SOST and rheumatoid arthritis: Its role has also been investigated in various pathological conditions: low Dkk-1 and sclerostin serum levels have been described in diffuse idiopathic hyperostosis (6, 7), while its excessive overexpression seems to correlate with osteolytic lesions in multiple myeloma (8), with cortical erosions, low bone formation, and secondary osteoporosis in rheumatoid arthritis (9, 10).