Carrier analysis and prenatal diagnosis of haemophilia A in North India.

The feasibility of DNA diagnosis for haemophilia A in North India was evaluated using intragenic polymorphic DNA markers in factor VIII gene for linkage analysis as well as direct detection of inversion mutation in intron 22 of the gene. The informativity of RFLP (HindIII, BclI and XbaI) and STR (introns 13 and 22) markers for linkage analysis in factor VIII gene was determined in 100 normal individuals. The observed heterozygosity for RFLP markers HindIII, BclI and XbaI was 0.63, 0.60 and 0.48 while that of STR markers introns 13 and 22 were 0.60 and 0.40 respectively. Six and four alleles were identified for introns 13 and 22 and the most frequent allele was 13(CA)26 and 22(AG)n(GT)26 with an allele frequency of 0.53 and 0.62 respectively. The heterozygosities observed for RFLP markers was higher (>70%) than the STR markers (50%) in the affected families with haemophilia A. Inversion mutation was detected in 37% of severely affected patients. Based on present and previous studies from India, a strategy has been proposed to provide molecular diagnosis to a large number of undiagnosed cases of haemophilia A.