Workup for thrombotic thrombocytopenic purpura (TTP), HUS, heparin-induced thrombocytopenia was grossly negative on this admission, including ADAMTS13 activity (43%), C3 level (154 mg/dL), C4 level (41 mg/dL), negative heparin platelet antibody and a peripheral blood smear negative for schistocytes. This evidence concerns the gene C4A and thrombotic thrombocytopenic purpura.