Mutations of the IL2RG gene, which encodes for the interleukin-2 receptor common gamma chain (γC, CD132), can lead to X-linked severe combined immunodeficiency (X-SCID) associated with a T−B+NK− phenotype as a result of dysfunctional γC-JAK3-STAT5 signaling. The gene discussed is GC; the disease is T-B+ severe combined immunodeficiency due to gamma chain deficiency.