Factor VIII: new clinical and genetic aspects.

Factor VIII is a complex molecule comprising a series of homologous oligomers with biological activity related to primary haemostasis (factor VIII related antigen/Willebrand factor; FVIIIRAg/WF). The structure or distribution of these oligomers is abnormal in von Willebrand's disease (vWd). The oligomers are associated with, or contain, a lower molecular weight entity with procoagulant activity (factor VIIIC) which has distinct antigenic determinants and is reduced or abnormal in haemophilia. Recessive and dominant forms of vWd have been recognised but two families are described each with features of both dominant and recessive inheritance; this is of importance in genetic counselling. Results of a new immunoradiometric assay for factor VIIIC antigen showed reduced levels in vWd and haemophilia and it was absent in 3 of 6 samples from fetuses of obligate carriers of haemophilia. The potential use of this assay for the prenatal diagnosis of haemophilia is described.