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Hemophilia A is a rare bleeding disorder in which a person’s blood doesn’t clot easily. It happens when a person makes too little of a type of clotting factor called factor VIII (or factor 8). Without enough factor VIII, a person may bleed longer after an injury, have large bruises, or develop painful, swollen joints. Hemophilia A is often passed down through family members due to changes in their DNA.
After receiving a hemophilia A diagnosis, some people may choose to have genetic testing. This testing looks for specific changes in DNA — called variants or mutations — that affect how the body makes clotting factors. Some families decide to get tested, while others choose not to.
Genetic testing looks for changes in a person’s DNA. DNA is like a set of instructions that tells the body how to make proteins it needs to stay healthy. Sometimes, mutations stop a gene from working correctly, and the body may not be able to make the proteins it needs. This can lead to problems such as hemophilia.
Genetic testing usually uses DNA from a blood sample to look for specific changes in genes that may affect a person’s health.
People may choose genetic testing for different reasons. The results can confirm a diagnosis or rule out other conditions. Genetic testing for hemophilia can also diagnose the condition in a fetus. This can help parents prepare for having a child with hemophilia.
Genetic testing can also show if a person is a carrier of a gene mutation. Carriers have one regular copy of a gene and one mutated copy. Carriers often have no symptoms, or only mild ones, because the working gene can usually do the job.
Genetic testing for hemophilia A is usually done to find out the exact gene mutation a person has after they’ve been diagnosed. Testing often confirms earlier blood test results showing low levels of clotting factor VIII. Family members may also choose to get tested to see if they carry the gene change linked to hemophilia A.
Hemophilia is a genetic disorder, which means it’s passed down in families. The gene involved is located on the X chromosome, so hemophilia is called an X-linked recessive disorder.
Most females have two X chromosomes, and most males have one X and one Y chromosome. A female inherits one X chromosome from each parent. A male inherits an X chromosome from their mother and a Y chromosome from their father. However, not everyone fits this pattern. Some people have different chromosome combinations due to genetic conditions or other biological differences.
A mother who has a gene mutation for hemophilia on one X chromosome can pass it on to their children. A daughter is less likely to develop hemophilia. Even if they inherit the gene from their mother, the other X chromosome — usually from their father — can provide a working copy of the gene. A daughter with one changed X chromosome and one typical X chromosome is called a carrier.
Rarely, women can develop hemophilia, according to the Centers for Disease Control and Prevention (CDC). This may happen if one of their X chromosomes is missing (such as in Turner syndrome) or if the X chromosome with the healthy gene becomes inactive. This process is called lyonization.
Hemophilia is caused by changes in genes that make clotting factors. The F8 gene provides instructions for making factor VIII. When this gene doesn’t work correctly, a person develops hemophilia A. The F9 gene makes factor IX, and mutations in this gene cause hemophilia B.
Two common mutations that cause hemophilia affect the F8 gene. These changes happen in portions of DNA called introns, which are numbered based on their location in the DNA sequence. People with hemophilia A can have an intron 1 or intron 22 inversion, meaning the DNA is flipped in the wrong direction. This affects the production of factor VIII, leading to hemophilia A symptoms.
Other types of mutations that can cause hemophilia A include:
Hemophilia B can be caused by one of more than 3,000 mutations in the F9 gene. These include duplications, insertions, and deletions.
Genetic testing for hemophilia typically confirms the type of mutation. If there’s a family history of hemophilia, doctors may run a specific test, such as an intron 22 inversion assay, to check for the same mutation seen in other relatives.
When there’s no known family history, broader testing is needed. Doctors often use next-generation sequencing to look at the F8 or F9 genes for any changes. This method can also identify female carriers of hemophilia.
Modern genetic testing can identify nearly all mutation types, from large DNA inversions to small changes. This means that most people with hemophilia A can now learn their exact genotype (genetic variant type). Knowing this information helps doctors better understand a person’s bleeding symptoms and make more informed decisions about treatment and family planning.
In addition to confirming a diagnosis, genetic testing can help doctors predict how a person might respond to treatment with coagulation factor concentrates. Some people develop inhibitors — antibodies that attack and destroy clotting factor treatments, making them less effective. Knowing a person’s genotype may give doctors some insight into this risk and help guide the choice of treatment.
Testing is also valuable for family members. It can identify who carries the gene, especially female carriers, and support family-planning decisions. Knowing carrier status allows people to prepare for the chance of having a child with hemophilia. Some carriers may also have mild hemophilia or other bleeding symptoms. Testing can help connect them with hematology providers for the care they need.
Deciding whether to have genetic testing is a personal choice. Some people feel reassured after getting their test results, while others may find the information overwhelming. It’s important to consider your own needs — and your family's — when making this decision.
If you’re unsure what to do, ask your doctor for a referral to genetic counseling. A genetic counselor can help you understand your hemophilia diagnosis, review your carrier status, and discuss how results may affect your treatment, family planning, and emotional health. They can also connect you to helpful resources and additional support.
The cost of genetic testing can vary widely. It depends on the type of test, such as a targeted mutation test or next-generation sequencing, and the laboratory that performs it. Many insurance plans cover testing if it’s ordered by a healthcare provider, but coverage rules differ.
If your insurance doesn’t cover the test, you may have out-of-pocket costs. The best way to prepare is to contact your insurance company. They can explain what your plan covers and what your testing options are.
To learn more about genetic testing and whether it’s right for you and your family, talk with your doctor. 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, including costs, as well as how the results may affect your treatment plans and peace of mind.
On MyHemophiliaTeam, people share their experiences with hemophilia, get advice, and find support from others who understand.
Have you or a loved one had genetic testing for hemophilia? Let others know in the comments below.
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