Hemophilia B (HEMB) is a condition that causes prolonged bleeding because the body does not have enough of a protein called factor IX, which is crucial for blood clotting.
HEMB comes in three levels of severity: severe, moderate, and mild.
Severe Hemophilia B: Symptoms usually appear in the first two years of life. Without regular treatment, people with severe HEMB can experience excessive bleeding after injuries and spontaneous bleeding into muscles and joints, leading to pain, swelling, and permanent joint damage.
Moderate Hemophilia B: Symptoms often show up between the ages of five and six. People with moderate HEMB also bleed for longer after injuries but have fewer spontaneous bleeding episodes than those with severe HEMB.
Mild Hemophilia B: People with mild HEMB typically only have prolonged bleeding after major injuries or surgeries and may not be diagnosed until later in childhood or adulthood. They may go years without a bleeding episode.
There is no cure for HEMB, but treatment focuses on replacing the missing factor IX protein, especially after injuries or before surgery. Those with severe HEMB may need regular IV infusions to prevent spontaneous bleeding. It’s also important for people with hemophilia to avoid high-risk activities, particularly those with a risk of head injury. Regular checkups with a hemophilia specialist are recommended. In 2022, the FDA approved a gene therapy called Hemgenix for adults with moderate to severe HEMB. This single-dose therapy offers a new treatment option for managing the condition.
HEMB is caused by pathogenic variants in the F9 gene that exhibit X-linked recessive inheritance. This means that one pathogenic variant is enough to cause the disease in both individuals assigned male at birth (who have one X chromosome and one Y chromosome) and individuals assigned female at birth (who have two X chromosomes) may experience symptoms depending on how many copies of the X chromosome that has the pathogenic variant are turned on in the cells.
Approximately 30% of female carriers will have symptoms that are more often mild but can be severe in some circumstances.
Resources:
The Coalition for Hemophilia B
Hemophilia Federation of America
Written August 2024
