Hemophilia is a blood clotting disorder that can be inherited. Caused by changes in the X chromosome, hemophilia is an autosomal recessive genetic disorder.

Hemophilia is a genetic disorder that affects the clotting factors in the blood. If you have hemophilia, your blood does not clot as it typically would. You may experience significant bleeding with surgery or trauma.

Here’s how hemophilia is inherited, who is more likely to have the disorder, and what tests may help with diagnosis.

Learn more about hemophilia.

Hemophilia A, also called factor VIII deficiency, and hemophilia B, also called factor IX deficiency, are inherited on the X chromosome in an autosomal recessive pattern. This means that you must inherit one affected X chromosome to have the condition — in this case, hemophilia.

Generally, individuals have either two X chromosomes or one X and one Y chromosome. These chromosomes determine sex characteristics, such as if you produce eggs or sperm, have a penis or a vagina, and many other traits.

If you have a Y chromosome, you are more likely to inherit the disorder because there are no genes for clotting factors on the Y chromosome. This means that if your X chromosome carries the genes for hemophilia, you will have the condition.

If you have two X chromosomes, you may be hemophilia carriers. If you inherit one affected gene, you may be a carrier but may not have the disorder. You must inherit two affected X chromosomes to develop it, making hemophilia rarer in individuals with XX chromosomes.

There are three scenarios for how a person may inherit affected genes.

Parent with XX chromosomes carries an affected gene

If the parent with XX chromosomes is the carrier of the affected gene and the parent with XY chromosomes does not, their children with XY chromosomes have a 50% chance of inheriting the disorder. Their children with XX chromosomes, on the other hand, have a 50% chance of carrying the affected gene.

Parent with XY chromosomes has hemophilia

If the XY parent has hemophilia and passes on the affected gene, each of their XY children has a 0% chance of inheriting the disorder. However, their children with XX chromosomes have a 100% chance of carrying the affected gene.

Both parents have affected genes

If both parents carry affected genes, each of their XY chromosome children has a 50% chance of inheriting the disorder. Their children with XX chromosomes have a 50% chance of inheriting one affected gene and becoming carriers. Additionally, children with XX chromosomes have a 50% chance of inheriting two copies of affected genes and having hemophilia.

Your doctor may suggest genetic testing if you or your partner have a family history of hemophilia. Before becoming pregnant, this can be done with a blood test. Your doctor will take a blood sample and send it to a laboratory to analyze the clotting factors.

During pregnancy, your levels of factor VIII will rise, making it difficult for a blood test to determine if you are carrying the affected gene. Levels of factor IX do not rise. However, other hemophilia tests can be done during pregnancy to find out if your child will have hemophilia.

They include:

  • chorionic villus sampling, where your doctor obtains a placenta cell sample through a needle inserted into your abdomen or a thin tube inserted through your cervix
  • amniocentesis, where your doctor obtains a sample of amniotic fluid using a needle that is inserted into the uterus through the abdomen

Symptoms may appear soon after birth or within the first year of a child’s life. An infant may have bleeding in the head after delivery, or an infant with a penis may experience bleeding after circumcision.

Additional symptoms over time:

  • swelling or tightness in and around joints from bleeding into the joints
  • bruising (hematoma) from bleeding into the skin or other soft tissues
  • bleeding inside the mouth and gums or after losing teeth
  • bleeding after vaccinations or other tests and injections performed with needles
  • bleeding into the stool (may look red, tarry, or black) or urine (may be tinged red)
  • bleeding from the nose (nosebleeds) that happens frequently

Blood tests are the primary means of diagnosis if a person is experiencing symptoms of hemophilia.

Tests include:

Hemophilia is treated by replacing the blood clotting factor, a protein that is missing from the blood. Treatments include injecting clotting factor concentrates into a person’s blood through their veins.

These treatments can be used episodically to help specific bleeding episodes or prophylactically to prevent future bleeding episodes.

Other treatment options:

People with hemophilia may need treatment throughout life to prevent bleeding episodes. They may also need additional monitoring as they age. Experts share that people with hemophilia are more likely to develop other health issues, like heart disease, joint disease, and kidney issues.

That said, life expectancy for people with hemophilia may be similar to that of the general population. In one recent study, people with mild to moderate hemophilia lived only one year less on average than people who did not have the condition.

How common is hemophilia?

Hemophilia A is four times more common than hemophilia B. Recent data suggests that up to 33,000 people assigned male at birth in the United States have hemophilia. The disorder impacts around 1 in every 5,000 births of people assigned male.

Why do people with XY chromosomes not pass hemophilia onto their offspring with XY chromosomes?

People with XY chromosomes do not inherit an X chromosome from their XY parent. Instead, they inherit the Y chromosome, which does not carry the disorder.

Is hemophilia always genetically inherited?

No. About one-third of people with hemophilia have no genetic link to other family members.

Hemophilia is inherited on the X chromosome. Having this disorder or carrying it does not guarantee that your child will inherit the affected genes.

If you have a family history of this disorder, make an appointment with your doctor. You may be referred to a genetic counselor so you can better understand the potential risks.