Hereditary multiple exostoses (HME) is characterized by growths of multiple exostoses, benign cartilage-capped bone tumors that grow outward from the metaphyses of long bones. Bone growths usually show up in childhood and lifetime risk for one to become cancerous is very low. HME does not affect intellegence. It has autosommal dominant inheritance and is due to mutations in the EXT1 and EXT2 genes.