Thrombophilia was present in 16 (17.8%) of the elastic stockings group (11 patients had factor V Leiden mutation, 1 had prothrombin G20210A mutation, 2 had deficiency of protein S, 1 had deficiency of protein C, and 1 had lupus-like anticoagulants), and in 17 (18.9%) of the control group (3 patients had factor V Leiden mutation, 5 had prothrombin G20210A mutation, 2 had deficiency of protein S, 1 had deficiency of protein C, and 6 had lupus-like anticoagulants). This evidence concerns the gene PROS1 and systemic lupus erythematosus.