• antibody;
  • genetics;
  • hemophilia A;
  • intensive FVIII exposure;
  • mild/moderate;
  • surgery

Summary. Background: A severe and challenging complication in the treatment of hemophilia A is the development of inhibiting antibodies (inhibitors) directed towards factor VIII (FVIII). Inhibitors aggravate bleeding complications, disabilities and costs. The etiology of inhibitor development is incompletely understood. Objectives: In a large cohort study in patients with mild/moderate hemophilia A we evaluated the role of genotype and intensive FVIII exposure in inhibitor development. Patients/methods: Longitudinal clinical data from 138 mild/moderate hemophilia A patients were retrospectively collected from 1 January 1980 to 1 January 2008 and analyzed by multivariate analysis using Poisson regression. Results: Genotyping demonstrated the Arg593Cys missense mutation in 52 (38%) patients; the remaining 86 patients had 26 other missense mutations. Sixty-three (46%) patients received intensive FVIII concentrate administration, 41 of them for surgery. Ten patients (7%) developed inhibitors, eight of them carrying the Arg593Cys mutation. Compared with the other patients, those with the Arg593Cys mutation had a 10-fold increased risk of developing inhibitors (RR 10; 95% CI, 0.9–119).The other two inhibitor patients had the newly detected mutations Pro1761Gln and Glu2228Asp. In both these patients and in five patients with genotype Arg593Cys, inhibitors developed after intensive peri-operative use of FVIII concentrate (RR 186; 95% CI, 25–1403). In five of the 10 inhibitor patients FVIII was administered by continuous infusion during surgery (RR 13; 95% CI, 1.9–86). Conclusion: The Arg593Cys genotype and intensive peri-operative use of FVIII, especially when administered by continuous infusion, are associated with an increased risk for inhibitor development in mild/moderate hemophilia A.