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: Unknown
Phenylketonuria is due to deficiency of: 
Select and explain. 
A. Phenylalanine, B. Phenylalanine hydroxylase (PAH), C. Galactokinase, D. Tyrosinase
B: Phenylalanine hydroxylase (PAH)
Answer: B: Phenylalanine hydroxylase (PAH) 
Explanation: Ref. Textbook of Biochemistry for Medical Students. Page.300
 
Phenylketonuria 

Defect in Phenyl alanine Hydroxylase
A variant, nonclassic PKU, is a result of a defective enzyme in tetrahydrobiopterin synthesis.
Mental retardation
Musty odor 
Microcephaly
Diet low in phe nyl-alanine
Avoid aspartame 
Diet important during pregnancy to prevent complication in the kid