Further investigations showed persistent hypophosphataemia with high renal phosphate wasting (phosphate excretion 87 mmol/24 h, normal: 12–42 mmol/24 h), high FGF23—423 RU/mL (0–100 RU/mL), and signs of severe osteoporosis in densitometry. Here, FGF23 is linked to osteoporosis.