Frequency of the DYT1 mutation in primary torsion dystonia without family history.

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Abstract
TORSION DYSTONIA is a syndrome in which sustained muscle contraction causes twisting, repetitive movements, or abnormal postures. In idiopathic torsion dystonia there is no known causative environmental factor and the syndrome is not associated with another disease.1 Idiopathic torsion dystonia is clinically very heterogeneous. Age at onset is variable (from childhood to late adult life); distribution may be focal, segmental, or generalized; disease progression slow or rapid; and family history may or may not be present. Idiopathic torsion dystonia is also genetically heterogeneous, with 7 loci mapped and 2 genes identified.2 A GAG deletion at position 946 in the DYT1 gene resulting in the loss of a glutamic acid residue in the torsin A protein is the cause of most cases of early-onset generalized dystonia with family histories, especially among Ashkenazi Jews.3 However, since the disease is associated with reduced penetrance, DYT1 deletion carriers are also found in isolated cases with no family history.3-5 In addition, some patients without the typical phenotype of early-onset limb dystonia that spreads to other limbs are found to carry the DYT1 deletion as well.3-6 To evaluate the role of the DYT1 locus in isolated cases with idiopathic torsion dystonia, we screened 100 patients with various forms of primary dystonia without family histories for the GAG deletion in the DYT1 gene.