[A new hereditary cause of portal vein thrombosis: the abnormal resistance to activated protein C by the Arg 506-->Gln mutation of the gene of factor V].
We report 2 cases of portal vein thrombosis associated with a single point mutation in the factor V gene that replaces arginine in residue 506 with glutamine. This mutation induces abnormal resistance to anticoagulant activity of activated protein C and increases the risk of deep vein thrombosis. Both patients had a personal and familial history of deep vein thrombosis. Intraabdominal neoplasia or infection, myeloproliferative disorder, antiphospholipid syndrome, paroxysmal nocturnal hemoglobinuria and coagulation inhibitor deficiency (antithrombin, proteins C and S) were excluded by exhaustive investigation. However, an abnormal resistance to activated protein C was found, and DNA analysis showed the factor V Arg506 to Gln mutation in both cases. Anticoagulant treatment was begun. A study of family history made in one case, showed the same genetic disease in one of the relatives. Resistance to activated protein C with factor V gene mutation should be investigated in patients with portal vein thrombosis. A study of family history, and anticoagulant treatment are justified for symptomatic patients.