PRF1 and hemophagocytic syndrome: The mean age of HLH onset was 3.4 ± 5 months in PERFORIN-deficient patients, 13.4 ± 19 months in RAB27A-deficient patients, 27.3 ± 37 months in SYNTAXIN-11-deficient patients and 37.7 ± 41.9 months in LYST-deficient patients.