This is a real-world medical entrance exam question, please give the true answer based on the question and selection. Topic name: Inborn Errors of Metabolism, Subject name: Pediatrics
Hyperphenylalaninemia is due to defect in the enzyme: 
Select and explain. 
A. Phenylalanine hydroxylase:, B. Tyrosinase, C. Homogentisic acid oxidase, D. Ornithine transcarbamylase
A: Phenylalanine hydroxylase:
Answer: A: Phenylalanine hydroxylase: 
Explanation: a. Phenylalanine hydroxylase(Ref: Nelson's 20/e p 636-636)Deficiency of the enzyme phenylalanine hydroxylase or of its cofactor tetrahydrobiopterin (BH4) causes accumulation of phenylalanine in body fluids and in the brain.