MTHFR and venous thromboembolism: In addition, an association between venous thromboembolism and genetic variation in HO-1 (HMOX1) [183,218], methylenetetrahydrofolate reductase (MTHFR) C677T polymorphism [219], affected homocysteine levels, and plasminogen activator inhibitor-1(PAI-1) 4G/5G mutation [220].