Background: Idiopathic torsion dystonia is a clinically and genetically heterogeneous movement disorder. A GAG deletion at position 946 of the DYT1 gene was the first mutation found, in early-onset dystonia, with an autosomal dominant transmission and reduced penetrance.
Objective: To evaluate the frequency of the DYT1 mutation in patients with idiopathic torsion dystonia but without a family history.
Design: Prospective cohort study.
Setting: Four botulinum toxin clinics in the Paris, France, area.
Patients: A French population of 100 patients with dystonia.
Main outcome: Frequency of the DYT1 mutation tested by polymerase chain reaction and enzyme restriction analysis for the 946 GAG deletion, and genotype-to-phenotype correlation.
Results: Only 5 mutation carriers were identified, 4 of whom were part of a group of 10 patients with generalized dystonia. Onset was between ages 5 and 12 years as in typical early-onset dystonia. All 4 patients had cranial muscle involvement, which is atypical for DYT1 mutation carriers. One had segmental dystonia. Molecular analysis of relatives in 2 families demonstrated that the lack of family history was due to reduced penetrance.
Conclusions: For accurate diagnosis and genetic counseling, screening for the DYT1 deletion is of great interest in cases with generalized dystonia without a family history. In other cases, positive results are rare.