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X-linked hypophosphataemic rickets — RACP Paediatrics MCQ

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HardEndocrineX-linked hypophosphataemic ricketsRACP Paediatrics

A 3-year-old has rickets that is not responding to vitamin D supplementation. Biochemistry shows low phosphate, elevated ALP, normal calcium, normal PTH, and normal 25-hydroxyvitamin D. Urine phosphate excretion is elevated. FGF23 is elevated. What is the most likely diagnosis and appropriate treatment?

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Correct answer: E — Phosphate supplementation + calcitriol

Hypophosphataemic rickets (most commonly X-linked hypophosphataemia due to PHEX mutation with elevated FGF23) presents with rickets resistant to vitamin D, renal phosphate wasting, and normal calcium/PTH/25-OH vitamin D. Treatment is oral phosphate supplementation plus calcitriol. Burosumab (anti-FGF23 antibody) is a newer targeted therapy.

Reference: RCH Melbourne – 2023 – Rickets CPG; RACP Paediatric Curriculum – Endocrine/Nephrology