IL2RG resides on the X-chromosome and loss of function mutations in this gene cause X-linked severe combined immunodeficiency (XSCID) which is characterized by a failure in T development, lack of class switching recombination of immunoglobin genes in B lymphocytes, and the absence of natural killer (NK) cells. This evidence concerns the gene IL2RG and T-B+ severe combined immunodeficiency due to gamma chain deficiency.