Hemophilia B

Hemophilia B is a rare inherited bleeding disorder. It happens when a gene that helps blood clot mutates or changes. Left untreated, hemophilia B may be life-threatening. Scientists are researching gene therapy and gene replacement therapy as new ways to treat hemophilia B and other forms of hemophilia.


What is hemophilia B?

Hemophilia B, once known as Christmas disease, is an inherited bleeding disorder. It happens when a gene that helps blood clot mutates or changes. People with hemophilia B don’t have the usual amount of a blood protein that helps blood clot. This protein is a clotting factor. In hemophilia B, people have less clotting factor IX, sometimes called factor 9, F9 or FIX. Left untreated, hemophilia B may be life-threatening. Healthcare providers treat hemophilia B with factor 9 replacements that help blood clot. Providers are researching gene therapy and gene replacement therapy as new ways to treat hemophilia B and other forms of hemophilia.


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How does this condition affect my body?

Like other forms of hemophilia, people who have hemophilia B bleed more than normal and/or longer than normal after being injured, having surgery or having dental procedures. Hemophilia B mostly affects men and people designated male at birth (DMAB) but women and people designated female at birth (DFAB) may develop the condition, too.

Healthcare providers classify hemophilia as being mild, moderate or severe. People who have severe hemophilia B may have bleeding into their joints that’s very painful and may cause arthritis. Some people may need surgery to replace damaged joints. They also may have bleeding inside of their brain that can be life-threatening.

How common is hemophilia B?

Experts estimate about 4 in 100,000 men and people DMAB in the United States have hemophilia B. Women and people DFAB can have hemophilia B, but it’s hard to estimate how many have this condition. That’s because they may have symptoms like heavy periods or excessive postpartum bleeding that many people don’t associate with hemophilia.


What is the difference between hemophilia A and B?

Both hemophilia types are inherited blood disorders with similar symptoms caused by different genetic mutations or changes. Studies show hemophilia B symptoms may be less serious than hemophilia A symptoms. Hemophilia B is still a serious medical condition, but people who have this form of hemophilia may have fewer issues with excessive bleeding. Some other differences between hemophilia A and B include:

  • Studies show people who have hemophilia B have fewer hemathroses (bleeding into their joints) and less joint damage.
  • People with hemophilia B have fewer episodes of spontaneous bleeding, meaning bleeding that happens without apparent cause.
  • Sometimes, people treated for hemophilia develop issues with antibodies that interfere with treatment. Studies show people who have hemophilia B are less likely to develop these issues.

Why did people once call hemophilia B Christmas disease?

For more than 100 years, healthcare providers thought there was just one type of hemophilia. In 1952, a researcher used plasma from seven people who had hemophilia — one with the last name Christmas — to treat other people who had hemophilia. The treatment worked. Researchers concluded Christmas’ hemophilia was a different form of hemophilia caused by a different genetic mutation. They named this second hemophilia type Christmas factor or Christmas disease. Later, Christmas disease was renamed hemophilia B.

Symptoms and Causes

What causes hemophilia B?

Hemophilia B is a genetic bleeding disorder. If you have hemophilia B, it means you inherited an abnormal gene that affects the amount of clotting factor 9 in your body. Normally, a gene called F9 carries instructions on how to create factor 9. Hemophilia B happens when that gene mutates and becomes an abnormal gene that leads to low factor 9 levels or even missing factor 9. Men or people DMAB inherit hemophilia B if their biological mothers carry the condition.

Here’s how that happens:

  • Everyone receives two X chromosomes from their biological mother and one X chromosome and one Y chromosome from their biological father.
  • If a woman or person DFAB has an abnormal F9 gene on one of their X chromosomes, they carry hemophilia B, but they won’t have symptoms. That’s because there’s a normal F9 gene on their second X chromosome.
  • This person can pass the chromosome carrying the abnormal F9 gene on to their biological male child. As men and people DMAB have just the one chromosome, they’ll develop hemophilia B.

Hemophilia B may happen without passing from mother to son through a process called spontaneous mutation. In spontaneous mutation, the embryo created when an egg and sperm combine starts to divide and produce more cells. The new cells contain copies of the genes in the single cell, and sometimes, mistakes or mutations happen during the gene copying process.

If there was a mistake when the F9 gene was copied, your child may have hemophilia B or carry hemophilia B. (Historians and medical researchers believe that was the case with Queen Victoria of England. Queen Victoria had hemophilia even though no one in her family had the disease. She passed the disease on to her children. When those children married into royal families in Spain and Russia, they passed the condition on to their children. That condition was later identified as hemophilia B.)


What are hemophilia B symptoms?

Hemophilia B symptoms are classified as mild, moderate or severe. Healthcare providers classify hemophilia symptoms by the level of factor 9 in people’s blood.

Mild hemophilia B

People who have factor 9 levels between 6% to 49% have mild hemophilia B and mild symptoms. In some cases, people with mild hemophilia B aren’t diagnosed until they’re adults and need surgery, give birth, have a serious injury or if they’re female, seek treatment to ease very heavy periods.

Moderate hemophilia B

People who have factor 9 levels between 1% to 5% have moderate hemophilia B and moderate symptoms. Children with moderate hemophilia B typically start showing symptoms when they’re 18 months old.

These children may have the following symptoms:

  • Bruises: They bruise very easily.
  • Unusual bleeding: If they have surgery, have an injury that causes bleeding or have a tooth pulled, they’ll bleed more than is normal and for longer than expected.
  • Spontaneous bleeding: Rarely, they’ll begin to bleed for no apparent reason.

Severe hemophilia B

People with factor 9 levels below 1% have severe hemophilia B and severe symptoms. Some children who have severe hemophilia B bleed as they’re being born, right after they’re born or when they’re undergoing circumcision. Other children develop symptoms a few months after they’re born. Common symptoms include:

  • Bleeding: Babies and toddlers may bleed from their mouths after minor injuries, like bumping their mouths on a toy.
  • Swollen lumps on their heads: Babies and toddlers who bump their heads often develop goose eggs — large round lumps on their heads.
  • Fussiness, irritability or refusing to crawl or walk: These symptoms may happen if babies and toddlers have internal bleeding into a muscle or joint. They may have areas on their bodies that look bruised and swollen, feel warm to your touch or make your child hurt when you gently touch the area.
  • Hematomas: A hematoma is a mass of congealed blood that gathers under babies’ or toddlers’ skin. Babies and toddlers may develop hematomas after receiving an injection.
  • Breathing difficulties: Sometimes, bleeding may cause your child’s tongue to swell so much that it blocks their airway.

Diagnosis and Tests

How do healthcare providers diagnose hemophilia B?

Healthcare providers diagnose hemophilia B by doing a physical examination, evaluating symptoms, like bruising and swollen joints, and asking about any biological family history of hemophilia or blood disorders.

What tests do healthcare providers use to diagnose hemophilia B?

  • Complete blood count (CBT): Providers use this test to measure and study blood cells.
  • Prothrombin time (PT) test: Providers use this test to see how quickly your blood clots.
  • Activated partial thromboplastin time test: This is another blood test to see how long it takes your blood to form a clot.
  • Fibrinogen test: This is a blood test to measure the amount of blood protein fibrinogen, which helps with clotting.
  • Clotting factor test: This blood test shows the hemophilia type and severity.

Management and Treatment

How do healthcare providers treat hemophilia B?

Healthcare providers typically treat hemophilia B with factor replacement therapy. In factor replacement therapy, providers inject concentrated factor 9 into people’s bloodstreams. The concentrated factor 9 takes the place of the missing factor and helps prevent excessive bleeding or control bleeding when it happens.

Usually, people with mild or moderate hemophilia B only need replacement therapy when they need surgery. People who have severe hemophilia B may need regular factor replacement therapy.

What are replacement therapy complications?

People receiving replacement therapy may develop complications, including inhibitors and viral infections.


People develop inhibitors when their bodies stop accepting factor replacement therapy as part of their normal blood. Inhibitors prevent factor replacement therapy from working, which makes it difficult to slow or stop bleeding episodes. People are more likely to develop this complication if they have severe bleeding disorders and are receiving high doses of factor replacement. Healthcare providers may treat this complication by using agents that can bypass factor 9 to complete clot formation.

Viral infections

Rarely, people may develop viral infections, particularly hepatitis C, if their treatment involves replacement therapy using donated blood.


How can I reduce my risk for developing hemophilia B?

Hemophilia B is an inherited condition, which means you can’t reduce your risk of developing it or passing it on to your children. Here’s information about the genetic process that drives hemophilia B:

  • If you’re a woman or a person DFAB with one chromosome carrying an abnormal F9 gene, there’s a 50% chance your biological sons will have hemophilia B and a 50% chance your biological daughters will carry the condition.
  • Your daughters who inherit the gene may pass hemophilia B on to their sons. Their daughters may carry the condition.
  • Your sons who have hemophilia B may pass the chromosome onto their daughters.
  • If you’re a man or a person DMAB who has hemophilia B, your biological sons won’t have the condition, but all of your biological daughters will carry the chromosome with abnormal F9 genes.

I’m pregnant and carry hemophilia B. Can I find out if my baby has this condition before they’re born?

Yes, healthcare providers can take a sample of blood from your umbilical cord to test clotting factors. That way, you and they will know what to expect during delivery and take steps to prevent any complications bleeding may cause.

Outlook / Prognosis

What can I expect if I have hemophilia B?

Hemophilia B is a chronic condition. Healthcare providers can’t cure it, but they do have treatments that prevent or ease serious joint pain and other medical issues. Most people receiving treatment for hemophilia B have a good prognosis or expected outcome.

People who have severe hemophilia B will need regular infusions or injections of replacement factor for bleeding issues. They may need to see their healthcare provider for treatment, ask a family member or caregiver to inject the treatment or they may be able to inject the treatment themselves. Regardless, people with severe hemophilia B will always need treatment to prevent excessive bleeding.

They may also develop other medical conditions that affect their overall health and lifespan. For example, many people who have hemophilia B develop severe problems with their knee or hip joints and need surgery to replace the damaged joints. If you have hemophilia B, ask your healthcare provider what you may expect. They know your situation, including your overall health, and are the best resource for information.

What can I expect if my child has this condition?

If your child has mild or moderate hemophilia B, you’ll need to make sure healthcare providers know about the condition so they can prevent excessive bleeding if your child needs surgery or dental treatment like having a tooth pulled. Here are some other suggestions. Your healthcare provider may have more:

  • While your children are very young, make sure their high chairs and car seats have adequate safety straps.
  • As they grow up and play with other children, their caregivers and teachers should know what to do if your child is accidentally hurt and starts bleeding.
  • Your child may need to avoid certain activities, like sports where they’re likely to bump hard into other people or take hard falls.

My child has severe hemophilia B. What should I expect?

Children who have severe hemophilia B will need medical treatment for the rest of their lives, whether it’s treatment to prevent or slow bleeding or treatment to ease symptoms. Here are some potential challenges you may encounter, and some suggestions that may help:

  • Babies and toddlers with hemophilia B may start bleeding simply by bumping into things or falling as they learn to walk. You can’t always prevent those tumbles, but it may make sense to put protective covering on any sharp edges on furniture.
  • As your child grows up and starts playing or running about, talk to your healthcare provider about protective gear like helmets and kneepads. Of course, all children should wear helmets when riding bikes. Your child may need extra protection to avoid bumps that could cause bleeding.
  • Your child will probably need regular medical treatment to prevent bleeding. They may get frustrated and angry if their appointments for treatment mean they can’t be with their friends or miss school activities.
  • A child who has hemophilia knows their teachers and other people are aware of their situation. They may feel awkward if teachers and other school staff try to be helpful by treating them differently.
  • Older children and teenagers may need help coping with their feelings and managing their reactions to other people. If that’s your child’s situation, talk to your provider about programs or support groups for young people.

Living With

I have hemophilia B. How do I take care of myself?

Living with hemophilia B means being vigilant about receiving treatment and taking extra steps to protect your overall health. Here are some suggestions:

  • Protect yourself from infection: Ask your healthcare provider what vaccinations make sense.
  • Aim for a weight that’s healthy for you: Managing your weight may help if you’re having trouble getting around because internal bleeding damaged your joints.
  • Develop an exercise routine: You may worry about hurting yourself during exercise. Talk to your provider about ways to reduce the risk of bleeding while staying active.
  • Manage your stress: Hemophilia B is a lifelong illness. It may take extra effort to balance your obligations to your family and your work.
  • Avoid certain pain medications: If you have hemophilia B, you shouldn’t take aspirin or ibuprofen. These pain medications interfere with blood clotting.

You should see your healthcare provider for your regular treatment and any time you have unusual bleeding or other symptoms like severe joint pain.

When should I go to the emergency room?

You should seek immediate medical help if you have a head injury. The following symptoms could mean you have brain bleed or hemorrhage (intracranial hemorrhage):

Contact your healthcare provider or go to the emergency room any time you can’t stop bleeding from any kind of injury or if you start to bleed for no apparent reason.

A note from Cleveland Clinic

Hemophilia B is a rare form of a rare disease. Like the more common form, hemophilia A, hemophilia B is an inherited bleeding d disorder. Studies show people with hemophilia B may have less serious symptoms than people who have hemophilia A. Even so, hemophilia B still poses medical, lifestyle and emotional challenges. Women and people designated female at birth (DFAB) who carry the condition may wonder and worry if they’ll pass it on to their children. Parents raising a child who has hemophilia B may feel anxious about protecting their children from accidental injury. Later, they may need to help their growing child learn to live with hemophilia B. People who have severe hemophilia B may need lifelong treatment to prevent excessive bleeding. Researchers are investigating new treatments like gene replacement or gene therapy that may make a huge difference in how healthcare providers treat severe hemophilia B. If you or your child have this condition, ask your healthcare provider for information about clinical trials that may be appropriate.

Medically Reviewed

Last reviewed by a Cleveland Clinic medical professional on 07/22/2022.

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