SEVERE COMBINED IMMUNODEFICIENCY DISEASE (SCID)-IL-2
 
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SEVERE COMBINED IMMUNODEFICIENCY DISEASE (SCID)-IL-2-IL-2

 

DEFINITION:

A variant of SCID characterized by a diminution of T cell number and function resulting in a combined severe immunodeficiency.

EPIDEMIOLOGY:

  • incidence: 1/100,000 (SCID)
  • age of onset:
    • first year of life
  • risk factors:
    • familial - x-linked recessive
      • chrom.#: Xq13.1-q21.1
      • gene: gamma chain of interleukin-2 receptor

PATHOGENESIS:

1. Background

  • the interleukin-2 (IL-2) receptor is made up of alpha, beta, and gamma chains and sits on the surface of cells of the immune system
  • when IL-2 binds to this receptor, it stimulates the growth and differentiation of the target cell
  • SCID-IL-2R represents one of at least 5 variants of SCID which is inturn a severe variant of Combined Immunodeficiency Disease

2. Genetic Defect

  • various mutations in the IL-2R gamma-chain gene -> IL-2 unable to bind to its receptor -> lack of growth and differentiation of target cells of the immune system -> total absence of T cells
  • a few patients with SCID have a mutant gene for IL-2 itself and have a normal number of T cells, although non-functioning

CLINICAL FEATURES:

1. Immunodeficiency Manifestations

1. Recurrent and Severe Infections

1. Fungal

  • chronic mucocutaneous candidiasis
  • systemic candidiasis

2. Bacterial/Viral

1. Respiratory
  • recurrent sinusitis, otitis media, bronchitis
  • pneumonia, pneumonitis, chronic cough
2. Gastrointestinal
  • chronic diarrhea
  • wasting, distended abdomen

2. Complications

  • failure to thrive
  • severe varicella and chronic papillomavirus
  • 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

1. Cell-Mediated

  • decrease number of natural killer cells
  • decrease number of CD4(+) and CD8(+) T cells
  • decrease proliferative response of T cells to allogeneic cells, mitogens, and antigens

2. Humoral-Mediated

  • normal immunoglobulin and B cells
  • restricted formation of IgG antibodies to immunogens

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 anti-viral agents and antibiotics), autoimmune diseases, and malignancies
    • Genetics - genetic counselling, prenatal diagnosis
    • Infectious Disease - ZIG upon varicella exposure
      • avoid immunizations with attenuated live viral vaccines

2. Bone Marrow Transplantation

  • may restore both B and T cell systems

 

 

 

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