Hemophilia Symptoms, Causes, Treatment - Inhibitors on MedicineNet

Hemophilia (cont.)

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Medical Author:

Melissa Conrad Stöppler, MD

Melissa Conrad Stöppler, MD, is a U.S. board-certified Anatomic Pathologist with subspecialty training in the fields of Experimental and Molecular Pathology. Dr. Stöppler's educational background includes a BA with Highest Distinction from the University of Virginia and an MD from the University of North Carolina. She completed residency training in Anatomic Pathology at Georgetown University followed by subspecialty fellowship training in molecular diagnostics and experimental pathology.

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Medical Editor:

Charles Patrick Davis, MD, PhD

Dr. Charles "Pat" Davis, MD, PhD, is a board certified Emergency Medicine doctor who currently practices as a consultant and staff member for hospitals. He has a PhD in Microbiology (UT at Austin), and the MD (Univ. Texas Medical Branch, Galveston). He is a Clinical Professor (retired) in the Division of Emergency Medicine, UT Health Science Center at San Antonio, and has been the Chief of Emergency Medicine at UT Medical Branch and at UTHSCSA with over 250 publications.

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Inhibitors

A major complication of treatment is the development of so-called inhibitors to the clotting factors. Inhibitors (antibodies) are produced because the body sees the factor concentrates used to treat patients to reduce or prevent bleeding, as foreign and activates an immune response in the patient to destroy the foreign substances (factor VIII or factor IX).

Inhibitors to factor VIII are the most common and occur in about one-third of those with severe hemophilia A and about 1 out of every 50 people with mild or moderate hemophilia A. They typically develop in childhood in those with severe hemophilia A and later in life in milder cases. Inhibitors destroy both the replacement factor VIII concentrates as well as any factor VIII that is present in the body. This is a serious complication of treatment because the factor concentrates are no longer effective in treating the condition. The action of inhibitors to destroy factor VIII concentrates shows different degrees of severity among individuals and can even vary over time in the same individual.

In about two-thirds of cases, the inhibitors disappear on their own or with treatment known as immune tolerance therapy (ITT) or immune tolerance induction (ITI). In cases of severe hemophilia A with persistence of inhibitors, other factor concentrates, such as activated prothrombin complex concentrate or recombinant factor VIIa, are administered to attempt to help control bleeding.

The development of inhibitors to factor IX is much less common and occurs in about 1% of those with hemophilia B. However, these can cause a very serious allergic reaction when factor IX concentrates are given. Immune tolerance therapy to eliminate inhibitors is less successful than with hemophilia A.

Infections

Blood-borne infections, such as the HIV virus and hepatitis B and C, were a major complication of treatment for hemophilia during the 1980s. These infections were transmitted through the factor concentrates and other blood products that were used to treat hemophilia. The use of large blood donor pools to prepare factor concentrates and the lack of specific tests for infectious agents both contributed to the contamination of blood products used to treat hemophilia. By 1985, about 90% of people with severe hemophilia were infected with the HIV virus, and about half of all people with hemophilia were HIV-positive. Today, improved screening and manufacturing practices including virus removing techniques as well as the development of recombinant factors have essentially eliminated this tragic complication of treatment.

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