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: Unknown
Expected change in Vitamin B12 deficiency - 
Select and explain. 
A. Increased homocysteine in urine, B. The increased methylmalonic acid in urine, C. FIGLU in urine, D. Phenylalanine in urine
B: The increased methylmalonic acid in urine
Answer: B: The increased methylmalonic acid in urine 
Explanation: Ans. is 'b' i.e., Increased methylmalonic acid in urine Isomerization of methylmalonyl CoA to succinyl CoAo In this reaction, the active form of vitamin B12 is deoxyadenosyl cobalamine.o Propionyl-CoA is produced as the catabolic end product of some aliphatic amino acids and b-oxidation of odd chain fatty acids.o Propionyl CoA is then converted to succinyl CoA through methyl malonyl-CoA.o Thus methylmalonyl-CoA is accumulated and excreted in urine as methylmalonic acid (methylmalonate) in vitamin B12 deficiency, i.e. methylmalonic aciduria.