A diagnosis is consistent with HLH if 5/8 of the below criteria are met, or if the patient has a molecular diagnosis of genetic HLH (including: PRF1, UNC13D, STX11, STXBP2, RAB27A, LYST, SH2D1A, or XIAP/BIRC4). This evidence concerns the gene XIAP and hemophagocytic syndrome.