About Hemophilia

Hemophilia is an inherited bleeding disorder^* caused by a shortage of “clotting factors”—proteins in the blood that are needed to seal wounds and stop bleeding. People with hemophilia are unable to form an effective clot to stop bleeding, such as after an injury or during a dental procedure. Bleeding can also occur inside a joint (hemarthrosis).

Hemophilia A or “classical hemophilia” is the most common type of hemophilia, making up about 80% of cases. It is caused by a deficiency of a specific clotting factor known as factor VIII (FVIII). An insufficient amount of clotting factor IX results in Hemophilia B, which accounts for most of the remaining 20% of hemophilia cases.

With few exceptions, hemophilia affects males; about 1 in 8,000 boys is born with hemophilia. (While it is very rare, girls can be born with hemophilia if they have a male relative with hemophilia. See Rhonda’s story: Kristin’s surprise diagnosis.)

A father with hemophilia cannot pass it to his sons. A son can only get the hemophilia gene if his mother is a “carrier”—that is, she has the X chromosome on which the gene for hemophilia resides. All women whose fathers have hemophilia are carriers. Sons born to female carriers have a 50% chance of having hemophilia. Daughters born to female carriers have a 50% chance of being carriers themselves, unless their father has hemophilia.

^*In rare cases, hemophilia can be acquired rather than inherited. Usually older adults are affected and the cause is typically an autoimmune disorder, cancer, or reaction to certain drugs. Joint bleeds in this kind of hemophilia are uncommon.

Learn about Signs and Symptoms of hemophilia.