Inheritable molecular variants of moderate and mild hemophilia A.

Factor VIII clotting activity (VIII:C) and factor VIII clotting antigen (VIII:CAg) were investigated in 54 patients with hemophilia A of moderate or mild severity. The patients belonged to 28 kindreds. The study showed a genetically determined molecular variation within hemophilia A of both moderate and mild forms. Each form can be classified into 3 types according to the content of demonstrable VIII:CAg. Type I has no demonstrable VIII:CAg, type IIa has VIII:CAg in an amount smaller than, or approximately equal to, that of VIII:C and type IIb has a larger amount of VIII:CAg than VIII:C. Affected members of one and the same kindred always have the same type of the disease.