PRTN3 and Arthritis: An early study by Stadt et al. suggested that multiple ACPA reactivities (≥2 vs 0–1) was a significant risk factor (odds ratio 2.1; 95% CI: 1.0, 4.4; P = 0.04) with a strong trend of prediction for arthritis development (HR: 1.7; 95% CI: 0.93, 3.16, P = 0.08) in the Risk-RA phase [23]; and we can in this study report a significant predictive value of presence of ACPA reactivity (≥1 vs 0) for arthritis (HR 8.0; 95% CI: 2.9, 22; P < 0.001).