1. dHPR-deficient form; an inherited disorder in which there is an absence or deficiency of dihydropteridine reductase (DHPR); this results in impaired regeneration of tetrahydrobiopterin, causing an elevation in phenylalanine levels;
2. gTP-CH form; an inherited disorder in which there is a deficiency of guanosine triphosphate cyclohydrolase, an enzyme used in the biosynthesis of tetrahydrobiopterin;
3. 6-PTS form; an inherited disorder in which there is a deficiency of 6-pyruvoyltetrahydropterin synthase, an enzyme that participates in the biosynthesis of tetrahydrobiopterin.
Synonym(s): nonclassical phenylketonuria