Multiple Exostoses, Hereditary

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Multiple osteochondroma; Multiple cartilaginous exostoses; Diaphyseal aclasis

Definition and Characteristics

Autosomal dominant bone disorder characterized by bony outgrowths (osteochondroma) mainly located at the juxtaepyphyseal parts of the long bones [1]. Number, size, site and shape of the osteochondroma can vary greatly between patients. Pressure of the osteochondromas on neighboring tissues and organs causes pain, reduced mobility and compression of nerves, muscles and blood vessels. Deformity of legs, forearms (resembling Madelung deformity) and shorter stature are frequently observed in osteochondroma patients. In 0.5–2% of these patients chondrosarcoma development is observed.


The prevalence of hereditary multiple exostoses is estimated to be one in 50,000 world wide.


EXT1 localized on chromosome 8q24 [2] and EXT2 localized on chromosome 11p11.2. [3,4].

Molecular and Systemic Pathophysiology