combined immunodeficiency, X-linked
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combined immunodeficiency, X-linkedA form of combined immunodeficiency (OMIM:312863) caused by a mutation in the same gene (IL2RG) as that causing severe combined immunodeficiency (SCIDX), a genetically and clinically heterogeneous group of rare congenital disorders characterised by impairment of both humoral and cell-mediated immunity, leukopaenia and low or absent antibody levels. XCID is more banal, and survival up to age 30 has been described.
Paucity of lymphoid tissue; recurrent sinusitis, otitis media, bronchitis, and pneumonia; severe varicella; chronic HPV infections.
Normal concentrations of serum immunoglobulins, but reduced IgG antibody response to antigens; normal numbers of B cells and NK cells, but decreased numbers of CD4+ and CD8+ T cells; diminished proliferative responses of blood T cells to allogeneic cells, mitogens and antigens; decreased production of IL2 by mitogen-stimulated lymphocytes.
Defects in IL2RG, which encodes the gamma chain, an important signalling component of many IL receptors (e.g., IL2, IL4, IL7 and IL21), cause XCID.