What Is Hemophilia?

Hemophilia is a rare bleeding disorder caused by deficiencies in specific clotting factors — the proteins that help blood form clots to prevent excessive bleeding.

Causes of hemophilia

The loss of clotting factors in hemophilia is usually caused by inherited mutations in the genes that provide the instructions for making them. However, in some cases, these mutations can occur spontaneously.

In rare cases, a malfunction in the body’s immune system can result in a type of acquired hemophilia in the absence of mutations in clotting factor genes.

Types of hemophilia

There are several types of hemophilia, with the different forms dependent on their specific underlying cause.

Hemophilia A typically occurs due to mutations in the F8 gene, while alterations in the F9 gene cause hemophilia B. These mutations lower the levels of clotting factor VIII (FVIII) in the case of hemophilia A, and factor IX, known as FIX, in hemophilia B.

These two types of hemophilia tend to affect males more than females, since both F8 and F9 genes are found on the X chromosome. While women inherit two such chromosomes, men inherit only one. This means that males need only to inherit one faulty X chromosome from their mothers to develop either condition.

A rarer form of the disease, hemophilia C stems from mutations in the F11 gene that encodes factor XI (FXI). However, since this gene is not located on the X chromosome, hemophilia C affects males and females equally. In rare cases, this type of hemophilia can be acquired instead of being inherited; this usually is associated with an underlying disorder.

Lastly, acquired hemophilia occurs when the immune system mistakes a clotting factor — usually FVIII — for something foreign and potentially harmful to the body, mounting an immune reaction against it.

Symptoms of hemophilia

Prolonged and excessive bleeding are hemophilia’s main symptoms.

Often such bleeding occurs internally, manifesting as bruises and painful swelling in the joints. Internal bleeding can be of greater concern than external bleeding, since it can lead to more serious complications. Other common types of bleeding associated with hemophilia include unexplained nosebleeds, blood in the stool or urine, and bleeding gums.

Bleeding patterns vary depending on the type and severity of an individual’s hemophilia. Bleeds also may occur spontaneously, without a clear reason, or after a traumatic event, such as surgery or a serious injury.

Diagnosis of hemophilia

A diagnosis of hemophilia is generally made through a combination of family history and blood tests that assess the body’s ability to make blood clots. Other tests typically measure the levels of several clotting factors. These clotting factor tests allow physicians to determine the specific type of hemophilia a patient has, as well as its severity, which are both critical in selecting an appropriate treatment plan.

Prenatal screening tests also exist to assess the presence of hemophilia in a developing fetus prior to birth. These tests, which typically are performed in families that have a history of the disease, enable physicians and the child’s family to prepare and start treatment as early as possible.

Treating hemophilia

Although treatment varies based on the type and severity of hemophilia, in most cases it involves supplying the missing clotting factor to patients. This form of treatment is known as replacement therapy. While factor replacement is possible in the U.S. for FVIII and FIX, FXI — used to treat hemophilia C — is still unavailable.

More recent replacement therapies include extended half-life products, such as Alprolix and Eloctate. These require fewer infusions to maintain clotting factor levels within an acceptable range, posing a lesser burden to patients compared with standard products.

Factor replacement therapies can be administered prophylactically, or as a preventive measure, to prevent bleeds from occurring, or on-demand to stop them once they have started.

Other treatments include antifibrinolytics, which slow the breakdown of blood clots, and bypassing agents, which are sometimes used to overcome the resistance some patients develop to replacement therapies.

Physiotherapy also forms an essential part of hemophilia’s overall management plan. This treatment helps to increase patients’ range of motion, ease joint pain and swelling, and repair injured muscles.


Last updated: July 23, 2021


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