Exclusion of the DYT1 locus in a non-Jewish family with early-onset dystonia.

The DYT1 gene on chromosome 9q34 underlies idiopathic torsion dystonia (ITD) in Jewish and non-Jewish families with childhood and adolescent-onset dystonia that usually starts in a limb, spreads to other limbs, and uncommonly involves cranial muscles. We examined 39 members of a Mennonite family of German ancestry in which seven were affected with ITD. Age at onset was 14.7 years (range 5-34 years) and symptoms began in a limb in four. The remaining three had onset in the neck, face, and larynx. Dystonia progressed to involve at least one arm and one leg in all seven and there was cranial involvement in six. Five of these six had moderate or severe speech impairment. Linkage analysis with 9q34 markers excluded the region containing the DYT1 locus in this family. This study suggests that a gene other than DYT1 underlies some cases of early limb-onset ITD. The clinical features of prominent cranial involvement and impaired speech distinguish this "non-DYT1" early-onset ITD family from the typical DYT1 phenotype.