Hemophilia B

Hemophilia B is caused by a deficiency of the clotting factor designated Factor IX. The main symptom is uncontrolled, often spontaneous bleeding. Internal bleeding into the joints can result in pain, swelling and, if left untreated, can cause permanent damage.

Patients receive recombinant Factor IX intravenously to cope with spontaneous bleeds. A subset of patients receive the clotting factors prophylactically.

Therapeutic Application

Gene therapy for Hemophilia B involves a one-time delivery of a normal copy of the Factor IX gene to the liver, allowing the liver to secrete enough enzyme to ameliorate symptoms without the need for repetitive infusion. 


St. Jude’s Childrens Research Hospital is sponsoring a Phase 1 clinical trial testing the safety of a self-complementary rAAV8 vector encoding Factor IX. Intravenous administration targets the vector primarily to the liver. Currently, six patients have been dosed with three different dose levels of vector.