Segawa’s disease (dopa-responsive dystonia, DRD) is an autosomal dominant hereditary syndrome, which was first described by Masaya Segawa and colleagues in 1970. It is caused by a mutation of the GCH 1 gene on 14q22.1-q22.2, which causes a biochemical defect in the synthesis of tetrahydrobiopterin. Due to the absence of co-factors for phenylalanine hydroxylase (PAH), the production of tyrosine is disrupted. Tyrosine is a substrate for the biological synthesis of dopamine, among others. In case of Segawa’s disease, the resultant lack of dopamine in particular affects the basal ganglia. The reported prevalence of Segawa’s disease is approximately 0.5/106, but it is likely to be underdiagnosed. Typical symptoms are progressive dystonia with diurnal fluctuation, frequently of the lower extremities (with a unilateral or bilatreral inner rotation of a single or both feet), and primarily rapid exhaustion. In most cases, the condition responds well to low doses of L-dopa (20-300 mg) with frequently complete remission of symptoms. Even after long-term treatment, no side effects (ON-OFF phenomena, freezing) have been observed in most patients.