Hemophilia B, also known as Christmas disease, is a bleeding disorder. Its characteristic feature is a deficiency of clotting factor IX. This is a protein present in the blood that helps with coagulation, or clotting.

Hemophilia describes a group of bleeding disorders where blood is unable to clot properly. This occurs due to a deficiency in certain proteins known as clotting factors. Many different clotting factors play a different role in the coagulation cascade.

The coagulation cascade refers to a series of steps that occur in response to bleeding. The process involves clotting factors, and the series of reactions ultimately leads to the formation of a blood clot. A deficiency in a clotting factor impairs this process and can result in spontaneous bleeding or severe bleeding following an injury.

A note about sex and gender

Sex and gender exist on spectrums. This article will use the terms “male,” “female,” or both to refer to sex assigned at birth. Click here to learn more.

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Hemophilia B primarily occurs due to a genetic variation in the F9 gene, which is present on the X chromosome. This is why medical professionals may describe hemophilia B as an X-linked condition.

The F9 gene is responsible for producing factor IX. As such, this gene alteration results in a deficiency, or impaired function, of clotting factor IX.

Clotting factor IX is one of the many clotting factors that play a crucial role in the blood clotting cascade. Without sufficient levels of factor IX, a person will experience difficulties forming blood clots and is susceptible to prolonged bleeding.

In most cases, people inherit the gene alteration for hemophilia B from a parent. However, in extremely rare cases, a person may develop acquired hemophilia B. This type of hemophilia is not present at birth — instead, an individual develops the condition later in life.

Acquired hemophilia B occurs when the body mistakenly produces antibodies against factor IX. The factor IX antibodies then destroy any circulating factor IX in the blood, resulting in the bleeding symptoms of hemophilia.

Hemophilia is a group of conditions that occur due to problems with clotting factors. There are multiple clotting factors and different types of hemophilia, which correspond to deficiencies of different clotting factors.

Hemophilia A is the most common type of hemophilia. Its characteristic feature is a deficiency of factor VIII due to variations in the F8 gene. Hemophilia C is also distinct from hemophilia B, as it instead occurs due to alterations in the F11 gene and affects clotting factor XI. There are also less common conditions that affect other blood clotting factors.

Hemophilia conditions typically share similar symptoms and treatment approaches but result from variations in different genes that affect different clotting factors.

Similar to other types of hemophilia, hemophilia B is an inherited bleeding disorder primarily affecting males. Evidence notes that the prevalence of hemophilia B is roughly 1 in 40,000 live males. This accounts for about 15% of cases of hemophilia.

Hemophilia B is typically a congenital condition, meaning people are born with it. In most cases, a person inherits the condition from a parent.

The F9 gene is present on the X chromosome. A male will usually inherit one X chromosome from a female parent, while females typically inherit an X chromosome from both parents. As such, males usually only require one gene alteration to develop the condition, which is why it is more common in males.

While much rarer, hemophilia can also affect females. They will typically require either two X chromosome alterations, or one with a variation and the other X chromosome is missing or nonfunctioning.

Evidence also notes that roughly 10–25% of female carriers for hemophilia B may also experience symptoms of the condition. Hemophilia B also affects all races and ethnic groups equally.

Some people may also refer to hemophilia B as the royal disease due to being prevalent in the royal families of England, Spain, Germany, and Russia.

Read on to learn more about how people inherit hemophilia.

The characteristic symptom of hemophilia is issues with blood clotting. This makes people with the condition more susceptible to prolonged periods of bleeding.

The severity of hemophilia B can range from mild to severe. The severity depends on the level of factor IX present in the blood. Symptoms of hemophilia B can include:

Severe hemophilia B

This describes a person with less than 1% clotting activity. They may experience:

  • hemophilic arthropathy, which is an irreversible type of joint damage
  • frequent and spontaneous bleeding
  • long episodes of bleeding or pain and swelling following minor injuries or surgery
  • frequent nosebleeds and easy bruising

Moderate hemophilia B

This typically refers to individuals with 1–5% clotting factor activity. Symptoms may include:

  • long episodes of bleeding following more significant injuries or surgery
  • occasional nosebleeds and easy bruising
  • occasional spontaneous bleeding

Mild hemophilia B

Mild hemophilia B usually describes factor activity between 5% and 40%. People may experience:

  • bleeding that typically only occurs after injuries, trauma, or surgery
  • infrequent or no spontaneous bleeding
  • symptoms may not manifest until later in life

Most people with severe hemophilia B will likely receive a diagnosis at birth. Individuals with moderate or mild hemophilia B may receive a diagnosis during adolescence or childhood.

The diagnosis of hemophilia B usually involves blood tests. These tests will measure the levels and activity of clotting factors. As such, the tests can also help determine the severity of hemophilia B. These may include:

  • serum IX activity
  • platelet count
  • fibrinogen level
  • prothrombin time
  • partial thromboplastin time (PTT)

A doctor may recommend genetic testing and counseling for individuals with a family history of hemophilia. These tests can help identify how likely a person is to potentially pass hemophilia to their children.

The Centers for Disease Control and Prevention (CDC) notes that hemophilia can lead to the following complications:

  • bleeding into vital organs, which can be fatal
  • bleeding in the brain, which may result in long-term issues such as seizures and paralysis
  • hemophilic arthropathy, which can lead to irreversible joint damage, pain, and limited mobility
  • anemia from blood loss

A person living with hemophilia may also develop inhibitors. This term refers to antibodies the immune system may produce, which attack replacement clotting factors a person receives to treat hemophilia. As such, inhibitors may make it more difficult to treat bleeding episodes.

Similar to treating other types of hemophilia, the primary treatment option for hemophilia B involves replacing factor IX. A person will usually receive replacement therapy through regular intravenous infusions through a vein in the arm or a port in the chest.

Before surgery or dental procedures, a doctor may also recommend aminocaproic acid. It is an antifibrinolytic, which means it prevents the breakdown of blood clots. As such, it may help to preserve a blood clot and keep it from breaking down prematurely.

Etranacogene dezaparvovec (Hemgenix) is a gene therapy that received approval from the Food and Drug Administration (FDA) in 2022 for treating hemophilia B in adults. The treatment uses a modified virus that contains copies of the F9 gene.

After injecting Hemgenix into a person’s vein, the virus travels to the liver, which allows the liver cells to produce factor IX and limit bleeding episodes.

Hemophilia B is a bleeding disorder. It typically occurs due to a variation in the F9 gene, which a person inherits from their parents.

Alterations in the F9 gene affect the production of clotting factor IX. This protein plays an important role in the formation of blood clots. Without sufficient levels of factor IX, a person is susceptible to long bleeding episodes.

Hemophilia B can vary in severity, depending on the levels present in the blood. Treatment for hemophilia B usually involves replacing the deficient factor IX to help with blood clotting and prevent excessive bleeding.