The first HLH/CSS-related molecular biological diagnostic criteria is to have HLH/CSS-related pathogenic gene mutations among the following genes: PRF1, UNC13D, STX11, STXBP2, RAB27A, LYST, SH2D1A, BIRC4, ITK, AP3β1, MAGTI, CD27 and so on (Tables 2 and 3) [14]. The gene discussed is PRF1; the disease is hemophagocytic syndrome.