IL-17 was first described in 1996 due to its effect on the production of IL-6 and IL-8 by rheumatoid arthritis (RA) synoviocytes (2) and the new cytokine was first named IL-17A but several other members of the family were subsequently identified, in particular IL-17F, which is approximately 50% homologous to IL-17A and both converge on TNFα, among other mediators (3, 4). The gene discussed is IL17F; the disease is rheumatoid arthritis.