MAFB and multicentric carpo-tarsal osteolysis with or without nephropathy: Here we report the use of denosumab, a monoclonal antibody against receptor activator of nuclear factor κB ligand (RANKL), as monotherapy for multicentric carpotarsal osteolysis syndrome (MCTO) in an 11.5-year-old male with a heterozygous missense mutation in <i>MAFB</i> (c.206C>T; p.Ser69Leu).