Segawa disease DYT 5

AD guanosine triphosphate cyclohydrolase I (GTP-1_ deficiency. Thsi is a hereditary doap response generalized dystonia, typically with onset in childhood, that responds to low dose levodopa. It is due to partial deficiency of tetrahydrobiopterin.

Clinical pearls include the presentation with equinovarus by age 6, and four extremity dystonia by teens, difficulty with hand pronation/supination, marked diurnal fluctuation, and rarer findings such as writer's cramp or guitarist's cramp. Adult onset may have bradykinesia,, tremor mimicking PD, or focal hand dystonia.