This is a real-world medical entrance exam question, please give the true answer based on the question and selection. Topic name: FMGE 2018, Subject name: Pediatrics
Mental retardation is seen in? 
Select and explain. 
A. Phenylketonuria, B. Alkaptonuria, C. Albinism, D. Von Gierke disease
A: Phenylketonuria
Answer: A: Phenylketonuria 
Explanation: Mental retardation is feature of PKU due to elevated level of phenylalanine hydroxylase in brain.