MUNC13-4 is known to prime cytolytic granules, rendering them competent to fuse to the plasma membrane of NK and CD8 T cells, and mutations affecting this gene are linked to the development of the subtype 3 of familial hemophagocytic lymphohistiocytosis (FHL), a genetic form of hemophagocytic lymphohistiocytosis (HLH) [83–85]. This evidence concerns the gene UNC13D and hemophagocytic syndrome.