Dopa-responsive dystonia (DRD) encompasses a clinically and genetically heterogeneous group of disorders that typically manifest as limb-onset dystonia that fluctuates diurnally and improves with levodopa treatment. DRD usually results from genetic defects in enzymes that are involved in the biosynthesis of dopamine. The most common condition is autosomal dominant GTP cyclohydrolase 1 deficiency (Segawa syndrome). An autosomal recessive form of Segawa syndrome is caused by mutation in the tyrosine hydroxylase gene.
