In addition, patients with phosphate-wasting tubulopathies (including nephropathic cystinosis) may have low fibroblast growth factor 23 (FGF23) and PTH levels despite advanced CKD, and significant metabolic bone disease characterized by hypophosphatemic rickets in infancy, bone pain, and deformities [40, 48]. Here, FGF23 is linked to chronic kidney disease.