No evidence of allelic heterogeneity in the DYT1 gene of European patients with early onset torsion dystonia

Genetic and clinical features of primary torsion dystonia

Primary torsion dystonia (PTD) is defined as a syndrome in which dystonia is the only clinical sign (except for tremor), and there is no evidence of neuronal degeneration or an acquired cause by history or routine laboratory assessment. Seven different loci have been recognized for PTD but only two of the genes have been identified. In this review we will describe the phenotypes associated with these loci and discuss the responsible gene. This article is part of a Special Issue entitled "Advances in dystonia".

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

Torsion dystonia is an autosomal dominant movement disorder characterized by involuntary, repetitive muscle contractions and twisted postures. The most severe early onset form of dystonia has been linked to mutations in the human DYT1 (TOR1A) gene encoding a protein termed torsinA. Moreover, dystonia and Parkinson disease share the common feature of reduced dopamine neurotransmission in the striatum, so we assumed that mutations in the DYT1 gene might have the same role in cases of early onset primary torsion dystonia (EOPTD) and early onset Parkinson disease (EOPD) that present dystonia. In this present study, 17 patients with EOPTD, 221 patients with EOPD and 164 control subjects were screened for mutations of the DYT1 gene by denaturing high performance liquid chromatography (DHPLC), polymerase chain reaction-restriction fragment length polymorphism (PCR-RFLP) analysis and DNA sequencing. Our results showed that the GAG deletion was identified in 7 EOPTD patients, which results in Glu302del of DYT1 gene. No mutations were found in EOPD patients and control subjects. By carefully reviewing the available literature on studies of sporadic, non-Ashkenazi Jewish populations, the results showed that the prevalence rate of DYT1 mutation was not significantly different (p=0.267) between European (27.3%) and Asian (22.2%) patients with early onset primary torsion dystonia.

First determination of the incidence of the uniqueTOR1A gene mutation, c.907delGAG, in a Mediterranean population

The c.907delGAG mutation in the TOR1A gene (also named DYT1) is the most common cause of early-onset primary dystonia. The mutation frequency and prevalence have so far been only estimated from rare clinical epidemiological reports in some populations. The purpose of this study was to investigate the incidence at birth of the c.907delGAG mutation in a French-representative mixed population of newborn from South-Eastern France. We applied an automated high-throughput genotyping method to dried blood spot samples from 12,000 newborns registered in Hérault between 2004 and 2005. Only one allele was found to carry the mutation, which allows to determine its incidence at birth as 1/12,000 per year in this area.

Genetics of dystonia

Primary torsion dystonia (PTD) has a broad clinical spectrum, with earlier onset of symptoms associated with more generalized muscle involvement. The causes for most dystonia are unknown although several monogenic subtypes have been identified. One important genetic cause of PTD is DYT1; a three base pair deletion in this gene is a major cause for early-onset dystonia. Its identification has allowed the development of cellular and animal models; it has also permitted studies that identify both "manifesting" and "non-manifesting" DYT1 mutation carriers. These studies have expanded our understanding of clinical expression to include psychiatric symptoms and also have enabled imaging studies of endophenotypes. These advances provide a widened platform for future research.

Atypical phenotypes and clinical variability in a large Italian family with DYT1-primary torsion dystonia

The GAG deletion in the DYT1 gene usually causes a typical form of primary torsion dystonia (PTD) with early onset in a limb, rapid generalization, and sparing of cranial-cervical muscles, but atypical phenotypes have often been reported. Here, we describe a large DYT1 Italian family with phenotypically heterogeneous PTD that recapitulates all the atypical features associated with the DYT1 mutation, including late age at onset, focal or segmental phenotypes, onset or spreading of dystonia to the cranial-cervical muscles. Of 38 healthy family members, 15 also carried the DYT1 mutation, with an estimated penetrance of 21%. A literature review of atypical familial cases of DYT1-PTD showed that late onset, cervical involvement, and limited progression of dystonia are features frequently seen in DYT1 families. However, nearly all of these atypical patients fall within at least one of the clinical categories that best predict the DYT1 carrier status, namely, early onset, onset in a limb, and family history positive for early-onset dystonia.

[Movement disorders in childhood: classification and genetic update]

Abnormal movements are not unusual in childhood. Recent genetic progresses provide a new approach of childhood movement disorders. Several loci have been identified in paroxysmal dyskinesia, or in Gilles de la Tourette syndrome. A gene has been cloned in Hallervorden-Spatz syndrome, and a gene has recently been implicated in benign hereditary chorea. Considerable advances concern the genetic of dystonic syndromes: several chromosomal localizations have been identified, and several genes have been cloned. Genetic advances allow nosographic reclassification of some entities and offer new molecular tools for a more appropriate diagnosis. The increasing wealth of genetic knowledge will provide further insight in the understanding of abnormal movement disorders in childhood.

Dystonia: clinical features, genetics, and treatment

PURPOSE OF REVIEW

The present review covers recent advances in dystonia research related to dystonia genetics and treatment. These have led to the discovery of novel dystonia genes and loci, to changing classification schemes, and to the introduction of improved and new treatment options.

RECENT FINDINGS

Currently 13 different forms of dystonia can be distinguished on a genetic basis (dystonia types 1-13). Recently, a novel gene locus (DYT13) was detected in a family with segmental dystonia, and the gene causing myoclonus-dystonia was identified (SGCE). Furthermore, a novel mutation in the DYT1 gene is associated with a myoclonus-dystonia phenotype. Regarding dystonia treatment, patients refractory to botulinum toxin type A can now be treated with botulinum toxin type B. Selective peripheral denervation remains an effective form of treatment for patients with secondary, but probably not with primary botulinum toxin treatment failure. Finally, a renaissance of functional surgical ablative procedures has taken place, with high frequency deep brain stimulation being introduced in dystonia treatment. Bilateral pallidotomy or pallidal stimulation may provide major benefit especially in patients with generalized, disabling dystonia with the most dramatic improvements in dystonia type 1 patients. Neurostimulation may also be effective in primary segmental axial dystonia, myoclonus-dystonia, and tardive dystonia.

SUMMARY

The recent mapping of additional dystonia gene loci, the identification of novel dystonia genes, and the characterization of proteins encoded by these genes have enhanced our understanding of various forms and aspects of the dystonias and have opened up new avenues for research. Treatment options include both medical and surgical therapies, with deep brain simulation being the most recent development.