Fibrous dysplasia (FD), caused by somatic activating mutations in GNAS, is characterized by woven bone lesions in skeletal bone due to defective osteoblast differentiation32, 33, 34; FD also shows increased osteoclastic bone resorption at the site of these lesions that is not a direct effect of Gsα signaling in osteoclasts but is a response by osteoclasts to increased interleukin-6 secretion by osteoblasts12. Here, GNAS is linked to fibrous dysplasia.