Factor VIII gene mutations and RFLP analysis in hemophilia A

Hemophilia A is an X-linked bleeding disorder caused by a quantitative or qualitative defect of coagulation factor VIII. Since factor VIII has been cloned and several intragenic and linked DNA polymorphisms discovered, DNA analysis is an accepted and commonly used method for carrier testing in hemophilia A. Both a direct method using detection of mutation and an indirect method based on linkage between the disease and DNA polymorphism are used for this purpose. In this study, DNA samples of 110 hemophilia A patients from 99 families were screened for factor VIII gene mutation using Southern blot analysis; in seven families, mutations were detected. In 13 females from six families with identified mutation, the direct diagnosis of carriers was performed. Four intragenic (BclI, XbaI, BglI and MspI in F8C locus) and two linked polymorphisms (TaqI in DXS52 locus and BglII in DXS15 locus) were studied in members of 47 hemophilia A families. BclI-XbaI-BglI haplotypes were analyzed in 90 unrelated X chromosomes. Eighteen out of 31 females (58%) were heterozygous for at least one intragenic polymorphism, and 29 out of 31 females (94%) were heterozygous for at least one intra- or extragenic polymorphism tested. Carrier diagnosis was made in 15 out of 25 possible carriers (60%) based on intragenic and in an additional 3 out of 25 (12%) only on linked polymorphism.