Although the physiological significance of alterations in serum osteocalcin levels in OA and RA is currently not known they may reflect the different bone phenotypes in these two joint diseases: serum osteocalcin levels are associated with bone formation, and while OA is rather characterized by an increase of subchondral bone mass (osteophytes, subchondral bone plate thickness), in RA bone resorption and loss of subchondral bone is characteristic [46,69,70]. Here, BGLAP is linked to rheumatoid arthritis.