Mutations in STXBP2 are associated with familial hemophagocytic lymphohistiocytosis (FHL), a life-threatening hyperinflammatory syndrome that results from an uncontrolled and ineffective immune response due to dysfunction of cytotoxic T lymphocytes (CTLs) and NK cells [18–20]. The gene discussed is STXBP2; the disease is hemophagocytic syndrome.