Clinical characteristics of carriers of a GAG deletion in the DYT1 gene amongst Polish patients with primary dystonia

Investigating DYT1 in a Taiwanese dystonia cohort

BACKGROUND/PURPOSE

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

METHODS

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

RESULTS

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

CONCLUSION

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

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.

Epidemiology of DYT1 dystonia: Estimating prevalence via genetic ascertainment

Objective

To estimate the prevalence of TOR1A sequence variants associated with DYT1 dystonia.

Methods

We determined the frequency of the common trinucleotide deletion that causes DYT1 in the Genome Aggregation Database and the Penn Medicine Biobank, totaling exomes from over 135,000 individuals. We also evaluated the prevalence of other possible pathogenic variants in this gene and asked whether the D216H polymorphism is linked to a higher diagnostic rate for dystonia independent of the DYT1-causing mutation.

Results

The estimated range of prevalence of the most common pathogenic variant that causes DYT1 is ∼17.6–26.1 carriers per 100,000 individuals. Based on the different data sets used, we predict that there are between 54,366 and 80,891 mutation carriers in the United States, which, due to the reduced penetrance of this variant, would translate into 16,475–24,513 DYT1 patients.

Conclusions

Our data provide a prevalence estimate of the most common DYT1 mutation in the general population. This information is specifically important for those with interest in the development of precision therapeutics for dystonia.

Atypical phenotypes of DYT1 dystonia in three children

DYT-1 dystonia is the most common primary dystonia seen in childhood. It is an autosomal dominantly inherited disorder caused by deletion of a GAG triplet in exon 5 of the DYT1 gene. It characteristically starts in a distal limb during late childhood, subsequently spreads to involve other body regions sparing oromandibular muscles. However, clinical presentation can vary remarkably with respect to age, site of onset and progression. In this study we present three early-onset DYT-1 dystonia patients who are atypical according to age of onset and localization. Dystonia has started at 2, 3 and 7years of age and generalized to involve other limbs in all patients and also oromandibular muscles in one patient. None of them have benefited from medical treatments including L-dopa. All had normal brain MRI scan, a history of normal birth without significant perinatal asphyxia, infection or trauma and all are neurodevelopmentally otherwise normal.

CONCLUSION

In children with dystonia; if brain imaging is unremarkable and when there is no history of CNS disorders such as perinatal asphyxia, infections, drug exposure or trauma; genetic analysis for GAG deletion of DYT-1 gene may be performed even if dystonia starts at a very young age or it spreads to involve oromandibular muscles.

Clinical features, DYT1 mutation screening and genotype-phenotype correlation in patients with dystonia from Iran

OBJECTIVE

To test Iranian patients with primary torsion dystonia to determine the frequency of 904-906 del GAG mutation in the DYT1 (TOR1A) gene and to investigate the genotype-phenotype association for this disease.

SUBJECTS AND METHODS

Sixty-three patients with primary dystonia were investigated. DNA was extracted from peripheral blood and these samples were subjected to PCR-sequencing for exon 5 of the DYT1 gene.

RESULTS

Of the 63 patients, 10 (15.9%) carried the triplet GAG deletion mutation; this is a high DYT1-positive rate in comparison with other populations and the type of dystonia in this positive group was generalized in all except 1. In our patients, limbs were the most severely involved site at the time of onset and in most cases it developed to generalized form. The majority of DYT1-positive cases showed higher leg onset (5 patients, 62.5%) in comparison with higher arm onset in negative patients (20 patients, 50%). Also, the progression to generalized dystonia in DYT1-positive patients was significantly higher than in DYT1-negative patients. The mean age at onset was 8.6 ± 1.6 years (7-12 years) in DYT1-positive patients, while mean age at onset in patients with no GAG deletion mutation was higher (15.7 ± 11.5 years).

CONCLUSIONS

The DYT1 904-906 del GAG mutation is responsible for some of Iranian dystonia patients, and screening for the DYT1 deletion is significant in cases with the generalized type of primary dystonia. Also, patients with leg or arm onset at a younger age are more likely to be DYT1-positive among primary torsion dystonia cases.

TorsinA and DYT1 early-onset dystonia

Early-onset torsion dystonia is a severe generalized form of primary dystonia, with most cases caused by a specific mutation (ΔGAG) in the DYT1 gene encoding torsinA. This mutation is autosomal dominant and is thought to result in reduced torsinA activity. TorsinA is an AAA protein located in the lumen of the endoplasmic reticulum and nuclear envelope of most cells (with high levels in some brain neurons). It is thought to serve as a chaperone protein and/or a link between these membranes and the cytoskeleton. Other sequence variations in DYT1 can affect penetrance of the ΔGAG mutation and may be associated with more common, late-onset focal forms of dystonia. Animal models of DYT1 dystonia are emerging that will allow preclinical evaluation of drugs that can be used to prevent or treat this non-neurodegenerative neurologic disease.