X-Linked Hypophosphataemic Rickets — RACP Paediatrics MCQ

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HardEndocrinologyX-Linked Hypophosphataemic RicketsRACP Paediatrics

A 2-year-old boy with X-linked hypophosphataemic rickets has bowed legs, short stature, and low serum phosphate with elevated ALP. What is the underlying defect?

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Correct answer: A — Renal phosphate wasting due to PHEX gene mutation causing excess FGF23

X-linked hypophosphataemic rickets (XLH) is caused by PHEX gene mutations leading to elevated FGF23, which causes renal phosphate wasting and impaired 1,25-dihydroxyvitamin D synthesis. Treatment includes oral phosphate supplementation and active vitamin D (calcitriol). Burosumab (anti-FGF23 antibody) is now available for XLH.

Reference: RCH Melbourne – 2024 – Clinical Practice Guidelines: Rickets