ADAMTS13 and thrombotic thrombocytopenic purpura: On the one hand, IgG4 autoantibody-dominant TTP serum samples were recently reported to have a stronger inhibitory effect on ADAMTS13 activity than IgG1 autoantibody-dominant TTP serum samples (Sinkovits et al., 2018), despite that this difference does not seem to correlate with disease course in the same study (Sinkovits et al., 2018).