Learn about familial hemophagocytic lymphohistiocytosis (HLH) disorders, including X-linked lymphoproliferative (XLP) disease, Chediak-Higashi syndrome, and X-linked immunodeficiency with magnesium defect, EBV infection, and neoplasia (XMEN) disease. This chapter is taken from the IDF Patient & Family Handbook for Primary Immunodeficiency Diseases, 6th Edition, copyright ©2019 by Immune Deficiency Foundation, USA.