Recent Advances in Hemophilia B

Written by Stephanie Booth
Medically Reviewed by Neha Pathak, MD on January 23, 2026

Living with hemophilia B (or "Christmas disease") means facing daily challenges. This rare disorder, which happens when your blood doesn't clot the way it should, can cause you to bleed more heavily than usual and, in some cases, for no clear reason. While there's still no cure, there are many reasons to be hopeful.

"We are in an age of discovery in the treatment for hemophilia B, with many new treatments already available and others on the horizon," says Deborah Brown, MD, director of pediatric hematology at UTHealth Houston.

Here's what to know about the recent advances that experts have made in treating this complex condition.

Usually, you have proteins in your blood called clotting factors that help stop bleeding. But if you have hemophilia B, you're missing a specific clotting factor called factor IX (FIX) or don't have enough of it in your body. That can cause symptoms like bruising or bleeding after a minor injury, bleeding longer than usual after surgery, or bleeding that starts without a clear cause. For instance, you may have sudden nosebleeds or bleeding that happens deep inside your joints.

Hemophilia B is often genetic. A gene that's passed down to you doesn't work the way it should.

Because this damaged gene is often found on the X chromosome, you're more likely to have it if you were assigned male at birth and have only one X chromosome.

Over the past decade, experts have made remarkable headway in treating hemophilia B.

"Like many things in medicine, there were long periods of slow progress, followed by a rapid expansion … fueled by the dedication of researchers and the passion of the hemophilia community," says Brown.

On-demand hemophilia B treatments can stop bleeding after it begins. But doctors now have more options than ever before to try to keep bleeding episodes from starting. They include:

Longer-lasting factor IX replacement therapy

Factor replacement therapy has been around for decades. It gives your body the missing clotting factor that it needs.

"For patients who are not actively bleeding, prophylaxis with standard half-life or extended half-life factor replacement therapy is used to prevent bleeding," says Alycia Foti, MD, a pediatric hematologist oncologist at Hackensack Meridian K. Hovnanian Children's Hospital at Jersey Shore University Medical Center in Neptune, New Jersey. 

Standard treatments are given by IV every one to three days, but newer extended half-life therapy options stay in your body longer. You may need them just once or twice a week. 

Using a longer-lasting treatment may make it easier to get through your daily routine and also improve your mental health and quality of life. It may also reduce the chances that you'll develop inhibitors. These are antibodies that your immune system makes by mistake. They attack the factor IX replacement before it can work.

Newer therapies help prevent bleeding episodes without requiring factor IX replacement. And, "[they] can offer effective and convenient treatment for those with hemophilia B who have inhibitors, which has always been our biggest challenge," Brown says. For instance:

Marstacimab (Hympavzi). This treatment for hemophilia B is given as a once-weekly shot using a prefilled pen to inject the medicine under the skin. It's a type of drug called an anti-tissue factor pathway inhibitor (anti-TFPI). Instead of replacing clotting factor, it targets a protein called tissue factor pathway inhibitor (TFPI), which plays a key role in the blood clotting process.

The FDA recently expanded the approval of marstacimab (Hympavzi). It is now approved to help prevent or reduce bleeding episodes in adults and children ages 6 and older with hemophilia A or hemophilia B, whether or not they have inhibitors (antibodies that can make clotting factor treatment less effective). A phase III clinical trial showed that marstacimab could reduce the annual bleeding rate (the number of bleeding episodes a person has in a year) in adults with severe hemophilia B who have inhibitors.

Concizumab (Alhemo). This treatment also blocks the TFPI protein to reduce or prevent bleeding issues. You give yourself a daily shot, which replaces your need for factor replacement therapy. Concizumab is approved for adults and kids 12 years and older who live with hemophilia B, both with and without factor IX inhibitors.

Fitusiran (Qfitlia). Antithrombin (AT) is an anti-clotting protein that your liver makes. This medication lowers your levels of it by using small interfering RNA (siRNA) technology. siRNA molecules "silence" the gene that makes AT.

To prevent bleeding episodes, you get this treatment as a shot once every two months. So far, it's approved for adults and kids older than 12 years old. It can help whether or not you have inhibitors.

Despite these treatment advances, researchers keep looking for more and better ways to treat hemophilia B. One drawback of the current therapies is that they require an "immense amount of education," says Foti.

For example, you not only need to learn how to give yourself or your child a treatment at home, but understand when to call your doctor or go to a hospital if you have any side effects. You'll still need to be prepared for the possibility of bleeding.

And "while there is a shift to allow patients with bleeding disorders to participate in all contact sports, this requires planned prophylaxis factor replacement and … likely does not fully absolve the bleeding risk," says Foti.

Gene therapy works by replacing a missing or damaged gene with a new, healthy one. And "after years of research and development, gene therapy [to treat hemophilia B] is a reality," Brown says. 

Etranacogene dezaparvovec (Hemgenix) is an option for adults with moderate to severe hemophilia B. It's based on a type of specially engineered virus (adeno-associated virus, or AAV) containing copies of the gene that makes factor IX. The virus carries this gene to your liver, which allows the cells there to start making their own factor IX.

A single treatment of etranacogene dezaparvovec, which you get through an IV, may have long-term benefits. One study found that 96% of people who received this type of gene therapy for hemophilia B didn't need factor IX replacement therapy for up to two years afterward. Clinical trials for other types of gene therapy are currently underway.

"Eventually, there will be gene therapy clinical trials for children less than 18 years and for those who have inhibitors or preexisting antibodies to adenovirus," says Brown. 

While treatments for hemophilia B keep getting better, experts hope the same will soon be true for diagnosing this rare condition.

"Diagnosis is still based on clotting assays, which have not changed much in 50 years," Brown says. "Eventually, genetic testing will be much quicker and more reliable, which could benefit women who are carriers and their infant sons."

Although it might not happen anytime soon, "the ultimate goal is for early diagnosis and curative therapies, which last a lifetime," Brown says. 

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