UNC13D and hemophagocytic syndrome: After antiviral and antifungal treatments, EBV-DNA levels normalized, cerebrospinal fluid examination returned to normal, and primary HLH with an UNC13D gene mutation was confirmed by gene sequencing.<h4>Conclusions</h4>While primary HLH is more prevalent in infants and young children, it can also occur in adolescents and adults, often being misdiagnosed as secondary HLH due to concurrent EBV infection.