The phenotype of AR-DRD with the Leu205Pro mutation in the TH gene, which produces a severe decrease in TH activity to 1.5% of that of the wild type, was severe, not dystonia/Segawa's syndrome, but early-onset parkinsonism.
These results indicate that tyrosine hydroxylase in the nigrostriatal dopamine neurons may be most sensitive to tetrahydrobiopterin deficiency causing dystonia.