Previous studies in humans and animal models, as well as the analysis of data collected for this study, appear to strongly support the role of genetic factors in the formation of inhibitors, in addition to the specific underlying factor VIII mutation. The elucidation of novel genes important to inhibitor development has the potential to lead to improved understanding of the pathogenic mechanisms underlying this immune response in humans and, ultimately, to the development of new approaches to prevention or treatment of this serious complication of hemophilia.