what is acquired hemophilia A?
When a person bleeds, clotting factors in the blood begin to work together by activation of a clotting cascade, or a pathway in which different clotting factors are activated in turn until a blood clot forms where the bleeding began.

Normally, when a person's immune system encounters a foreign material (such as a flu virus or a bacteria that causes infection), the immune system will mount a response to kill and/or get rid of the invader. Acquired hemophilia A is a medical condition in which a person's immune system mistakes the normally-occurring clotting factor VIII as foreign and attacks it as if it was an invader. The body generates an inhibitor that destroys factor VIII when immune cells in the blood encounter the factor. Factor VIII levels drop, and a blood clot is unable to form due to lack of factor VIII needed to continue activation of the clotting cascade. This has severe consequences for the acquired hemophilia A patient:

• joint damage or "hemophilic arthropathy" may occur when there is bleeding into joints, which may lead to chronic swelling and later joint deformity
• injuries from contact sports or any other cause can be a problem because any acute bleeding episodes will likely require prompt administration of recombinant factor VIIa (also known as NovoSeven, a product by Novo Nordisk), blood transfusion (if loss of blood is great), and/or hospitalization
• they bruise easily when bumping into things, and it takes much longer than normal for these bruises to heal because of the delay in clotting
• surgery and usually simple dental procedures pose problems, because of the difficulty of the doctor to predict and/or prepare for any complications

how common is acquired hemophilia A?
One to 1.5 cases of acquired hemophilia A cases per 1 million people are estimated to be identified per year, according to the Canadian Association of Nurses in Hemophilia Care. In contrast, it is estimated that 1 in 5,000 males born in the United States has hemophilia; hemophilia (not acquired hemophilia A) has a higher incidence in the population than acquired hemophilia A because hemophilia is a sex-linked condition and can be inherited from parent to child.

what causes acquired hemophilia A? Is acquired hemophilia A preventable?
To date, doctors cannot find a single agent that causes the onset of acquired hemophilia A. Suggested underlying disease states that may be associated with acquired hemophilia A include autoimmune disease, use of certain medications (such as penicillin), certain cancers, and solid tumors. Pregnancy may also be another risk factor. However, it is estimated that over half of all diagnosed acquired hemophilia A cases occur by idiopathic (or unidentifiable) means. No, acquired hemophilia A is not preventable, as doctors have been unable to identify a single cause for the condition.

is acquired hemophilia A the same thing as hemophilia A?
Acquired hemophilia A is not hemophilia A (also known as factor VIII deficiency or classic hemophilia) or hemophilia B (also known as factor IX deficiency), and these medical conditions should not be confused. Hemophilias A and B are inherited, sex-linked conditions that can be passed on from parent to child via the X chromosome. Approximately one in 5,000 males born in the United States has hemophilia; because of the nature of inheritance, hemophilias A and B are rare in women. All races and economic groups are affected equally by hemophilias A and B, and these conditions are not linked to other conditions, such as disorders of the immune system, cancer, or the use of certain medications. The usual treatment for bleeding in a hemophilia A patient is factor replacement (factor VIII for hemophilia A and factor IX for hemophilia B).

Note, factor VIII replacement treatment has no beneficial effect for people with acquired hemophilia A and will not stop acute bleeding; in fact, the introduction of additional factor VIII may increase factor VIII inhibitor levels in the blood of a person with acquired hemophilia A. Because every individual with acquired hemophilia A is different, it is unknown if any of the treatments given to a patient (see below) will diminish the levels of factor VIII inhibitor, so it is important that a person with acquired hemophilia A wear Medic-Alert identification to assist medical personnel if he/she requires treatment in an emergency situation.

how is acquired hemophilia A treated?
Usually, doctors will try these treatments, but which treatment they will try first, second, etc. and in which order depends on the individual's patient history. Treatments may include:

• high doses of intravenous (IV) corticosteroids (methylprednisolone), an immunosuppressive drug commonly used in its oral and IV forms as an anti-inflammatory drug for the treatment of arthritis and asthma
• IV immunoglobulin (IVIG), a plasma-derived product that may grab excess inhibitor and keep it from attacking factor VIII
• recombinant factor VIIa (NovoSeven), a factor produced by genetic engineering that acts further down the blood clotting activation cascade
• blood transfusion, a process in which blood is taken out of the body and replaced by plasma from donors
• plasmapheresis, a process in which blood is taken out of the body by a special machine, processed to remove certain parts, and then put back into the body
• rituximab (Rituxan), a biologic agent that likely attaches to the factor VIII inhibitor and marks it so the immune system will destroy it

More information on how these treatments work are available on the treatment page.

Some of the information contained on this page can be found on the National Hemophilia Foundation and Canadian Hemophilia Society Web sites.

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M. Chang
16 November 2006

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