PRTN3 and rheumatoid arthritis: Interestingly, a pronounced risk interaction of silica dust and cigarette smoking for ACPA+ RA development was seen amongst co-exposed workers: silica only, OR 1.15 (95% CI 0.42-3.15); current smoking, OR 2.78 (95% CI 1.77-4.38); silica + current smoking OR 7.36 (95% CI 3.31-16.38), rising to OR 14.9, (95% CI 5.32-37.84) for >20 pack years smoked Fig. (3).