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Alternative namesChristmas disease; Factor IX hemophilia
DefinitionHemophilia B is a hereditary blood coagulation disorder . It is caused by a deficiency of a blood plasma protein called factor IX that affects the clotting property of blood.
Causes, incidence, and risk factors
Hemophilia is a hereditary bleeding disorder of specific blood clotting factors. There are several types of hemophilia, including hemophilia A and B. Hemophilia A is 7 times more common than hemophilia B. Hemophilia B is the result of a deficiency of clotting factor IX.
The disorder is caused by an inherited sex-linked recessive trait with the defective gene located on the X chromosome. Females carry two copies of the X chromosome, so if the factor IX gene on one chromosome is defective, the other can compensate. Males, however, carry only one X chromosome, so if the factor IX gene on that chromosome is defective, they have the disease.
Females with one defective factor IX gene are carriers of this trait. Fifty percent of the male offspring of female carriers will have the disease, and 50% of their female offspring will be carriers. All female children of a male hemophiliac will be carriers of the trait.
Mild cases may go unnoticed until later in life, when they occur in response to surgery or trauma. Internal bleeding may occur anywhere and bleeding into joints is common. Risk factors are a family history of bleeding and being male. Hemophilia B occurs in about 1 out of 32,000 men.
Signs and testsCoagulation studies involving many tests are performed if the person tested is the first one in the family to have a bleeding disorder. Once the defect has been identified, other family members will need less testing to diagnose the disorder.
TreatmentStandard treatment is infusion of factor IX concentrates to replace the defective clotting factor. The amount infused depends upon the severity of bleeding, the site of the bleeding, and the size of the patient. Hepatitis B vaccine is recommended for individuals with Hemophilia B because they are at increased risk of developing hepatitis due to exposure to blood products.
To prevent a bleeding crisis, people with hemophilia and their families can be taught to administer factor IX concentrates at home at the first signs of bleeding. People with severe forms of the disease may need regular prophylactic infusions.
Depending on the severity of the disease, factor IX concentrate may be given prior to dental extractions and surgery to prevent bleeding.
Support GroupsFor additional information, see hemophilia support group.
Expectations (prognosis)The outcome is usually good with treatment. Most people with hemophilia are able to lead relatively normal lives. A small percentage of people develop inhibitors of factor IX, and may die from loss of blood.
Calling your health care provider
PreventionGenetic counseling may be advised. Female carriers can be identified by testing.
Update Date: 4/25/2003Ezra E. W. Cohen, M.D., Section of Hematology/Oncology, Department of Medicine, The University of Chicago, Chicago, IL. Review provided by VeriMed Healthcare Network.
Last updated: Tue, 06 Jan 2009 00:20:03 GMT