Background and purpose: DYT1 dystonia is the most common form of inherited primary dystonia. The aim of the study was: 1) to evaluate the prevalence of the DYT1 mutation in a population of Polish patients with early-onset generalized dystonia and with other forms of familial dystonia, 2) to evaluate the frequency of the DYT1 mutation in patients with writer's cramp, 3) to characterize the phenotype of the DYT1 mutation in the Polish population, and 4) to define the group of patients in whom genetic testing is recommended.
Material and methods: The following groups of patients were included in the study: 1) patients with early-onset (<30 years) generalized dystonia and those patients with onset after age 30 years who have relatives with early-onset dystonia, 2) patients with writer's cramp (focal or as part of segmental dystonia) independently of age of onset, 3) asymptomatic (adult only) relatives of the diagnosed DYT1 carriers. Genetic tests were performed in 63 subjects---28 sporadic cases of dystonia, 20 patients with familial dystonia, and 15 asymptomatic relatives of patients with confirmed DYT1 mutation.
Results: The DYT1 mutation was found in 17 subjects--10 patients with dystonia and 7 asymptomatic relatives (from 6 families). In all mutation carriers dystonia occurred in one limb before age 26 years. In 8 patients, generalization of dystonia was observed and in 2 cases it remained in a focal form.
Conclusions: 1. The prevalence of DYT1 mutation among patients with early-onset (<or= 24 years) dystonia was 20.8% and it was similar to that found in other European populations. 2. No DYT1 mutation was found among sporadic cases of writer's cramp. 3. In the studied group the most common was the phenotype with early onset (<or= 24 years) and the first symptoms localized in one of the limbs. 4. The obtained results confirm that the recommendations available in the literature concerning DYT1 genetic testing can be applied to the Polish population.