FDA Approves Etranacogene Dezaparvovec to Treat Adults With Hemophilia B

The adeno-associated virus vector-based gene therapy is the first gene therapy to be approved by the FDA for hemophilia B.

The FDA approved etranacogene dezaparvovec (Hemgenix, CSL Behring), which is an adeno-associated virus vector-based gene therapy for the treatment of adults with hemophilia B (congenital Factor IX deficiency) who currently use Factor IX prophylaxis therapy or have current or historical life-threatening hemorrhage, or who have repeated, serious spontaneous bleeding episodes. Etranacogene dezaparvovec is the first gene therapy to be approved by the FDA for the treatment of hemophilia B.

“Gene therapy for hemophilia has been on the horizon for more than 2 decades. Despite advancements in the treatment of hemophilia, the prevention and treatment of bleeding episodes can adversely impact individuals’ quality of life,” said Peter Marks, MD, PhD, director of the FDA’s Center for Biologics Evaluation and Research, in a press release. “Today’s approval provides a new treatment option for patients with hemophilia B and represents important progress in the development of innovative therapies for those experiencing a high burden of disease associated with this form of hemophilia.”

Hemophilia B is a genetic bleeding disorder resulting from missing or insufficient levels of blood clotting Factor IX, a protein needed to produce blood clots to stop bleeding. Some symptoms can include prolonged or heavy bleeding after an injury, surgery, or dental procedure. In severe cases, bleeding episodes can occur spontaneously without a clear cause. Additionally, prolonged bleeding episodes can lead to serious complications, like bleeding into joints, muscles, or internal organs, including the brain.

Men mostly experience hemophilia B and have symptoms, and the prevalence of it in the population is approximately 1 in 40,000. Although many women carriers do not have symptoms, an estimated 10% to 25% of women carriers have mild symptoms.

Treatment for hemophilia B involves replacing the missing or deficient clotting factor to improve the body’s ability to stop bleeding and promote healing. Further, patients who have severe hemophilia B typically require a routine treatment regimen of intravenous (IV) infusions of Factor IX replacement products to maintain sufficient levels of clotting factor to prevent bleeding episodes.

Etranacogene dezaparvovec is a one-time gene therapy product given as a single dose by IV infusion and consists of a viral vector carrying a gene for clotting Factor IX. This gene is expressed in the liver to produce Factor IX protein to increase blood levels of Factor IX and limit bleeding episodes.

Two studies that enrolled 57 adult men between ages of 18 and 75 years looked to evaluate the safety and efficacy of etranacogene dezaparvovec for patients with severe or moderately severe hemophilia B. The effectiveness was established based on decreases in the men’s annualized bleeding rate (ABR).

One of the studies had 54 participants, and the subjects had increases in Factor IX activity levels, a decreased need for routine Factor IX replacement prophylaxis, and a 54% reduction in ABR compared to baseline.

The most common adverse events seen with etranacogene dezaparvovec were liver enzyme elevations, headache, mild infusion-related reactions, and flu-like symptoms. Patients should also be monitored for adverse infusion reactions and liver enzyme elevations in their blood.


FDA Approves First Gene Therapy to Treat Adults with Hemophilia B. FDA. November 22, 2022. Accessed November 23, 2022. https://content.govdelivery.com/accounts/USFDA/bulletins/3396c72