Rare Nephrology News

Disease Profile

Hereditary multiple osteochondromas

Prevalence estimates on Rare Medical Network websites are calculated based on data available from numerous sources, including US and European government statistics, the NIH, Orphanet, and published epidemiologic studies. Rare disease population data is recognized to be highly variable, and based on a wide variety of source data and methodologies, so the prevalence data on this site should be assumed to be estimated and cannot be considered to be absolutely correct.

1-9 / 100 000

US Estimated

Europe Estimated

Age of onset






Autosomal dominant A pathogenic variant in only one gene copy in each cell is sufficient to cause an autosomal dominant disease.


Autosomal recessive Pathogenic variants in both copies of each gene of the chromosome are needed to cause an autosomal recessive disease and observe the mutant phenotype.


dominant X-linked dominant inheritance, sometimes referred to as X-linked dominance, is a mode of genetic inheritance by which a dominant gene is carried on the X chromosome.


recessive Pathogenic variants in both copies of a gene on the X chromosome cause an X-linked recessive disorder.


Mitochondrial or multigenic Mitochondrial genetic disorders can be caused by changes (mutations) in either the mitochondrial DNA or nuclear DNA that lead to dysfunction of the mitochondria and inadequate production of energy.

Multigenic or multifactor Inheritance involving many factors, of which at least one is genetic but none is of overwhelming importance, as in the causation of a disease by multiple genetic and environmental factors.


Not applicable


Other names (AKA)

HMO; Hereditary multiple exostoses; Hereditary multiple exostosis;


Congenital and Genetic Diseases; Metabolic disorders; Musculoskeletal Diseases;


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]


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.

Medical Terms Other Names
Learn More:
80%-99% of people have these symptoms
Abnormality of the humerus
Abnormality of tibia morphology
Abnormality of the shankbone
Abnormality of the shinbone

[ more ]

Failure to thrive
Faltering weight
Weight faltering

[ more ]

Multiple exostoses
30%-79% of people have these symptoms
Abnormality of femur morphology
Abnormality of the thighbone
Abnormality of the dentition
Abnormal dentition
Abnormal teeth
Dental abnormality

[ more ]

Abnormality of the metaphysis
Abnormality of the wide portion of a long bone
Anteverted nares
Nasal tip, upturned
Upturned nasal tip
Upturned nose
Upturned nostrils

[ more ]

Avascular necrosis
Death of bone due to decreased blood supply
Bone pain
Cranial nerve paralysis
Genu valgum
Knock knees
Hypoplasia of the ulna
Underdeveloped inner large forearm bone
Madelung deformity
Smaller or shorter than typical limbs
Muscle weakness
Muscular weakness
Radial bowing
Bowing of outer large bone of the forearm
Short stature
Decreased body height
Small stature

[ more ]

5%-29% of people have these symptoms
Abnormal pericardium morphology
Abnormal pyramidal sign
Elbow dislocation
Dislocations of the elbows
Elbow dislocations

[ more ]

Paralysis or weakness of one side of body
Degenerative joint disease
Breakdown of bone
Pelvic bone exostoses
Recurrent fractures
Increased fracture rate
Increased fractures
Multiple fractures
Multiple spontaneous fractures
Varying degree of multiple fractures

[ more ]

Synostosis of joints
Fusion of joints
Vascular dilatation
Wider than typical opening or gap


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.


    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

        Learn more

        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

        • MedlinePlus Genetics 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.
          • 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.


            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; https://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; https://ghr.nlm.nih.gov/condition/hereditary-multiple-exostoses.

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