Elevated intact FGF23 concentrations in children with hypophosphatemia might seem to indicate FGF23-dependent renal phosphate wasting, e.g., autosomal dominant hypophosphatemic rickets, X-linked hypophosphatemia, or tumor-induced osteomalacia [15,55,56]. The gene discussed is FGF23; the disease is autosomal dominant hypophosphatemic rickets.