This is a real-world medical entrance exam question, please give the true answer based on the question and selection. Topic name: None, Subject name: Biochemistry
Phenylalanemia I is due to deficiency of ? 
Select and explain. 
A. Phenylalanine hydroxylase, B. Homogentisate oxidase, C. Tyrosinase, D. None
A: Phenylalanine hydroxylase
Answer: A: Phenylalanine hydroxylase 
Explanation: Phenylalanine hydroxylase i) Classical phenylketonuria (hyperphenylalanemia type I) Deficiency of phenylalanine hydroxylase.ii) Atypical phenylketonuria (hyperphenylalanemia type II and III) * Defect in dihydrobiopterin reductase.iii) Hyperphenylalanemia type IV and V * Defect in dihydrobiopterin synthesis.