PROS1 and antiphospholipid syndrome: This could be further distinguished into genetic thrombophilia (e.g., deficiency of antithrombin III, protein C, and protein S, factor V Leiden positivity, or mutations in the methylenetetrahydrofolate reductase (MTHFR) gene) and acquired thrombophilia (e.g., antiphospholipid syndrome, hyperhomocysteinemia, or elevation of lupus anticoagulant).