X-linked severe combined immunodeficiency

X-linked severe combined immunodeficiency, usually shortened to X-linked SCID or X-SCID, is an inherited disorder of the immune system that occurs almost exclusively in boys and men. It is caused by changes (variants) in the IL2RG gene on the X chromosome. That gene makes a protein needed for developing immune cells called lymphocytes to grow and mature, so affected infants lack the cells that defend the body against certain bacteria, viruses and fungi. Without treatment they are prone to recurrent and persistent infections, poor growth, chronic diarrhea, thrush and skin rashes, and can develop life-threatening infections. The condition follows an X-linked recessive pattern of inheritance. It is the most common form of the severe combined immunodeficiency disorders, which together affect about 1 in 60,000 newborns, and roughly a quarter to a third of those cases are X-linked. Newborn screening can detect it soon after birth, allowing prompt treatment.