Hemophilia A: Role of FVIIIC/vWF Ag in Assisting Linkage Analysis for Carrier Detection

Abstract

Carrier detection for hemophilia A was carried out in 52 females from 30 families presenting to the Haematology Department AIIMS, using linkage analysis and factor VIIIC (FVIIIC)-von Willebrand factor (vWF) antigen assay. The allelic frequency for the marker Bcl 1 and Xba 1 was 0.58 and 0.54, respectively, for the positive alleles and 0.42 and 0.46, respectively, for the negative alleles. The heterozygosity frequency of Bcl I and Xba 1 was 0.65 and 0.55, respectively. Of the 52 females, 30 were mothers of hemophilic patients and 22 were sisters of hemophilic patients. Of the 30 mothers, positive family history was present in 14. In these patients, the defective X chromosome was tracked in 10, and in four the defective X chromosome could not be tracked because the mothers were homozygous for the marker used. Of the 16 mothers without a family history of disease, three were observed to be carriers based on linkage analysis and reduced factor VIII levels in mother/sister. Possible defective X chromosome was tracked in 11 mothers and five were noninformative because they did not show heterozygosity for the markers used. Using linkage analysis, nine of the 22 sisters were found to be definite carriers, 10 noncarriers, and three were noninformative. It is thus concluded that using Bcl 1 and Xba 1 linkage analysis, carrier status can be definitely ascertained in 50% females and this level of information can be increased to 61.5% by measuring FVIIIC/vWF antigen levels in them.