EXT1 and hereditary multiple exostoses: Patients may develop solitary osteochondromas due to injuries at the metaphysis or multiple osteochondromas associated with mutations in the Exostosin 1 (EXT1) and 2 (EXT2) genes, a condition known as hereditary multiple osteochondromas (HMO; previously called hereditary multiple exostoses, HME) [2,3].