Ultra-large VWF multimers (UL-VWF) are stored in endothelial Weibel-Palade bodies or in alpha granules of platelets7 and can only be detected in the plasma after endothelial cell activation, i.e. in endotoxemia, thrombosis or thrombotic thrombocytopenic purpura (TTP)8. The gene discussed is VWF; the disease is thrombotic thrombocytopenic purpura.