Patients with “X-linked immunodeficiency with magnesium defect, Epstein-Barr virus (EBV) infection, and neoplasia” (XMEN), resulting from a loss-of-function mutation in the magnesium transporter 1 (MAGT1), have low intracellular free magnesium levels and an increased risk for malignancies and chronic EBV infections [3]. Here, MAGT1 is linked to X-linked immunodeficiency with magnesium defect, Epstein-Barr virus infection and neoplasia.