Biallelic germline inactivation of the PRF1 gene (10q22.1) is associated with familial hemophagocytic lymphohistiocytosis (FHL), a severe hereditary syndrome characterized by excessive inflammation; this condition is caused by the inability of NK and CD8+ T cells to eliminate target cells through perforin-dependent and granule-mediated cytotoxicity [31,32]. The gene discussed is PRF1; the disease is hereditary hemophagocytic lymphohistiocytosis.