ADAMTS13 and thrombotic thrombocytopenic purpura: Thrombotic thrombocytopenic purpura (TTP) is a rare hematological disorder caused by a deficiency in the enzymatic function of a member of the disintegrin and metalloprotease with thrombospondin-type motifs family, an enzyme called ADAMTS13, which is synthesized primarily in the liver and, in limited quantities, by vascular endothelial cells, megakaryocytes, platelets, glomerular podocytes and glial cells.