The importance of such studies can be inferred from the fact that VWF unable to form high molecular weight (MW) multimers is one cause of von Willebrand disease (VWD), the most common inherited bleeding disorder (Sadler et al., 2000), yet elevated levels of highly-multimerized (HM) VWF in the blood can lead to vascular occlusions, as in thrombotic thrombocytopenic purpura (TTP) (Levy et al., 2001). This evidence concerns the gene VWF and thrombotic thrombocytopenic purpura.