Hemophilia B is a rare genetic bleeding disorder in which a person’s blood is unable to clot properly, which can lead to episodes of uncontrolled and spontaneous bleeding. Also known as Christmas disease, hemophilia B occurs when a person’s body can’t produce enough clotting factor IX (9). You will usually see Roman numerals in any discussion of clotting factors. Risk factors include having a family history of bleeding and being male. About 30 percent of people with hemophilia B don’t have a family history of it.

Some people opt to undergo genetic testing after receiving a hemophilia B diagnosis. This type of testing identifies mutations — specific changes in DNA — that affect a person’s ability to make clotting factors.

Members of MyHemophiliaTeam sometimes ask about genetic testing. “Just wondering what the recommendations have been for testing children and grandchildren for genetic hemophilia. What age is recommended? Generally, how would insurance view coverage for familial blood testing?” asked one member.

What Is Genetic Testing?

Genetic testing looks for changes in a person’s DNA that may cause certain diseases, including hemophilia. It entails examining a blood sample for specific gene changes. Genes provide instructions for making proteins. Sometimes, genes have mutations that impair their function, and they can’t properly produce proteins. This can lead to diseases and other health conditions.

How Is Hemophilia B Inherited?

Hemophilia is a recessive X-linked disorder, meaning the genes involved are found on the X chromosome and only one mutated gene copy is necessary for the disease to occur.

Females have two X chromosomes, one inherited from each parent. Males have an X and a Y chromosome: The X chromosome comes from their mother, and the Y chromosome comes from their father.

A mother who has a mutated factor IX gene on one of their X chromosomes may pass it along to their children. In this situation, a daughter has a 50 percent chance of becoming a carrier of the mutated gene. A daughter is less likely to develop hemophilia: Even if they receive the mutation from their mother on one X chromosome, the X chromosome from their father can compensate with a healthy gene.

A son of that mother has a 50 percent chance of receiving the X chromosome containing the mutation and developing hemophilia. This is because the Y chromosome can’t compensate for it the way the second X can in the daughter.

Genetic Testing and Hemophilia B

For people diagnosed with hemophilia, genetic testing is mainly used to see which type of mutation they have. Typically, these tests confirm the results of blood tests that show low levels of clotting factors. Family members may also undergo genetic testing to see if they have a mutated gene.

Gene Mutations in Hemophilia B

Two X chromosome genes are involved in hemophilia: the F8 gene and the F9 gene. The F9 gene provides instructions for making factor IX, the gene associated with hemophilia B.

Hemophilia B can be caused by one of more than 900 mutations in the F9 gene. These include:

• Duplications — The same pieces of DNA are repeated.
• Insertions — Extra pieces of DNA are added.
• Deletions — Some pieces of DNA are missing.

Learn more about the similarities and differences between the main forms of hemophilia.

Genetic Testing for Hemophilia B

Genetic testing can confirm a hemophilia diagnosis and the type of mutation causing it. Genetic tests for hemophilia can look for different deletions and duplications of pieces of DNA in the F9 gene or search for a specific mutation.

Next-generation sequencing can also be used to:

• Confirm on a molecular level a clinical diagnosis of hemophilia B in males
• Identify changes in the F9 gene
• Help determine whether a female with a family history of hemophilia B is a carrier
• Confirm whether a fetus has hemophilia B

“For the most accurate genetic test, a male relative with hemophilia should have a genetic test to locate the gene change in the family,” according to Nationwide Children’s Hospital.

Benefits of Genetic Testing for Hemophilia B

Genetic testing can yield valuable information on mutations in a person’s DNA. It can also help predict someone’s response to treatment. During or after hemophilia treatment, some people develop antibodies known as inhibitors. These antibodies attack and destroy the clotting factors, making them ineffective. Genetic testing may offer doctors some insight into who may develop inhibitors, which can help them select the best treatment plan.

Genetic testing can help a person determine if they are a carrier, which can assist with family planning. Additionally, some carriers have mild hemophilia symptoms and — prior to genetic testing — don’t know why. Testing can help them get any necessary treatment.

“I am a mom of a hemophiliac, but I am being tested. Finally, they are taking me seriously that I have issues too, and bleeding problems, after suffering for years,” a MyHemophiliaTeam member wrote.

Is Genetic Testing Right for You?

When deciding on genetic testing, it’s important that you take yourself and your family’s needs into consideration. Many people find knowing the results beneficial, but others may find the test results stressful.

If you need help understanding or processing a diagnosis, your doctor may provide a referral to a genetic counselor. Genetic counseling can help you and your family better understand your hemophilia diagnosis and how it affects your lives. Genetic counselors can also provide resources and support for emotional and financial concerns.

How Much Does Genetic Testing for Hemophilia B Cost?

Insurance will generally cover genetic testing as long as it’s ordered by a health care provider. Calling your insurance company before undergoing testing is prudent to ensure it’s covered.

Out-of-pocket costs vary and typically depend on the type of testing. For example, testing from the University of Pennsylvania ranges from $360 to $840.

Talk to Your Doctor About Genetic Testing for Hemophilia B

Talk to your doctor to learn more about genetic testing. They may refer you to a hemophilia treatment center for testing and treatment. Ultimately, the decision to be tested is up to you and your family. Be sure to consider the pros and cons of testing, including costs, how the results may affect your treatment plans, and the benefits of knowing the results.

Find Your Team

On MyHemophiliaTeam, people living with hemophilia come together to ask questions, give advice, and share their stories with others who understand life with the condition.

Have you or a loved one had genetic testing for hemophilia? What was your experience? Share your hemophilia journey in the comments below, or start a conversation by posting on your Activities page.