JAK3 has a key role in the signaling downstream of the common gamma‐chain subunit that is an essential component of the IL‐2, IL‐4, IL‐7, IL‐9, IL‐15, and IL‐21 receptor complexes; indeed, JAK3‐deficiency is the main cause of T‐B+NK‐ AR‐SCID (OMIM: #600802; Wu & Sun, 2011; Rochman, Spolski, & Leonard, 2009). The gene discussed is JAK3; the disease is severe combined immunodeficiency.