PRTN3 and lung disorder: In several more recent studies, the association between smoking and ACPA was not specific for ACPA, but found to be largely due to the co‐occurrence of ACPA and RF, as smoking is associated with RF rather than ACPA125, 126 or with double positivity alone.127 In ACPA‐positive patients with lung disease and without signs of joint inflammation, smoking was not associated with higher ACPA titers or transition toward RA.128 This indicates that smoking might not be the unique factor linking lung inflammation with ACPA production and RA development.