Clinically, IL-18 has been demonstrated to be a cytokine crucial in MAS pathogenesis as: 1) many patients presenting with hyperinflammatory disease present with significantly elevated plasma levels of IL-18 (Yasin et al., 2020a; Kawashima et al., 2001) and, 2) plasma concentration of IL-18 correlates strongly with disease severity (Weiss et al., 2018) and, 3) targeting IL-18 signalling seems to be a promising strategy to treat MAS (Yasin et al., 2020b). The gene discussed is IL18; the disease is macrophage activation syndrome.