GTP cyclohydrolase deficiency; intrafamilial variation in clinical phenotype, including levodopa responsiveness

A family with a dominant form of partial GTP cyclohydrolase deficiency is d escribed. Clinical severity varied from mild involvement with complete resp onsiveness to levodopa to severe dystonia precluding any voluntary activity including talking, progressive contractures, and only partial responsivene ss to levodopa. Although there are several possible reasons for intrafamili al variability, any patient with dystonia, the cause of which is not clearl y identified, should receive a trial of levodopa.