The principal subtypes of TMA are thrombotic thrombocytopenic purpura (TTP) mainly due to anti-ADAMTS13 autoantibodies and the hemolytic uremic syndrome (HUS) associated with shigatoxin-related endothelial toxicity (shiga-toxin related HUS) or with complement alternative pathway dysregulation (atypical HUS or aHUS). The gene discussed is ADAMTS13; the disease is thrombotic thrombocytopenic purpura.