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Your guide to hemophilia A.

Everyone’s hemophilia A needs are unique. More information at your fingertips can help transform how you think about and navigate what’s right for you or your child. Read on to learn about hemophilia A inheritance, common symptoms, and hemophilia A treatment options.

What is hemophilia A?

Hemophilia A is a rare, lifelong bleeding disorder. It’s usually inherited (passed down from parent to child) but can develop later in life, too.

People with hemophilia A have a missing or deficient clotting protein called factor VIII. Without enough of this protein, blood doesn’t coagulate like it should, which can lead to spontaneous bleeding or heavy, prolonged bleeding after an injury or surgery.

The good news: modern treatments can help manage symptoms and open up new possibilities for life with hemophilia A.

80%

of people with hemophilia have hemophilia A.

How is hemophilia A inherited?

Hemophilia A is primarily a hereditary condition caused by a mutation on the X chromosome (meaning hemophilia is sex-linked). If hemophilia A runs in your family, understanding the genetics of how it’s inherited can help you make informed decisions for yourself and your family.

Father with hemophilia A, Mother without hemophilia A, Son without hemophilia A, Son without hemophilia A, Daughter with the hemophilia A gene, Daughter with the hemophilia A gene

Father without hemophilia A, Mother with the hemophilia A gene, Son without hemophilia A, Son with hemophilia A, Daughter without the hemophilia A gene, Daughter with the hemophilia A gene

Please note: This chart is meant to help clarify the inheritance pattern of hemophilia A by aligning gender identity to both sex assigned at birth and chromosomal makeup. If your gender does not match your sex assigned at birth or if your chromosomal makeup is not represented here, talk with your care team about your inheritance risk.

Male inheritance

Males inherit a Y chromosome from their fathers and an X chromosome from their mothers. If they inherit an X chromosome carrying the hemophilia A gene from their mother, they will have hemophilia A.

Female inheritance

Females inherit two X chromosomes, one from their mothers and one from their fathers. If one or both of the X chromosomes carry the hemophilia A gene, they will either have hemophilia A or be a carrier. Learn more about hemophilia in women.

What are the symptoms of hemophilia A?

Common hemophilia A signs and symptoms include:

Swelling, pain, or tightness in the joints, particularly the knees, elbows, or ankles
Bleeding after having shots, which could lead to muscle bleeds
Heavy menstrual periods
Bruising on the skin
Blood in the urine or stool
Low iron levels or anemia
Bleeding in the mouth and gums that’s difficult to stop
Frequent and hard-to-stop nosebleeds

These signs and symptoms of hemophilia A can vary based on the levels of clotting factor in your blood and the hemophilia severity. If you or someone you care for is experiencing one or more of these symptoms, contact your doctor. Bleeds that go unaddressed can potentially affect joint health. Learn more about joint health and bleed management.

Phil is a promotional speaker compensated by Sanofi.

“We’ve come a long way, and I am ecstatic that there is more awareness and understanding of hemophilia than there was when I was a kid. I encourage those of you living with hemophilia to continue educating yourselves and working with your doctor to manage your hemophilia.”

Phil, living with hemophilia

Understanding the clotting process

Knowing what happens inside your body during a bleed can help you understand the impacts of hemophilia A—and how different treatments can help.

Illustration of scales, representing balance achieved during the clotting process. Thrombin, factor VII, factor IX, factor X, and other procoagulants are on the left, and antithrombin and other anticoagulants are on the right.

The goal: balance

Your blood contains procoagulants, which help with blood clotting, and anticoagulants, which reduce clotting to help keep blood moving through your body.

When a bleed occurs, more procoagulants are needed to help stop the bleeding and regain the balance in your body. Achieving this balance is called hemostasis, and it happens in two parts.

Primary hemostasis

When a bleed first happens, platelets assemble at the site of the injury and create an initial clot called a “platelet plug” to slow the bleeding.

Secondary hemostasis

After the platelet plug forms, a multistep process called the clotting cascade is activated to help bind the platelets together and stabilize the clot.

Illustration of factor VIII, factor IX, factor X

Several clotting proteins become activated, including factor VIII.

After all of the clotting proteins are activated, they work together to generate thrombin, which is necessary to form a stable clot.

Illustration of fibrin mesh forming a blood clot

Once thrombin is activated, it helps create the crucial fibrin mesh that spreads over the platelets, binding them together into the stable clot that stops the bleeding.

The role of factor VIII

Factor VIII is one of several proteins needed to form stable blood clots. But when there isn’t enough factor VIII in the blood, the clotting cascade doesn’t produce enough thrombin to achieve hemostasis and a stable clot. This can lead to excessive or uncontrolled bleeding.

Primary hemostasis

When a bleed first happens, platelets assemble at the site of the injury and create an initial clot called a “platelet plug” to slow the bleeding.

How is hemophilia A treated?

Hemophilia A treatments are all designed to help the body achieve hemostasis, but in different ways. The right hemophilia treatment depends on your factor activity levels, whether or not you have hemophilia inhibitors, and your lifestyle and treatment goals.

Learn more about Sanofi treatments for hemophilia A:

Discover an extended half-life factor replacement therapy.

LEARN MORE