T-B+Severe combined immunodeficiency

Definition:

Severe combined immunodeficiency (SCID) comprises a heterogeneous group of monogenic disorders that result in early-onset severe infections by a range of pathogens (such as bacteria, viruses and fungi). Typically, patients with SCID have a severe defect in T-cell differentiation, along with direct or indirect impairment of B-cell development and function. SCIDs with lack of circulating T cells but a normal number of B cells accounts for 30 to 50% of all cases of human SCIDs. The most frequent form of SCID, X-linked SCID (SCID-X1), is caused by mutations in the gamma-chain-encoding gene. Gamma-chain is a common subunit shared by several cytokine receptors. It results in an absence of both mature T lymphocytes and NK lymphocytes. The second most common variant is autosomal recessive and due to mutations of the JAK3 gene. IL-7R alpha gene mutations result in a pure T-cell deficiency. Rare cases of SCID consisting of pure T-cell deficiencies have been attributed to defects in key proteins involved in pre-TCR/TCR signaling. Deficiency in the CD45 phosphatase has been reported in two cases of SCID, while defects in CD3 delta, CD3 epsilon and CD3 zeta have also been described.

References:

[1]. Alain Fischer, et al. Severe combined immunodeficiency. A model disease for molecular immunology and therapy. Immunol Rev. 2005 Feb;203:98-109. [Content Brief]

[2]. Capucine Picard, et al. Primary Immunodeficiency Diseases: an Update on the Classification from the International Union of Immunological Societies Expert Committee for Primary Immunodeficiency 2015. J Clin Immunol. 2015 Nov;35(8):696-726. [Content Brief]

[3]. Divya Punwani, et al. Multisystem Anomalies in Severe Combined Immunodeficiency with Mutant BCL11B. N Engl J Med. 2016 Dec 1;375(22):2165-2176. [Content Brief]

[4]. Massimo Morra, et al. Genetic diagnosis of primary immune deficiencies. Immunol Allergy Clin North Am. 2008 May;28(2):387-412, x. [Content Brief]

[5]. Raif S Geha, et al. Primary immunodeficiency diseases: an update from the International Union of Immunological Societies Primary Immunodeficiency Diseases Classification Committee. J Allergy Clin Immunol. 2007 Oct;120(4):776-94. [Content Brief]

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