IL-17 is an osteoclastogenic inflammatory cytokine promoting the production of other destructive cytokines such as the macrophage migration inhibitory factor (MIF), tumour necrosis factor-alpha (TNF-α) and RANK-L which in turn increase reactive oxygen species (ROS) and osteoclastic differentiation in rheumatoid arthritis (RA). The gene discussed is IL17A; the disease is rheumatoid arthritis.