Mikuls TR, Edison J, Meeshaw E, et al. - This study was undertaken to assess serum autoantibodies to malondialdehyde‐acetaldehyde (MAA) prior to rheumatoid arthritis (RA) diagnosis. Researchers assessed anti‐MAA antibody isotypes, anti‐CCP2, and RF‐IgM in pre‐ and post‐RA diagnosis samples (n=214 cases, 210 controls). The separate mixed‐models were applied to explore the timing of elevations in autoantibody concentrations relative to RA diagnosis for each antibody and/or isotype. The mixed-effects linear regression models were applied to analyze the relationships between pre‐diagnosis autoantibody concentrations in cases. In comparison with anti‐CCP2 or RF, IgG and IgA anti‐MAA autoantibodies are elevated pre‐RA diagnosis but seem later in the pre‐clinical course. These outcomes imply that MAA formation and anti‐MAA immune responses could have a role in the transition from subclinical autoimmunity to clinically apparent arthritis.