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.
Health
Related Websites
The National Cancer
Institute
The National Eye
Institute
The National Heart, Lung,
and Blood Institute

National Institute on
Aging

National Institute of
Allergy and Infectious Diseases

National Institute of
Arthritis and Musculoskeletal and Skin Diseases

National Institute of
Diabetes and Digestive and Kidney Diseases

National Institute on Drug
Abuse

National Institute of Mental
Health

National Institute of
Neurological Disorders and Stroke
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