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Genetic and Rare Diseases Information Center (GARD)

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Hereditary multiple osteochondromas

Other Names for this Disease
  • Hereditary multiple exostoses
  • Hereditary multiple exostosis
  • HMO
  • Multiple exostoses
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Your Question

I have hereditary multiple osteochondromas. My granddaughter has been having swelling of her joints with pain in her hands. I am suspicious that this may be a manifestation of my disease. I had always been under the impression that my children did not have this disease. My father was the one who passed the disease on to my sister and I. I would like to find someone that would like to help me follow up on this and to find out if this could be present in my daughter or grandchildren.

Our Answer

We have identified the following information that we hope you find helpful. If you still have questions, please contact us.

What is hereditary multiple osteochondromas?

Hereditary multiple osteochondromas (HMO) (formerly called hereditary multiple exostoses) is a genetic condition in which people develop multiple benign (noncancerous) bone tumors that are covered by cartilage (called osteochondromas). The number and location of osteochondromas varies greatly among affected individuals. These tumors are not present at birth, but almost all affected people develop multiple osteochondromas by the time they are 12 years old. Once the bones stop growing, the development of new osteochondromas also usually stops. Osteochondromas can cause abnormal growth of the arms, hands, and legs, which can lead to uneven limb lengths (limb length discrepancy) and short stature. These tumors may cause pain, limit joint movement, and exert pressure on nerves, blood vessels, and surrounding tissues. Osteochondromas are typically benign; however, researchers estimate that people with HMO have about a 1% lifetime risk of these tumors becoming a cancerous osteochondrosarcoma. HMO is caused by mutations in the EXT1 and EXT2 genes and is inherited in an autosomal dominant pattern.[1]
Last updated: 6/1/2011

How is hereditary multiple osteochondromas inherited?

HMO is caused by mutations in the EXT1 and EXT2 genes. It is inherited in an autosomal dominant pattern, which means that one copy of the altered gene in each cell is sufficient to cause this condition. In most cases, an affected individual inherits the mutation from one affected parent. Other cases result from new mutations in the gene and occur in people with no history of the condition in their family.[2]

Most affected individuals (96%) that have inherited a gene mutation from their parent show signs and symptoms of this condition. However, the family history may appear negative because of the failure to recognize the disorder in family members and/or reduced penetrance. Reports have suggested that some females may not show clinical features of HMO but still have the gene mutation that causes this condition.[1]
Last updated: 6/27/2011

Is genetic testing available for hereditary multiple osteochondromas?

GeneTests lists the names of laboratories that are performing genetic testing for hereditary multiple osteochondromas. To view the contact information for the clinical laboratories conducting testing for the EXT1 gene, click here.  To view the contact information for the clinical laboratories conducting testing for the EXT2 gene, click here.

Please note:  Most of the laboratories listed through GeneTests do not accept direct contact from patients and their families; therefore, if you are interested in learning more, you will need to work with a health care provider or a genetics professional.  Below, we provide a list of online resources that can assist you in locating a genetics professional near you.
Last updated: 6/1/2011

How can I find a genetics professional in my area?

Genetics clinics are a source of information for individuals and families regarding genetic conditions, treatment, inheritance, and genetic risks to other family members. More information about genetic consultations is available from Genetics Home Reference. To find a genetics clinic, we recommend that you contact your primary healthcare provider for a referral.

The following online resources can help you find a genetics professional in your community:
Last updated: 10/18/2013