Hypogammaglobulinemia has been sporadically reported in patients with hypomorphic mutations in STXBP2 (FHL-5) and late HLH onset (Rohr et al., 2010; Meeths et al., 2010; Pagel et al., 2012; Esmaeilzadeh et al., 2015). This evidence concerns the gene FHL5 and hemophagocytic syndrome.