TH and dopa-responsive dystonia: GTP cyclohydrolase is involved in the production of an essential cofactor for biosynthesis of monoamine neurotransmitters, and additionally mutations in other enzymes leading to deficiency in the dopamine synthesis were reported to cause dopa-responsive dystonia, including tyrosine hydroxylase (TH), sepiapterin reductase (SPR), and 6-pyruvoyl tetrahydrobiopterin (PTP) synthase (41).