An analysis of factors affecting the incidence of inhibitor formation in patients with congenital haemophilia in Japan

Summary. Studies conducted in European and North American countries have demonstrated that various factors including races affect the frequency of inhibitor formation in haemophilia patients. The present study was undertaken to analyse factors affecting the incidence of inhibitor formation in Japanese haemophilia A and B patients. Analytical data were retrospectively collected from haemophilia A and B patients born after 1988, the year when monoclonal antibody‐purified factor VIII products were first marketed in Japan. Various data were collected from 184 patients (153 cases of haemophilia A; 31 cases of haemophilia B). The sample size of haemophilia B cases was too small to reveal any significant differences between the inhibitor formation group and the inhibitor‐free group in any of background variables. For patients with haemophilia A, on the other hand, univariate analysis identified the severity of haemophilia and a positive family history of inhibitor development as risk factors for the formation of inhibitors. In analyses of the clotting factor products used, the incidence of inhibitor formation did not differ significantly between the group treated with plasma‐derived products (29.7%) and the group treated with recombinant products (25.0%). When background variables were compared, age was higher in the group treated with plasma‐derived products but none of the other background variables differed between the two groups. These results suggest that in Japanese haemophilia patients, the type of clotting factor preparations used for therapy has not influenced the incidence of inhibitor formation.