(See also Overview of Blood Clotting Disorders.)
Hemophilia is a hereditary bleeding disorder caused by a deficiency in one of two blood clotting factors: factor VIII or factor IX.
Clotting factors are proteins that interact to help the blood clot, stopping bleeding. There are two forms of hemophilia.
The bleeding patterns and consequences of these two types of hemophilia are similar.
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 (see also X-Linked Inheritance).
The main symptom is excessive bleeding. The bleeding may be into a joint or muscle, inside the abdomen or head, or from cuts, dental procedures, or surgery. A child who has hemophilia bruises easily.
The severity of the bleeding depends on how a particular gene abnormality affects the blood clotting activity of factor VIII or IX.
When hemophilia is severe, serious episodes of bleeding occur and recur after minor injury or 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.
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.
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 person's clotting is abnormally slow. If it is, further blood tests to measure the levels of factor VIII and IX can confirm the diagnosis of hemophilia and can determine its type and severity.
At some specialized centers, genetic testing is available for women who may be carriers of the abnormal gene and for prenatal testing of a fetus.
People who have hemophilia should avoid situations that might provoke bleeding and should avoid drugs (for example, aspirin and probably also nonsteroidal anti-inflammatory drugs) 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 normally present in the liquid component of blood (plasma). Clotting factors may be obtained from donated blood by concentrating or purifying them from plasma. Clotting factors purified from plasma are treated to inactivate most of the viruses that might be present in the donated plasma. Clotting factors also may be produced in a laboratory using special technological procedures. These manufactured clotting factors are called highly purified recombinant factor concentrates. Recombinant forms of both factor VIII and IX are available. Because recombinant forms are not obtained from human donors, they do not have the slight 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.