A significant, positive correlation was observed between the serum levels of anti-PPAD IgG and anti-CCP IgG (p = 0.04), but not between the serum levels of PAD-4 and anti-CCP IgG. Also, during Arvikar et al. research, the results showed, that a subset of early RA patients had positive Pg antibody responses [11]. The gene discussed is PADI4; the disease is rheumatoid arthritis.