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]. The gene discussed is SH2D1A; the disease is Epstein-Barr virus infection.