Hemophilia B

Hemophilia B is an X-linked bleeding disorder with bleeding caused by inability to generate adequate thrombin. It affects nearly 1:25,000 live male births and is diagnosed by an elevated partial thromboplastin time and decreased plasma factor IX (FIX) activity level. Bleeding severity increases as the circulating FIX activity decreases. The most common bleeding sites include intraarticular and intramuscular hemorrhage as well as postsurgical, oral, and soft tissue bleeding. Hemophilic arthropathy from recurrent bleeding is the most significant morbidity for patients with hemophilia. Both plasma-derived and recombinant FIX concentrates are available to prevent or treat bleeding. Inhibitory antibodies to infused FIX occur rarely but often manifest as anaphylaxis to infused concentrate and later as nephrotic syndrome. Curative gene therapy and nonfactor replacement therapies are rapidly evolving.