PROTEOLYTIC PROCESSING OF VON-WILLEBRAND-FACTOR SUBUNIT - HETEROGENEITY IN TYPE-IIA VON-WILLEBRAND DISEASE

Type IIA von Willebrand disease (vWD) is a heterogeneous disorder for which two different pathogenetic mechanisms have been proposed: increa sed proteolytic susceptibility of von Willebrand factor (vWF), and/or interference of its post-translational processing. Subunit analysis of vWF in type-IIA vWD has revealed an increased relative proportion of the 176- and 140-kDa subunit-derived fragments, suggesting an augmente d fragmentation of vWF, even in the resting state. We analyzed the sub unit pattern of vWF in plasma from five previously described patients with type-IIA vWD. All of them showed the above-mentioned pattern. In addition, the presence of a new band with an apparent molecular mass o f 200 kDa, not described in normal individuals or in patients with vWD , was repeatedly observed in one of these patients. This patient also exhibited an abnormal vWF multimeric structure in platelets and in pla sma, before and after desmopressin administration, when the blood was collected either in the presence or in the absence of proteinase inhib itors. We believe that an abnormal primary structure of vWF could be r esponsible for this abnormal proteolytic fragmentation pattern, as wel l as for the abnormal multimerization of vWF. Moreover, an abnormal su sceptibility to proteolysis appears to be present, as suggested by the increase in the relative proportion of the 176-kDa fragment observed in the same patient. Future sequencing studies and genetic analysis ma y clarify whether there are one or two different defects related to th e vWF of that patient. Our results indicate that the subunit analysis of vWF may reveal additional defects present in type-IIA vWD that may help our understanding of the pathogenesis of such disease.