Prenatal diagnosis in hemophilia A using factor VIII gene polymorphism--Indian experience

The heterogeneous nature of the mutations, the size, and the complexity of the factor VIII gene makes direct mutation analysis in hemophilia A families in India an option that is not very feasible and practical. Thus, carrier screening and prenatal diagnosis of hemophilia A often depends on haplotype analysis using restriction fragment length polymorphisms (RFLP) and short tandem repeat (STR) markers to track the defective factor VIII gene within a family. The main objective of this present study was to assess the utility of using polymerase chain reaction (PCR)-based five polymorphic markers: four intragenic Hind III, Bcl I, intron 13, and intron 22 STRs and one extragenic marker St14 in prenatal diagnosis. Forty-one chorionic villus samples (CVS) were studied from 41 families with a history of hemophilia A. PCR and RFLP were used for screening. Intron 22 STR showed the highest informativeness (60.9%), followed by Hind III (51.2%), Bcl I (46.3%), & intron 13 STR (51.2%); the extragenic marker St14 (VNTR) was informative in 46.3% of families. Linkage analysis, with the combined use of these five PCR-based polymorphic markers, gives good informativeness of 87.8% in the Indian population. Of the 41 CVS tested, 21 were found to be male fetuses and of these 13 were found likely to be affected with hemophilia A. Only in 12.2% of the families were none of the markers informative.