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: Biochemistry
Homocystinuria is due to abnormal metabolism of 
Select and explain. 
A. Methionine, B. Valine, C. Tryptophan, D. Leucine
A: Methionine
Answer: A: Methionine 
Explanation: Homocystinuria is a group of disorder of methionine metabolism.