On the other hand, patients with high levels of IgG1 and low levels of IgG4 anti-ADAMTS13 autoantibodies were reported to have high mortality rate (Ferrari et al., 2009); and IgG1 and IgG3, not IgG4 anti-ADAMTS13 autoantibody titers, were among the most strongly associated factors with clinical severity of acute TTP (Bettoni et al., 2012). Here, ADAMTS13 is linked to thrombotic thrombocytopenic purpura.