NKG2D surface expression on NK and CD8+ T cells is reduced due to inefficient glycosylation by loss-of-function mutations in the Mg2+ transporter MAGT1 in patients with X-linked immunodeficiency with magnesium defect, Epstein-Barr virus (EBV) infection, and neoplasia (XMEN) (Chaigne-Delalande et al., 2013; Dhalla et al., 2015; Patiroglu et al., 2015; Brigida et al., 2017; Ravell et al., 2020a). Here, KLRK1 is linked to X-linked immunodeficiency with magnesium defect, Epstein-Barr virus infection and neoplasia.