(also known as X-linked SCID)
Reviewed November 2005
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. These infections can be very serious or life-threatening. The organisms that cause infection in people with X-linked SCID are described as opportunistic because they ordinarily do not cause illness in healthy people. 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. The exact incidence is unknown, but the condition probably affects at least 1 in 50,000 to 100,000 births.
What genes are related to X-linked SCID?
Mutations in the IL2RG gene cause X-linked severe combined immunodeficiency.
The IL2RG gene provides instructions for making a protein that is essential to 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. A condition is considered X-linked if the mutated gene that causes the disorder is located on the X chromosome, 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 must be present in both copies of the gene to cause the disorder; this situation occurs only rarely. Therefore, males are affected by X-linked recessive disorders much more frequently than females.
Where can I find information about treatment for X-linked SCID?
These resources address the management of X-linked SCID and may include treatment providers.
You might also find information on treatment of X-linked SCID in
Educational resources and Patient support.
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?
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
See How can I find a genetics professional in my area? in the Handbook.