The product of this enzyme, tetrahydrobiopterin (BH-4), is an essential cofactor for phenylalanine, tyrosine, and tryptophan hydroxylases.
Involvement in disease
Defects in QDPR are the cause of BH4-deficient hyperphenylalaninemia type C (HPABH4C) [MIM:261630]; also called dihydropteridine reductase deficiency (DHPR deficiency) or hyperphenylalaninemia tetrahydrobiopterin-deficient due to DHPR deficiency or quinoid dihydropteridine reductase deficiency (QDPR deficiency). HPABH4C is a rare autosomal recessive disorder characterized by hyperphenylalaninemia and severe neurologic symptoms (malignant hyperphenylalaninemia) including axial hypotonia and truncal hypertonia, abnormal thermogenesis, and microcephaly. These signs are attributable to depletion of the neurotransmitters dopamine and serotonin, whose syntheses are controlled by tryptophan and tyrosine hydroxylases that use BH-4 as cofactor. These patients do not respond to phenylalanine-restricted diet. HPABH4C is lethal if untreated.
Belongs to the short-chain dehydrogenases/reductases (SDR) family.