Case Report: Development of Factor VIII Inhibitor in a Patient with an Uncommon de novo Mutation in the Factor VIII Gene.

The development of factor VIII inhibitors remains a significant clinical challenge in the management of hemophilia A. We present a patient of mixed ethnicity with severe hemophilia A who was found to have a F8 gene hemizygous c.5815G>T mutation resulting in an Ala1939Ser substitution (Ala1920Ser in legacy nomenclature) and possible splice site change that has been reported in only 1 patient previously. He developed an inhibitor shortly after starting replacement recombinant factor VIII (Advate®; Baxalta, Bannockburn, IL, USA) and was successfully treated with immune tolerance therapy. Our report describes the second patient reported to have severe hemophilia due to this mutation and the only case of a factor VIII inhibitor associated with this mutation.