As a new treatment option, burosumab is available as a fully human monoclonal antibody (AK, IgG1) that specifically binds to the phosphaturic factor FGF23 in adults and children with TIO associated with phosphaturic mesenchymal tumors that cannot be curatively resected or localized [16–19]. The gene discussed is FGF23; the disease is mesenchymal cell neoplasm.