PADI3 and rheumatoid arthritis: The objectives of this study are therefore: to determine the prevalence of serum anti-PAD4 antibodies (including anti-PAD4/PAD3 cross-reactive antibodies) in African Americans with RA; to describe the temporal changes in anti-PAD4 and anti-PAD4/PAD3 cross-reactive antibody titers; and to compare the radiographic score and radiographic progression of anti-PAD4-positive and anti-PAD4/PAD3-positive African-American patients with those of patients lacking these antibodies.