A complete deletion of the factor IX gene and new TaqI variant in a hemophilia B kindred.

We report a hemophilia B kindred in which the proband has a complete deletion of the factor IX gene extending a minimum of 80 kilobase pairs (kb) 3' of the gene. This individual has severe factor IX deficiency with no detectable circulating factor IX protein. In common with one previous report, despite a total deletion of the factor IX gene, this patient has not developed antibodies to factor IX. The mother of the proband was found to have a new TaqI variant of the factor IX gene on the nondeletion-bearing X chromosome. The location of the altered TaqI site was found to be 5' of exon IV between residues 9731-9734 and does not affect the function of the factor IX protein. The familial natures of both the variant allele and the deletion were established. In addition a study of this kindred at the DXS99 locus demonstrated the first reported recombination event between this site and the factor IX gene.