PR and RA are closely linked, with shared genetic risk factors, a similar distribution of affected joints—the wrists, metacarpophalangeal joints and proximal interphalangeal joints, and a similar prevalence of RA-related autoantibodies; anti-citrullinated protein antibodies (ACPA) and rheumatoid factor (RF) [2, 3]. This evidence concerns the gene PRTN3 and rheumatoid arthritis.