Pathogenic variants in PHEX are associated with elevated serum concentrations of fibroblast growth factor 23 (FGF23), a molecule secreted by osteocytes and osteoblasts, which downregulating the expression of sodium-dependent phosphate transport proteins 2A and 2C, leading to a diminished reabsorption of phosphate in the proximal renal tubule, an increase in urinary elimination of phosphate, and, as a result, hypophosphatemia. The gene discussed is FGF23; the disease is hypophosphatemia.