Thrombotic thrombocytopenic purpura (TTP) is caused by a hereditary (cTTP) or immune-mediated (iTTP) deficiency of the enzyme ADAMTS13 (a disintegrin and metalloproteinase with a thrombospondin type 1 motif, member 13) [3,4] and is one of the best characterized TMAs [5,6,7,8]. The gene discussed is ADAMTS13; the disease is thrombotic thrombocytopenic purpura.