CD4 and X-linked immunodeficiency with magnesium defect, Epstein-Barr virus infection and neoplasia: 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).