 JAK3 is involved in signal transduction by receptors that employ the common gamma chain (γc) of the type I cytokine receptor family (e.g.IL-2R, IL-4R, IL-7R, IL-9R, IL-15R, and IL-21R).Mutations that abrogate Janus kinase 3 function cause an autosomal SCID (severe combined immunodeficiency disease), while activating Janus kinase 3 mutations lead to the development of leukemia.