Genetic, rheumatologic, immunologic, metabolic, and renal studies of a father and son with idiopathic multicentric osteolysis are reported. The disorder appeared through mutation. The father developed symptoms as an infant, his son at age 4 years and 9 months. Both have micrognathia and hypotelorism and were exceptionally tall during the symptomatic phase of their disease. Biopsies of the son's wrist showed normal synovium, encroachment on cartilage by fibrocellular tissue, and both osteoclastic resorption and repair of affected bone. Hydroxyproline in his urine was increased. No immunologic, renal, or other metabolic abnormalities were identified. Idiopathic multicentric osteolysis (IMO) is the name chosen by Tyler and Rosenbaum ( I ) in 1976 for a rare disorder characterized by multifocal articular bone destruction beginning in infancy or childhood. Typically, pain and swelling of the wrists and ankles begin after an episode of trauma, persist during childhood, and then remit during adolescence leaving variable deformity of the hands and feet. Since the carpal and tarsal bones are invariably affected, this disease had previously been called "carpal and tarsal osteolysis" (2,3) or "disappearing carpal bones" (4). Little is known about its pathogenesis, hence, some chose to describe it as "essential" ( S I I ) , whereas others emphasized that the disorder in some cases was hereditary (12-14) or occasionally associated with fatal nephropathy (6,8,11,13,15). Recent and comprehensive reviews have been published (1,2,7,12). Our purpose is to describe the results of clinical, genetic, and laboratory studies of a family in which dominant transmission of IMO followed its appearance through mutation.
FAMILY DESCRIPTIONCase 1 (Figure 1, 111-1) An 8% year old boy was the product of a normal first pregnancy and delivery. H e was well until age 4% when he injured his left elbow. Although clinical examination did n o t indicate trauma, radiographs reportedly disclosed a "hairline"