Burosumab, a monoclonal antibody against FGF23 approved for the treatment of XLH, was shown to reverse hypophosphatemia and improve clinical outcomes in both children and adults with XLH.12, 13, 19, 20, 21 Consistent with those published studies, the current study in adults with XLH demonstrates that 48 weeks of burosumab treatment restores phosphorus homeostasis. The gene discussed is FGF23; the disease is hypophosphatemia.