The p.A900V SNP is a common SNP found in approximately 8% of the normal population and in several TTP patients,5, 6including cases of pregnancy-onset TTP.9, 11, 26A neutral effect of this SNP was predicted, as this valine is present in C57BL/6J mice.27Indeed, our present findings as well as the study of Edwards et al28show that the p.A900V SNP does not affect ADAMTS13 secretion or ADAMTS13 activity. The gene discussed is ADAMTS13; the disease is thrombotic thrombocytopenic purpura.