[The factor VIII complex: hemophilia A and von Willebrand disease]

The factor VIII complex is a macromolecule with two distinct components. One is the coagulation factor VIII. The other, known as the Willebrand factor, is a polymer which probably acts as a carrier for serum factor VIII. Hereditary disorders can affect either of these two components. Hemophilia A is a coagulation disorders due to decreased factor VIII coagulant activity. Increase of partial activated thromboplastin time parallels disease severity. Hematomas and hemarthrosis in large joints are the main clinical features. In von Willebrand disease, mucocutaneous bleeding is the main symptom. Diagnosis is established by demonstrating disorders of primary hemostasis: prolonged bleeding time and decreased ristocetin-induced platelet aggregation. Two forms of von Willebrand disease have been described. In the quantitative form, decreased synthesis of von Willebrand factor is often responsible for severe clinical manifestations. The qualitative form probably results from defective polymerization of von Willebrand factor subunits. In both these forms, deficient primary hemostasis is a consequence of decreased platelet adhesion to the vascular wall. Clinical and biological features of hemophilia A and von Willebrand disease, as well as their management, are discussed.