A high clinical suspicion should prompt a discussion about further investigations to exclude underlying hypercoagulable conditions including the presence of protein C, protein S, antithrombin III deficiency, factor V Leiden mutation, prothrombin gene mutation, antiphospholipid antibody syndrome, and hyper-homocysteinemia, all of which could contribute to the formation of clots and recurrence of DVT. This evidence concerns the gene PROS1 and deep vein thrombosis.