Influence of the type of F8 gene mutation on inhibitor development in a single centre cohort of severe haemophilia A patients

The development of neutralizing antibodies against factor VIII (FVIII) is a major complication of treatment with FVIII in patients with severe haemophilia A. This study was designed to describe the relationship between the type and location of the factor 8 (F8) gene mutation and the development of clinically relevant inhibitors in patients with severe haemophilia A. We conducted a single centre cohort study among 318 consecutive patients (baseline FVIII activity level < 0.01 IU mL-1) born between 1934 and 2007 who were treated with FVIII on at least 50 exposure days. The primary outcome was clinically relevant inhibitor development, defined as the occurrence of at least two positive inhibitor titres and a decreased recovery. Clinically relevant inhibitors were diagnosed in 14% (43) of patients (30 high-titre). The cumulative incidence of inhibitor development was 18% (35 of 200) in high-risk gene defects (67% in patients with large deletions, 30% in patients with nonsense mutations, 15% in patients with intron 1 or 22 inversions) and 7% (8 of 118) in low-risk gene defects (7% in patients with small deletions and insertions, 6% in patients with missense mutations, 8% in patients with splice site mutations). In patients with point mutations, the cumulative risk of developing inhibitors was highest in patients with mutations in the A3 and C2 domains (13% and 17% respectively). In conclusion, in agreement with earlier observations, the type and location of the F8 gene mutation were important determinants of inhibitor development in patients with severe haemophilia A.