Lack of familiarity with AHA symptoms and differential diagnosis; isolated aPTT with normal prothrombin time should prompt differential diagnosis. A hemophilia expert might recommend a mixing assay and an assay to confirm the presence of inhibitors (Bethesda assay, Nijmegen-Bethesda assay, or an anti-FVIII antibody ELISA). The gene discussed is F2; the disease is hemophilia.