PADI4 and rheumatoid arthritis: The prevalence levels for anti-PAD4 IgA in RA were almost identical between our current investigation and the studies by Darrah et al. Interestingly, in the latest study, anti-PAD4 IgA antibodies were strongly associated with anti-PAD3/4 cross-reactivity antibodies, an antibody population that is associated with erosive RA [7].