ANALYSIS OF FACTOR IX GENE IN NORMAL SUBJECTS AND HEMOPHILIA B PATIENTS IN JAPAN

We have examined DNA samples from 25 hemophilia B patients (21 B^- patients, 2 B^R patients and 2 B⁺ patients) and 51 normal subjects with molecular probes (pHFIX and 2 genomic fragments). By structural gene analysis, 4 out of 7 patients who developed anti-factor IX antibodies were detected to have gross factor IX gene deletion. Although these four patients showed normal pattern of HPRT gene detected by pCDHPRT, the gene deletions were found to expand more than 34kb including with entire factor IX exons. Quantitative Southern blot analysis of factor IX gene of the patient's family members indicated that the gene deletion was inherited in one family, establishing the carrier status of 2 aunts, 2 cousins and one sister. The 'de novo' mutation of factor IX gene was also established in 2 families. Three patients with anti-factor IX antibodies and 17 patients without antibody to factor IX had normal pattern of factor IX gene by several restriction enzyme digestions. Analysis of factor IX gene of three patients with anti-factor IX antibodies and two B⁺ patients are now underway to detect the unique gene defects which may be responsible for the disease Phenotypes. Common RFLPs in factor IX gene were studied in normal Japanese subjects. More than 80 X chromosomes were analysed with BamHI, Ddel, MspI, TaqI or XmnI digestion, followed by hybridization with pHFIX. RFLPs produced by these enzymes were found to be uncommon or possibly absent in normal Japanese subjects. These results imply that racial differences in the frequency of gene polymorphisms should be seriously considered before initiating the gene counseling by the genetic probes.