FAM20C and polyostotic fibrous dysplasia: Other rare forms of FGF23-dependent hypophosphatemic rickets include Raine syndrome due to mutation in the FAM20C gene (11), polyostotic fibrous dysplasia (PFD) due to gain-of-function mutation of the GNAS gene (12), hypophosphatemic rickets and hyperparathyroidism due to translocation of the KLOTHO promoter (13), osteoglophonic dysplasia caused by dominant activation variants in FGFR1 (14), opsismodysplasia (15), and Jansen-type metaphyseal chondrodysplasia due to mutations in the parathyroid hormone 1 receptor gene (16, 17).