ADAMTS13 and congenital thrombotic thrombocytopenic purpura: An imbalance between VWF and ADAMTS13 is pathognomonic for thrombotic thrombocytopenic purpura, a thrombotic microangiopathy, in which uncleaved VWF, due to severe deficiency in the function of ADAMTS13, causes microthrombosis, thrombocytopenia, and microangiopathic hemolytic anemia, eventually leading to organ ischemia.