Missense and nonsense mutations and inhibitor development in patients with hemophilia A and B.

Hemophilia A and B are X-linked bleeding disorders caused by mutations in the F8 and F9 genes, resulting in deficiencies of coagulation factors VIII (FVIII) and IX (FIX), respectively. A major complication of replacement therapy is the development of neutralizing antibodies (inhibitors), which occur in approximately 30% of patients with severe hemophilia A and about 3% of those with hemophilia B. The role of missense and nonsense mutations in inhibitor formation has been increasingly recognized. In hemophilia A, missense mutations within immunogenic domains may alter FVIII structure, eliciting immune responses. Nonsense mutations especially those located in the light chain are associated with higher inhibitor risk due to the production of truncated, non-functional proteins. In hemophilia B, missense mutations rarely result in inhibitor development, whereas nonsense mutations and large deletions carry a significantly higher risk. Molecular genotyping contributes to predicting inhibitor formation and supports individualized treatment planning.