Haemophagocytic lymphohistiocytosis (HLH) is a life-threatening disorder of immune regulation, and HLH patients with mutations in genes including PRF1, UNC13D, STX11, STXBP2, SH2D1A, XIAP, and ITK were reported to be primary HLH. The gene discussed is UNC13D; the disease is hemophagocytic syndrome.