Higher serum levels of Wnt inhibitor Dkk-1 found in RA patients than in controls and its decrease after biological treatment (TNFα inhibitors, IL-1Ra, anti-IL-6 antibody), suggest the strong connection between the dysregulation of Wnt signaling leading to bone loss—both locally and systemically—in RA and the pro-inflammatory state typical of the disease. Here, DKK1 is linked to rheumatoid arthritis.