<h4>Background</h4>X-linked severe combined immunodeficiency (X-SCID), caused by mutations in the gamma-chain gene of the interleukin-2 receptor (<i>IL2RG</i>), is a prevalent form of SCID characterized by recurrent and fatal opportunistic infections that occur early in life. This evidence concerns the gene IL2RG and T-B+ severe combined immunodeficiency due to gamma chain deficiency.