Dopa-responsive dystonia, a rare disorder typically presenting in early childhood with lower limb dystonia and gait abnormality, responds well to levodopa.
A classic phenotype of young-onset lower-limb dystonia, diurnal fluctuations and excellent response to levodopa has been well recognised in association with GCH1 mutations, and rare atypical presentations have been reported.
Mutations in the GCH1 gene, encoding GTP cyclohydrolase 1, the enzyme critically important for dopamine production in nigrostriatal neurons, are the most common cause of dopa-responsive dystonia (DRD), characterized predominantly by limb dystonia, although parkinsonian features may also be present.