X-linked severe combined immunodeficiency (X-SCID) is a disorder that affects the immune system, leading to frequent and severe infections, high fevers, and skin rashes. This condition mostly impacts males.
People with X-SCID lack two crucial components of the immune system: T lymphocytes and natural killer lymphocytes. Their B lymphocytes also don’t function properly. As a result, the immune system is unable to defend the body against infections. Symptoms usually appear between three and six months of age. Untreated male infants with X-SCID may experience slower growth, significant diaper and oral rashes, and persistent infections despite treatment. They might also have missing tonsils and lymph nodes. In some cases, babies with an unusual form of X-SCID may show immune system issues, rashes, gastrointestinal problems, and short stature. The most common treatment for X-SCID is bone marrow transplantation. Replacing the bone marrow of a person with X-SCID with that of a healthy individual allows the body to produce new, functional blood cells and lymphocytes. The success rate of bone marrow transplantation is significantly higher when done shortly after birth. Cord blood transplantation is another effective treatment for X-SCID. Gene therapy may be considered for patients who are not suitable candidates for bone marrow or cord blood transplantation.
X-SCID is caused by pathogenic variants in the IL2RG gene exhibit X-linked recessive inheritance. This means that one pathogenic variant is enough to cause the disease in both males (who have one X chromosome and one Y chromosome) and females (who have two X chromosomes) may experience symptoms depending on how many copies of the X chromosome that has the pathogenic variant are turned on in the cells.
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Revised November 2023
