HLH is a hyperinflammatory syndrome in which familial (primary) forms arise from biallelic variants in cytotoxic-pathway genes (e.g., PRF1, UNC13D, STX11, STXBP2), and in neonates the presentation may closely mimic sepsis (Zhang et al., 2024). Here, STXBP2 is linked to hemophagocytic syndrome.