The Use of Factor VII/VWF Complex Activity Tests and SDS-Agarose Electrophoresis in the Analysis of Von Willebrand Disease
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Maintenance of a proper blood volume in a mammal is dependent on the formation of clots at sites where a blood vessel has been injured. Coagulation requires a series of clotting factors present in plasma as well as adhesion of platelets to the subendothelial wall of the damaged vessel. Defects in either of these components can result in bleeding disorders. The adhesion of platelets to subendothelial tissue depends on a plasma glycoprotein called von Willebrand Factor, which occurs as a series of multimers with molecular weights of 1-20 x 10 6. Genetically transmitted quantitative and qualitative deficiencies in von Willebrand Factor are collectively referred to as von Willebrand Disease. Type I, the most common form of vWD, is characterized by variably decreased levels of apparently normal vWF. Type II, or variant vWD, appears to be more of a qualitative defect and is characterized by an absence of the larger molecular-weight forms or multimers of vWF (Ruggeri, 1987). Type III is the most rarely seen type. It is considered the "severe"form of vWD and is a recessive autosomal trait. To diagnose among the different forms of the disease, a technique based on discontinuous sodium dodecyl sulfate (SDS) agarose gel electrophoresis was developed. Different numbers of von Willebrand Factor multimers could be detected by directly staining gels with immunoglobulins, an avidin-biotin peroxidase complex, and the noncarcinogenic substrate 4-chloro-1-naphthol. Thirteen patients were screened for vWD. Of these one had Type I, two had normal clotting activity and the remainder were diagnosed as Type II. This study of normal blood and that of patients with vWD indicated that discontinuous sodium dodecyl sulfate (SDS) agarose gel electrophoresis, in combination with routine coagulation tests, allows precise detection and diagnosis of vWD.