Therapeutic Response to Burosumab in a Child with X-Linked Hypophosphatemia: A Case Report

X-linked hypophosphatemic rickets (XLH) is a rare disorder caused by mutations in the PHEX gene, resulting in the overexpression of fibroblast growth factor 23 (FGF23), a hormone that decreases renal phosphate reabsorption and active vitamin D synthesis. This report presents the case of a 3-year-old girl clinically diagnosed with XLH, presenting with bone deformities such as genu valgum, delayed motor development, and dysmorphic features. The diagnosis was confirmed through genetic testing identifying a pathogenic variant in the PHEX gene. The patient was treated with burosumab, a monoclonal antibody that inhibits FGF23. Following treatment, significant improvements were observed, including an increase in serum phosphate levels and decreases in alkaline phosphatase and parathyroid hormone (PTH) levels, demonstrating burosumab's role in improving clinical outcomes.