Gene sequences of HLH-related genes (UNC13D, PRF1, STX11, STXBP2, RAB27A, etc.)in the patient and his family were amplified using polymerase chain reaction (PCR) and subsequently analyzed.<h4>Results</h4>The confirmed case involved a 42-year-old male patient presenting with recurrent fever, pancytopenia, hepatosplenomegaly, lymphadenopathy, elevated serum ferritin (600 ng/mL), significantly decreased NK cell activity (3.57%), and elevated soluble CD25 (2777 U/mL), all of which led to a diagnosis of HLH according to the HLH-2004 diagnostic criteria. The gene discussed is UNC13D; the disease is Hepatosplenomegaly.