16 Chapter 1 Figure 1, panel A: Severe bone deformation of the left leg and left iliac bone by FD in a 43-yearold female patient with polyostotic fibrous dysplasia from our study [12] using 3D rendering from low-dose CT. Figure 1, panel B: A 5-year-old girl, with hyperpigmented skin lesions (café au lait macules) with McCune-Albright syndrome. Source: Adapted fromCollins MT, Singer FR, Eugster E. McCune-Albright syndrome and the extraskeletal manifestations of fibrous dysplasia. Orphanet J Rare Dis. 2012 May 24;7 Suppl 1(Suppl 1):S4. doi: 10.1186/1750-1172-7-S1-S4 (Open Access, Creative Commons Attribution License). To date, there is no cure for FD/MAS. However, treatment with denosumab, altering bone remodeling by targeting Receptor Activator of Nuclear Factor-κB ligand (RANKL), has recently shown promising results in the management of selected FD patient groups, for both pain reduction and prevention of pathological fractures [14]. Increased bone formation, such as caused by FD/MAS, can be biochemically reflected by an increase in serum alkaline phosphatase (ALP) and procollagen type 1 N-terminal propeptide (P1NP) in serum analysis, whereas the observed increased