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X-linked severe combined immunodeficiency
(often shortened to X-linked SCID)
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Reviewed May 2009
What is X-linked SCID?
X-linked severe combined immunodeficiency (SCID) is an inherited disorder of the immune system that occurs almost exclusively in males. Boys with X-linked SCID are prone to recurrent and persistent infections caused by certain bacteria, viruses, and fungi. The organisms that cause these infections are described as opportunistic because they ordinarily do not cause illness in healthy people. However, in people with X-linked SCID they cause very serious or life-threatening illnesses. Many infants with X-linked SCID experience chronic diarrhea and skin rashes, and grow more slowly than other children. Without treatment, affected males usually do not live beyond infancy.
How common is X-linked SCID?
X-linked SCID is the most common form of severe combined immunodeficiency. Its exact incidence is unknown, but the condition probably affects at least 1 in 50,000 to 100,000 newborns.
What genes are related to X-linked SCID?
Mutations in the IL2RG gene cause X-linked SCID. The IL2RG gene provides instructions for making a protein that is critical for normal immune system function. This protein is necessary for the growth and maturation of developing immune system cells called lymphocytes. Lymphocytes defend the body against potentially harmful invaders, make antibodies, and help regulate the entire immune system. Mutations in the IL2RG gene prevent these cells from developing and functioning normally. Without functional lymphocytes, the body is unable to fight off infections.
Read more about the IL2RG gene.
How do people inherit X-linked SCID?
This condition is inherited in an X-linked recessive pattern. The gene associated with this condition is located on the X chromosome, which is one of the two sex chromosomes. In males (who have only one X chromosome), one altered copy of the gene in each cell is sufficient to cause the condition. In females (who have two X chromosomes), a mutation would have to occur in both copies of the gene to cause the disorder. Because it is unlikely that females will have two altered copies of this gene, males are affected by X-linked recessive disorders much more frequently than females. A characteristic of X-linked inheritance is that fathers cannot pass X-linked traits to their sons.
Where can I find information about diagnosis or management of X-linked SCID?
These resources address the diagnosis or management of X-linked SCID and may include treatment providers.
General information about the diagnosis and management of genetic conditions is available in the Handbook. Read more about genetic testing, particularly the difference between clinical tests and research tests.
To locate a healthcare provider, see How can I find a genetics professional in my area? in the Handbook.
Where can I find additional information about X-linked SCID?
You may find the following resources about X-linked SCID helpful. These materials are written for the general public.
You may also be interested in these resources, which are designed for healthcare professionals and researchers.
What other names do people use for X-linked SCID?
What if I still have specific questions about X-linked SCID?
Where can I find general information about genetic conditions?
The Handbook provides basic information about genetics in clear language.
These links provide additional genetics resources that may be useful.
What glossary definitions help with understanding X-linked SCID?
bacteria ; cell ; chromosome ; chronic ; failure to thrive ; gene ; immune system ; immunodeficiency ; incidence ; inheritance ; mutation ; newborn screening ; protein ; recessive ; screening ; sex chromosomes ; X-linked recessive
You may find definitions for these and many other terms in the Genetics Home Reference Glossary.
See also Understanding Medical Terminology.
References (7 links)
The resources on this site should not be used as a substitute for professional medical care or advice. Users seeking information about a personal genetic disease, syndrome, or condition should consult with a qualified healthcare professional. See How can I find a genetics professional in my area? in the Handbook.