Magnesium (Mg2+) has previously been associated with anti-viral immunity as mutations of the magnesium transporter 1 (MAGT1) gene causes an immunodeficiency called X-linked immunodeficiency with Mg2+ defect, EBV infection, and neoplasia (XMEN) which is characterized by CD4 lymphopenia, chronic viral infections, and impaired T lymphocyte activation (75). The gene discussed is CD4; the disease is Epstein-Barr virus infection.