ACPA− individuals also had increased IgA levels compared to controls, yet the levels were slightly higher in ACPA+ RA (ACPA− n = 730, 2.28 ± 1.0 mg/ml [median 2.15]; ACPA+ n = 1250, 2.39 ± 0.97 mg/ml [median 2.25], p = 0.003). This evidence concerns the gene PRTN3 and rheumatoid arthritis.