Genetic thrombophilias, including mutations in factor V Leiden, prothrombin G20210A, methylenetetrahydrofolate reductase (MTHFR), and plasminogen activator inhibitor-1 (PAI-1), constitute important yet under-recognized causes of arterial and venous thrombosis [8-10]. The gene discussed is MTHFR; the disease is Venous thrombosis.