Essential thrombocytopenia

Definition

Wiskott-Aldrich syndrome is an X-linked immunodeficiency disorder marked by a low level of blood platelets (thrombocytopenia), eczema, recurrent infections, and a high risk of leukemia or lymph node tumors.

Description

Wiskott-Aldrich syndrome is a genetic disease that selectively affects male children because the defect that causes it is on the short arm of the X chromosome. Females have two X chromosomes, one of which is usually normal. Males have only one X chromosome. The syndrome affects one in every 250,000 male children.

Causes & symptoms

Wiskott-Aldrich syndrome is hereditary. Although females do not get the disorder unless both of their X chromosomes are defective, they can transmit it to offspring. The syndrome is caused by the absence (deletion) of a specific gene called the WASP gene. The deletion of this gene means that the immune system of patients with Wiskott-Aldrich syndrome produces too few B and T cells. B cells are the only cells in the body that make antibodies. There are many types of T cells. Both B and T cells are needed to defend the body against infection. Because both types of cells are affected, these patients are subject to repeated infections from bacteria, fungi, and viruses. Ear infections, meningitis, and pneumonia are common in boys with Wiskott-Aldrich syndrome.

Wiskott-Aldrich patients also have low platelet counts. This condition is called thrombocytopenia. Platelets are small blood cells that help to form blood clots and prevent uncontrolled bleeding. Some of the earliest symptoms of the syndrome are hemorrhage from circumcision, bloody diarrhea, and a tendency to bruise very easily.

Other symptoms include itching skin rashes (eczema), anemia, and an enlarged spleen (splenomegaly). About 10% of patients develop malignancies, usually leukemia or tumors in the lymph nodes (lymphomas).

Diagnosis

The diagnosis is usually made on the basis of the patient's sex, early symptoms, and the results of blood tests. The blood serum of Wiskott-Aldrich patients will show a low platelet count, a weak antibody response to certain specific (polysaccharide) antigens, and low levels or absence of blood clotting factors.

Treatment

Standard treatments for Wiskott-Aldrich patients include antibiotics for infections and platelet transfusions to limit bleeding. Immune globulin is given to strengthen the patient's immune system. Eczema can be treated with corticosteroid creams applied directly to the skin. The spleen is sometimes removed to reduce the risk of bleeding. In Wiskott-Aldrich patients, however, removal of the spleen also increases the risk of infection unless antibiotics are given to prevent infections. About 50% of patients are helped by treatment with transfer factor, which is a substance derived from the T cells of a healthy person. Transfer factor is given to improve both blood clotting and immune functions. The most successful form of treatment as of 1998 is bone marrow transplantation from a sibling whose tissues are compatible with the patient's.

Prognosis

The prognosis for patients with Wiskott-Aldrich syndrome is poor. The average patient lives about four years; the few that survive into adolescence often develop cancer. Death usually occurs from severe bleeding or overwhelming infection in the first few years of life.

Prevention

Parents of a child with Wiskott-Aldrich syndrome may benefit from genetic counseling if they are planning to have more children.

Key Terms

Antibody

A protein made by B cells that attacks foreign cells and other material.

B cell

A type of lymphocyte or white blood cell that is derived from precursor cells in the bone marrow.

Eczema

An inflammation of the skin marked by itching, scaly patches, and a watery oozing discharge.

Lymphoma

A tumor that develops in the lymph nodes. Wiskott-Aldrich patients who survive the first few years of childhood are at high risk of developing lymphomas.

Platelet

A small blood cell that is produced in the bone marrow and is important in the blood clotting process.

T cell

A type of white blood cell that originates in the thymus gland. T cells regulate the immune system's response to infections.

Thrombocytopenia

An abnormally low level of platelets in the blood.

Transfer factor

A product of T cells that carries immunity to a particular antigen. The transfer factor can be extracted and given to another person to give them immunity to the same antigen.

WASP gene

A gene on the short arm of the X chromosome whose absence causes Wiskott-Aldrich syndrome.

Further Reading

For Your Information

Books

• Abbas, Abul K., et al. Cellular and Molecular Immunology. Philadelphia: W. B. Saunders Company, 1997.
• "Immunodeficiency with Eczema and Thrombocytopenia (Wiskott-Aldrich syndrome)." In Professional Guide to Diseases, edited by Stanley Loeb, et al. Springhouse, PA: Springhouse Corporation, 1991.
• "Immunology: Immunodeficiency Diseases." In The Merck Manual of Diagnosis and Therapy, edited by Robert Berkow, et al. Rahway, NJ: Merck Research Laboratories, 1992.
• Physicians' Guide to Rare Diseases, edited by Jess G. Thoene. Montvale, NJ: Dowden Publishing Company, Inc., 1995.
• Roitt, Ivan M. Roitt's Essential Immunology. Oxford, UK: Blackwell Science Ltd., 1997.

  Organizations

• Immune Deficiency Foundation. 25 West Chesapeake Avenue, Suite 206, Towson, MD 21204. (410)321-6647.
• National Organization for Rare Disorders (NORD). P.O. Box 8923, New Fairfield, CT 06812-8923. (800) 999-NORD. (203) 746-6927 (TDD).

Gale Encyclopedia of Medicine. Gale Research, 1999.