Our first study related to the investigation of the primary causes of thrombophilia in Mexican Mestizos was carried out on 102 persons with clinical features of inherited thrombophilia, who were tested for the activated protein C resistance (APCr) genotype and phenotype as well as levels of coagulation proteins C and S, antithrombin, plasminogen, tissue type plasminogen activator activity, plasminogen activator inhibitor activity, plasminogen activator inhibitor type I, anti-phospholipid antibodies and lupus anticoagulants. The gene discussed is SERPINE1; the disease is Rare hereditary thrombophilia.