LYST and Immunodeficiency: The cohort included 99 molecularly confirmed p-HLH cases, comprising 28 familial (with PRF1/UNC13D/STX11/STXBP2 mutations), 34 immunodeficiency-associated cases (with RAB27A/CHS1/AP3B1 mutations), and 37 EBV-driven cases (with SH2D1A/BIRC4/MAGT1 mutations), as well as 165 s-HLH cases associated with EBV infection and negative genetic results.