ADAMTS13 and congenital thrombotic thrombocytopenic purpura: Thrombotic thrombocytopenic purpura (TTP) is a rare and life-threatening thrombotic microangiopathy characterized by a severe deficiency of A Disintegrin And Metalloprotease with ThromboSpondin type-1 repeats, member 13 (ADAMTS13), a specific von Willebrand factor-cleaving protease, resulting in disseminated microvascular platelet-rich thrombi that cause microangiopathic hemolytic anemia, severe thrombocytopenia, and organ ischemia.