hemophilia B

What is Hemophilia B?

Hemophilia B (HEMB) is a condition that causes prolonged bleeding. It is caused by harmful changes (variants) in the F9 gene. Individuals with HEMB do not have enough of an important protein called factor IX (nine). This protein helps to form blood clots after an injury. Individuals with the condition may experience life-threatening blood loss after an injury or medical procedures. HEMB is an X-linked disease. This means the condition is typically more severe in biological males (XY). However, biological females (XX) may also have symptoms of the condition.

HEMB has different levels of severity: severe, moderate, and mild. The severity of the condition depends on how much factor IX an individual has. The type of harmful change an individual has can help determine which severity they are at risk for. All individuals with a harmful change in F9 should speak with a genetic counselor to understand their risks.

The symptoms of each level of severity are described below.

Severe hemophilia B

Individuals with severe HEMB usually have less than 1% factor IX clotting activity. These individuals often show symptoms in the first two years of life. Without ongoing treatment, they can experience excess bleeding after injury and episodes of spontaneous bleeding into muscles and joints. These episodes can lead to joint pain, swelling, and permanent damage.

Moderate hemophilia B

Individuals with moderate HEMB usually have 1-5% factor IX clotting activity. These individuals often show symptoms in the first five to six years of life. Individuals with the moderate form also experience prolonged bleeding after injury, but they have less spontaneous bleeding than individuals with the severe form.

Mild hemophilia B

Individuals with mild HEMB usually have 6-40% factor IX clotting activity. These individuals often only experience prolonged bleeding after severe injury or surgery. These individuals may not be identified as having the condition until late childhood or adulthood. Individuals with the mild form may go years between prolonged bleeding episodes.

Additional considerations for carriers

About 30% of carrier females will exhibit symptoms. Most symptomatic carriers will have mild HEMB. However, there can be a wide range of severities.

How common is Hemophilia B?

The incidence of HEMB in the population is 1 in 20,000 to 1 in 30,000 male births.

How is Hemophilia B treated?

There is no cure for HEMB. Treatment for the condition is directed at replacing the missing factor IX protein in situations where the individuals need it. This is usually after an injury and before surgery or dental work. Individuals with severe disease may receive factor IX through an IV more regularly to prevent spontaneous bleeding episodes. Individuals diagnosed with hemophilia will often benefit from avoidance of high-risk activities, especially those with a high risk of head injury. Regular checkups with a physician specializing in treating hemophilia are recommended.

In addition to factor IX treatment, in 2022, the FDA approved a gene therapy treatment called etranacogene dezaparvovec–drlb (Hemgenix). This single-dose therapy is approved for use in adults with moderate to severe HEMB.

What is the prognosis for an individual with Hemophilia B?

With treatment, individuals with HEMB have a good prognosis with a normal or near-normal lifespan. Individuals with HEMB are at higher risk of early death due to bleeding in the brain.