SEVERE COMBINED IMMUNODEFICIENCY DISEASE (SCID)
 
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SEVERE COMBINED IMMUNODEFICIENCY DISEASE (SCID)

 

DEFINITION:

A heterogeneous group of disorders characterized by a diminution of T cell number and/or function resulting in a combined immunodeficiency.

EPIDEMIOLOGY:

  • incidence: 1/100,000
  • age of onset:
    • depends upon severity of T cell defect
    • newborn period -> first few years of life
  • risk factors:
    • familial - transmission depends upon type

PATHOGENESIS:

1. Background

  • SCID represents a heterogeneous group of inherited disorders inwhich there is a profound disruption in the number and/or function of T cells which results in a combined immunodeficiency, the severity of which depends on the extent of the T cell defect
  • SCID is considered a severe variant of Combined Immunodeficiency Disease (CID)

2. Genetic Defect

  • genetic defect -> SCID secondary to:
  • 1. defects in purine salvage pathway
  • 2. defects in stem cells
  • 3. defects in cell surface molecules
  • 4. defects in interleukin-2 (IL-2 variant)
  • 5. associated with Letterer-Siwe Syndrome (Omenn Disease)

3. Immunological Manifestations

  • 1. Recurrent and Severe Infections
  • 1. Fungal
    • monilial infections of oropharynx, esophagus, skin
    • common and early manifestation
  • 2. Viral
    • RSV -> giant cell pneumonia
    • adenovirus, CMV, HSV, measles, rotavirus, varicella
    • inoculation with attenuated live viral vaccines can be fatal (as with BCG)
  • 3. Bacterial
    • Pneumocystis carinii -> chronic progressive pneumonitis

    • CLINICAL FEATURES:

    1. Immunodeficiency Manifestations

    1. Recurrent and Severe Infections

  • 1. Fungal
    • chronic mucocutaneous candidiasis
    • systemic candidiasis
  • 2. Bacterial/Viral
    • 1. Respiratory
      • pneumonia, pneumonitis, chronic cough
  • 2. Gastrointestinal
    • esophagitis, gastroenteritis, chronic diarrhea
    • hepatitis
    • wasting, distended abdomen

    • 2. Complications

    • failure to thrive
    • graft vs host disease after transfusion with non-irradiated blood products
    • autoimmune diseases
    • lymphoreticular malignancies - leukemia, lymphoma
    • absence of tonsils and other lymphoid tissue

    INVESTIGATIONS:

    1. Serum

    • deficiencies of T and B cell number and function depends upon variant of disease

    2. Imaging Studies

  • 1. Chest X-Ray
    • chronic pulmonary infiltrates
    • absence of thymic shadow

    • MANAGEMENT:

    1. Supportive

    • multidisciplinary approach:
      • Paediatrics - moniter for infections (treat with antiviral agents and antibiotics), autoimmune diseases, and malignancies
      • Genetics - genetic counselling, prenatal diagnosis
      • ID - ZIG upon varicella exposure; avoid immunizations with attenuated live viral vaccines

    2. Bone Marrow Transplantation

    • may restore both B and T cell systems

    INTERNET LINKS:

    SCID Homepage

     

     

     

    Pediatric Database - SEVERE COMBINED IMMUNODEFICIENCY DISEASE (SCID)

     

    Pediatric Organization - Pedbase [at] Gmail.com

     
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