Case presentation

The patient was a woman in her 30s diagnosed with XLH at 3 years of age. Her height was 148.1 cm, and her weight was 46.1 kg. Despite receiving conventional therapy as a child and corrective surgery at the age of 15, she experienced recurrent fractures and persistent bone pain as an adult. At the age of 31, she suffered femoral fractures requiring intramedullary fixation (Fig. 1). She had no history of treatment interruption and maintained excellent medication adherence throughout the course. She presented at the age of 32 with severe bone pain and needed a cane to walk. Her biochemical profile showed serum phosphate at the lower limit of the reference range (serum phosphate of 2.7 mg/dL [SI: 0.87 mmol/L]) (reference range, 2.7-4.6 mg/dL [SI: 0.87-1.49 mmol/L]) along with elevated intact FGF23 (78.1 pg/mL [SI: 3.1 pmol/L]) (reference range, 19.9-52.9 pg/mL [SI: 0.79-2.10 pmol/L]) and renal phosphate wasting, with tubular reabsorption of phosphate (TmP/GFR) of 1.70 mg/dL (SI: 0.55 mmol/L) (reference range, 2.6-4.4 mg/dL [SI: 0.84-1.41 mmol/L]), despite treatment with alfacalcidol (0.75 mcg/day) and oral phosphate (1500 mg/day).

Figure 1: Radiographic finding of the mother. Anteroposterior radiograph of the mother's hips at age 32, with intramedullary nails inserted for femoral fractures, demonstrating the severity of her bone disease prior to burosumab treatment.