SFRP4 and rheumatoid arthritis: To confirm the differential gene expression detected by the microarray analysis and pathway analysis, we sampled 12 genes (Il1rn, Sfrp2, Sfrp4, Wnt7a, Frzb, Fzd2, Bmp1, Tcf3, Spp1, Mapk14, Csf1r and Ptk2b) involved in the significant signaling pathway “role of osteoblasts, osteoclasts and chondrocytes in rheumatoid arthritis” and “Wnt/β-catenin signaling” for verification using qRT-PCR.