PRTN3 and rheumatoid arthritis: Most patients with PsA present with oligoarticular or polyarticular arthritis and can be differentiated from patients with rheumatoid arthritis (RA), the most common inflammatory joint disease, by specific non-articular clinical features being present, as well as the infrequent seropositivity for rheumatoid factor (RF) and anti-citrullinated peptide antibody (ACPA).