FGF23 and X-linked hypophosphatemia: XLH is characterized by excess circulating fibroblast growth factor-23 (FGF-23) concentrations and manifests with chronic hypophosphatemia, renal phosphate wasting, and multiple skeletal complications, including short stature, bone deformities (such as leg bowing), which often require corrective surgery, musculoskeletal pain and stiffness, early-onset osteoarthritis, enthesopathy, muscle weakness and fatigue, dental complications, fractures, and impaired quality of life.2-5