Familial expansile osteolysis (FEO) is a rare autosomal dominant disorder causing bone dysplasia. It is characterized by increased osteoclast activity, medullary expansion, and hearing and dental problems. The mutations in the TNFRSF11A gene encoding RANK have been identified. FEO is similar in some respects to Paget's disease but distinct enough in its clinical, radiological and histological findings to be classified as a separate disease.
