Familial hemophagocytic lymphohistiocytosis (FHL) is a lethal disorder of immune regulation, characterized by uncontrolled T-lymphocyte and macrophages activation. This would lead activated T-lymphocyte and macrophages to infiltrate the liver, spleen, bone marrow, and central nervous system resulting in a multisystem disorder with early onset infancy. The main features of the disease are: a high, persistent or intermittent fever, splenomegaly, cytopenia (anemia, thrombocytopenia, neutropenia, and leucopenia), hypertriglyceridemia, hypofibrinogenemia, hyperferritinemia, and hemophagocytosis in the bone marrow, spleen or lymph nodes by activated macrophages.
FHL exhibits genetic heterogeneity, it is caused by several genes: one is located in 10q21-22 (PRF1), a second in 17q25.1 (UNC13D), a third in 6q24 (STX11), while another gene is located in 9q21.3-q22 region, but the gene responsible for the FHL1 in this region is not identified.