Hemophilia B is characterized by coagulation system malfunction of the factor IX (FIX) gene, resulting in increased uncontrolled hemorrhages as well as severe hemarthroses and ensuing arthropathies.1,2 Increased life expectancy due to an expanding array of treatment options has placed patients with hemophilia at greater risk for developing hemophilic arthropathy as well as age-related comorbidities, often requiring cardiac, abdominal, or orthopedic surgical intervention. The gene discussed is F9; the disease is hemophilia B.