Childen's Hospital Boston 300 Longwood Avenue
Boston, MA 02115
(617) 355-6000
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Clinical Services (Boston Hemophilia Center):
About Hemophilia
Hemophilia is an inherited bleeding, or clotting, disorder. People with hemophilia lack specific blood proteins, called factors, that are necessary for clotting. The two most common genetic factor deficiencies are factor VIII deficiency (hemophilia A) and factor IX deficiency (hemophilia B). In the US, there are about 20,000 people with hemophilia. Each year, approximately 400 babies are born with the disorder. Most people with hemophilia are male, but women, who may or may not have symptoms, are carries of the disorder.

There are three main forms of hemophilia:

  • Hemophilia A - caused by a lack of factor VIII; approximately 85 percent of hemophiliacs have type A disease.
  • Hemophilia B - caused by a deficiency of factor IX.
  • von Willebrand disease - caused by low levels of another clotting factor protein, von Willebrand factor. This factor helps platelets (blood cells that control bleeding) attach to the lining of a vein or artery. When this factor is absent or deficient, there is an increased risk of bleeding.
Hemophilia is also divided into categories - mild, moderate, or severe - that reflect the levels of clotting factor in the blood. Since hemophilia "breeds true," the levels of severity are the same within families, but vary from one family to the next. The level of severity usually remains consistent throughout life.

Mild Hemophilia

  • Factor levels are greater than 5% of normal levels
  • Bleeding episodes are usually related to surgery or dental work
  • Joint bleeding is rare
Moderate Hemophilia
  • Factor levels are 2-5% of normal levels
  • Bleeding episodes can result from surgery, dental work, or an injury
  • Joint bleeding can occur
Severe Hemophilia
  • Factor levels are 1% of normal or less.
  • Spontaneous bleeding can occur
  • Joint bleeding is common
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