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. This evidence concerns the gene ADAMTS13 and thrombotic thrombocytopenic purpura.