Genetic defects of PFR1, Mun13-4, STX11, STXBP2, ITK (autosomal recessive), SH2D1A/SAP, and XIAP (X-linked) are responsible for hereditary HLH, with increased susceptibility to recurrent, and/or fatal EBV infection [15]–[20]. Here, STXBP2 is linked to hemophagocytic syndrome.