Thrombotic thrombocytopenic purpura (TTP) is caused by a reduced activity of the matrix metalloproteinase ADAMTS-13 (a disintegrin and metalloproteinase with a thrombospondin type 1 motif, member 13) due to congenital deficiency or acquired, inhibiting antibodies. The gene discussed is ADAMTS13; the disease is thrombotic thrombocytopenic purpura.