One immunodeficiency affects cytosolic Mg2+ levels, required for PLCγ1 activation, via mutations in the magnesium transporter 1 (MAGT1) in patients with X-linked immunodeficiency with magnesium defect, EBV infection, and neoplasia (XMEN) [47–51]. The gene discussed is PLCG1; the disease is Epstein-Barr virus infection.