Gene deletions in patients with haemophilia B and anti-factor IX antibodies.

Christmas disease, or haemophilia B, is an inherited X-linked haemorrhagic disease which at present occurs in 798 known cases in the United Kingdom, corresponding to a frequency of about 1 in 30,000 males. Patients are deficient in the intrinsic clotting factor IX and are treated by replacement of this protein prepared from pooled plasma obtained from normal individuals. Occasionally treatment is complicated by the appearance of specific anti-factor IX antibodies. It seemed to us that this might be due to the absence of 'self' factor IX causing the immune system to regard the infused normal factor IX as foreign. The absence of all or part of the factor IX gene was an obvious possible reason for this, which we have now tested using our previously isolated gene probe. We have found four patients with gross gene defects.