X-linked Severe Combined Immunodeficiency (X-SCID) is a profound and severe immunodeficiency characterized by the complete absence of NK cells and T cells in the peripheral blood. Cause It is caused by mutations of the IL2RG gene. This gene codes for the Cytokine receptor common gamma chain, a receptor for a number of cytokines involved in maintaining T cell homeostasis and stimulating immune cell development. Without a functional receptor, the cells can't develop normally, and are unable to pr… (More on X-scid)