This is a real-world medical entrance exam question, please give the true answer based on the question and selection. Topic name: Proteins and Amino Acids, Subject name: Biochemistry
Which enzyme defect causes phenylketonuria? 
Select and explain. 
A. Phenylalanine oxidase, B. Phenylalanine hydroxylase, C. Tyrosinase, D. Tyrosine transaminase
B: Phenylalanine hydroxylase
Answer: B: Phenylalanine hydroxylase 
Explanation: Ans. is 'b' i.e., Phenylalanine hydroxylaseMetabolic diseaseEnzyme deficientMaple syrup urine diseaseBranched chain ketoacid dehydrogenaseMethyl-melonic aciduriaMethyl-malonyl CoA mutase (isomerase)Sweaty feet odor in bodyIsovaleryl-CoA dehydrogenaseTyrosinemia I (Tyrosinosis)Fumarylacetoacetate hydroxylaseTyrosinemia IITyrosine transaminase (Tyrosine aminotransferase)Neonatal tyrosinemiaHydroxyphenyl pyruvate hydroxylaseAlbinismTyrosinaseAlkaptonuriaHomogentisate oxidasePhenylketonuriaPhenylalanine hydroxylaseOrotic aciduriaOMP decarboxylaseHomocystinuriaCystathionine synthataseLesh-Nyhan syndromeComplete deficiency of enzyme HGPRTCystinosisCystine reductase