Direct carrier detection for severe haemophilia A: application to families with no available affected male.

Haemophiliae A is a common hereditary disorder of blood coagulation resulting from deficiency of factor VIII. Mutation analysis is the factor VIII gene has been hampered by the large size of the gene and the heterogeneity of molecular defects. In severe haemophiliae A, the most efficient methods of screening for point mutations can detect the lesions in 50 percent of cases only; this is explained by the recent finding (5) of an intragenic inversion that disrupts the factor VIII gene. Since this anomaly could not be characterized by these methods, Lakich et al. have also described a Southern blotting assay that allows a direct determination of the mutation. The use of this assay should greatly increase the feasibility and accuracy with which carrier detection and prenatal diagnosis can be made, as illustrated by the analysis of families with no available affected male that we present here.