Hemophilia A is a rare bleeding disorder caused by a genetic mutation (change). Many people with hemophilia A are diagnosed as babies or children when they experience bleeding episodes that can’t be controlled. However, families with a history of hemophilia may choose to have babies genetically tested for the mutation at birth.

Read more about hemophilia A and how it’s passed down in families, as well as what roles race, sex, and age may play in the development of this health condition.

What Is Hemophilia A?

Hemophilia A — also known as classical hemophilia — occurs when someone has below-normal levels of clotting factor VIII (8). Clotting factors are specialized proteins that help blood clot when a person bleeds. When there’s not enough of the clotting factor, bleeding may not stop, even if the wound is superficial. In more severe cases, people with hemophilia may experience spontaneous bleeds (without known cause) in the organs or joints.

Hemophilia A is caused by changes to the F8 gene, which is on the X chromosome. These genetic changes can occur spontaneously in families with no history of hemophilia, although this is extremely rare. More often, this mutation is passed down from parents to children.

The genetic changes affect some people more than others, although researchers aren’t always sure why. Doctors will do blood tests to determine how much factor VIII a person has, and that level will determine how severe their hemophilia is and the kind of medical care they need.

Hemophilia A is considered mild when factor levels are above 5 percent but under 40 percent of the normal levels. The condition is assessed as moderate when factor levels are 1 percent to 5 percent, and levels below 1 percent are considered severe.

Read more about how the severity of hemophilia is assessed.

What Are the Symptoms of Hemophilia A?

The most common symptom of hemophilia A is bleeding that won’t stop or keeps starting again after it ends. People with hemophilia A don’t necessarily bleed more often or faster than others, but they lose more blood because of the continued bleeding.

This bleeding isn’t always apparent only on the skin. It often occurs internally, into muscles or joints. Joint bleeds can damage joints, sometimes leading to chronic pain or disability. People with hemophilia may also be likely to have nosebleeds that won’t stop, bruise often and severely, and vomit blood.

For people with mild hemophilia A, prolonged bleeding may occur only after medical procedures, like surgery or dental extractions, or from minor injuries. People with moderate hemophilia A are more likely to also experience bleeding without a cause (spontaneous bleeding) or bruise easily.

Babies with severe hemophilia A may be fussy because they’re in pain from bleeds. They may also experience large hematomas (areas of congealed blood under the skin’s surface), develop lumps on their heads or other places from bleeding, or even have breathing trouble related to bleeding issues.

How Common Is Hemophilia A?

In the United States, hemophilia A occurs in about 1 out of every 5,617 male births, per new statistics from the Centers for Disease Control and Prevention (CDC), and about 30,000 to 33,000 males are living with hemophilia. “Hemophilia A is four times as common as hemophilia B,” according to the National Bleeding Disorders Foundation.

These estimated numbers don’t include people with mild or moderate hemophilia A who may not know that they have the condition. For example, women and people assigned female at birth can also have hemophilia but aren’t affected as often as others, according to Cleveland Clinic. In a 2021 study in the journal Haemophilia, about 16 percent of participants with mild hemophilia A were female, but moderate or severe disease among females was less common.

Is Hemophilia More Common in Some Races Than Others?

Hemophilia A can occur in anyone, regardless of race or ethnicity. Researchers have yet to determine if it might be more common in certain populations.

A 2020 study compared the prevalence (number of affected people) of hemophilia A and hemophilia B among U.S. males. The researchers reported prevalence rates of:

• 15.1 per 100,000 for non-Hispanic white males
• 12.4 per 100,000 for non-Hispanic Black males
• 12.4 per 100,000 for Hispanic males of either race

The findings suggest that race and ethnicity may play a role in the prevalence of hemophilia, but there’s not enough data to be certain.

Researchers have also looked into differences in how hemophilia affects racial and ethnic groups. One small study found that, among people ages 13 to 25 with hemophilia, the non-white participants were more likely to develop inhibitors. Inhibitors are antibodies produced by the immune system to attack infused clotting factor concentrates. Having inhibitors can make standard replacement therapy or treatment options less effective or ineffective.

More research is needed to fully understand whether hemophilia A affects members of some racial and ethnic groups more than others — and if so, why.

Why Are Males More Likely To Have Hemophilia A?

Hemophilia A and B involve sex-linked recessive inheritance. The F8 mutation in the factor VIII gene is located on the X chromosome. Males inherit one X chromosome only from their mothers, while females inherit two X chromosomes, one from each parent, according to the CDC.

If the mother passes down the F8 mutation on the X chromosome to a male child, that child will have hemophilia. Females must inherit the F8 mutation from both parents to develop hemophilia. People assigned male at birth need only one copy of the mutated X chromosome, so they’re more likely to develop hemophilia.

Genetic Carriers

People assigned female at birth who inherit just one copy of an X chromosome with the F8 mutation become hemophilia carriers — they don’t have the condition, but they can pass it down to their children. “For each man with hemophilia, 1.6 female carriers can be identified,” wrote the authors of a 2020 study in the Journal of Thrombosis and Haemostasis.

If you have hemophilia A or are a carrier, you can’t reduce the risk of passing it down to your children. You can undergo genetic testing to look for the mutation that causes hemophilia A. Genetic counseling may be available to help you better understand your and your family’s risk of developing hemophilia A.

When Does Hemophilia A Usually Develop?

People who have hemophilia A are born with the condition. Severe disease often shows up during or shortly after birth, such as with prolonged bleeding after undergoing circumcision. People with moderate hemophilia A usually develop symptoms as toddlers. Mild cases are generally diagnosed later, during adolescence or adulthood, unless a child with hemophilia A has surgery or a dental procedure.

How Is Hemophilia A Managed?

Hemophilia A is a lifelong condition that can’t be cured, but it can be treated. Replacement clotting factor therapy has greatly improved the life expectancy and quality of life for individuals with hemophilia.

In addition, the first gene therapy for people with severe hemophilia A, Valoctocogene roxaparvovec-rvox (Roctavian), was recently approved by the U.S. Food and Drug Administration. It’s given as a one-time IV infusion and provides a working copy of the gene for factor VIII.

If you or your child has hemophilia A, be sure to follow the treatment plan closely to prevent serious bleeding episodes. Be open with your health care provider about any concerns, and keep up with regular hematology appointments to ensure getting the most effective treatment possible.

Talk With Others Who Understand

MyHemophiliaTeam is the social network for people with hemophilia and their loved ones. On MyHemophiliaTeam, more than 6,100 members come together to ask questions, give advice, and share their stories with others who understand life with hemophilia.

Are you or a loved one living with hemophilia A? Do you have more questions about who is most likely to get this condition? Share your experience in the comments below, or start a conversation by posting on your Activities page.