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Severe Combined Immunodeficiency

Severe Combined Immunodeficiency is a topic covered in the Select 5-Minute Pediatrics Topics.

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Severe combined immunodeficiency (SCID) is a primary immunodeficiency characterized by functional defects in both the humoral and cellular immune systems. Most babies present with lymphopenia. Even the suspicion of SCID constitutes a pediatric emergency. Untreated, SCID is universally fatal, usually within the 1st year of life.


Most patients present in the 1st year of life as immunity from maternal antibody wanes.


  • Estimated to be 1 in 100,000 births but may be underreported because of early infant mortality
  • Highest in regions where consanguineous marriages take place
  • SCID due to Artemis defects occurs in 1 in 2,500 births in the Navajo and Apache populations because of a founder mutation.


  • At least 13 known genetic defects that cause SCID
  • Approximately 50% of cases are X-linked (mutation in the IL2 gamma chain); the others are autosomal recessive or de novo mutations.
  • Classified by the lymphocytes subsets affected (e.g., T− B+ NK+, T− B− NK+, etc.)


Caused by mutations in genes required for T-cell growth and development, purine salvage pathway function (e.g., adenosine deaminase), and expression of histocompatibility (HLA) antigens.

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Cabana, Michael D., editor. "Severe Combined Immunodeficiency." Select 5-Minute Pediatrics Topics, 7th ed., Wolters Kluwer Health, 2015. Medicine Central, im.unboundmedicine.com/medicine/view/Select-5-Minute-Pediatric-Consult/14073/all/Severe_Combined_Immunodeficiency.
Severe Combined Immunodeficiency. In: Cabana MD, ed. Select 5-Minute Pediatrics Topics. 7th ed. Wolters Kluwer Health; 2015. https://im.unboundmedicine.com/medicine/view/Select-5-Minute-Pediatric-Consult/14073/all/Severe_Combined_Immunodeficiency. Accessed April 24, 2019.
Severe Combined Immunodeficiency. (2015). In Cabana, M. D. (Ed.), Select 5-Minute Pediatrics Topics. Available from https://im.unboundmedicine.com/medicine/view/Select-5-Minute-Pediatric-Consult/14073/all/Severe_Combined_Immunodeficiency
Severe Combined Immunodeficiency [Internet]. In: Cabana MD, editors. Select 5-Minute Pediatrics Topics. Wolters Kluwer Health; 2015. [cited 2019 April 24]. Available from: https://im.unboundmedicine.com/medicine/view/Select-5-Minute-Pediatric-Consult/14073/all/Severe_Combined_Immunodeficiency.
* Article titles in AMA citation format should be in sentence-case
TY - ELEC T1 - Severe Combined Immunodeficiency ID - 14073 ED - Cabana,Michael D, BT - Select 5-Minute Pediatrics Topics UR - https://im.unboundmedicine.com/medicine/view/Select-5-Minute-Pediatric-Consult/14073/all/Severe_Combined_Immunodeficiency PB - Wolters Kluwer Health ET - 7 DB - Medicine Central DP - Unbound Medicine ER -