<b>Background:</b> X-linked immunodeficiency with magnesium defect, Epstein-Barr virus (EBV) infection, and neoplasia (XMEN) disease is a rare inborn error of immunity caused by loss-of-function mutations in <i>MAGT1</i>, leading to impaired N-linked glycosylation. The gene discussed is MAGT1; the disease is Epstein-Barr virus infection.