Segawa syndrome is a rare genetic disorder characterized by an uncoordinated or clumsy manner of walking (abnormal gait) and dystonia. Dystonia is a general term for a group of muscle disorders generally characterized by involuntary muscle contractions that force the body into abnormal, sometimes painful, movements and positions (postures). Dystonia in Segawa syndrome usually affects the legs, but some children may first develop dystonia in the arms. In some cases, usually in adolescents and adults, the symptoms of Segawa syndrome may become noticeably worse or more pronounced in the afternoon and evening than in the morning (marked diurnal fluctuation). The symptoms of Segawa syndrome usually become apparent by around six years of age. Intelligence is not affected. Children with Segawa syndrome usually show a dramatic and sustained improvement when treated with levodopa. Levodopa is an amino acid that is converted to dopamine, a brain chemical that serves as a neurotransmitter. Dopamine is deficient in children with Segawa syndrome. The disorder is caused by mutations of the GCH-1 gene. The GCH-1 gene mutation is inherited as an autosomal dominant trait.