It was found that the expression of KIAA1199 mRNA and protein were higher in the synovial tissues of RA patients than healthy subjects; ELISA also showed that the levels of KIAA1199 protein expression were higher in the serum, synovial fluid and synovial tissue from RA patients than healthy subjects, suggesting that the over-expression of KIAA1199 plays an important role in the pathogenesis of RA. The gene discussed is CEMIP; the disease is rheumatoid arthritis.