From OMIM
X-linked lymphoproliferative syndrome, or Duncan disease, is a primary immunodeficiency characterized by severe immune dysregulation often after viral infection, typically with Epstein-Barr virus (EBV). It is a complex phenotype manifest as severe or fatal mononucleosis, acquired hypogammaglobulinema, hemophagocytic lymphohistiocytosis (HLH), and/or malignant lymphoma. Other features may include aplastic anemia, red cell aplasia, and lymphomatoid granulomatosis (Purtilo et al., 1977; Purtilo, 1981; Purtilo and Grierson, 1991; Coffey et al., 1998; Booth et al., 2011). Genetic Heterogeneity of X-linked/Autosomal Lymphoproliferative Syndrome See XLP2 (300635), caused by mutation in the XIAP gene (300079), also on Xq25; LPFS1 (613011), caused by mutation in the ITK gene (186973) on chromosome 5q33; LPFS2 (615122), caused by mutation in the CD27 gene (186711) on chromosome 12p13; and LPFS3 (618261), caused by mutation in the CD70 gene (TNFSF7; 602840) on chromosome 19p13.  http://www.omim.org/entry/308240

From MedlinePlus Genetics
X-linked lymphoproliferative disease (XLP) is a disorder of the immune system and blood-forming cells that is found almost exclusively in males. More than half of individuals with this disorder experience an exaggerated immune response to the Epstein-Barr virus (EBV). EBV is a very common virus that eventually infects most humans. In some people it causes infectious mononucleosis (commonly known as "mono"). Normally, after initial infection, EBV remains in certain immune system cells (lymphocytes) called B cells. However, the virus is generally inactive (latent) because it is controlled by other lymphocytes called T cells that specifically target EBV-infected B cells.

XLP can be divided into two types based on its genetic cause and pattern of signs and symptoms: XLP1 (also known as classic XLP) and XLP2. People with XLP2 have not been known to develop lymphoma, are more likely to develop hemophagocytic lymphohistiocytosis without EBV infection, usually have an enlarged spleen (splenomegaly), and may also have inflammation of the large intestine (colitis). Some researchers believe that these individuals should actually be considered to have a similar but separate disorder rather than a type of XLP.

People with XLP may respond to EBV infection by producing abnormally large numbers of T cells, B cells, and other lymphocytes called macrophages. This proliferation of immune cells often causes a life-threatening reaction called hemophagocytic lymphohistiocytosis. Hemophagocytic lymphohistiocytosis causes fever, destroys blood-producing cells in the bone marrow, and damages the liver. The spleen, heart, kidneys, and other organs and tissues may also be affected. In some individuals with XLP, hemophagocytic lymphohistiocytosis or related symptoms may occur without EBV infection.

About one-third of people with XLP experience dysgammaglobulinemia, which means they have abnormal levels of some types of antibodies. Antibodies (also known as immunoglobulins) are proteins that attach to specific foreign particles and germs, marking them for destruction. Individuals with dysgammaglobulinemia are prone to recurrent infections.

Cancers of immune system cells (lymphomas) occur in about one-third of people with XLP.

Without treatment, most people with XLP survive only into childhood. Death usually results from hemophagocytic lymphohistiocytosis.  https://medlineplus.gov/genetics/condition/x-linked-lymphoproliferative-disease