Hemophagocyticlymphohistocytosis (HLH) is a severe inflammatory disorder characterized by a significant accumulation of activated CD8+T lymphocytes and histiocytes in the bone marrow (BM) and lymphoid tissues. People with HLH usually develop symptoms within the first month or years of life. Symptoms may include fever, enlarged liver or spleen, cytopenia and neurological abnormalities. HLH may be inherited in an autosomal recessive manner or it can have non–genetic causes in which case it is called Acquired HLH. There are five subtypes of inherited HLH which are designated as familial HLH, Types 1–5 . Each subtypes is caused by a change (mutation) in a different gene. The genetic cause of type–1 is currently unknown. Type 2–5 are caused by mutations in the PRF 1 gene , the UNC13D gene, the STX11 gene, and The STX BP2 gene, respectively. Treatment depends on the number of factors including the severity of symptoms, the age of onset and the underlying cause of the condition. HLH is a rare disease that affects one in 50,000 births.