Carriers with excessively low factor VIII procoagulant activity (VIII AHF): A study of two unrelated families with mild hemophilia A

2 unrelated families are described with mild hemophilia A in whom 6 obligate carriers had unusually low VIII AHF levels. In each family, successive generations of males were affected with hemophilia A as determined by low VIII AHF in the presence of normal VIII AGN and VIII VWF levels. In the first family, 2 of 5 obligate carriers had low VIII AHF levels associated with clinical bleeding and 1 other had a history of bleeding. While receiving oral contraceptives, 1 of these 2 carriers was found to have a normal VIII AHF level. In the second family, 4 cousins below age 10 who were obligate carriers had significantly low VIII AHF levels, while a paternal aunt and paternal grandmother who were also obligate carriers had VIII AHF levels within the normal range. Hemorrhagic diathesis in multiple obligate carriers in these families is not readily explained by the Lyon hypothesis, and suggests that these families may be examples of an unusual allelic form of hemophilia A or that they may be transmitting several independent genes affecting VIII AHF levels. Our experience suggests that VIII AHF levels should be determined on all obligate or possible carriers prior to surgery to identify those individuals at risk for postoperative bleeding. Furthermore, it is suggested that hormonal therapy might be effective in the management of carriers with low levels of VIII AHF and clinical bleeding.