Moreover, the levels of IL-40 are markedly up-regulated in double-positive (RF+/anti-CCP+) compared to double-negative (RF-/anti-CCP-) patients with RA in the synovial fluid [66.6 (41.5-93.1) vs. 9.9 (3.7-24.0) ng/ml; p<0.0001], as well as in the serum [10.9 (4.2-96.0) vs. 3.3 (1.6-6.6) ng/ml; p<0.001]. The gene discussed is C17orf99; the disease is rheumatoid arthritis.