DiGeorge syndrome
DiGeorge syndrome: Excerpt from Professional Guide to Diseases (Eighth Edition)
DiGeorge syndrome, also called congenital thymic hypoplasia or aplasia, is a disorder characterized by the partial or total absence of cell-mediated immunity that results from a deficiency of T lymphocytes. It typically produces life-threatening hypocalcemia that may be associated with cardiovascular and facial anomalies. Patients seldom live beyond age 2 without a fetal thymus transplant; the prognosis improves when this transplant, correction of hypocalcemia, and repair of cardiac anomalies are possible.
Causes
DiGeorge syndrome is probably caused by abnormal fetal development (12th week of gestation) of the third and fourth pharyngeal pouches, which interferes with thymus formation. As a result, the thymus is completely absent or partially present in an abnormal location, causing deficient T cell-mediated immunity. (See Role of the thymus in immune response.) This syndrome has been associated with maternal alcoholism and resultant fetal alcohol syndrome.
Signs and symptoms
Symptoms are usually obvious at birth or shortly thereafter. An infant with DiGeorge syndrome may have low-set prominent ears, notched ear pinnae, a mouth without the usual bow-shaped lip, an undersized jaw, and abnormally wide-set eyes (hypertelorism) that are low-set and posteriorly angulated. Additionally, an infant may have a bifid uvula and a high, arched palate. Congenital heart anomalies are common. Cardiovascular abnormalities include great blood vessel anomalies (these may also develop soon after birth) and tetralogy of Fallot.
An infant with thymic hypoplasia (rather than aplasia) may experience a spontaneous return of cell-mediated immunity but can develop severe T-cell deficiencies later in life. This allows exaggerated susceptibility to viral, fungal, or bacterial infections, which may be overwhelming. Hypoparathyroidism, usually associated with DiGeorge syndrome, typically causes tetany, hyperphosphatemia, and hypocalcemia. Hypocalcemia (calcium levels less than 7 mg/dl) develops early and is unusually resistant to treatment. It can lead to tetany, seizures, central nervous system damage, and early heart failure.
Rare cases of partial immunoglobulin (Ig) A deficiency have been linked to chromosome 1 and deletions of the IgA1 or IgA2 genes. Alterations in chromosome 6 suggest altered major histocompatibility complex, which is reflected in decreased T-cell responses. Aberrations in chromosome 18 are linked to facial abnormalities, nystagmus, hypotonia, atretic or stenotic ear canals, hearing loss, and mental retardation.
Diagnosis
Immediate diagnosis is difficult unless the infant has typical facial anomalies — normally the first clues to the disorder. A definitive diagnosis depends on successful treatment of hypocalcemia and other life-threatening birth defects during the first few weeks of life. Such diagnosis rests on proof of decreased or absent T lymphocytes (sheep cell test, lymphopenia), partial B-cell immunodeficiency, and of an absent thymus (chest X-ray). Immunoglobulin assays are useless because antibodies present are usually from maternal circulation.
Additional tests showing low serum calcium level, elevated serum phosphorus level, and missing parathyroid hormone confirm hypoparathyroidism.
Treatment
Life-threatening hypocalcemia must be treated immediately, but it’s unusually resistant and requires aggressive treatment, for example, with a rapid I.V. infusion of 10% solution of calcium gluconate. During such an infusion, monitor heart rate and watch carefully to avoid infiltration. Remember that calcium supplements must be given with vitamin D, or sometimes also with parathyroid hormone, to ensure effective calcium utilization. After hypocalcemia is under control, a fetal thymus transplant may restore normal cell-mediated immunity. Cardiac anomalies require surgical repair when possible.
Special considerations
❑ Instruct the patient with DiGeorge syndrome to follow a low-phosphorus diet and educate him about measures to prevent infection.
❑ Teach the parents of an infant with DiGeorge syndrome to watch for signs of infection and have it treated immediately, to keep the infant away from crowds or any other potential sources of infection, and to provide good hygiene and adequate nutrition and hydration.
❑ Advise the parents to schedule and keep regular follow-up visits to the infant’s pediatrician.
Pictures
Book Source Details
- Book Title: Professional Guide to Diseases (Eighth Edition)
- Author(s): Springhouse
- Year of Publication: 2005
- Copyright Details: Professional Guide to Diseases (Eighth Edition), Copyright © 2005 Lippincott Williams & Wilkins.
More About DiGeorge's syndrome
More Medical Textbooks Online about DiGeorge's syndrome
Review other book chapters online related to DiGeorge's syndrome:
Medical Books Excerpts
- Pharyngitis
- "Professional Guide to Diseases (Eighth Edition)" (2005)
- [ read ]
- Pharyngitis
- "The 10-Minute Diagnosis Manual: Symptoms and Signs in the Time-Limited Encounter" (2000)
- [ read ]
Copyright notice for book excerpts: Copyright © 2008 Lippincott Williams & Wilkins. All rights reserved.
» Next page:
Pharyngitis (Professional Guide to Diseases (Eighth Edition))
Rate This Website
What do you think about the features of this website?
Take our user survey and have your say:
Website User Survey
Medical Tools & Articles:
Next articles:
Tools & Services:
Medical Articles:
Forums & Message Boards
- Ask or answer a question at the Boards:
