To further confirm whether IHC with PIDs for FGF23 has the potential to differentiate FGF23-related hypophosphatemic osteomalacia due to ectopic oversecretion of FGF23 from that due to excess orthotopic FGF23 secretion from the bone, bone samples from TIO patients with concomitant hypophosphatemia were subjected to IHC with PIDs (TIO group). The gene discussed is FGF23; the disease is hypophosphatemia.