This is a real-world medical entrance exam question, please give the true answer based on the question and selection. Topic name: Metabolism of protein and amino acid, Subject name: Biochemistry
PKU is a congenital amino acid metabolic disorder. In the following rare variants of PKU, dihydrobiopterin synthesis is affected. The enzyme deficient is 
Select and explain. 
A. Histidine decarboxylase, B. Phenylalanine hydroxylase, C. Dihydropterin reductase, D. Tyrosine deficiency
C: Dihydropterin reductase
Answer: C: Dihydropterin reductase 
Explanation: In Type 2 and 3 of PKU, there is deficiency of enzyme dihydrobiopterin reductase. Hence there is deficiency of dihydrobiopterin.Ref: DM Vasudevan - Textbook of Biochemistry, 7th edition, page no: 236