PRF1 and hemophagocytic syndrome: Defective apoptosis is another cellular defect in HLH, as activated lymphocytes in some patients with HLH are found to have decreased spontaneous activation of caspase-3-like enzyme activity [6]. Our patient was evaluated for the Syntaxin 11 (STX-11), MUNC13-4, SH2D1A, and Perforin 1 (PRF1) genes, which did not reveal any demonstrable evidence of FHL.