X-linked severe combined immunodeficiency (SCID)
- Francisco A Bonilla, MD, PhD
Francisco A Bonilla, MD, PhD
- Section Editor — Immunology and Immunodeficiency
- Associate Professor of Pediatrics
- Harvard Medical School
X-linked severe combined immunodeficiency (X-SCID) is due to defects in the common gamma chain (gamma-c, interleukin-2 receptor gamma [IL2RG]).
X-SCID is discussed here. An overview of specific forms of SCID and a general overview of SCID are presented separately. (See "Severe combined immunodeficiency (SCID): Specific defects" and "Severe combined immunodeficiency (SCID): An overview".)
In a cohort of 42 severe combined immunodeficiency (SCID) infants diagnosed prospectively by newborn screening in the US, nine (21 percent) had X-linked SCID (SCIDX1 or X-SCID, MIM 300400) . X-SCID is a smaller proportion of SCID in regions of the world where parental consanguinity is common .
X-linked severe combined immunodeficiency (X-SCID) is caused by defects in a gene on the X chromosome encoding the cytokine receptor subunit gamma-c (the interleukin receptor common gamma chain [IL2RG]) . This receptor subunit is shared by at least six different cytokine receptor complexes: the receptors for interleukins-2, -4, -7, -9, -15, and -21 . Mutations in this gene lead to profound derangement of the immune system via the blockade of multiple cytokine pathways important for lymphocyte development and function.
The gamma-c subunit is also involved in growth hormone receptor signaling . Thus, growth failure seen in children with X-SCID may be due to both the underlying genetic defect and to recurrent infections and nutritional deficiencies . This could explain why many patients continue to have growth failure with severe short stature after partial correction of the defect with hematopoietic cell transplantation.To continue reading this article, you must log in with your personal, hospital, or group practice subscription. For more information on subscription options, click below on the option that best describes you:
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