Severe combined immunodeficiency disease
Severe combined immunodeficiency disease: Excerpt from Professional Guide to Diseases (Eighth Edition)
In severe combined immunodeficiency disease (SCID), both cell-mediated (T-cell) and humoral (B-cell) immunity are deficient or absent, resulting in susceptibility to infection from all classes of microorganisms during infancy. It’s the most severe form of T-cell and B-cell deficiency. At least three types of SCID exist: reticular dysgenesis, the most severe type, in which the hematopoietic stem cell fails to differentiate into lymphocytes and granulocytes; Swiss-type agammaglobulinemia, in which the hematopoietic stem cell fails to differentiate into lymphocytes alone; and enzyme deficiency, such as adenosine deaminase (ADA) deficiency, in which the buildup of toxic products in the lymphoid tissue causes damage and subsequent dysfunction.
Causes and incidence
SCID is usually transmitted as an autosomal recessive trait, although it may be X-linked. In most cases, the genetic defect seems associated with failure of the stem cell to differentiate into T and B lymphocytes. Many molecular defects such as mutation of the kinase ZAP-70 can cause SCID. X-linked SCID is due to a mutation of a subunit of the interleukin (IL)-2, IL-4, and IL-7 receptors. Less commonly, it results from an enzyme deficiency.
SCID affects more males than females. Its estimated incidence is 1 in every 100,000 to 500,000 births. Most untreated patients die from infection within 1 year of birth.
Signs and symptoms
An extreme susceptibility to infection becomes obvious in the infant with SCID in the first months of life. The infant fails to thrive and develops chronic otitis; sepsis; watery diarrhea (associated with Salmonella or Escherichia coli); recurrent pulmonary infections (usually caused by Pseudomonas, cytomegalovirus, or Pneumocystis carinii); persistent oral candidiasis, sometimes with esophageal erosions; and possibly fatal viral infections such as chickenpox.
P. carinii pneumonia usually strikes a severely immunodeficient infant in the first 3 to 5 weeks of life. Onset is typically insidious, with gradually worsening cough, low-grade fever, tachypnea, and respiratory distress. Chest X-ray characteristically shows bilateral pulmonary infiltrates.
Diagnosis
Diagnosis is generally made clinically because most SCID infants suffer recurrent overwhelming infections within 1 year of birth. Some infants are diagnosed after a severe reaction to vaccination.
Defective humoral immunity is difficult to detect before age 5 months. Before then, even normal infants have very small amounts of serum immunoglobulin (Ig) M and IgA. Normal IgG levels merely reflect maternal IgG.
Confirming diagnosis Severely diminished or absent T-cell number and function, as well as lymph node biopsy showing absence of lymphocytes, can confirm diagnosis of SCID.
Treatment
Treatment aims to restore the immune response and prevent infection. Histocompatible bone marrow transplantation is the only satisfactory treatment available to correct immunodeficiency. Because bone marrow cells must be human leukocyte antigen and mixed leukocyte culture matched, the most common donors are histocompatible siblings. However, because bone marrow transplant can produce a potentially fatal graft-versus-host (GVH) reaction, newer methods of bone marrow transplant that eliminate GVH reaction (such as lectin separation and the use of monoclonal antibodies) are being evaluated.
Fetal thymus and liver transplants have achieved limited success. Immune globulin administration may also play a role in treatment. Some SCID infants have received long-term protection by being isolated in a completely sterile environment. However, this approach isn’t effective if the infant already has had recurring infections.
Gene therapy is being used to treat ADA deficiency.
Special considerations
Patient care is primarily preventive and supportive.
❑ Constantly monitor the infant for early signs of infection. If infection develops, provide prompt and aggressive drug therapy as ordered. Watch for adverse effects of any medications given.
❑ Avoid vaccinations and give only irradiated blood products if a transfusion is ordered.
❑ Although SCID infants must remain in strict protective isolation, try to provide a stimulating atmosphere to promote growth and development. Encourage the parents to visit their child often, to hold him, and to bring him toys that can be easily sterilized. If the parents can’t visit, call them often to report on the infant’s condition. Explain all procedures, medications, and precautions to them. Maintain a normal day and night routine for the child and talk to him as much as possible.
❑ Because the parents will have questions about the vulnerability of future offspring, refer them for genetic counseling.
❑ Arrange for psychological and spiritual support for the parents and siblings to help them cope with the child’s inevitable long-term illness and early death.
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 SCID
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Copyright notice for book excerpts: Copyright © 2008 Lippincott Williams & Wilkins. All rights reserved.
» Next page: Common variable immunodeficiency (Handbook of Diseases)
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