Fig. (1).

he biosynthetic pathway of dopamine. Tetrahydrobiopeterin (BH4) is generated from Guanosine triphosphate (GTP) by consecutive catalytic steps involving the enzymes GTP cyclohydrolase (GCH1), 6-pyrovoyl-tetrahydropetrin synthase (PTPS) and sepiapterin reductase (SR). A pool of BH4 is maintained by the action of Dihydropterine reductase (DHPR) and carbinaloamine-4a-dehydratase (PCD). Tyrosine Hydroxylase (TH) is dependent on BH4 to catalyze the first step in the biosynthesis of dopamine and Aromatic L-amino acid decarboxylase (AADC) generates Dopamine from its precursor L-dopa. Mutations in any of the underlined enzymes have been linked to DRD.