Digeorge Syndrome

DiGeorge syndrome - also known as congenital thymic hypoplasia or aplasia - is marked by a partial or total absence of cell-mediated immunity that results from a deficiency of T cells. It characteristically produces life-threatening hypocalcemia and is associated with abnormalities of the great vessels, atrial and ventricular septal defects, esophageal atresia, bifiduvula, short philtrum, mandibular hypoplasia, hypertelorism, and low-set notched ears. Also, the thymus may be absent or underdeveloped and abnormally located.

An infant with thymic hypoplasia (rather than aplasia) may experience a spontaneous return of cell­mediated immunity but can develop severe T-cell deficiencies later in life. This results in an exaggerated susceptibility to viral, fungal, and bacterial infections that may be overwhelming.

Few patients live beyond age 2 without fetal thymic transplantation. If transplantation, correction of hypocalcemia, and repair of cardiac anomalies can take place, the prognosis improves.

Causes

DiGeorge syndrome may result from abnormal fetal development of the third and fourth pharyngeal pouches (during the 6th to 12th week of gestation) that interferes with the formation of the thymus and parathyroid glands. As a result, the thymus is completely or partially absent and abnormally located, causing deficient cell-mediated immunity.

This syndrome has been linked to maternal alcoholism and resultant fetal alcohol syndrome.

Symptoms

The symptoms vary greatly between individuals. Researches believe that the variation in the symptoms is related to the amount of genetic material lost in the chromosomal deletion. The more genetic material is lost, the greater the amount of symptoms.

Some common symptoms are:

• Learning disabilities
• Hypocalcemia
• Recurrent infections
• Underdeveloped parathyroid glands
• Underdeveloped chin
• Speech impairments
• Immune deficiency
• Downward slanting eyes
• Hypoparathyroidism
• Lack of T-cells

Diagnostic tests

Diagnosis is usually made on the basis of symptoms present at birth or within the first few weeks of life. Some children have the syndrome's distinctive facial characteristics. Others may have low blood calcium, or symptoms of a heart defect such as a heart murmur. If DiGeorge syndrome is suspected, these tests may be helpful:

• Blood tests to evaluate the immune system
• Blood tests for low calcium
• Chest x-ray to look at the heart and thymus
• Cardiac catheterization to examine the heart closely
• Genetic studies to look for the Chromosome 22 problem

Treatment

Life-threatening hypocalcemia needs immediate, aggressive treatment, for example, with a rapid I.V. infusion of 10% calcium gluconate. Transplantation of thymic tissue can help the patient to develop immunocompetent T cells of host origin.

When possible, congenital cardiac deformities can be repaired with surgery.

Prevention

Genetic counseling is recommended for parents of children with DiGeorge syndrome because the disorder can be detected prior to birth. Although most children with DiGeorge syndrome did not inherit the chromosome deletion from their parents, they have a 50% chance of passing the deletion on to their own children.

Because of the association between DiGeorge syndrome and fetal alcohol syndrome, pregnant women should avoid drinking alcoholic beverages.

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