A patient with a history of recurrent arterial thrombosis is found to have elevated levels of homocysteine. What is the most likely underlying cause?

Elevated levels of homocysteine are associated with an increased risk of arterial thrombosis. The most common cause of hyperhomocysteinemia is a deficiency of methylene tetrahydrofolate reductase (MTHFR), an enzyme involved in the metabolism of homocysteine.