GDNF and McCune-Albright syndrome: We conducted a systematic search in the PubMed database, Web of Science, China Knowledge Network (CNKI) with the following keywords: “McCune–Albright syndrome (MAS); polyfibrous dysplasia (FD); bone pain; bone remodeling; G protein coupled receptors; GDNF family receptors; purinergic receptors and glycogen synthase kinase”, as well as other keywords were systematically searched.