IL17A and rheumatoid arthritis: Furuya et al. studied the associations between human leukocyte antigen DRB1 (HLA-DRB1) shared epitope, RANK, RANK ligand, osteoprotegerin (OPG), and interleukin 17 (IL17) genotypes with age of disease onset and radiographic progression in Japanese patients with early rheumatoid arthritis (RA) [25].