This phenomenon has been already described in patients with myeloma [34] and patients with rheumatoid arthritis [11], where increased serum DKK1 directly impaired new bone formation through the reduction of osteoblast function and increased the production of RANKL and decreased the production of OPG by stromal cells and thus leading to increased bone resorption. This evidence concerns the gene DKK1 and rheumatoid arthritis.