This information is provided by the National Institutes of Health (NIH) Genetic and Rare Diseases Information Center (GARD).
Hereditary multiple osteochondromas (HMO), also called hereditary multiple exostoses, is a genetic disorder that causes the development of multiple, cartilage-covered tumors on the external surfaces of bones (osteochondromas). The osteochondromas typically become apparent during childhood or adolescence, and the number, size and location of osteochondromas varies from person to person. Signs and symptoms may include pain, decreased range of motion, nerve impingement, deformity, differences in limb length, short stature, and fractures. Osteochondromas of the ribs may cause complications such as a collapsed lung (pneumothorax), hemothorax, or pericardial effusion. Osteochondromas typically grow throughout childhood and stop growing when the growth plates close. However, they do recur later on in some people. While the vast majority of osteochondromas are benign (noncancerous), they may become malignant (cancerous) in adulthood in 2% to 5% of people with HMO.
Most cases of HMO are caused by a mutation in the EXT1 or EXT2 gene with autosomal dominant inheritance. About 96% of females with a mutation responsible for HMO will develop osteochondromas (a phenomenon known as reduced penetrance), and 100% of males will develop osteochondromas.
Treatment depends on the locations and sizes of osteochondromas and the severity of symptoms they cause. Examples of treatment options include a “watch and wait” approach (when no symptoms are present), surgical removal of the tumor, corrective osteotomy, and growth plate arrest or limb-lengthening procedures. While benign osteochondromas generally do not affect life expectancy, they still may cause a variety of health problems and debilitating symptoms that can impair quality of life. Osteochondromas that become malignant (turning into chondrosarcomas or osteosarcomas) can be life-threatening, but the outlook in these cases may depend on the tumor grade.
For more information, visit GARD.