Spontaneous mutation in the male gamete as a cause of hemophilia A: clarification of a case using DNA probes.

The carrier status of two sisters of the mother of a hemophilic boy was clarified by the use of DNA probes in a family with a single case of hemophilia A and no family history of the disease. The extragenic polymorphic site demonstrated by probe DX13 (locus DXS15) and the intragenic polymorphic site demonstrated by BgI I digestion and a factor VIII partial cDNA probe indicated that the mother of the index case carried a mutation in the X-chromosome received from her nonhemophilic father rather than the X-chromosome received from her mother. In spite of equivocal coagulation data, the mother's two sisters were shown not to be carriers of hemophilia A.