Factor VIII and IX gene polymorphisms and carrier analysis in Indian population

The efficacy of the three common intra- and extragenic polymorphic sites of the factor VIII and IX genes has been examined in the Indian population, with an aim to develop a strategy that would be accurate and informative, yet economical. The approach for hemophilia A carrier detection includes tests for BclI, XbaI, and TaqI polymorphic sites for introns 18 and 22 and the extragenic locus St 14, respectively, whereas for hemophilia B, tests include detection of TaqI, DdeI, and HhaI polymorphic sites for introns 4 and 1, and the 3' flanking region of the factor IX gene, respectively. In hemophilia A, the cumulative efficiency of these three polymorphisms has been found to be 100%, since all 37 tested families were informative for at least one of these three polymorphisms. It is of interest to note that a case of recombination between St 14 and the factor VIII gene was also observed. Of the 47 unrelated X chromosomes examined (normal = 10, factor VIII:C deficiency = 37), heterozygosity for BclI, XbaI, and St 14 was found to be 47%, 36%, and 86%, respectively, in the factor VIII gene. However, when 37 unrelated X chromosomes (normal =10, factor IX:C = 27) were analyzed for polymorphism with TaqI, DdeI, and HhaI, it was found that the polymorphism detection rate was only 18% for the TaqI site but 45% each for the DdeI and HhaI sites, in the factor IX gene. This indicates a low effectiveness of the TaqI restriction site in carrier analysis of hemophilia B families in our population.