What is severe combined immunodeficiency (SCID)?

Updated: Aug 11, 2020
  • Author: Francisco J Hernandez-Ilizaliturri, MD; Chief Editor: Emmanuel C Besa, MD  more...
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Severe combined immunodeficiency (SCID) is a group of medical disorders that result from genetic defects in both cellular and humoral immunity. Those immune defects lead to infections with bacterial, viral, and fungal pathogens that begin during infancy and, if untreated, result in a fatal outcome in the first few years of life. [1]  

There has been a considerable gain in knowledge of the pathologic conditions of the immune system since the recognition of primary immunodeficiency as an entity in 1950, highlighted by the discovery of X-linked agammaglobulinemia, congenital neutropenia, and SCID. Over 200 diseases with more than 300 genetic etiologies have been described, which has provided opportunities for diagnosis and genetic counseling. [2]  

Moreover, an understanding of the pathogenesis of primary immunodeficiencies has paved the way for immunologic interventions and new treatments, such as immunoglobulin G (IgG) replacement, bone marrow transplantation, and gene therapy. The discovery of the HLA system in 1968 led to successful bone marrow transplantations, and patients with immunodeficiency syndromes were the first to benefit from this novel therapy.

For patient education information, see the Immunodeficiency Disorders Directory.

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