Gene therapy is a new treatment for people with hemophilia. It involves a one-time intravenous (IV) infusion that stimulates your body to make a protein it needs for blood clotting.

About 1 in 40,000 people have hemophilia B. It’s caused by low levels of a protein called blood clotting factor IX. This protein is produced by your liver and circulates through your blood. It becomes active when one of your blood vessels is injured.

Hemophilia B is also called Christmas disease since it was first reported in a person named Stephen Christmas. It’s a congenital condition, meaning present from birth. It’s caused by a mutation in your F9 gene found on chromosome X.

Gene therapy is a promising new treatment for hemophilia B that involves infusing genetic information into your bloodstream to teach your cells how to produce blood clotting factor IX.

Read on to learn about gene therapy for hemophilia B including how it works, what the procedure entails, and its cost.

The difference between hemophilia A and B

Hemophilia is a group of conditions that cause problems with your blood’s ability to clot. Hemophilia B is the second most common type of hemophilia. It’s caused by an underproduction of clotting factor IX.

The most common type of hemophilia is hemophilia A, which is caused by a deficiency in blood clotting factor VIII.

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The Food and Drug Administration (FDA) approved the first type of gene therapy for treating hemophilia B in November 2022, called Hemgenix. Hemgenix is the brand name of the drug etranacogene dezaparvovec. It’s still the only type of gene therapy approved by the FDA in the United States for treating hemophilia B.

In June 2023, the FDA accepted Pfizer’s application for another gene therapy called fidanacogene elaparvovec. It may be available in the future.

Hemgenix is a virus vector-based gene therapy. These therapies use the shell of a virus to deliver a working gene into your cells to replace a defective gene.

In the case of Hemgenix, the virus is delivered into your bloodstream through an IV so that it can be carried to the cells in your liver that produce blood clotting factor IX.

Gene therapy was also recently FDA approved for hemophilia A on June 29, 2023.

People eligible for Hemgenix include those with hemophilia B who:

  • have moderate or severe symptoms and currently use factor IX prophylactic therapy
  • have a history of life-threatening bleeding
  • have repeated bouts of bleeding with no obvious cause

According to the Hemgenix website, Hemgenix is administered as a one-time infusion through an IV that takes about 1–2 hours. You receive the infusion at a special administration center. As of August 2023, their website lists 10 centers in the United States.

If you have to travel for your infusion, it’s a good idea to plan to be in the city for another 1 or 2 days after your treatment.

Weekly monitoring is recommended for the first 3 months. During this time, your doctor will likely want to run tests to measure your liver enzymes and factor IX levels.

Potential side effects

There’s a small chance of developing an infusion reaction, which can be caused by a hypersensitivity or allergy to an ingredient in the infusion. These reactions are rare but can be life-threatening. Your team will monitor you during your infusion and for at least 3 hours after your infusion for signs of these reactions.

Side effects that occurred in more than 5% of people during clinic trials were:

Gene therapy comes with a high price since it’s a new treatment for hemophilia. In one article, Hemgenix earned the nickname of the “world’s most expensive drug.” The cost of Hemgenix is about $3.5 million in the United States.

Despite the high price tag, the overall cost could be less than the current standard treatment of prophylactic factor IX therapy, which requires ongoing treatment that can cost hundreds of thousands of dollars per year.

In a 2021 study, researchers estimated the cost of gene therapy at 2 million dollars. At this price, they found gene therapy was more cost-effective than prophylactic therapy in people with severe hemophilia B.

In a June 2023 press release, the company that makes Hemgenix noted that insurance providers covering about 60% of the American population have already established guidelines for providing coverage for Hemgenix. For example, Blue Cross/Blue Shield has identified the following requirements for Hemgenix coverage.

In a 2023 phase 3 clinical trial, researchers compared the effectiveness of Hemgenix with prophylactic therapy. The researchers found that gene therapy offered superior results with a better safety profile.

Phase 1–3 clinic trials showed that people who received gene therapy had 53%–96% fewer bleeding episodes when they discontinued prophylactic injections.

Minor hemophilia B may not require treatment. If treatment is required, it usually entails prophylactic factor IX therapy where you receive regular injections of this protein. You may receive injections once every 1–2 weeks or 2–3 times per week.

Taking steps to avoid injury can help minimize the chances of developing serious bleeding.

Gene therapy is a relatively new treatment for hemophilia B that involves infusing a virus shell filled with genetic information into your bloodstream. This one-time infusion provides your body with the information that it needs to create the protein your body is lacking.

Gene therapy is very expensive, but research suggests that it’s safer and more effective than current prophylactic treatment. In the long-term, it may also be the cheaper option.