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Normally, bleeding is supposed to stop quickly after a cut or injury. However, for people with hemophilia A, it doesn’t always work that way. This rare condition makes blood take much longer to clot because the body has too little of a protein called factor VIII (also written as factor 8 or F8). When there’s not enough of this clotting protein, even a small scrape can become a serious problem.
In this article, we’ll discuss who gets diagnosed with hemophilia A and why. We’ll look at how family history, sex, age, and race may play a role, and what this means for people living with this disorder and their family members.
Hemophilia A — also known as classical hemophilia — is a congenital bleeding disorder. Congenital means you’re born with it — it’s not something you catch later in life. Hemophilia A occurs when the body makes low levels of factor VIII, a clotting protein needed to stop bleeding. Without enough factor VIII, blood doesn’t clot properly. This means bleeding can last too long, even after a small cut. In severe cases, bleeding may happen inside the body for no clear reason (spontaneous bleeding). This can affect joints, soft tissues, or even organs, and may cause long-term joint disease or pain.
Hemophilia A is an X-linked condition caused by changes in the F8 gene, which is located on the X chromosome. This gene is usually passed down through families, though it can also appear in people with no family history of the condition. Doctors confirm the diagnosis with blood assays (tests) that measure factor VIII activity.
There’s also a rare condition called acquired hemophilia A, which develops later in life when the immune system attacks factor VIII. However, this condition is different from the congenital form.
The severity of hemophilia depends on factor VIII levels:
The most common symptom of hemophilia A is bleeding that won’t stop or keeps restarting after it ends. People with hemophilia A don’t bleed faster than others, but they lose more blood because clotting takes longer.
Bleeding can happen on the surface of the skin or inside the body. Internal bleeding often occurs in joints or soft tissues. Repeated bleeding in the joints may cause swelling, pain, and long-term joint disease.
Other common signs and symptoms of hemophilia A include:
One of the most serious risks of severe hemophilia A is hemorrhage (bleeding) in the brain. This can be triggered by even a small bump, and while rare, it can be life-threatening. Warning signs include:
If you experience any of these symptoms, seek emergency medical care right away.
Babies with severe hemophilia A may be fussy because they’re in pain from bleeds. They may also experience large hematomas, develop lumps on their heads or elsewhere from bleeding, or even have difficulty breathing because of bleeding issues.
According to the U.S. Centers for Disease Control and Prevention (CDC), about 12 out of 100,000 males are born with hemophilia A in the U.S. Each year, about 400 boys are born with the condition, according to the National Bleeding Disorders Foundation. Researchers there estimate that around 30,000 to 33,000 males in the U.S. currently have hemophilia.
However, these numbers only reflect people who have been diagnosed and entered into publicly accessible registries. Many people with mild or moderate hemophilia may not even know they have it. So, the true number of people living with the condition could be higher.
Although hemophilia A is much less common in females, it can happen. Women and people assigned female at birth may also have low levels of factor VIII, especially if they inherit an altered gene from both parents. One study found that about 18 percent of participants with mild hemophilia A were female. However, moderate or severe cases in females are very rare.
Hemophilia A can affect people of any race or ethnic group. Current research shows no strong genetic link to a specific population. Still, studies suggest that the prevalence (number of affected people) may vary slightly across demographic groups.
A 2020 study compared the prevalence of hemophilia A and hemophilia B among U.S. males. In the journal Haemophilia, researchers reported prevalence rates of:
These differences are small. Experts believe they may reflect differences in diagnosis, access to hemophilia treatment centers, and reporting, rather than true biological risk factors tied to race.
Recent research using data from more than 6,000 people with hemophilia A found that Black and Hispanic males with severe hemophilia were more likely to develop inhibitors than white males. Inhibitors are antibodies (specialized proteins) produced by the immune system that 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.
Hemophilia A is an X-linked condition, meaning the F8 gene change is carried on the X chromosome. People assigned male at birth have one X and one Y chromosome. If their single X chromosome has the altered F8 gene, they will have hemophilia.
People assigned female at birth have two X chromosomes. If one X chromosome carries the mutation, the other usually makes enough factor VIII to balance out the lower production. This protection means both X chromosomes must carry the mutation for hemophilia to fully develop, which is very rare. Another rare mechanism in which women may develop hemophilia is a process called lyonization, which involves one X chromosome becoming inactivated. As a result, the other X chromosome carrying the mutated (changed) gene for factor VIII causes hemophilia.
According to the CDC, females who inherit one altered X chromosome with the F8 mutation are called carriers. Carriers can pass the gene change to their children, even if they don’t have hemophilia themselves. One study found that for every male with hemophilia, there are about 1.6 female carriers.
Some women and girls who are carriers can still have bleeding symptoms, according to the CDC. This happens because their factor VIII levels are lower than normal, even with one working copy of the gene. Symptoms are often milder than in males, but in rare cases, carriers can still experience bleeding as severe as males with hemophilia.
If you have hemophilia A or are a carrier, genetic testing and genetic counseling can help you and your family understand the risks.
People are born with hemophilia A, but symptoms may appear at different ages. Severe hemophilia is often discovered in newborns, sometimes after circumcision (surgical removal of foreskin). Moderate hemophilia may not be noticed until early childhood if a toddler shows unusual bruising. Mild hemophilia may be diagnosed in adolescents or young adults, often after surgery, dental work, or injury.
Hemophilia A is a lifelong condition, but treatments now help people live healthier, longer lives. Replacement therapy with factor VIII has been the standard, raising factor levels to prevent or stop bleeding episodes. Many people use it on a prophylactic (preventive) schedule to protect joints and improve quality of life.
Newer nonfactor therapies are also available. These treatments don’t replace factor VIII directly. Instead, they help the blood clot in other ways. They can be used in people with or without inhibitors. Nonfactor options are often given as injections under the skin and may require less frequent dosing than traditional infusions.
In 2023, the U.S. Food and Drug Administration (FDA) approved the first gene therapy for adults with severe hemophilia A. This one-time intravenous (IV) infusion provides a working copy of the factor VIII gene. Eligibility depends on health status and prior treatments, so not everyone will qualify.
If you or your child has hemophilia A, follow your treatment plan closely to prevent serious bleeding episodes. Be open with your healthcare provider about any concerns, and keep up with regular hematology appointments to get the most effective treatment possible.
On MyHemophiliaTeam, people share their experiences with hemophilia, get advice, and find support from others who understand.
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