Inherited thrombophilia is found in patients with splanchnic vein thrombosis, although diagnosis of inherited deficiencies of antithrombin, protein C, and protein S is difficult in the presence of liver impairment, which causes a reduced synthesis of the natural anticoagulant proteins.13,23,29,30 This difficulty is not present with the factor V Leiden and prothrombin G20210A mutations. The gene discussed is PROS1; the disease is thrombophilia.