Catalyzes the conversion of quinonoid dihydrobiopterin into tetrahydrobiopterin

Hyperphenylalaninemia, BH4-deficient, C

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. Patients do not respond to phenylalanine-restricted diet. HPABH4C is lethal if untreated.

Positively regulates nitric oxide synthesis in umbilical vein endothelial cells (HUVECs). May be involved in dopamine synthesis. May modify pain sensitivity and persistence. Isoform GCH-1 is the functional enzyme, the potential function of the enzymatically inactive isoforms remains unknown

CytoplasmNucleus

Hyperphenylalaninemia, BH4-deficient, B

A disease characterized by malignant hyperphenylalaninemia due to tetrahydrobiopterin deficiency, and defective neurotransmission due to depletion of the neurotransmitters dopamine and serotonin. The principal symptoms include: psychomotor retardation, tonicity disorders, convulsions, drowsiness, irritability, abnormal movements, hyperthermia, hypersalivation, and difficulty swallowing. Some patients may present a phenotype of intermediate severity between severe hyperphenylalaninemia and mild dystonia. In this intermediate phenotype, there is marked motor delay, but no intellectual disability and only minimal, if any, hyperphenylalaninemia.

Involved in the biosynthesis of tetrahydrobiopterin, an essential cofactor of aromatic amino acid hydroxylases. Catalyzes the transformation of 7,8-dihydroneopterin triphosphate into 6-pyruvoyl tetrahydropterin

Hyperphenylalaninemia, BH4-deficient, A

An autosomal recessive disorder characterized by hyperphenylalaninemia, depletion of the neurotransmitters dopamine and serotonin, and progressive cognitive and motor deficits. Neurological symptoms are unresponsive to the classic phenylalanine-low diet.

Involved in tetrahydrobiopterin biosynthesis (By similarity). Seems to both prevent the formation of 7-pterins and accelerate the formation of quinonoid-BH2. Coactivator for HNF1A-dependent transcription (By similarity). Regulates the dimerization of homeodomain protein HNF1A and enhances its transcriptional activity (By similarity). Also acts as a coactivator for HNF1B-dependent transcription (PubMed:24204001)

CytoplasmNucleus

Hyperphenylalaninemia, BH4-deficient, D

An autosomal recessive disease characterized by primapterinuria, a variant form of hyperphenylalaninemia defined by increased excretion of 7-substituted pterins in the urine. Patients with primapterinuria show an increased ratio of neopterin to biopterin in the urine, excretion of subnormal levels of biopterins, and normal levels of biogenic amines in cerebrospinal fluid. Neurologic signs are mild, present in the neonatal period only, and include hypotonia, delayed motor development and tremor.