IL7R mutations cause an autosomal recessive form of severe combined immune deficiency (SCID). As in all forms of SCID, cellular and humoral immunity is defective and children present with persistent severe viral, bacterial and fungal infections. In IL7R deficiency, T cells are severely reduced but B and NK cell numbers are normal. IL7R or IL7R alpha are both names for the unique alpha chain of the interleukin 7 receptor, which is necessary for T cell development. In contrast the gamma chain of the IL7 receptor is shared by the receptors for IL2 and IL4, and its deficiency causes a T- B+ NK- form of SCID. ILR7 alpha deficiency is clinically indistinguishable from other forms of T- B+ NK+ SCID caused by mutations in the CD45, CD3D, and CD3E genes and may overlap with other types of SCID. An Omenn-like phenotype has been described.