Germline inactivating mutations in OPG are responsible for the autosomal dominant diseases: early-onset and familial Paget'disease, familial expansile osteolysis and expansile skeletal hyperphosphatasia, which are characterised by the development of expansile osteolytic bone lesions.37, 38 Myeloma cells express RANKL and treatment of mice models of MM with OPG has been demonstrated to prevent lytic bone lesions, maintaining cancellous bone volume and inhibiting OC formation.12, 32. This evidence concerns the gene TNFRSF11B and plasma cell myeloma.