Hyperhomocysteinemia and venous thromboembolism

Homocysteine (Hcy) is a sulfhydryl amino acid derived from the metabolic conversion of methionine, which is dependent on vitamins (folic acid, B-12 and B-6) as cofactors or cosubstrates. Severe hyperhomocysteinemia (homocystinuria), due to inherited metabolic defects of Hcy metabolism, is associated with very high risk of venous thromboembolism (VTE); treatment with vitamins is associated with dramatic decrease of VTE risk. Several case-control and prospective studies showed that also mild/moderate hyperhomocysteinemia (which is caused by the interaction of environmental factors with mild genetic abnormalities of Hcy metabolism) is associated with heightened risk of VTE; however, it is uncertain whether treatment with vitamins also decreases the VTE risk in these patients.