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
Enzyme deficient in maple syrup urine disease? 
Select and explain. 
A. a-ketoacid decarboxylase, B. Transaminase, C. Isomerase, D. Mutase
A: a-ketoacid decarboxylase
Answer: A: a-ketoacid decarboxylase 
Explanation: Maple syrup urine disease is due to deficiency of a-ketoacid dehydrogenase (also called a-ketoacid decarboxylase). In maple syrup urine disease there is excretion of branched chain amino acids (isoleucine, leucine, valine) and their keto acids (a-keto b-methylvalerate, a-ketoisocaproate, a-ketoisovalerate) in urine.