Segawa disease with a novel heterozygous mutation in exon 5 of the GCH-1 gene (E183K).

We report a novel missense mutation in the GCH-1 gene resulting in Segawa disease. The patient, a 6-year-old girl, presented with dystonia. Her CSF biopterin and neopterin levels were reduced, suggesting Segawa disease. L-dopa administration led to clinical improvement. Genetic analysis revealed a missense mutation in exon 5 of the GCH-1 gene (E183K). Although dystonia or other movement disorders were not identified in her family, this may be explained by the low penetrance of Segawa disease.