The level of PAD4 was significantly greater in SF from the patients with RA and a high anti-CCP titer than in SF from patients with OA (means ± SD; 88.9 ± 137.0 and 7.3 ± 18.6 ng/mL, respectively; P < 0.05; Fig. 4c). The gene discussed is PADI4; the disease is rheumatoid arthritis.