If you’ve ever had a nosebleed, cut yourself, or been bruised, you’ve seen the importance of your body’s ability to clot and form a scab. Usually, when a person bleeds, platelets (tiny pieces of cells) and proteins called clotting factors come together in a series of events leading to clot formation.

However, people with hemophilia — a bleeding disorder that occurs when the body makes too little or an abnormal version of a clotting factor — can have worse, uncontrolled, or even spontaneous bleeding. Most people with hemophilia lack factor VIII (8), known as classic hemophilia. A less familiar type is hemophilia B — also called Christmas disease — in which factor IX is missing or defective. This rare disease has similarities with other forms of hemophilia but also has some key differences. (You will usually see Roman numerals in any discussion of clotting factors.)

Here are four notable — and possibly surprising — facts about hemophilia B.

1. “Christmas Disease” Refers to a Person

Christmas disease is named after the first person diagnosed with hemophilia B — a 5-year-old boy named Stephen Christmas. Born in England in 1947, the child had bruised easily as a baby and had been hospitalized nine times for hematomas (blood clots). Doctors initially diagnosed him with a variety of conditions, including classic hemophilia, but researchers looking into his case discovered that he lacked clotting factor IX, not XIII. They reported their findings in the British Medical Journal study “Christmas Disease: A Condition Previously Mistaken for Haemophilia” — interestingly, it was published on December 27, 1952.

Why such a relatively recent discovery, when doctors had known about hemophilia in general since the early 1800s? The condition might have gone unidentified for so long because hemophilia B is far more rare than other types of hemophilia. According to the Centers for Disease Control and Prevention (CDC), hemophilia B occurs in only about 1 in 19,200 male births in the United States, compared with about 1 in 5,617 for the most common type. Like most hemophilias, hemophilia B affects males much more than females.

2. Hemophilia B Tends To Be Milder Than Other Types

As with all types of hemophilia, symptoms can range from mild to severe in hemophilia B. However, newer studies are showing that people living with hemophilia B are more likely to have milder cases than those with other types.

People with milder forms may have few or no symptoms and may need pretreatment only before surgery or another invasive procedure. Those with more severe hemophilia B are at risk of hemorrhage (life-threatening and sudden bleeds), such as in the joints or gastrointestinal tract, and require frequent treatment to prevent excessive bleeding. However, researchers have reported that even among people with moderate to severe disease, those who have hemophilia B are less likely to bleed than those living with classic hemophilia.

3. Hemophilia B Responds Better to Factor Treatment

All hemophilias involve the body’s shortage of a specific clotting factor, so treatment involves infusions to administer the insufficient factor — factor IX, in the case of hemophilia B. One reason the disease is generally milder may be that those with hemophilia B tend not to develop inhibitors (antibodies that target and destroy infused factors). Only 3 out of 100 people with hemophilia B may develop an inhibitor, compared with an estimated 20 to 30 in 100 with classic hemophilia.

An inhibitor can destroy infused clotting factors before they have a chance to work. Most people with hemophilia B don’t develop inhibitors, so their treatment is more likely to be successful.

4. Many People With Hemophilia B Didn’t Inherit It

Hemophilia is a genetic condition — it’s caused by mutations (changes) in genes. These mutations can be sporadic (acquired at random) or passed on from parents. Hemophilia B, like other hemophilias, is an X-linked condition, meaning it is carried only on an X chromosome, not a Y chromosome. Males are born with an X and a Y chromosome, so — unlike females, who are born with two X chromosomes— they don’t have another X chromosome to essentially balance out the one with the mutation. About one-third of males born with hemophilia B have no family history of hemophilia, so researchers believe that it is more common for hemophilia B mutations to be sporadic.

These mutations may someday be corrected through gene therapy. This approach has shown some promise in clinical trials (studies that test new treatments in people), in which some participants have produced more factor IX after gene therapy. Researchers suggest that gene therapy could eventually lead to a cure, so those affected by hemophilia B would not have to rely on repeated doses of factor IX.

Work With Your Medical Team

Hemophilia B can be a complex condition to understand. Be sure to bring up any questions you have during visits with your hematologist (blood disorder specialist). If you have been diagnosed with hemophilia B, it’s important to keep up regular appointments with your hematologist, so they can work with you to create an effective treatment plan. Your hematologist will consider many factors — including the severity of your disease, your genetics, any other medical conditions you have, and if you have an inhibitor — when recommending a plan to best treat your condition.

Talk to Others Who Understand

MyHemophiliaTeam is the social network for people with hemophilia B and their loved ones. On MyHemophiliaTeam, more than 6,000 members come together to ask questions, give advice, and share their stories with others who understand life with hemophilia and its complications.

Are you or a loved one living with hemophilia? Do you have questions about how hemophilia B differs from other types? Share your experience in the comments below, or start a conversation by posting on your Activities page.

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