Burosumab Anti-FGF23 XLH Targeted Therapy — ESENeph MCQ

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HardTubular DisordersBurosumab Anti-FGF23 XLH Targeted TherapyESENeph

A 45-year-old man with X-linked hypophosphataemia (XLH, PHEX mutation) has recurrent fractures, bone pain, and dental abscesses. His phosphate is 0.5 mmol/L despite oral phosphate and alfacalcidol supplementation. FGF23 is markedly elevated. What is the targeted biological therapy for XLH?

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Correct answer: A — Burosumab (anti-FGF23 monoclonal antibody)

Burosumab is a fully human monoclonal antibody that binds and neutralises FGF23 — the pathogenic driver of phosphate wasting in XLH. PHEX gene mutations cause elevated FGF23, which inhibits renal phosphate reabsorption (via NaPi-IIa/IIc downregulation) and suppresses 1-alpha-hydroxylase (reducing active vitamin D). Burosumab directly blocks FGF23 action, normalising serum phosphate and improving mineralisation. The pivotal trials demonstrated significant improvement in rickets, phosphate levels, and growth in children, and fracture healing in adults. Burosumab is administered subcutaneously every 2-4 weeks. It has largely replaced conventional therapy (oral phosphate + alfacalcidol), which is burdensome and associated with nephrocalcinosis from calcium-phosphate supersaturation.

Reference: NICE HST6 – Burosumab for XLH; Carpenter et al 2018 – Burosumab Phase 3