Utility of Clinical Exome Sequencing in Dystonia: A Single-Center Study From India

Genetic Landscape of Dystonia in Asian Indians

BACKGROUND

Genomic variations associated with dystonia in Asian Indians remain largely unknown.

OBJECTIVES

To identify genomic alterations associated with dystonia in the Asian Indian population using next generation sequencing approaches.

METHODS

From September 2018 to December 2023, we enrolled 745 individuals including probands with dystonia and family members, in the Indian Movement Disorder Registry and Biobank. Clinical and demographic data were captured on a REDCap platform. We performed whole exome sequencing (WES) on DNA specimens obtained from 267 individuals with isolated, combined or complex dystonia. Variants were classified according to joint guidelines of American College of Medical Genetics and Genomics (ACMG) and Association of Molecular Pathology (AMP).

RESULTS

The mean age of the WES cohort was 33.8 ± 16.2 years, and mean age at onset (AAO) of dystonia was 25.6 ± 17.7 years. 62.2% had isolated dystonia, 7.9% combined and 29.2% had complex phenotypes. WES identified pathogenic/ likely pathogenic variants in 54 patients (20.2%) including 14 novel variants in known dystonia genes. Variants in THAP1 were most common followed by PANK2, GLB1, PLA2G6, TOR1A, ANO3, VPS16, SGCE, SPG7, FTL and other genes. Multifocal/generalized distribution of dystonia [OR: 4.1; 95% CI 1.4-12.2, P = 0.011] and family history [OR: 4.3; 95% CI 2.1-8.9, P < 0.001] were associated with positive yield on WES.

CONCLUSION

THAP1 was the most frequent dystonia associated gene in this cohort. Singleton WES identifiedpotentially pathogenic variants in approximately one out of five patients tested, and contributed to management decisions in 4%.

Spectrum of Inherited Childhood-Onset Dystonia: Case Series of 19 Families With Genotype and Phenotype Characterization Highlighting the Treatable Causes

Childhood-onset dystonia, a clinically and genetically diverse group of disorders, can be challenging to diagnose. Information on the genotype and phenotype spectrum in the Indian population is limited. This study reports the clinical and molecular findings of monogenic childhood-onset dystonia in 22 individuals from 19 Indian families. Complex dystonia was the most frequent type, followed by combined and isolated forms. A total of 23 variants across 17 genes were identified, including nine novel ones. These disorders include four autosomal dominant, one X-linked recessive, one mitochondrial, and the remaining 11 autosomal recessive conditions. Five potentially treatable disorders were identified, and treatment was initiated in three families, showing satisfactory responses, particularly in dopa-responsive dystonias. Our study contributes four additional genes-CYP27A1, NDUFAF3, FUCA1, and FIG4-to the list of genes associated with complex dystonia. Exome sequencing proved crucial in diagnosing the etiology of dystonia, identifying treatable forms, and aiding genetic counseling. This study emphasizes the significance of using NGS for early genetic diagnosis to enable timely targeted therapies, offer precise genetic counseling to families, and prevent recurrence in the family.

Long-Read Sequencing: The Third Generation of Diagnostic Testing for Dystonia

Long-read sequencing methodologies provide powerful capacity to identify all types of genomic variations in a single test. Long-read platforms such as Oxford Nanopore and PacBio have the potential to revolutionize molecular diagnostics by reaching unparalleled accuracies in genetic discovery and long-range phasing. In the field of dystonia, promising results have come from recent pilot studies showing improved detection of disease-causing structural variants and repeat expansions. Increases in throughput and ongoing reductions in cost will facilitate the incorporation of long-read approaches into mainstream diagnostic practice. Although these developments are likely to transform clinical care, there is currently a discrepancy between the potential benefits of long-read sequencing and the application of this technique to dystonia. In this review we highlight current opportunities and limitations of adopting long-read sequencing methods for the investigation of patients with dystonia. We provide examples of long-read sequencing integration into diagnostic evaluation and the study of pathomechanisms in individuals with dystonic disorders. The goal of this article is to stimulate research into the application and optimization of long-read analysis strategies in dystonia, thus enabling more precise understanding of the underlying etiology in the future. © 2025 The Author(s). Movement Disorders published by Wiley Periodicals LLC on behalf of International Parkinson and Movement Disorder Society.

Dissecting genetic architecture of rare dystonia: genetic, molecular and clinical insights

BACKGROUND

Dystonia is one of the most common movement disorders. To date, the genetic causes of dystonia in populations of European descent have been extensively studied. However, other populations, particularly those from the Middle East, have not been adequately studied. The purpose of this study is to discover the genetic basis of dystonia in a clinically and genetically well-characterised dystonia cohort from Turkey, which harbours poorly studied populations.

METHODS

Exome sequencing analysis was performed in 42 Turkish dystonia families. Using co-expression network (CEN) analysis, identified candidate genes were interrogated for the networks including known dystonia-associated genes and genes further associated with the protein-protein interaction, animal model-based characteristics and clinical findings.

RESULTS

We identified potentially disease-causing variants in the established dystonia genes (PRKRA, SGCE, KMT2B, SLC2A1, GCH1, THAP1, HPCA, TSPOAP1, AOPEP; n=11 families (26%)), in the uncommon forms of dystonia-associated genes (PCCB, CACNA1A, ALDH5A1, PRKN; n=4 families (10%)) and in the candidate genes prioritised based on the pathogenicity of the variants and CEN-based analyses (n=11 families (21%)). The diagnostic yield was found to be 36%. Several pathways and gene ontologies implicated in immune system, transcription, metabolic pathways, endosomal-lysosomal and neurodevelopmental mechanisms were over-represented in our CEN analysis.

CONCLUSIONS

Here, using a structured approach, we have characterised a clinically and genetically well-defined dystonia cohort from Turkey, where dystonia has not been widely studied, and provided an uncovered genetic basis, which will facilitate diagnostic dystonia research.

Whole exome sequencing and clinical investigation of young onset dystonia: What can we learn?

BACKGROUND

Dystonia is a heterogeneous movement disorder involving various genetic backgrounds, and the implication of whole exome sequencing (WES) has yet to be clearly elucidated. In this study, we performed WES in Korean patients with young-onset dystonia.

METHODS

We recruited patients with young-onset dystonia based on the new MDS dystonia classification at Samsung Medical Centre from 2015 to 2019. We excluded subjects diagnosed by single gene tests (GCH1, TOR1A, PANK2, PRRT2, and SGCE) or levodopa trials and subjects with focal or possible secondary dystonia. We performed WES in all enrolled subjects and confirmed the results with Sanger sequencing.

RESULTS

Of the 43 patients, we detected 11 disease-causing variants, classified as either pathogenic or likely pathogenic, in 9 patients (20.9%). Generalized dystonia, infancy-childhood-onset dystonia, and other combined neurologic manifestations were related with PV/LPV. When we retrospectively reviewed the patients with PV/LPV, brain imaging was diagnostic in 3 subjects (HTRA1, SCL20A, and WDR45), clinical characteristics of paroxysmal presentation were observed in 2 (ADCY5 and ATP1A3), and microcephaly was noted in 1 patient (KMT2B).

CONCLUSION

Clinical exome sequencing is helpful for the diagnosis of dystonia, especially for that with infancy-childhood onset, and generalized dystonia with other neurologic manifestations. Additionally, careful evaluations and examinations could provide information for selecting candidates for genetic testing.