Thrombotic thrombocytopenic purpura (TTP) is a thrombotic microangiopathy caused by a severe functional deficiency in a disintegrin and metalloprotease with thrombospondin type I repeats-13 (ADAMTS13), the specific von Willebrand factor (VWF)-cleaving protease [1]. The gene discussed is ADAMTS13; the disease is thrombotic microangiopathy.