Severe Combined Immunodeficiency

Original Editor - Anna Fuhrmann Top Contributors - Anna Fuhrmann

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Description[edit | edit source]

Severe Combined Immunodeficiency (SCID) is a collective term used for multiple congenital conditions caused by genetic defects, which inhibit the function of various parts of the immune system. Especially T- and B-cell function is impaired, the regular function of the immune response is impeded.[1]Children born with this condition are born seemingly healthy, but develop recurrent infections very early in life. If left untreated, SCID will lead to severe conditions approximately at the age of six months and the death of the infant mostly within the first year. Earlier onset can be triggered by contracting bacterial, viral or fungal diseases.[2] SCID became known to the public through the story of the 1971 born American David Vetter who became known as the "boy in the bubble" because he spent most of his 12-years of life in a hermetically sealed suit.

Prevalence[edit | edit source]

Prevalence ranges between 1/40,000 and 1/75,000 live births.[3]

Etiology[edit | edit source]

SCID is most likely inherited X-linked or autosomal recessive.[3] 20 genes have been linked to SCID, but in 15% of cases the involved genes are unknown.[3][4] SCID conditions are classified by their pathogenic mechanisms:[3]

  • Toxic metabolite accumulation
    • Adenosine deaminase (ADA) deficiency: most common and severe form of SCID, with a prevalence of 15%.
  • Defective survival of haematopoietic precursors (Formation of blood cellular components is corrupted)
  • T-cell receptor abnormalities
  • Cytokine signalling abnormalities
  • Recombinations and alterations in T-cell receptors

Diagnosis[edit | edit source]

In high-income countries, all newborns are routinely screened for SCID.[4] A T-cell receptor excision circle screening of dried blood spots is used as an identification method for newborns with SCID or other types of Lymphopenia.[3] By diagnosing the conditions immediatly after birth, early haematopoietic stem cell transplantation can prevent severe infections and long term effects.

Health professionals need to be aware of newborns within their first year of life with recurring infections, especially persistant respiratory or fungal infections, and diarrhoea. If left untreated, these diseases are life-threatening to the infants since their own immunesystem cannot fight the pathogens.

Medical management[edit | edit source]

Although SCID is a rather rare condition, researchers had been very keen in finding a cure. Treatment depends on the exact genetic component which is affected. ADA deficiency for example is treated with enzyme replacement therapy, early haematopoietic stem cell transplantation or gene therapy.[3]The sooner the therapy is implemented, the higher are the child's chances of survival, and the lesser the danger of developing long term effects of previous infections.

  1. Gennery A R, Cant AJ. Diagnosis of Severe Combined Immunodeficiency. Journal of Clinical Pathology. 2001; 54:191-195.
  2. Justiz Vaillant A, Mohseni M. Severe Combined Immunodeficiency. Treasure Island (FL): StatPearls Publishing, 2022.
  3. 3.0 3.1 3.2 3.3 3.4 3.5 Kumrah R, Vignesh P, Patra P, Singh A, Anjani G, Saini P, Sharma M, Kaur A, Rawat A. Genetics of severe combined immunodeficiency. Genes Dis. 2019;7(1):52-61.
  4. 4.0 4.1 National Institute of Allergy and Infectious Diseases, Severe Combined Immunodeficiency, April 2019, Available from: [last accessed 13 March 2022].