Hemophilia

A number of different techniques are available for carrier detection. Linkage analysis using DNA polymorphisms to track defective FVIII or FIX genes is possible in large families. Use of intragenic polymorphisms in both the FVIII and FIX genes allows precise detection of carrier females in most families studied. In persons with hemophilia A, the FVIII gene inversion can be tested for by Southern blotting.

If the gene defect in the family is not known, the inversion mutation in an affected male is generally sought first, as this mutation accounts for at least 20 percent of all cases of hemophilia A, and the test is relatively simple to perform. Although more time-consuming, point-mutation screening also can be done, using a variety of methods. For researchers working on the FVIII or FIX genes, there are sites on the Internet that are valuable resources, as they contain regularly updated listings of all reported mutations in each of these genes, and other useful information.

Because of a high mutation rate, approximately one-third of infants found to have hemophilia A or B have no family history of the disorder, the condition having occurred spontaneously. However, hemophilia is genetically transmitted to future generations.