Question

A patient with vitamin B12 deficiency presents with anemia, positive Romberg sign, and elevated homocysteine. Which amino acid is most likely deficient?

• A. Cysteine
• B. Methionine
• C. Tyrosine
• D. Glutamate

Hint:

Vitamin B12 deficiency causes increased homocysteine because homocysteine cannot be converted efficiently to methionine.

Answer 1

The Correct Option is B

Concept: Vitamin B12 is required for conversion of homocysteine to methionine. Deficiency causes elevated homocysteine and reduced methionine formation.

Step 1: Recall B12-dependent reaction.
Vitamin B12 acts as a cofactor for methionine synthase: \[ \text{Homocysteine} \rightarrow \text{Methionine} \]

Step 2: Effect of B12 deficiency.
When B12 is deficient: \[ \text{Homocysteine increases} \] and methionine synthesis decreases.

Step 3: Select the deficient amino acid.
Therefore, the amino acid most likely deficient is: \[ \text{Methionine} \]