Identification of a highly polymorphic microsatellite VNTR within the argininosuccinate synthetase locus: Exclusion of the dystonia gene on 9q32-34 as the cause of dopa-responsive dystonia in a large kindred

Dopa-responsive dystonia is a clinical variant of idiopathic torsion dystonia that is distinguished from other forms of dystonia by the frequent cooccurrence of parkinsonism, diurnal fluctuation of symptoms, and its dramatic therapeutic response to L-dopa.Linkage of a gene causing classic dystonia in a large non-Jewish kindred (DYT1) and in a group of Ashkenazi Jewish families, to the gelsolin (GSN) and argininosuccinate synthetase (ASS) loci on chromosome 9q32-34, respectively, was recently determined.Here we report the discovery of a highly informative (GT)n repeat VNTR polymorphism within the ASS locus.Analysis of a large kindred with dopa-responsive dystonia, using this new polymorphism and conventional RFLPs for the 9q32-34 region, excludes loci in this region as a cause of this form of dystonia.This provides proof of genetic heterogeneity between classic idiopathic torsion dystonia and dopa-responsive dystonia.