This is a real-world medical entrance exam question, please give the true answer based on the question and selection. Topic name: Metabolism of protein and amino acid, Subject name: Biochemistry
In Phenylketonuria the main aim of first-line therapy is 
Select and explain. 
A. Replacement of the defective enzymes, B. Replacement of the deficient product, C. Limiting the substrate for deficient enzyme, D. Giving the missing amino acid by diet
C: Limiting the substrate for deficient enzyme
Answer: C: Limiting the substrate for deficient enzyme 
Explanation: In PKU Phenylalanine hydroxylase enzyme is deficient.So alternative pathways are opened. Leading to the formation of Phenylketone,Phenyllactate and Phenylacetate. This can be prevented by limiting the substrate for deficient enzyme.Ref: DM Vasudevan - Textbook of Biochemistry, 7th edition, page no: 236