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Hemophilia
is a bleeding disorder caused by a deficiency in one of two blood
clotting factors: factor VIII or factor IX.
There are two forms of hemophilia. Hemophilia A, which accounts for about 80% of all cases, is a deficiency in clotting factor VIII. Hemophilia B is a deficiency in clotting factor IX. The bleeding patterns and consequences of these two types of hemophilia are similar.
Deficiency of clotting factor XI also causes a hereditary bleeding disorder. About 50% of cases of factor XI deficiency occur among people of Eastern European Jewish ancestry. Factor XI deficiency affects both males and females and may cause bleeding after injury or surgery. Spontaneous bleeding episodes are usually less frequent and milder than in hemophilia A or B.
Hemophilia is caused by several different gene abnormalities. They are sex-linked, which means that the gene abnormalities are inherited through the mother and that nearly everyone with hemophilia is male.
Symptoms and
Complications
The severity of the symptoms depends on how a particular gene abnormality affects the blood clotting activity of factor VIII or IX. People whose clotting activity is 5 to 25% of normal have very mild hemophilia that may go undiagnosed; however, these people may bleed more than expected after surgery, dental extractions, or a major injury. People whose blood clotting activity is 1 to 5% of normal may have only mild hemophilia. They have few unprovoked bleeding episodes, but surgery or injury may cause uncontrolled and fatal bleeding. When the clotting activity is less than 1% of normal, hemophilia is severe. Serious episodes of bleeding occur and recur for no apparent reason.
In severe hemophilia, the first bleeding episode often occurs during or immediately after delivery. The infant may develop a collection of blood under the scalp (cephalhematoma) or may bleed excessively during circumcision. A bleeding episode generally occurs before 18 months of age and may follow a minor injury. A child who has hemophilia bruises easily. Even an injection into a muscle can cause bleeding that results in a large bruise and hematoma. Recurring bleeding into the joints and muscles can lead to crippling deformities. Bleeding can swell the base of the tongue until it blocks the airway, making breathing difficult. A slight bump on the head can trigger substantial bleeding in the brain or between the brain and the skull, causing brain damage and death.
Diagnosis and
Treatment
A doctor may suspect hemophilia in a child (especially a boy) who bleeds without an apparent cause or bleeds more than expected after injury. A blood test can determine whether the boy's clotting is abnormally slow. If it is, further blood tests can confirm the diagnosis of hemophilia and can determine its type and severity.
People who have hemophilia should avoid situations that might provoke bleeding and should avoid drugs (for example, aspirin ) that interfere with the function of platelets. They should be conscientious about dental care so that they will not need to have teeth extracted. If people who have milder forms of hemophilia need to have dental or other surgery, the drugs aminocaproic acid or desmopressin may be given to improve temporarily the body's ability to control bleeding so that transfusions can be avoided.
Often, treatment involves transfusions to replace the deficient clotting factor. These factors are found normally present in normal the liquid component of blood (plasma). Clotting factors may be obtained from donated blood by concentrating or purifying them from plasma products, or they may be produced using special technological procedures as highly purified recombinant factor concentrates. Recombinant forms of both factor VIII and IX are available; because they are not obtained from human donors, they do not have the risk of infection that is present with factors derived from donated blood. The dose, frequency, and duration of therapy are determined by the site and severity of the bleeding problem. Clotting factors may also be used to prevent bleeding before surgery or at the first sign of bleeding.
Some people with hemophilia develop antibodies to transfused clotting factors, which destroy the factors. As a result, factor replacement therapy becomes less effective. If antibodies are detected in the blood of a person with hemophilia, the dosage of the recombinant factor or plasma concentrates may be increased, or different types of clotting factors or drugs to reduce the antibody levels may be needed.
Last full review/revision May 2006 by Joel L. Moake, MD
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