Panel A demonstrates the relationship and significant negative correlation between serum FGF23 and the degree of phosphate wasting, supporting the concept that FGF23 is responsible for the phosphate wasting that can be seen in association with FD. Panel B depicts the relationship and significant positive correlation between the serum FGF23 and the skeletal burden of FD, which supports the hypothesis that the FD tissue is the source of FGF23. Panels C&D are low and high power views, respectively, of in situ hybridization studies using probes for FGF23 that demonstrate that FD tissue demonstrates high levels of FGF23 transcripts. Panels E&F show high levels of FGF23 transcripts in bone from control, normal bone; E osteocytes and F osteoblasts in healing fracture callus. FD = fibrous dysplasia, wb = woven bone, b = bone, double arrows designate FD stromal cells, arrow heads designate osteocytes, single arrows designate osteoblasts. Adapted from reference .