Thrombotic thrombocytopenic purpura (TTP) is a life-threatening thrombotic microangiopathy caused by severely reduced activity of the von-Willebrand factor-cleaving protease ADAMTS13 (a disintegrin and metalloprotease with thrombospondin motifs 13), mainly caused by anti-ADAMTS-13 antibodies (acquired TTP). The gene discussed is ADAMTS13; the disease is thrombotic thrombocytopenic purpura.