IL2RG contains one fibronectin type-III domain. IL2RG is an important signaling component of many interleukin receptors, including those of interleukin -2, -4, -7 and -21, and is thus referred to as the common gamma chain. IL2RG interacts with SHB upon interleukin stimulation and HTLV-1 accessory protein p12I. Defects in IL2RG are the cause of X-linked combined immunodeficiency (XCID) and severe combined immunodeficiency X-linked T-cell-negative /B-cell-positive / NK-cell-negative (XSCID).