Summary
Thirty patients with various forms of von Willebrand’s disease were investigated for VIIIR: Ag in their platelets. VIIIR: Ag was extracted from washed platelets and measured both with electroimmunoassay and a sensitive immunoradiometric assay. Six patients had severe von Willebrand’s disease, type I, with very low or no VIIIR: Ag in their plasma. None of these patients had any VIIIR: Ag detectable in their platelets. All 19 patients with mild von Willebrand’s disease had VIIIR: Ag in their platelets but the values often fell below those of normal controls. Five patients with genetic variants of von Willebrand’s disease also had values in their platelets corresponding to those in plasma.
Von Willebrand’s disease is a bleeding disorder caused by an inherited defect in so-called factor VIII related antigen (VIIIR: Ag), which is a protein normally occurring in plasma (Zimmerman et al. 1971), endothelial cells (Bloom et al. 1973), platelets (Howard et al. 1974) and megakaryocytes (Piovella et al. 1974). The defect leads to a prolonged bleeding time and as a rule a secondary decrease in factor VIII clotting activity (VIII: C) in plasma. Von Willebrand’s disease is a heterogeneous condition (Holmberg and Nilsson 1972). It varies widely in severity, and a genetic variation causing a qualitative abnormality of VIIIR :Ag is also known (Peake et al. 1974). The disease is, as a rule, transmitted as an autosomal and dominant trait, but some severely affected individuals have been suspected to be homozygous for an autosomal and more or less recessive gene (Italian Working Group 1977, Shoa’i et al. 1977).
The clinical severity of the disease varies with the amount of functional VIIIR :Ag (VIIIR: RCF) in plasma (Holmberg and Nilsson 1972, Meyer et al. 1974). Patients with severe von Willebrand’s disease have very little or no VIIIR: Ag in their plasma. They also lack the protein in their endothelial cells (Holmberg et al. 1974 b). There is evidence that also their platelets are devoid of VIIIR :Ag. In the present investigation we studied the platelet content of VIIIR: Ag in a series of patients with various types of von Willebrand’s disease. Both electroimmunoassay (EIA) and a more sensitive immunoradiometric assay (IRMA) for VIIIR: Ag were used.
