What is hemophilia?

Hemophilia is a bleeding disorder that slows down the blood clotting process. People who have hemophilia often have longer bleeding after an injury or surgery. People who have severe hemophilia have spontaneous bleeding into the joints and muscles. Hemophilia occurs more commonly in males than in females.

The two most common types of hemophilia are hemophilia A (also known as classic hemophilia) and hemophilia B (also known as Christmas disease). People who have hemophilia A have low levels of a blood clotting factor called factor eight (FVIII). People who have hemophilia B have low levels of factor nine (FIX).

The two types of hemophilia are caused by permanent gene changes (mutations) in different genes. Mutations in the FVIII gene cause hemophilia A. Mutations in the FIX gene cause hemophilia B. Proteins made by these genes have an important role in the blood clotting process. Mutations in either gene keep clots from forming when there is an injury, causing too much bleeding that can be difficult to stop.

Hemophilia A is the most common type of this condition. One in 5,000 to 10,000 males worldwide have hemophilia A. Hemophilia B is less common, and it affects 1 in 20,000 to 34,500 males worldwide.