DiGeorge syndrome

Definition

DiGeorge syndrome, which is also called congenital thymic hypoplasia, or third and fourth pharyngeal pouch syndrome, is a birth defect that affects the immune system. (The pharynx is a passage between the mouth and one of the openings of the nasal cavity).The syndrome is marked by absence or underdevelopment of the thymus and parathyroid glands. It is named for the pediatrician who first described it in 1965.

Description

DiGeorge syndrome occurs about once in every 50,000 live births. It is sometimes described as one of the "CATCH 22" disorders, so named because of their characteristics -- Cardiac defects, Abnormal facial features, Thymus underdevelopment, Cleft palate, and Hypocalcemia -- caused by defects in chromosome 22. The specific facial features associated with DiGeorge syndrome include low-set ears, wide-set eyes, a small jaw, and a short groove in the upper lip. The male/female ratio is 1:1.

Causes & symptoms

DiGeorge syndrome is caused by inheritance of a defective chromosome 22 -- from the mother in most cases. The third and fourth pharyngeal pouches fail to develop normally during the 12th week of pregnancy, which results in completely or partially absent thymus gland and parathroid glands. The child is born with a defective immune system and an abnormally low level of calcium in the blood.

These defects usually become apparent within 48 hours of birth. The infant's heart defects may lead to heart failure, or there may be seizures and other evidence of a low level of calcium in the blood (hypocalcemia).

Diagnosis

Diagnosis of DiGeorge syndrome is sometimes suggested by the child's facial features at birth. In other cases, the doctor makes the diagnosis during heart surgery when he or she notices the absence or abnormal location of the thymus gland. The diagnosis can be confirmed by blood tests for calcium, phosphorus, and parathyroid hormone levels, and by the sheep cell test for immune function.

Treatment

Hypocalcemia

Hypocalcemia in DiGeorge patients is unusually difficult to treat. Infants are usually given calcium and vitamin D by mouth. Severe cases have been treated by transplantation of fetal thymus tissue or bone marrow.

Heart defects

Infants with life-threatening heart defects are treated surgically.

Defective immune function

Children with DiGeorge syndrome should be kept on low-phosphorus diets and kept away from crowds or other sources of infection. They should not be immunized with vaccines made from live viruses or given corticosteroids.

Prognosis

The prognosis is variable; many infants with DiGeorge syndrome die from overwhelming infection, seizures, or heart failure within the first year. Advances in heart surgery indicate that the prognosis is most closely linked to the severity of the heart defects and the partial presence of the thymus gland. In most children who survive, the number of T cells, a type of white blood cell, in the blood rises spontaneously as they mature.

Prevention

Genetic counseling is recommended for parents of children with DiGeorge syndrome. The disorder can be detected prior to birth.

Key Terms

Hypocalcemia

An abnormally low level of calcium in the blood.

Hypoplasia

A deficiency or underdevelopment of a tissue or body structure.

T cells

A type of white blood cell produced in the thymus gland. T cells are an important part of the immune system. Infants born with an underdeveloped or absent thymus do not have a normal level of T cells in their blood.

Further Reading

For Your Information

Books

• "Common Multiple Congenital Anomaly Syndromes." In Neonatology: Management, Procedures, On-Call Problems, Diseases and Drugs, edited by Tricia Lacy Gomella, et al. Norwalk, CT: Appleton & Lange, 1994.
• "DiGeorge Syndrome." In Physicians' Guide to Rare Diseases, edited by Jess G. Thoene. Montvale, NJ: Dowden Publishing Company, Inc., 1995.
• "DiGeorge's Syndrome." In Professional Guide to Diseases, edited by Stanley Loeb, et al. Springhouse, PA: Springhouse Corporation, 1991.
• Hayward, Anthony R. "DiGeorge Syndrome." In Encyclopedia of Immunology, vol. I, edited by Ivan M. Roitt, and Peter J. Delves. London: Academic Press, 1992.
• "Immunology; Allergic Disorders: Immunodeficiency Diseases." In The Merck Manual of Diagnosis and Therapy, vol. II, edited by Robert Berkow, et al. Rahway, NJ: Merck Research Laboratories, 1992.
• Magalini, Sergio I., et al. Dictionary of Medical Syndromes. Philadelphia: J. B. Lippincott Company, 1990.
• Sujansky, Eva, et al. "Genetics & Dysmorphology." In Current Pediatric Diagnosis & Treatment, edited by William W. Hay, Jr., et al. Stamford, CT: Appleton & Lange, 1997.

Gale Encyclopedia of Medicine. Gale Research, 1999.