National Center for Advancing and Translational Sciences Genetic and Rare Diseases Information Center, a program of the National Center for Advancing and Translational Sciences

Hereditary multiple osteochondromas


Other Names:
HMO; Hereditary multiple exostoses; Hereditary multiple exostosis; HMO; Hereditary multiple exostoses; Hereditary multiple exostosis; Multiple exostoses See More
Categories:
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.[1][2][3] Osteochondromas typically grow throughout childhood and stop growing when the growth plates close.[1] However, they do recur later on in some people.[1] While the vast majority of osteochondromas are benign (noncancerous), they may become malignant (cancerous) in adulthood in 2% to 5% of people with HMO.[1][2]

Most cases of HMO are caused by a mutation in the EXT1 or EXT2 gene with autosomal dominant inheritance.[1][3] 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.[1][3]

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.[1][3] 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.[2][4] 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.[2][4]
Last updated: 9/4/2018

This table lists symptoms that people with this disease may have. For most diseases, symptoms will vary from person to person. People with the same disease may not have all the symptoms listed. This information comes from a database called the Human Phenotype Ontology (HPO) . The HPO collects information on symptoms that have been described in medical resources. The HPO is updated regularly. Use the HPO ID to access more in-depth information about a symptom.

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Medical Terms Other Names
Learn More:
HPO ID
80%-99% of people have these symptoms
Abnormality of the humerus 0003063
Abnormality of tibia morphology
Abnormality of the shankbone
Abnormality of the shinbone
[ more ] 		0002992
Failure to thrive
Faltering weight
Weight faltering
[ more ] 		0001508
Multiple exostoses 0002762
30%-79% of people have these symptoms
Abnormality of femur morphology
Abnormality of the thighbone
0002823
Abnormality of the dentition
Abnormal dentition
Abnormal teeth
Dental abnormality
[ more ] 		0000164
Abnormality of the metaphysis
Abnormality of the wide portion of a long bone
0000944
Anteverted nares
Nasal tip, upturned
Upturned nasal tip
Upturned nose
Upturned nostrils
[ more ] 		0000463
Avascular necrosis
Death of bone due to decreased blood supply
0010885
Bone pain 0002653
Cranial nerve paralysis 0006824
Genu valgum
Knock knees
0002857
Hypoplasia of the ulna
Underdeveloped inner large forearm bone
0003022
Madelung deformity 0003067
Micromelia
Smaller or shorter than typical limbs
0002983
Muscle weakness
Muscular weakness
0001324
Radial bowing
Bowing of outer large bone of the forearm
0002986
Short stature
Decreased body height
Small stature
[ more ] 		0004322
5%-29% of people have these symptoms
Abnormal pericardium morphology 0001697
Abnormal pyramidal sign 0007256
Chondrosarcoma 0006765
Dilatation
Wider than typical opening or gap
0002617
Elbow dislocation
Dislocations of the elbows
Elbow dislocations
[ more ] 		0003042
Hemiplegia/hemiparesis
Paralysis or weakness of one side of body
0004374
Osteoarthritis
Degenerative joint disease
0002758
Osteolysis
Breakdown of bone
0002797
Pelvic bone exostoses 0003276
Recurrent fractures
Increased fracture rate
Increased fractures
Multiple fractures
Multiple spontaneous fractures
Varying degree of multiple fractures
[ more ] 		0002757
Scoliosis 0002650
Synostosis of joints
Fusion of joints
0100240
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Last updated: 7/1/2020
Inheritance of HMO is autosomal dominant, which means that having a mutation in one copy of a gene responsible for HMO is sufficient to cause a person to develop HMO.[1][3][5] In most cases, a person with HMO inherits the mutation from a parent with HMO. Other cases may result from a new mutation in the gene, occurring in people with no family history of HMO.[1][3] 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.[3] It is not known why some females with a mutation responsible for HMO do not develop signs and symptoms.
Last updated: 9/4/2018

Making a diagnosis for a genetic or rare disease can often be challenging. Healthcare professionals typically look at a person’s medical history, symptoms, physical exam, and laboratory test results in order to make a diagnosis. The following resources provide information relating to diagnosis and testing for this condition. If you have questions about getting a diagnosis, you should contact a healthcare professional.

Testing Resources

  • The Genetic Testing Registry (GTR) provides information about the genetic tests for this condition. The intended audience for the GTR is health care providers and researchers. Patients and consumers with specific questions about a genetic test should contact a health care provider or a genetics professional.

Related diseases are conditions that have similar signs and symptoms. A health care provider may consider these conditions in the table below when making a diagnosis. Please note that the table may not include all the possible conditions related to this disease.

Conditions with similar signs and symptoms from Orphanet
MO should be distinguished from metachondromatosis, dysplasia epiphysealis hemimelica and Ollier disease (see these terms).
Visit the Orphanet disease page for more information.

Research helps us better understand diseases and can lead to advances in diagnosis and treatment. This section provides resources to help you learn about medical research and ways to get involved.

Clinical Research Resources

  • ClinicalTrials.gov lists trials that are related to Hereditary multiple osteochondromas. Click on the link to go to ClinicalTrials.gov to read descriptions of these studies.

    Please note: Studies listed on the ClinicalTrials.gov website are listed for informational purposes only; being listed does not reflect an endorsement by GARD or the NIH. We strongly recommend that you talk with a trusted healthcare provider before choosing to participate in any clinical study.

Support and advocacy groups can help you connect with other patients and families, and they can provide valuable services. Many develop patient-centered information and are the driving force behind research for better treatments and possible cures. They can direct you to research, resources, and services. Many organizations also have experts who serve as medical advisors or provide lists of doctors/clinics. Visit the group’s website or contact them to learn about the services they offer. Inclusion on this list is not an endorsement by GARD.

Organizations Supporting this Disease

Social Networking Websites

These resources provide more information about this condition or associated symptoms. The in-depth resources contain medical and scientific language that may be hard to understand. You may want to review these resources with a medical professional.

Where to Start

  • Genetics Home Reference (GHR) contains information on Hereditary multiple osteochondromas. This website is maintained by the National Library of Medicine.
  • The National Organization for Rare Disorders (NORD) has a report for patients and families about this condition. NORD is a patient advocacy organization for individuals with rare diseases and the organizations that serve them.

In-Depth Information

  • GeneReviews provides current, expert-authored, peer-reviewed, full-text articles describing the application of genetic testing to the diagnosis, management, and genetic counseling of patients with specific inherited conditions.
  • Medscape Reference provides information on this topic. You may need to register to view the medical textbook, but registration is free.
  • The Monarch Initiative brings together data about this condition from humans and other species to help physicians and biomedical researchers. Monarch’s tools are designed to make it easier to compare the signs and symptoms (phenotypes) of different diseases and discover common features. This initiative is a collaboration between several academic institutions across the world and is funded by the National Institutes of Health. Visit the website to explore the biology of this condition.
  • Orphanet is a European reference portal for information on rare diseases and orphan drugs. Access to this database is free of charge.
    Orphanet
    Orphanet
  • PubMed is a searchable database of medical literature and lists journal articles that discuss Hereditary multiple osteochondromas. Click on the link to view a sample search on this topic.

Questions sent to GARD may be posted here if the information could be helpful to others. We remove all identifying information when posting a question to protect your privacy. If you do not want your question posted, please let us know. Submit a new question

  • Is there information available about the risk of cancer in people with hereditary multiple exostosis? I would like to know what testing etc is required if this is suspected. See answer


  1. Tis JE. Benign bone tumors in children and adolescents. UpToDate. Waltham, MA: UpToDate; April 10, 2018; https://www.uptodate.com/contents/benign-bone-tumors-in-children-and-adolescents.
  2. Pacifici M. Hereditary Multiple Exostoses: New Insights into Pathogenesis, Clinical Complications, and Potential Treatments. Send to Curr Osteoporos Rep. June, 2017; 15(3):142-152. https://www.ncbi.nlm.nih.gov/pmc/articles/pmid/28466453/.
  3. Wuyts W, Schmale GA, Chansky HA, & Raskind WH. Hereditary Multiple Osteochondromas. GeneReviews. November 21, 2013; http://www.ncbi.nlm.nih.gov/books/NBK1235/.
  4. Bovee JVMG. Multiple osteochondromas. Orphanet J Rare Dis. 2008; 3:3:https://ojrd.biomedcentral.com/articles/10.1186/1750-1172-3-3.
  5. Hereditary multiple exostoses. Genetics Home Reference. March, 2016; http://ghr.nlm.nih.gov/condition/hereditary-multiple-exostoses.