Individuals with hereditary multiple exostoses (HME) often develop benign cartilage-capped tumors (exostoses) at the ends of the long bones or the surface of flat bones. Exostoses develop prior to skeletal maturity only. Bony deformity, bowing of the long bones, limited range of motion, and premature osteoarthrosis may be associated with HME. Exostoses also may cause complications by putting pressure on nearby issues, nerves or blood vessels. A rare but severe risk in patients with multiple exostoses is the development of malignant chondrosarcoma, which occurs in 1-5% of patients. Mutations in the EXT1 gene seem to be associated with a more severe disease and higher risk of developing chondrosarcoma than EXT2 gene mutation.