SOST and rheumatoid arthritis: Studies on human and animal tissues have provided compelling evidence that increased levels of antagonists of the Wnt signaling pathway like Dickkopf-related protein 1 (DKK1), soluble Frizzled-related protein 1 (sFRP1) and sclerostin (SOST) in the inflammatory milieu of RA synovium might be responsible for the phenotype [6, 127].