• Factor VIII;
  • factor IX;
  • haemophilia A;
  • haemophilia B;
  • inhibitor

Aim: To survey the entire population (n= 116) afflicted with severe haemophilia A or B born in Sweden over a 20-y period (1980–1999), and to examine the epidemiological, genetic and clinical aspects of development of inhibitors to factors VIII and IX (FVIII/FIX). Methods: One hundred of the subjects had haemophilia A and 16 had haemophilia B. All of these subjects had received prophylactic treatment and had a check-up of inhibitor status at least twice a year. Sixty-one were born between 1980 and 1989 and 55 between 1990 and 1999. Results: Nineteen percent (19/100) of those with haemophilia A and 37% (6/16) with haemophilia B developed inhibitors at 12–18 mo of age, after exposure to FVIII/FIX concentrates for an average of 14 d in the case of haemophilia A and 16 d in haemophilia B. All patients with inhibitors carried mutations that impaired protein synthesis. The high incidence of FIX inhibitors may have been due to the large number of complete deletions (13%) in the Swedish haemophilia B population. Patients with haemophilia A showed no significant increase (p= 0.65) in incidence of inhibitors (n= 10/48, total incidence 21%) in the 1990s, when they were treated mainly with recombinant products, as compared to the 1980s (n= 9/52,17%), when they received intermediate/high-purity plasma-derived concentrates.

Conclusion: Our population-based study verifies that genotype has a general impact on the incidence of FVIII/FIX inhibitors, and that recombinant FIII/FIX concentrates are not a predisposing factor for inhibitor development.