![]() ![]() These B cells are inherently nonfunctional because they fail to produce immunoglobulin even after bone marrow transplantation and restoration of T-cell function. Its defect is mapped to the Xq13 region, and the faulty gene is identified as IL2RG, which encodes the γc chain shared by 6 cytokine receptors that are critical for maintaining immune homeostasis: interleukins (ILs) 2, 4, 7, 9, 15, and 21.Īlthough SCID-X1 patients lack T- and B-cell function and have low numbers of T or NK cells, they produce normal or elevated numbers of B cells. The most prevalent form of SCID, SCID-X1, is characterized by the absence of T and NK lymphocytes and by nonfunctional B lymphocytes. ![]() Table 111-1 Classification of Severe Combined Immunodeficiency (SCID) (Reproduced with permission from Buckley. ADA, adenosine deaminase JAK3, Janus kinase 3 IL7R, interleukin 7 receptor α chain RAG1 or RAG2, recombination activating genes 1 or 2. The most common type is X-linked SCID, which disables common gamma (γc) signaling. SCID can also be inherited as an autosomal recessive disease that results from deficiencies in adenosine deaminase (ADA), Janus kinase 3 ( JAK3), interleukin 7 receptor α chain ( IL7R), recombination activating genes ( RAG1 or RAG2), Artemis gene, CD45, and others ( Table 111-1).įIGURE 111-1 The relative frequencies of particular genetic mutations were evaluated in 174 consecutive cases of human severe combined immunodeficiency (SCID) evaluated at Duke University over 30 years. The most common type is X-linked SCID (SCID-X1), which accounts for approximately 46% of cases in the United States ( Figure 111-1). Since SCID was initially described over 50 years ago, 15 specific genetic mutations that contribute to disease development have been identified. If left untreated, babies with SCID most often die within 1 to 2 years of life because of severe, recurrent infections. Patients with SCID have reduced numbers and function of both T and B lymphocytes (and in some cases, natural killer cells) and hypogammaglobulinemia. Severe combined immunodeficiency (SCID) is a fatal primary immune condition characterized by the absence of both humoral and cellular immunity with severe lymphopenia. ![]()
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