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
[{'content': 'Phenylketonuria is due to deficiency of: \nSelect and explain. \nA. Phenylalanine, B. Phenylalanine hydroxylase (PAH), C. Galactokinase, D. Tyrosinase', 'role': 'user'}, {'content': 'Answer: B \nExplanation: Ref. Textbook of Biochemistry for Medical Students. Page.300\n\xa0\nPhenylketonuria\u2028\n\nDefect in Phenyl alanine Hydroxylase\nA variant, nonclassic PKU, is a result of a defective enzyme in tetrahydrobiopterin synthesis.\nMental retardation\nMusty odor\u2028\nMicrocephaly\nDiet low in phe\u2028nyl-alanine\nAvoid aspartame\u2028\nDiet important during pregnancy to prevent complication in the kid', 'role': 'assistant'}]