GTP cyclohydrolase I mutations in patients with dystonia responsive to anticholinergic drugs.

OBJECTIVES To investigate the hypothesis that GTP cyclohydrolase I (GCH1) mutations are responsible for the phenotype of highly anticholinergic responsive dystonia in patients with apparent primary torsion dystonia. METHODS From 107 British patients with clinically diagnosed primary torsion dystonia, seven patients were identified with an excellent response to anticholinergic drugs. All six exons of the GCH1 gene were sequenced in these patients to identify mutations. RESULTS Three novel GCH1 mutations were identified in two patients. One patient was a compound heterozygote with asymptomatic carrier parents. The clinical phenotype of patients with and without GCH1 mutations was similar. CONCLUSIONS These findings show that a proportion of patients with apparent primary torsion dystonia and a good response to anticholinergic drugs have GCH1 mutations and therefore have a variant of dopa responsive dystonia. The difficulty in distinguishing clinically between patients with and without mutations underscores the importance of considering the diagnosis of a levodopa responsive dystonia in all such patients.