SFRP4 and rheumatoid arthritis: In the pathological mechanism of RA model rats, DNA methyltransferase 1 (DNMT1) mediates the hypermethylation of SFRP4 and SFRP2 promoter regions, and the enrichment and binding of methyl-CpG binding protein 2 (MeCP2) in the hypermethylation regions of SFRP4 and SFRP2 promoters, resulting in the inhibition of the expression of SFRP4 and SFRP2 and the activation of Wnt signaling pathway (Miao et al., 2015a; Miao et al., 2018b).