[A retrospective study on the development of inhibitors in Japanese hemophiliacs (second report, 1994 study). Research Group of Blood Products for Hemophilia Inhibitor].

In this report, we discuss the findings of a 1994 retrospective study concerning the rate of inhibitor formation in Japanese hemophiliacs. The study was the second of its kind, following on the first in 1991 (Kamiya et al. 1995 Int. J. Hematology). The records of 77 medical institutions were examined. Inhibitors were found in 6.50% (140 of 2154) of the patients with hemophilia A (HA), and 5.21% (22 of 422) of those with hemophilia B (HB). The median age for antibody formation was 10.7 years in patients with HA, and 4.5 years in those with HB. The median period (exposure period) from initial plasma factor concentrates exposure to inhibitor formation was 46 days and 20 days, respectively, in the HA and HB patients. Among the HA inhibitor patients, those with a large deletion or a nonsense mutation were aged 17.4 years or less (0.58, 1.7, 3.5, 5.5, 7.0 and 17.4), whereas those with intron 22 inversion were aged 55.7 years or less (1.3, 1.3, 1.8, 33.0, 36.1, 37.7, 43.9, 47.9 and 55.7).