Hemophilia B occurs when clotting factor IX is either absent or not present in sufficient amounts.1 Hemophilia B is also known as Christmas disease. It is named after the first person to be diagnosed with the disorder in 1952, Stephen Christmas.1 As the second most common type of hemophilia, it occurs in about 1 in 25,000 male births and affects about 4,000 individuals in the United States.1,2
The severity of hemophilia B is related to the amount of clotting factor that is either missing or deficient.3
Patients with severe hemophilia B are usually diagnosed around birth or within the first two years of life. Moderate hemophilia B may not be diagnosed until ages 5 or 6 while mild hemophilia B may not be diagnosed until later in life—and even on into adulthood.1
When considering the levels of severity, keep in mind that individual bleeding patterns vary, and in some cases people with severe hemophilia do not have frequent bleeding or spontaneous bleeds, while others with moderate hemophilia may have more bleeding than expected.4
If hemophilia B is suspected, blood tests are often used to measure how long it takes blood clots to form. However, a specific factor IX activity test must be performed to confirm the diagnosis of hemophilia B, or another clotting factor deficiency since mild cases may not be detected otherwise.
“When my first boy was diagnosed, there was shock and disbelief.” — Jane, parent
Once the diagnosis of hemophilia B is made, genetic testing can help predict a patient’s risk of developing inhibitors to factor treatment. Analysis of the specific gene mutation can also help identify female carriers of hemophilia B in a given family. Genetic information like this can also help in the prior-to-birth diagnosis of hemophilia B in other carrier pregnancies.1
Hemophilia B is an inherited disorder that is more common in males. However, approximately 10% to 25% of female hemophilia B carriers will develop mild symptoms—and have been known to have moderate and severe symptoms.1
The diagram above shows how the mutated gene found on the X chromosome is inherited. Because hemophilia is an X-linked recessive disorder, it can only be passed from a mother to her child via the X chromosome. A female who has one of the affected gene mutations is known as a 'carrier.'2
This diagram shows the inheritance pattern of a mother who is a carrier and a father who does not have hemophilia.2 Each pregnancy has a 25% chance of resulting in a male with hemophilia, a 25% chance of resulting in an unaffected male, a 25% chance of an unaffected female, and a 25% chance of a female carrier.1,2
In rare instances, females may also develop hemophilia if both of their X chromosomes have the mutation or one is affected and the other is missing or inactive.2
Although very rare, hemophilia B does have available treatment options.
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