Interestingly, higher levels of anti-PAD4 IgG and IgA, but not ACPA, were found in the RA patients with erosive disease vs. individuals without erosions (p = 0.0166, p = 0.0176, and p = 0.7883, respectively) (Figure 2A,B), and in patients under biological treatment vs. those that were not on biologics (p = 0.0002, p = 0.0009, and p = 0.7752, respectively) (Figure 2C,D). Here, PADI4 is linked to rheumatoid arthritis.