Summary
We have characterized the genetic defects of 17 hemophilia B patients of Chinese origin by means of the polymerase chain reaction (PCR) and direct sequencing. The single-strand conformation polymorphism (SSCP) was used as an initial screening method to analyze the entire coding region and the flanking introns of each individual’s factor IX gene. The abnormal exons were subsequently amplified and the nucleotide sequence determined. Of the 17 patients studied, 16 had single point mutations and one had a gross gene deletion of exons VII and VIII of factor IX. Among these 16 factor IX variants with point mutations 13 were missense and two were nonsense mutations. The remaining one had a nucleotide deleted, resulting in frame shifting at amino acid residue 97. A total of ten novel mutations, including the one with gross gene deletion, are reported in this study which have not been described previously. Five of the remaining seven variants were missense mutations with novel amino acids substituted for residues 127, 132, 180, 207, and 215, respectively. Mutations containing different amino acid residues at those positions have been reported. The last two are variants that have already been described to contain mutations at amino acid residues 333 and 365, respectively. To evaluate the efficiency of SSCP analysis in assessing the mutated exons and to further confirm our results we sequenced the entire exons of all 17 factor IX genes. The mutations detected by SSCP method were indeed the only mutation identified in each factor IX variant. The SSCP analysis and direct sequencing have also allowed us to circumvent the difficulties of carrier determination for Chinese by direct detection of the abnormal factor IX alleles inherited by the females.
