More than half the sporadic cases of hemophilia A in Sweden are due to a recent mutation.

The aim of this study was to ascertain how many of the sporadic cases of severe Haemophilia A in Sweden are due to recent mutation, and establish its origin. DNA analysis was performed in 18 randomly selected families with a sporadic case of severe haemophilia A. Restriction fragment length polymorphism (RFLP) patterns were investigated, two intragenic (Bc1 I, Xba I/Kpn I) and two extragenic (DX 13, St 14) RFLP being used. In 10/18 families a haemophilia-linked gene was found to have derived from the healthy maternal grandfather; on the basis of clotting and immunological assay results, the odds were high (greater than 104:1) for maternal carriership in four of these 10 cases, and for maternal non-carriership in two, four being indeterminate. In 4/18 families a haemophilia-linked gene derived from the healthy maternal grandmother; according to clotting and immunological assay results, in two cases the odds were high for maternal non-carriership. In the remaining 4/18 families no conclusions could be drawn from the RFLP pattern as to the origin of mutation. We conclude that at least 55% of the sporadic cases of severe hemophilia A in Sweden are due to a recent mutation within the last two generations.