Familial expansile osteolysis.

Familial expansile osteolysis (FEO) is a unique bone dysplasia, which has, over five generations, affected 42 members of a Northern Ireland family. The disease follows a classic autosomal dominant pattern of inheritance. The condition is distinct enough in its clinical features and natural history to be recognized as a new and unique disease. There are both general and focal skeletal changes, the latter having a predominantly peripheral distribution and an onset from the second decade. Progressive osteoclastic resorption accompanied by medullary expansion leads to severe and painful disabling deformities with a tendency to pathologic fracture. Most affected members of the family have an associated early-onset deafness and loss of dentition as a result of unique middle ear and dental abnormalities. The serum alkaline phosphatase and urinary hydroxyproline are elevated to a variable degree, whereas other biochemical indices are normal. The response of the disease to a therapeutic trial using parenteral dichloro-methylene-diphosphonate (dichloro-MDP) produced an initial rapid biochemical response, which was not sustained.