THE RELATIVE EFFICACY OF GENETIC ANALYSIS AND COAGULATION TESTING IN THE DIAGNOSIS OF CARRIERS OF HEMOPHILIA A

Abstract

This study has assessed the relative benefits of restriction fragment length polymorphism (RFLP) linkage and coagulation testing in the diagnosis of carriers of hemophilia A. 221 samples from 55 families have been studied for intragenic and flanking RFLPs. All samples were tested for the Factor VIII intragenic Bell RFLP and for the flanking marker St 14. 83% of obligate carrier females were heterozygous at oneor both of these two polymorphicsites. However, only38% of these women were heterozygous at the intragenic site and might safely be offered prenatal diagnosis using this marker for the hemophilia mutation. Carrier diagnosis was obtained in 52% of 81 potential carriers tested. Diagnosis wasbased on intragenic RFLP information in only 48% of these cases. Genetic diagnosis was possible in 27 atrisk women from families with no prior history of hemophilia. Four of these women were diagnosed as carriers on the basis of a gross Factor VIII gene deletion and the remaining 23 women were identified as non-carriers by the Bell (11) and Stl4 (12) RFLP data. 39 women remained undiagnosed after gene analysis studies. 23 of these women were female relatives of sporadic hemophiliacs and thus RFLP segregation analysis was inappropriate. A further 9 potential carriers were undiagnosed because of homozygosity in key individuals in their families. In 31 potential carriers we have quantitated Factor VIII:C (one stage assay) and vWf:Ag (Laurell and ELISA) and derived probabilities for carrier status. In 3 women there was conflicting genetic and coagulation data. Meanwhile, in 12 undiagnosed women from sporadic families, carrier diagnostic probabilities of > 0.9 were obtained. These studies indicate that optimal carrier detection for hemophilia A requires more intragenic and closely linked RFLPs and the continuance of coagulation testing to assist women from sporadic families.