Question

The serum level of which of the following metabolites can effectively distinguish "Vitamin B12 deficiency" from "Folate deficiency" ?

• A. Homocysteine
• B. Methyl Malonyl CoA
• C. Methionine
• D. Thymine

Hint:

Elevated homocysteine with elevated methylmalonic acid = Vitamin B12 deficiency.
Elevated homocysteine with normal methylmalonic acid = Folate deficiency.

Answer 1

The Correct Option is B

Step 1: Understanding the Concept:
Vitamin B12 (cobalamin) and folate (Vitamin B9) deficiencies both result in megaloblastic anemia due to their close interaction in 1-carbon metabolism. However, they can be distinguished by analyzing specific metabolic pathway intermediates.

Step 2: Detailed Explanation:
- Both folate and Vitamin B12 are required for the conversion of homocysteine (A) to methionine (C) by the enzyme methionine synthase.
Therefore, a deficiency in either vitamin causes an accumulation of homocysteine in the serum.
- However, Vitamin B12 is also uniquely required as a coenzyme (adenosylcobalamin) for the enzyme methylmalonyl-CoA mutase.
This enzyme catalyzes the conversion of methylmalonyl-CoA to succinyl-CoA.
In Vitamin B12 deficiency, this pathway is blocked, leading to an accumulation of methylmalonyl-CoA and its free acid form, methylmalonic acid (MMA), in the blood and urine.
Because folate does not participate in this pathway, methylmalonyl-CoA levels remain normal in folate deficiency.

Step 3: Final Answer:
Thus, Methyl Malonyl CoA is the metabolic marker that distinguishes Vitamin B12 deficiency from folate deficiency.