A patient with anemia is found to have a low serum level of folate and a high homocysteine level. Which of the following enzymes is most likely deficient in this patient?

A Methionine synthase
B Dihydrofolate reductase
C Methylenetetrahydrofolate reductase ✓
D Cystathionine beta-synthase

Explanation

The patient's low folate level and high homocysteine level suggest a defect in the methylation of homocysteine to methionine, which is catalyzed by methylenetetrahydrofolate reductase.

Source

Wintrobe's Clinical Hematology
Hematology Hematology: Anemia Hematology: Anemia Hard MEDICAL Confidence: high