A patient with a history of recurrent arterial thrombosis is found to have elevated levels of homocysteine in their blood. Which of the following enzymes is most likely deficient in this patient?

Elevated levels of homocysteine in the blood can increase the risk of arterial thrombosis. Methylenetetrahydrofolate reductase (MTHFR) is an enzyme involved in the metabolism of homocysteine, and deficiency of this enzyme can lead to hyperhomocysteinemia.