC on behalf of International Parkinson and Movement Disorder Society.

Dystonia and dopamine: From phenomenology to pathophysiology

A line of evidence suggests that the pathophysiology of dystonia involves the striatum, whose activity is modulated among other neurotransmitters, by the dopaminergic system. However, the link between dystonia and dopamine appears complex and remains unclear. Here, we propose a physiological approach to investigate the clinical and experimental data supporting a role of the dopaminergic system in the pathophysiology of dystonic syndromes. Because dystonia is a disorder of motor routines, we first focus on the role of dopamine and striatum in procedural learning. Second, we consider the phenomenology of dystonia from every angle in order to search for features giving food for thought regarding the pathophysiology of the disorder. Then, for each dystonic phenotype, we review, when available, the experimental and imaging data supporting a connection with the dopaminergic system. Finally, we propose a putative model in which the different phenotypes could be explained by changes in the balance between the direct and indirect striato-pallidal pathways, a process critically controlled by the level of dopamine within the striatum. Search strategy and selection criteria References for this article were identified through searches in PubMed with the search terms « dystonia », « dopamine", « striatum », « basal ganglia », « imaging data », « animal model », « procedural learning », « pathophysiology », and « plasticity » from 1998 until 2018. Articles were also identified through searches of the authors' own files. Only selected papers published in English were reviewed. The final reference list was generated on the basis of originality and relevance to the broad scope of this review.

Cost-Analysis of the Different Treatment Modalities in X-Linked Dystonia-Parkinsonism

Background: X-linked dystonia-parkinsonism (XDP) is a debilitating disease endemic in the Philippines. Several oral medications as well as botulinum toxin A (BoNT-A) injection and deep brain stimulation (DBS) surgery appear to be the cornerstone of treatment in XDP, which are commonly used in combination. Being a chronic progressive disease, it is an economic burden to the patient and their families. Thus, we aim to perform a comparative analysis of the associated healthcare costs for the therapeutic options used in XDP.

Methodology: A questionnaire assessing the healthcare costs in the management of XDP was designed and administered through an interview with the XDP patients or their caregivers. We analyzed the data and a bootstrap analysis was also done to obtain a more generalizable estimation of the costs.

Results: A total of 110 gene-positive XDP patients were included in this study. The mean total annual cost per patient was USD 4,861.23 (USD:PHP 1:50, as of January 8, 2018). More than half of the patients (n = 61, 55.5%) received both oral medications and BoNT-A injection while 42 patients (38.2%) received oral medications alone. Only seven patients underwent DBS with a reported estimated cost of USD 50,931.43. The bootstrap analysis confirmed the estimates done in this study.

Conclusion: The estimated costs in the management of XDP was shown to be 30 times the average annual health expenditure of an average Filipino. This calls for more government effort to provide comprehensive care for chronic and debilitating diseases such as XDP.