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Severe Combined Immunodeficiency
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Basics
Description
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.
Epidemiology
Most patients present in the 1st year of life as immunity from maternal antibody wanes.
Incidence
- 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.
Genetics
- 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.)
Etiology
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.
-- To view the remaining sections of this topic, please log in or purchase a subscription --
Basics
Description
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.
Epidemiology
Most patients present in the 1st year of life as immunity from maternal antibody wanes.
Incidence
- 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.
Genetics
- 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.)
Etiology
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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