From MedlinePlus Genetics
X-linked immunodeficiency with magnesium defect, Epstein-Barr virus infection, and neoplasia (typically known by the acronym XMEN) is a disorder that affects the immune system in males. In XMEN, certain types of immune system cells called T cells are reduced in number or do not function properly. Normally these cells recognize foreign invaders, such as viruses, bacteria, and fungi, and are then turned on (activated) to attack these invaders in order to prevent infection and illness. Because males with XMEN do not have enough functional T cells, they have frequent infections, such as ear infections, sinus infections, and pneumonia.

In particular, affected individuals are vulnerable to the Epstein-Barr virus (EBV). EBV is a very common virus that infects more than 90 percent of the general population and in most cases goes unnoticed. Normally, after initial infection, EBV remains in the body for the rest of a person's life. However, the virus is generally inactive (latent) because it is controlled by T cells. In males with XMEN, however, the T cells cannot control the virus, and EBV infection can lead to cancers of immune system cells (lymphomas). The word "neoplasia" in the condition name refers to these lymphomas; neoplasia is a general term meaning abnormal growths of tissue. The EBV infection itself usually does not cause any other symptoms in males with XMEN, and affected individuals may not come to medical attention until they develop lymphoma.  https://medlineplus.gov/genetics/condition/x-linked-immunodeficiency-with-magnesium-defect-epstein-barr-virus-infection-and-neoplasia