Hemophilia A and B are the first and second most common types of hemophilia, respectively. Both conditions cause problems with blood clotting.

Hemophilia is a group of conditions that cause problems with blood clotting. Most forms, including hemophilia A and hemophilia B, are caused by genetic mutations present from birth.

Hemophilia A is the most common type. About 400 babies are born with it in the United States each year. Hemophilia B is the second most common type. It’s about 8 times rarer.

The treatment and outlook for hemophilia A and B are similar. Usually, treatment involves receiving injections to replace the missing protein in your blood.

Read on to learn about the similarities and differences between these two conditions.

Why is hemophilia B called Christmas disease?

Hemophilia B is also called Christmas disease because it was first diagnosed in a man named Stephen Christmas in 1952. It has also been called the “Royal disease” because historians believe Queen Victoria of England was a carrier of the hemophilia B gene. Her son Leopold died of bleeding after a fall at the age of 30.

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Hemophilia AHemophilia B
Incidence1 in 5,000 males1 in 40,000 males
Genetic causeMutation in F8 geneMutation in F9 gene
Missing protein in bloodBlood clotting factor VIIIBlood clotting factor IX

Hemophilia A and B are distinct forms of hemophilia caused by different genetic mutations.

Both are caused by recessive mutations on the X chromosomes. Females have two X chromosomes while males only have one, which makes males much more likely to develop hemophilia.

People with hemophilia A have a mutation in their F8 gene, which leads to the underproduction of blood clotting factor VIII. People with hemophilia B have a mutation in their F9 gene and underproduce blood clotting factor IX.

Is hemophilia A or B more severe?

There’s a limited amount of research directly comparing the severity of hemophilia A or B.

Some research over the past 75 years suggests that people with hemophilia B may be less likely to have severe disease and may be less likely to have serious bleeding if someone has severe disease.

Some research suggests there’s no significant difference in the severity of the two diseases.

Hemophilia A and B versus Von Willebrand disease

Von Willebrand disease (VWD) is another condition that causes improper blood clotting. VWD is almost always passed down through families. In rare cases, it develops with no family history.

Unlike hemophilia, VWD occurs evenly in men and women. It’s less likely to cause bleeding in your joints and more likely to cause:

Learn more about von Willebrand disease.

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Family history is the top risk factor for developing hemophilia A or B. It’s also possible to develop either condition spontaneously without a family history.

Hemophilia A and B are much more common in males than females due to the gene mutations occurring on the X chromosome. Females need to receive the abnormal gene from both parents to develop hemophilia, whereas males only need to receive it from one parent.

Hemophilia in females

Hemophilia can develop in females or people assigned female at birth, but it’s much rarer and usually milder.

According to the CDC, researchers found that 14 times fewer females received care at hemophilia treatment centers in the United States than males between 2012 and 2020. Only 8% of women had severe hemophilia compared to 70% of men.

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Symptoms are the same between hemophilia A and B but vary depending on the severity of your disease.

Disease severity is categorized as:

SeverityBlood clotting factor VIII or IX levels
Mildbetween 5–40% of normal
Moderate1–5% of normal
Severeless than 1% of normal

Symptoms can include:

  • frequent or severe nosebleeds
  • blood in urine or stool
  • easy bleeding or bruising, even with minor injury
  • frequent or severe bleeding of the gums or mouth
  • bleeding in joints or muscles

People with severe disease might have:

People with hemophilia A usually receive regular infusions of blood factor clotting protein VIII injected into their bloodstream over about an hour.

This protein is sourced from recombinant products made in a laboratory or from animal or human blood. Recombinant products are usually favored because they don’t have a risk of transmitting bloodborne viruses.

People with mild to moderate hemophilia may only need replacement therapy to treat specific bleeding. People with severe hemophilia need prophylactic injections regularly to prevent complications.

Treatment for hemophilia B is the same but involves injecting blood clotting protein IX instead of VIII.

Gene therapy is a newer treatment option. It can potentially cure hemophilia with a one-time injection, but it’s currently very expensive.

Gene therapy was FDA-approved for hemophilia B in November 2022. The FDA approved gene therapy for hemophilia A in June 2023.

The current price of gene therapy for hemophilia B is $3.5 million in the United States.

The outlook for hemophilia A and B varies widely depending on the level of blood clotting factor you have. Life expectancies continue to improve as treatments become more accessible.

In a 2020 study, researchers found that the average life expectancy of people with hemophilia A or B was about 6 years less than the national average.

Hemophilia A and B are both genetic conditions that interfere with your blood’s ability to clot. Although they’re caused by different gene mutations, their symptoms are similar.

The treatment and outlook for hemophilia varies significantly based on the severity of your disease. Many people are able to live full lives with proper treatment.