Burosumab (Crysvita®), a fully human IgG1 monoclonal antibody directed at 
fibroblast growth factor 23 (FGF23), is indicated for the treatment of X-linked 
hypophosphatemia (XLH), a condition associated with excessive FGF23 production. 
It directly addresses the excessive FGF23 activity in patients with XLH by 
binding to FGF23, and inhibiting its signaling. This leads to increased 
gastrointestinal phosphate absorption and renal phosphate reabsorption, thereby 
improving serum phosphate levels, and, ultimately, bone mineralization and the 
risk of bone disease. In clinical trials, subcutaneous burosumab increased serum 
phosphorus levels in pediatric and adult patients with XLH, as well as 
significantly improving the severity of rickets in children, and improving pain, 
stiffness, physical functioning, and fracture/pseudofracture healing in adults. 
Burosumab is well tolerated by children and adults with XLH, with most 
treatment-emergent adverse events being of mild to moderate severity.