Hemophilia B, also known as factor IX hemophilia, is a rare genetic disorder in which your blood does not clot properly. It’s sometimes also called Christmas disease, named after Stephen Christmas, the first person diagnosed with the condition in 1952.

If you have hemophilia B, your body produces little or no factor IX, a protein that helps the blood to clot. This leads to prolonged or spontaneous bleeding. The less factor IX your body produces, the worse your symptoms are. Without treatment, hemophilia B can be fatal.

A person is born with hemophilia B, but it may not be diagnosed until later in life. It’s estimated that two-thirds of cases are inherited, according to the National Hemophilia Foundation.

The other cases are caused by spontaneous gene mutations that occur for unknown reasons during fetal development. The disease occurs almost exclusively in people assigned male at birth.

The gene responsible for hemophilia B is carried on the X chromosome.

Male children have one X and one Y chromosome. They inherit a Y chromosome from their biological father and an X chromosome from their biological mother. If a male child inherits a mutated gene on his X chromosome from his mother, he will develop hemophilia B.

Female children have two X chromosomes, one inherited from each biological parent. If a female child inherits a mutated gene on one of their X chromosomes, they will not develop hemophilia B because the other X chromosome produces enough factor IX for blood clotting.

However, their body may produce lower amounts of factor IX, which can result in symptoms like easy bruising and heavy menstrual bleeding. Sometimes they may have low enough levels of factor IX to be diagnosed with hemophilia.

Rarely, a female child can inherit hemophilia B if both parents pass on a mutated gene. However, it’s uncommon for a female child to have two parents with a mutated gene.

Fathers with the mutated gene will always pass that gene on to their daughters. A father does not pass the mutated gene on to his sons.

Female children with one mutated gene are called carriers. A carrier does not have hemophilia B but can pass the gene responsible for the disease on to their children.

With each pregnancy, female carriers have a:

  • 25 percent chance of having a son with hemophilia B
  • 25 percent chance of having a daughter who’s a carrier of the disease
  • 25 percent chance of having an unaffected son
  • 25 percent chance of having an unaffected daughter

Severe cases of hemophilia B are usually diagnosed in babies younger than 1 year old. Mild cases may not be diagnosed until a child reaches their toddler years or sometimes even adulthood.

In all cases, diagnosis usually happens after abnormal bleeding from an injury or surgery.

Events that may lead your doctor to suspect hemophilia B include:

  • prolonged bleeding, which can occur during circumcision, after surgical procedures or tooth extractions, following vaccinations, or from cuts or other wounds
  • unexplained, excessive bruising or prolonged nosebleeds
  • unexplained blood in urine or feces caused by internal bleeding in the gastrointestinal or urinary tract
  • internal bleeding that pools in the joints, which causes pain and swelling

Severe cases of hemophilia B may cause unexplained bleeding in the skull after childbirth and spontaneous bleeding.

If you or your child shows symptoms of hemophilia B, your doctor may order blood screenings and tests to confirm the diagnosis. These may include:

  • factor IX test: determines how much of the clotting factor is present in your blood
  • activated partial thromboplastin time test (APTT): detects how fast your blood clots
  • prothrombin time (PT) test: another test that detects how quickly your blood clots
  • fibrinogen test: determines your body’s ability to form a clot
  • complete blood count (CBC): checks the size, type, and amount of various components of the blood, including red and white blood cells

Genetic testing

If you’re female with a family history of hemophilia B, you can have genetic testing to see if you carry the faulty gene. Genetic testing is a very accurate way to detect the responsible gene.

There’s no cure for hemophilia B, but there are treatments for the condition. Regular treatment is essential for managing the symptoms of hemophilia B.

Factor IX injections

Hemophilia B can be treated with factor IX injections to prevent or stop bleeding. The factor IX can be derived from donated human blood or made in a laboratory.

Artificial factor IX is called recombinant factor IX and is recommended over blood-derived factor because it’s safer.

Blood-derived factor IX is rarely used in the United States.

Preventive treatment

If you have a severe form of hemophilia B, you may need preventive blood transfusions to avoid or reduce prolonged and heavy bleeding, which is known as prophylaxis. These are especially important in children. If you receive blood-derived factor or blood transfusions, you should be vaccinated for hepatitis B.

People with severe hemophilia B are at a slight risk of:

  • life threatening blood loss
  • bleeding in the brain
  • long-term joint problems from internal bleeding

In rare cases, the treatment for hemophilia B may result in an abnormal thrombosis, or clot formation.

You can lower your risk of hemophilia B complications by getting your annual checkups and regular blood testing for infections. You should also avoid aspirin and other medications that can interfere with blood platelet function.

A small percentage of people with hemophilia B will develop antibodies (known as inhibitors) against factor IX replacement therapy. These antibodies destroy replacement factor in factor IX injections, causing this treatment to be ineffective.

People who develop inhibitors need to use alternative recombinant products that do not contain any FIX protein to control bleeding. Your doctor can order tests to check whether you’re at increased risk for developing inhibitors.

With treatment, most people with hemophilia B are likely to lead normal lives. It’s important to make sure you avoid situations in which excess bleeding could occur since there’s currently no cure for the disease.

You also can receive blood-clotting therapy before any surgery or after any injury.

Living with hemophilia B can be stressful, especially when accidents or injuries that could lead to excessive bleeding occur. Talk with your doctor about ways you can prevent bleeding, tips on how to manage your condition if an injury occurs, and other supportive resources.

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