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The recent advent of techniques to purify the factor VIII/von Willebrand factor (f.VIII/vWf) protein from plasma to quantitate the f.VIII/vWf protein and to measure the vWf (plasma ristocetin cofactor) have greatly added to our understanding of von Willebrand’s disease (vWd). The initial studies of antigen, procoagulant and vWf levels revealed a parallel reduction in all three activities in vWd suggesting a quantitative deficiency of the f. VIII/vWf protein and its biologic activities.  Recent studies, however, have suggested three major forms of vWd. The first group of patients have a quantitative defect with a parallel reduction of the f.VIII/vWf protein and of the antigen, vWf and procoagulant activities. The second group of patients appear to have a qualitative defect of the f.VIII/vWf protein. These individuals have normal levels of the antigen and procoagulant activity; however, the vWf activity is reduced or absent. The third group of patients have a combination of a qualitative and quantitative deficiency. These variants resemble both previous groups in that there are reduced levels of the antigen, procoagulant and vWf activities but usually greater reduction of the vWf activity.  Three major defects of the f.VIII/vWf protein have been recognized in vWd: 1) decreased plasma concentration of the f. VIII/vWf protein, 2) the apparent molecular weight of the protein is reduced and/or the largest molecular weight polymers are absent, and 3) there is a partial or total carbohydrate deficiency. For the f.VIII/vWf protein to express vWf activity, it must be of a minimal molecular size and have a specific carbohydrate content and/or sequence.

Heterogeneity of the Factor VIII/Von Willebrand Factor Protein in Von Willebrand’s Disease