ADAMTS13 and thrombotic thrombocytopenic purpura: Thrombotic thrombocytopenic purpura (TTP) is a thrombotic microangiopathy (TMA) caused by severely reduced ADAMTS13 or the von Willebrand factor-cleaving protease (VWFCP) enzyme resulting in low platelet and red blood cell counts along with severe renal, cardiac, and neurological dysfunction.