PRTN3 and rheumatoid arthritis: Compared with young-onset RA (YORA), elderly-onset RA (EORA) has a higher proportion of males, and many are seronegative for rheumatoid factor (RF) and anti-cyclic citrullinated peptide antibody (ACPA), which causes difficulties in differentiating EORA from polymyalgia rheumatica (PMR) [4,5].