X-linked immunodeficiency with magnesium defect, Epstein-Barr virus infection and neoplasia is a rare combined T and B cell immunodeficiency characterized by recurrent sinopulmonary and viral infections, persistent elevated Epstein-Barr virus (EBV) viremia and increased susceptibility to EBV-associated B-cell lymphoproliferative disorders. Immunological analyzes show normal lymphocyte count or mild to moderate lymphopenia, inverted CD4:CD8 T-cell ratio and hypogammaglobulinemias. The disease is X-linked immunodeficiency with magnesium defect, Epstein-Barr virus infection and neoplasia (MONDO_0010455, a Monarch Disease Ontology id). Also known as: Cid due to MAGT1 deficiency, XMEN, combined immunodeficiency due to MAGT1 deficiency, immunodeficiency, X-linked, with magnesium defect, Epstein-Barr virus infection and neoplasia, X-linked recessive.