Other patients have an inherited disorder predisposing to HLH, and are classified as (i) familial HLH (due to mutations in PRF1, UNC13D, STX11, or STXBP2), (ii) pigmentary disorders associated with HLH, due to mutations in RA827A (Griscelli syndrome type 2), LYST (Chediak‐Higashi syndrome) or AP3B1 (Hermansky‐Pudlak syndrome 2), (iii) X‐linked lymphoproliferative diseases (XLP) due to mutations in SH2D1A (XLP1) or XIAP (XLP2), and iv). This evidence concerns the gene PRF1 and hemophagocytic syndrome.