Genetics of movement disorders in the next-generation sequencing era

Next-generation sequencing and bioinformatics in rare movement disorders

The ability to sequence entire exomes and genomes has revolutionized molecular testing in rare movement disorders, and genomic sequencing is becoming an integral part of routine diagnostic workflows for these heterogeneous conditions. However, interpretation of the extensive genomic variant information that is being generated presents substantial challenges. In this Perspective, we outline multidimensional strategies for genetic diagnosis in patients with rare movement disorders. We examine bioinformatics tools and computational metrics that have been developed to facilitate accurate prioritization of disease-causing variants. Additionally, we highlight community-driven data-sharing and case-matchmaking platforms, which are designed to foster the discovery of new genotype-phenotype relationships. Finally, we consider how multiomic data integration might optimize diagnostic success by combining genomic, epigenetic, transcriptomic and/or proteomic profiling to enable a more holistic evaluation of variant effects. Together, the approaches that we discuss offer pathways to the improved understanding of the genetic basis of rare movement disorders.

Applicability of clinical genetic testing for deep brain stimulation treatment in monogenic Parkinson's disease and monogenic dystonia: a multidisciplinary team perspective

In this perspective article, we highlight the possible applicability of genetic testing in Parkinson's disease and dystonia patients treated with deep brain stimulation (DBS). DBS, a neuromodulatory technique employing electrical stimulation, has historically targeted motor symptoms in advanced PD and dystonia, yet its precise mechanisms remain elusive. Genetic insights have emerged as potential determinants of DBS efficacy. Known PD genes such as GBA, SNCA, LRRK2, and PRKN are most studied, even though further studies are required to make firm conclusions. Variable outcomes depending on genotype is present in genetic dystonia, as DYT-TOR1A, NBIA/DYTPANK2, DYT-SCGE and X-linked dystonia-parkinsonism have demonstrated promising outcomes following GPi-DBS, while varying outcomes have been documented in DYT-THAP1. We present two clinical vignettes that illustrate the applicability of genetics in clinical practice, with one PD patient with compound GBA mutations and one GNAL dystonia patient. Integrating genetic testing into clinical practice is pivotal, particularly with advancements in next-generation sequencing. However, there is a clear need for further research, especially in rarer monogenic forms. Our perspective is that applying genetics in PD and dystonia is possible today, and despite challenges, it has the potential to refine patient selection and enhance treatment outcomes.

Genetic Testing in Parkinson's Disease

Genetic testing for persons with Parkinson's disease is becoming increasingly common. Significant gains have been made regarding genetic testing methods, and testing is becoming more readily available in clinical, research, and direct-to-consumer settings. Although the potential utility of clinical testing is expanding, there are currently no proven gene-targeted therapies, but clinical trials are underway. Furthermore, genetic testing practices vary widely, as do knowledge and attitudes of relevant stakeholders. The specter of testing mandates financial, ethical, and physician engagement, and there is a need for guidelines to help navigate the myriad of challenges. However, to develop guidelines, gaps and controversies need to be clearly identified and analyzed. To this end, we first reviewed recent literature and subsequently identified gaps and controversies, some of which were partially addressed in the literature, but many of which are not well delineated or researched. Key gaps and controversies include: (1) Is genetic testing appropriate in symptomatic and asymptomatic individuals without medical actionability? (2) How, if at all, should testing vary based on ethnicity? (3) What are the long-term outcomes of consumer- and research-based genetic testing in presymptomatic PD? (4) What resources are needed for clinical genetic testing, and how is this impacted by models of care and cost-benefit considerations? Addressing these issues will help facilitate the development of consensus and guidelines regarding the approach and access to genetic testing and counseling. This is also needed to guide a multidisciplinary approach that accounts for cultural, geographic, and socioeconomic factors in developing testing guidelines. © 2023 The Authors. Movement Disorders published by Wiley Periodicals LLC on behalf of International Parkinson and Movement Disorder Society.

Paroxysmal Movement Disorders

Paroxysmal movement disorders (PxMDs) are a clinical and genetically heterogeneous group of movement disorders characterized by episodic involuntary movements (dystonia, dyskinesia, chorea and/or ataxia). Historically, PxMDs were classified clinically (triggers and characteristics of the movements) and this directed single-gene testing. With the advent of next-generation sequencing (NGS), how we classify and investigate PxMDs has been transformed. Next-generation sequencing has enabled new gene discovery (RHOBTB2, TBC1D24), expansion of phenotypes in known PxMDs genes and a better understanding of disease mechanisms. However, PxMDs exhibit phenotypic pleiotropy and genetic heterogeneity, making it challenging to predict genotype based on the clinical phenotype. For example, paroxysmal kinesigenic dyskinesia is most commonly associated with variants in PRRT2 but also variants identified in PNKD, SCN8A, and SCL2A1. There are no radiological or biochemical biomarkers to differentiate genetic causes. Even with NGS, diagnosis rates are variable, ranging from 11 to 51% depending on the cohort studied and technology employed. Thus, a large proportion of patients remain undiagnosed compared to other neurological disorders such as epilepsy, highlighting the need for further genomic research in PxMDs. Whole-genome sequencing, deep-sequencing, copy number variant analysis, detection of deep-intronic variants, mosaicism and repeat expansions, will improve diagnostic rates. Identifying the underlying genetic cause has a significant impact on patient care, modification of treatment, long-term prognostication and genetic counseling. This paper provides an update on the genetics of PxMDs, description of PxMDs classified according to causative gene rather than clinical phenotype, highlighting key clinical features and providing an algorithm for genetic testing of PxMDs.

Scoring Algorithm-Based Genomic Testing in Dystonia: A Prospective Validation Study

BACKGROUND

Despite the established value of genomic testing strategies, practice guidelines for their use do not exist in many indications.

OBJECTIVES

We sought to validate a recently introduced scoring algorithm for dystonia, predicting the diagnostic utility of whole-exome sequencing (WES) based on individual phenotypic aspects (age-at-onset, body distribution, presenting comorbidity).

METHODS

We prospectively enrolled a set of 209 dystonia-affected families and obtained summary scores (0-5 points) according to the algorithm. Singleton (N = 146), duo (N = 11), and trio (N = 52) WES data were generated to identify genetic diagnoses.

RESULTS

Diagnostic yield was highest (51%) among individuals with a summary score of 5, corresponding to a manifestation of early-onset segmental or generalized dystonia with coexisting non-movement disorder-related neurological symptoms. Sensitivity and specificity at the previously suggested threshold for implementation of WES (3 points) was 96% and 52%, with area under the curve of 0.81.

CONCLUSIONS

The algorithm is a useful predictive tool and could be integrated into dystonia routine diagnostic protocols. © 2021 The Authors. Movement Disorders published by Wiley Periodicals LLC on behalf of International Parkinson Movement Disorder Society.

Worldwide barriers to genetic testing for movement disorders

BACKGROUND AND PURPOSE

Despite enormous advances in identifying genetic variants responsible for many neurological diseases, access to genetic testing may be limited in clinical practice. The objective of this study was to assess worldwide access to genetic tests for movement disorders and factors impacting their utilization.

METHODS

The Rare Movement Disorders Study Group of the International Parkinson and Movement Disorder Society designed an online survey electronically mailed to all 7815 members.

RESULTS

Survey data completed by 1269 participants from 109 countries were analysed. Limited access to geneticists and genetic counsellors was reported in many world regions compared to Europe and North America. Availability of genetic testing was limited, with rates of access lower than 50%. Genetic testing for chorea was the most commonly available. For parkinsonism, dystonia, ataxia, hereditary spastic paraplegias and metabolic disorders, there was limited access to genetic testing in all countries compared to Europe and North America, with significant differences found for Africa, Central/South America, Asia. In many regions, genetic testing was supported by either private or public funding. Genetic testing was free of charge in Europe according to 63.5% of respondents. In North America, Africa, Central/South America, Asia and the Middle East access to free of charge genetic testing was by far significantly lower compared to Europe.

CONCLUSIONS

This survey highlights difficulties in accessing genetic testing and individuals with expertise in genetics at the worldwide level. In addition, major disparities in genetic testing amongst world regions are highlighted, probably due to a variety of factors including financial barriers.

Challenges in Clinicogenetic Correlations: One Gene - Many Phenotypes

Background

Progress in genetics – particularly the advent of next‐generation sequencing (NGS) – has enabled an unparalleled gene discovery and revealed unmatched complexity of genotype–phenotype correlations in movement disorders. Among other things, it has emerged that mutations in one and the same gene can cause multiple, often markedly different phenotypes. Consequently, movement disorder specialists have increasingly experienced challenges in clinicogenetic correlations.

Objectives

To deconstruct biological phenomena and mechanistic bases of phenotypic heterogeneity in monogenic movement disorders and neurodegenerative diseases. To discuss the evolving role of movement disorder specialists in reshaping disease phenotypes in the NGS era.

Methods

This scoping review details phenomena contributing to phenotypic heterogeneity and their underlying mechanisms.

Results

Three phenomena contribute to phenotypic heterogeneity, namely incomplete penetrance, variable expressivity and pleiotropy. Their underlying mechanisms, which are often shared across phenomena and non‐mutually exclusive, are not fully elucidated. They involve genetic factors (ie, different mutation types, dynamic mutations, somatic mosaicism, intragenic intra‐ and inter‐allelic interactions, modifiers and epistatic genes, mitochondrial heteroplasmy), epigenetic factors (ie, genomic imprinting, X‐chromosome inactivation, modulation of genetic and chromosomal defects), and environmental factors.

Conclusion

Movement disorders is unique in its reliance on clinical judgment to accurately define disease phenotypes. This has been reaffirmed by the NGS revolution, which provides ever‐growing sequencing data and fuels challenges in variant pathogenicity assertions for such clinically heterogeneous disorders. Deep phenotyping, with characterization and continual updating of “core” phenotypes, and comprehension of determinants of genotype–phenotype complex relationships are crucial for clinicogenetic correlations and have implications for the diagnosis, treatment and counseling.

Spinocerebellar ataxia type 14: refining clinicogenetic diagnosis in a rare adult-onset disorder

Objectives

Genetic variant classification is a challenge in rare adult‐onset disorders as in SCA‐PRKCG (prior spinocerebellar ataxia type 14) with mostly private conventional mutations and nonspecific phenotype. We here propose a refined approach for clinicogenetic diagnosis by including protein modeling and provide for confirmed SCA‐PRKCG a comprehensive phenotype description from a German multi‐center cohort, including standardized 3D MR imaging.

Methods

This cross‐sectional study prospectively obtained neurological, neuropsychological, and brain imaging data in 33 PRKCG variant carriers. Protein modeling was added as a classification criterion in variants of uncertain significance (VUS).

Results

Our sample included 25 cases confirmed as SCA‐PRKCG (14 variants, thereof seven novel variants) and eight carriers of variants assigned as VUS (four variants) or benign/likely benign (two variants). Phenotype in SCA‐PRKCG included slowly progressive ataxia (onset at 4–50 years), preceded in some by early‐onset nonprogressive symptoms. Ataxia was often combined with action myoclonus, dystonia, or mild cognitive‐affective disturbance. Inspection of brain MRI revealed nonprogressive cerebellar atrophy. As a novel finding, a previously not described T2 hyperintense dentate nucleus was seen in all SCA‐PRKCG cases but in none of the controls.

Interpretation

In this largest cohort to date, SCA‐PRKCG was characterized as a slowly progressive cerebellar syndrome with some clinical and imaging features suggestive of a developmental disorder. The observed non‐ataxia movement disorders and cognitive‐affective disturbance may well be attributed to cerebellar pathology. Protein modeling emerged as a valuable diagnostic tool for variant classification and the newly described T2 hyperintense dentate sign could serve as a supportive diagnostic marker of SCA‐PRKCG.

Review of Hereditary and Acquired Rare Choreas

Background:

Movement disorders are often a prominent part of the phenotype of many neurologic rare diseases. In order to promote awareness and diagnosis of these rare diseases, the International Parkinson’s and Movement Disorders Society Rare Movement Disorders Study Group provides updates on rare movement disorders.

Methods:

In this narrative review, we discuss the differential diagnosis of the rare disorders that can cause chorea.

Results:

Although the most common causes of chorea are hereditary, it is critical to identify acquired or symptomatic choreas since these are potentially treatable conditions. Disorders of metabolism and mitochondrial cytopathies can also be associated with chorea.

Discussion:

The present review discusses clues to the diagnosis of chorea of various etiologies. Authors propose algorithms to help the clinician in the diagnosis of these rare disorders.

Targeted next-generation sequencing identifies novel variants in candidate genes for Parkinson's disease in Black South African and Nigerian patients

BACKGROUND

The prevalence of Parkinson's disease (PD) is increasing in sub-Saharan Africa, but little is known about the genetics of PD in these populations. Due to their unique ancestry and diversity, sub-Saharan African populations have the potential to reveal novel insights into the pathobiology of PD. In this study, we aimed to characterise the genetic variation in known and novel PD genes in a group of Black South African and Nigerian patients.

METHODS

We recruited 33 Black South African and 14 Nigerian PD patients, and screened them for sequence variants in 751 genes using an Ion AmpliSeq™ Neurological Research panel. We used bcftools to filter variants and annovar software for the annotation. Rare variants were prioritised using MetaLR and MetaSVM prediction scores. The effect of a variant on ATP13A2's protein structure was investigated by molecular modelling.

RESULTS

We identified 14,655 rare variants with a minor allele frequency ≤ 0.01, which included 2448 missense variants. Notably, no common pathogenic mutations were identified in these patients. Also, none of the known PD-associated mutations were found highlighting the need for more studies in African populations. Altogether, 54 rare variants in 42 genes were considered deleterious and were prioritized, based on MetaLR and MetaSVM scores, for follow-up studies. Protein modelling showed that the S1004R variant in ATP13A2 possibly alters the conformation of the protein.

CONCLUSIONS

We identified several rare variants predicted to be deleterious in sub-Saharan Africa PD patients; however, further studies are required to determine the biological effects of these variants and their possible role in PD. Studies such as these are important to elucidate the genetic aetiology of this disorder in patients of African ancestry.

Postsynaptic movement disorders: clinical phenotypes, genotypes, and disease mechanisms

Movement disorders comprise a group of heterogeneous diseases with often complex clinical phenotypes. Overlapping symptoms and a lack of diagnostic biomarkers may hamper making a definitive diagnosis. Next-generation sequencing techniques have substantially contributed to unraveling genetic etiologies underlying movement disorders and thereby improved diagnoses. Defects in dopaminergic signaling in postsynaptic striatal medium spiny neurons are emerging as a pathogenic mechanism in a number of newly identified hyperkinetic movement disorders. Several of the causative genes encode components of the cAMP pathway, a critical postsynaptic signaling pathway in medium spiny neurons. Here, we review the clinical presentation, genetic findings, and disease mechanisms that characterize these genetic postsynaptic movement disorders.

Genetics of Movement Disorders and the Practicing Clinician; Who and What to Test for?

PURPOSE OF REVIEW

This review aims to provide the basic knowledge on the genetics of hypokinetic and hyperkinetic movement disorders to guide clinicians in the decision of "who and what to test for?"

RECENT FINDINGS

In recent years, the identification of various genetic causes of hypokinetic and hyperkinetic movement disorders has had a great impact on a better definition of different clinical syndromes. Indeed, the advent of next-generation sequencing (NGS) techniques has provided an impressive step forward in the easy identification of genetic forms. However, this increased availability of genetic testing has challenges, including the ethical issue of genetic testing in unaffected family members, "commercially" available home testing kits and the increasing number and relevance of "variants of unknown significance." The emergent role of genetic factors has important implications on clinical practice and counseling. As a consequence, it is fundamental that practicing neurologists have a proper knowledge of the genetic background of the diseases and perform an accurate selection of who has to be tested and for which gene mutations.

Targeted gene capture sequencing in diagnosis of dystonia patients

BACKGROUND

Dystonia is a movement disorder with high clinical and genetic heterogeneity. Molecular diagnosis is important for an accurate diagnosis of dystonia. Targeted gene capture sequencing has been an effective method for screening multiple candidate genes simultaneously. This method, however, has been rarely reported to be used with dystonia patients.

OBJECTIVES AND METHODS

To assess the effectiveness of the targeted gene capture sequencing in dystonia, we performed custom target gene capture followed by next-generation sequencing in dystonia patients from China. Sanger sequencing was utilized to substantiate the findings. The effects of identified variants were classified according to the American College of Medical Genetics and Genomics (ACMG) standards and guidelines.

RESULTS

A total of 65 patients (34 female and 31 male) were recruited in this study. The mean age at onset was 22.7 ± 13.3 years ranging from 2 to 59 years. According to ACMG standards and guidelines, of 65 patients, 12 were identified with pathogenic variants (12/65, 18.5%) in gene TOR1A, PANK2 or ATP1A3, and another four were identified with likely-pathogenic variants (4/65, 6.2%) in gene PRRT2, GCH1 or THAP1. In total, 24.6% of patients in this cohort were detected to have a genetic cause of dystonia. Another four patients (4/65, 6.2%) were identified with variants which were considered to be VUS (Variants of Uncertain Significance) in gene SGCE, TH, ANO3 and ATP1A3 respectively. The most common detected gene was TOR1A, known to be causative for DYT1 (8/65, 12.3%).

CONCLUSIONS

The study demonstrates that targeted gene capture sequencing is an effective tool for identifying the genetic cause of heterogeneous dystonia patients.

The relevance of gene panels in movement disorders diagnosis: A lab perspective

Next-Generation Sequencing (NGS) is a group of new methods that allow sequencing a variable number of known genes (targeted resequencing) or even the whole human genome (whole genome sequencing-WGS) and have contributed to an exponential genetic knowledge growth, especially in rare diseases, in the past few years. Since 2015, in the Molecular Neurogenetics Unit of Neurological Institute "Carlo Besta", some gene panels have become available to screen all the known genes associated with Movement Disorders (MD) in children and adults as a diagnostic package. Over 221 patients analyzed (part of the Telethon Network of Genetic Biobanks - TNGB), pathogenic variants were found in 25 (11.31%), allowing a definitive genetic diagnosis. Among them, we found mutations in 10/114 patients with dystonia (8.8%); 10/59 patients with Parkinson's disease (16.9%); 1/25 patients with Neurodegeneration with Brain Iron Accumulation (NBIA) (4%) and 4/23 patients with neurotransmitter and biopterin metabolism synthesis defect (17.4%). Our results are in line with those published in literature; targeted resequencing does not replace Sanger sequencing totally, but its usage needs to be discussed with clinicians taking into account both the patient's clinical picture and radiological and neurophysiological data.

Biomarkers for Parkinson's Disease: Recent Advancement

As a multi-factorial degenerative disease, Parkinson's disease (PD) leads to tremor, gait rigidity, and hypokinesia, thus hampering normal living. As this disease is usually detected in the later stages when neurons have degenerated completely, cure is on hold, ultimately leading to death due to the lack of early diagnostic techniques. Thus, biomarkers are required to detect the disease in the early stages when prevention is possible. Various biomarkers providing early diagnosis of the disease include those of imaging, cerebrospinal fluid, oxidative stress, neuroprotection, and inflammation. Also, biomarkers, alone or in combination, are used in the diagnosis and evolution of PD. This review encompasses various biomarkers available for PD and discusses recent advances in their development.

Past, present, and future of Parkinson's disease: A special essay on the 200th Anniversary of the Shaking Palsy

This article reviews and summarizes 200 years of Parkinson's disease. It comprises a relevant history of Dr. James Parkinson's himself and what he described accurately and what he missed from today's perspective. Parkinson's disease today is understood as a multietiological condition with uncertain etiopathogenesis. Many advances have occurred regarding pathophysiology and symptomatic treatments, but critically important issues are still pending resolution. Among the latter, the need to modify disease progression is undoubtedly a priority. In sum, this multiple-author article, prepared to commemorate the bicentenary of the shaking palsy, provides a historical state-of-the-art account of what has been achieved, the current situation, and how to progress toward resolving Parkinson's disease. © 2017 International Parkinson and Movement Disorder Society.

Treatable inherited rare movement disorders

There are many rare movement disorders, and new ones are described every year. Because they are not well recognized, they often go undiagnosed for long periods of time. However, early diagnosis is becoming increasingly important. Rapid advances in our understanding of the biological mechanisms responsible for many rare disorders have enabled the development of specific treatments for some of them. Well-known historical examples include Wilson disease and dopa-responsive dystonia, for which specific and highly effective treatments have life-altering effects. In recent years, similarly specific and effective treatments have been developed for more than 30 rare inherited movement disorders. These treatments include specific medications, dietary changes, avoidance or management of certain triggers, enzyme replacement therapy, and others. This list of treatable rare movement disorders is likely to grow during the next few years because a number of additional promising treatments are actively being developed or evaluated in clinical trials. © 2017 International Parkinson and Movement Disorder Society.

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.

A post hoc study on gene panel analysis for the diagnosis of dystonia

BACKGROUND

Genetic disorders causing dystonia show great heterogeneity. Recent studies have suggested that next-generation sequencing techniques such as gene panel analysis can be effective in diagnosing heterogeneous conditions. The objective of this study was to investigate whether dystonia patients with a suspected genetic cause could benefit from the use of gene panel analysis.

METHODS

In this post hoc study, we describe gene panel analysis results of 61 dystonia patients (mean age, 31 years; 72% young onset) in our tertiary referral center. The panel covered 94 dystonia-associated genes. As comparison with a historic cohort was not possible because of the rapidly growing list of dystonia genes, we compared the diagnostic workup with and without gene panel analysis in the same patients. The workup without gene panel analysis (control group) included theoretical diagnostic strategies formulated by independent experts in the field, based on detailed case descriptions. The primary outcome measure was diagnostic yield; secondary measures were cost and duration of diagnostic workup.

RESULTS

Workup with gene panel analysis led to a confirmed molecular diagnosis in 14.8%, versus 7.4% in the control group (P = 0.096). In the control group, on average 3 genes/case were requested. The mean costs were lower in the gene panel analysis group (€1822/case) than in the controls (€2660/case). The duration of the workup was considerably shorter with gene panel analysis (28 vs 102 days).

CONCLUSIONS

Gene panel analysis facilitates molecular diagnosis in complex cases of dystonia, with a good diagnostic yield (14.8%), a quicker diagnostic workup, and lower costs, representing a major improvement for patients and their families. © 2016 International Parkinson and Movement Disorder Society.

Deep brain stimulation for dystonia: a novel perspective on the value of genetic testing

The dystonias are a group of disorders characterized by excessive muscle contractions leading to abnormal movements and postures. There are many different clinical manifestations and underlying causes. Deep brain stimulation (DBS) provides an effect treatment, but outcomes can vary considerably among the different subtypes of dystonia. Several variables are thought to contribute to this variation including age of onset and duration of dystonia, specific characteristics of the dystonic movements, location of stimulation and stimulator settings, and others. The potential contributions of genetic factors have received little attention. In this review, we summarize evidence that some of the variation in DBS outcomes for dystonia is due to genetic factors. The evidence suggests that more methodical genetic testing may provide useful information in the assessment of potential surgical candidates, and in advancing our understanding of the biological mechanisms that influence DBS outcomes.

Clinical exome sequencing in early-onset generalized dystonia and large-scale resequencing follow-up

BACKGROUND

Dystonia is clinically and genetically heterogeneous. Despite being a first-line testing tool for heterogeneous inherited disorders, whole-exome sequencing has not yet been evaluated in dystonia diagnostics. We set up a pilot study to address the yield of whole-exome sequencing for early-onset generalized dystonia, a disease subtype enriched for monogenic causation.

METHODS

Clinical whole-exome sequencing coupled with bioinformatics analysis and detailed phenotyping of mutation carriers was performed on 16 consecutive cases with genetically undefined early-onset generalized dystonia. Candidate pathogenic variants were validated and tested for cosegregation. The whole-exome approach was complemented by analyzing 2 mutated yet unestablished causative genes in another 590 dystonia cases.

RESULTS

Whole-exome sequencing detected clinically relevant mutations of known dystonia-related genes in 6 generalized dystonia cases (37.5%), among whom 3 had novel variants. Reflecting locus heterogeneity, identified unique variants were distributed over 5 genes (GCH1, THAP1, TOR1A, ANO3, ADCY5), of which only 1 (ANO3) was mutated recurrently. Three genes (GCH1, THAP1, TOR1A) were associated with isolated generalized dystonia, whereas 2 (ANO3, ADCY5) gave rise to combined dystonia-myoclonus phenotypes. Follow-up screening of ANO3 and ADCY5 revealed a set of distinct variants of interest, the pathogenicity of which was supported by bioinformatics testing and cosegregation work.

CONCLUSIONS

Our study identified whole-exome sequencing as an effective strategy for molecular diagnosis of early-onset generalized dystonia and offers insights into the heterogeneous genetic architecture of this condition. Furthermore, it provides confirmatory evidence for a dystonia-relevant role of ANO3 and ADCY5, both of which likely associate with a broader spectrum of dystonic expressions than previously thought. © 2016 International Parkinson and Movement Disorder Society.

Applications of CRISPR/Cas9 for Gene Editing in Hereditary Movement Disorders

Gene therapy is a potential therapeutic strategy for treating hereditary movement disorders, including hereditary ataxia, dystonia, Huntington’s disease, and Parkinson’s disease. Genome editing is a type of genetic engineering in which DNA is inserted, deleted or replaced in the genome using modified nucleases. Recently, clustered regularly interspaced short palindromic repeat/CRISPR associated protein 9 (CRISPR/Cas9) has been used as an essential tool in biotechnology. Cas9 is an RNA-guided DNA endonuclease enzyme that was originally associated with the adaptive immune system of Streptococcus pyogenes and is now being utilized as a genome editing tool to induce double strand breaks in DNA. CRISPR/Cas9 has advantages in terms of clinical applicability over other genome editing technologies such as zinc-finger nucleases and transcription activator-like effector nucleases because of easy in vivo delivery. Here, we review and discuss the applicability of CRISPR/Cas9 to preclinical studies or gene therapy in hereditary movement disorders.