Recent work has highlighted key roles for the IL-23–IL-17 axis and T helper 17 (Th17) cells in driving periodontitis (Cardoso et al., 2009; Dutzan et al., 2016, 2018; Moutsopoulos et al., 2014; Tsukasaki et al., 2018). The gene discussed is IL17A; the disease is periodontitis.