The serum concentrations of APE1/Ref-1 in the RA patient group were significantly increased compared to those of the HC group and OA patient group (0.44 ± 0.39 ng/mL for RA group vs. 0.19 ± 0.14 ng/mL for HC, p < 0.001 and 0.19 ± 0.11 ng/mL for OA group, p < 0.001) (Figure 1a). This evidence concerns the gene APEX1 and rheumatoid arthritis.