DYT1 mutations in early onset primary torsion dystonia and Parkinson disease patients in Chinese populations

Integrated Genome and Transcriptome Sequencing to Solve a Neuromuscular Puzzle: Miyoshi Muscular Dystrophy and Early Onset Primary Dystonia in Siblings of the Same Family

BACKGROUND

Neuromuscular disorders (NMD), many of which are hereditary, affect muscular function. Due to advances in high-throughput sequencing technologies, the diagnosis of hereditary NMDs has dramatically improved in recent years.

METHODS AND RESULTS

In this study, we report an family with two siblings exhibiting two different NMD, Miyoshi muscular dystrophy (MMD) and early onset primary dystonia (EOPD). Whole exome sequencing (WES) identified a novel monoallelic frameshift deletion mutation (dysferlin: c.4404delC/p.I1469Sfs∗17) in the Dysferlin gene in the index patient who suffered from MMD. This deletion was inherited from his unaffected father and was carried by his younger sister with EOPD. However, immunostaining staining revealed an absence of dysferlin expression in the proband's muscle tissue and thus suggested the presence of the second underlying mutant allele in dysferlin. Using integrated RNA sequencing (RNA-seq) and whole genome sequencing (WGS) of muscle tissue, a novel deep intronic mutation in dysferlin (dysferlin: c.5341-415A > G) was discovered in the index patient. This mutation caused aberrant mRNA splicing and inclusion of an additional pseudoexon (PE) which we termed PE48.1. This PE was inherited from his unaffected mother. PE48.1 inclusion altered the Dysferlin sequence, causing premature termination of translation.

CONCLUSION

Using integrated genome and transcriptome sequencing, we discovered hereditary MMD and EOPD affecting two siblings of same family. Our results added further weight to the combined use of RNA-seq and WGS as an important method for detection of deep intronic gene mutations, and suggest that integrated sequencing assays are an effective strategy for the diagnosis of hereditary NMDs.

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.

Dystonia and Parkinson's disease: What is the relationship?

Dystonia and Parkinson's disease are closely linked disorders sharing many pathophysiological overlaps. Dystonia can be seen in 30% or more of the patients suffering with PD and sometimes can precede the overt parkinsonism. The response of early dystonia to the introduction of dopamine replacement therapy (levodopa, dopamine agonists) is variable; dystonia commonly occurs in PD patients following levodopa initiation. Similarly, parkinsonism is commonly seen in patients with mutations in various DYT genes including those involved in the dopamine synthesis pathway. Pharmacological blockade of dopamine receptors can cause both tardive dystonia and parkinsonism and these movement disorders syndromes can occur in many other neurodegenerative, genetic, toxic and metabolic diseases. Pallidotomy in the past and currently deep brain stimulation largely involving the GPi are effective treatment options for both dystonia and parkinsonism. However, the physiological mechanisms underlying the response of these two different movement disorder syndromes are poorly understood. Interestingly, DBS for PD can cause dystonia such as blepharospasm and bilateral pallidal DBS for dystonia can result in features of parkinsonism. Advances in our understanding of these responses may provide better explanations for the relationship between dystonia and Parkinson's disease.

Membrane defects and genetic redundancy: Are we at a turning point for DYT1 dystonia?

Heterozygosity for a 3-base pair deletion (ΔGAG) in TOR1A/torsinA is one of the most common causes of hereditary dystonia. In this review, we highlight current understanding of how this mutation causes disease from research spanning structural biochemistry, cell science, neurobiology, and several model organisms. We now know that homozygosity for ΔGAG has the same effects as Tor1a^KO , implicating a partial loss of function mechanism in the ΔGAG/+ disease state. In addition, torsinA loss specifically affects neurons in mice, even though the gene is broadly expressed, apparently because of differential expression of homologous torsinB. Furthermore, certain neuronal subtypes are more severely affected by torsinA loss. Interestingly, these include striatal cholinergic interneurons that display abnormal responses to dopamine in several Tor1a animal models. There is also progress on understanding torsinA molecular cell biology. The structural basis of how ΔGAG inhibits torsinA ATPase activity is defined, although mutant torsinA^ΔGAG protein also displays some characteristics suggesting it contributes to dystonia by a gain-of-function mechanism. Furthermore, a consistent relationship is emerging between torsin dysfunction and membrane biology, including an evolutionarily conserved regulation of lipid metabolism. Considered together, these findings provide major advances toward understanding the molecular, cellular, and neurobiological pathologies of DYT1/TOR1A dystonia that can hopefully be exploited for new approaches to treat this disease. © 2016 International Parkinson and Movement Disorder Society.

Clinical feature and DYT1 mutation screening in primary dystonia patients from South-West China

BACKGROUND

Clinical presentation and DYT1 status amongst Chinese patients with primary dystonia have not been well studied.

METHODS

One hundred and twenty patients with primary dystonia from South-West China were studied in a prospective survey for 3.5 years. Severity and the resulting disability were assessed using the Burke-Fahn-Marsden dystonia rating scale (BFMDRS). Health related quality of life (HRQL) was measured through the 36-item short-form (SF-36). The Hospital Anxiety and Depression Scale (HADS) was utilized to identify and quantify depression and anxiety. Mutations in the DYT1 exon 5 were screened by direct sequencing.

RESULTS

Cervical dystonia was found to be the most frequent form of focal dystonia and was discovered to occur at an early age. Pain and tremor were the common associated symptoms. Family history was positive in 19.5% of the cases, with a trend of earlier onset. Depression (14.5%) and anxiety (6.6%) were the main HRQL impairments. Multiple linear regression analysis suggested that gender, depression, anxiety and functional disability were amongst the principal determinants of lower HRQL. Only one instance of DYT1 GAG deletion (1.4%) was detected in 71 patients.

CONCLUSION

Our data on a cohort of Chinese patients show some difference from descriptions in other ethnic groups. This includes an earlier age of onset, a lower incidence of depression and female serving as a predictor factor of a HRQL. Similar to other cohorts, DYT1 gene mutations are rare.