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EXT1 gene
Reviewed by Medicinsk Expert•Last updated: 2026-10-22•Gene

EXT1 gene

The EXT1 gene provides instructions for producing the exostosin-1 protein, which is vital for heparan sulfate modification and normal bone development.

Normal Function

The EXT1 gene provides instructions for producing a protein called exostosin-1. Located in the Golgi apparatus, exostosin-1 binds to exostosin-2 to form a complex that modifies a protein called heparan sulfate.

Heparan sulfate is a complex of sugar molecules that regulates body processes, including:

  • Cell signaling and interactions
  • Immune system functions
  • Bone formation (ossification)
  • Growth and specialization of cartilage-forming cells (chondrocytes)

Health Conditions Related to Genetic Changes

Hereditary multiple osteochondromas

Hundreds of pathogenic variants in the EXT1 gene can cause hereditary multiple osteochondromas type 1. This condition is characterized by the development of multiple noncancerous (benign) bone tumors called osteochondromas.

Most of these are "loss-of-function variants" that prevent the production of functional exostosin-1. Without this protein, heparan sulfate is not properly modified, which disrupts ossification and chondrocyte differentiation, leading to tumor formation.

Trichorhinophalangeal syndrome type II

Trichorhinophalangeal syndrome type II (TRPS II) is caused by a deletion of genetic material on chromosome 8 that includes the EXT1 gene. Affected individuals are missing one copy of the gene, leading to a shortage of exostosin-1 proteins. This causes osteochondromas, while the deletion of neighboring genes contributes to other features such as distinctive facial features, intellectual disabilities, and abnormalities of the skin, hair, and nails.

Other Names for This Gene

  • exostosin 1
  • EXT
  • EXT1_HUMAN

Frequently Asked Questions

Treatment for osteochondromas usually involves monitoring their growth and impact. If they cause pain, restrict movement, or compress nerves, surgical removal may be recommended. Physical therapy can help manage symptoms and improve function after surgery or for non-surgical cases.
Osteochondromas are benign (noncancerous) bone tumors that develop on the surface of bones, often near growth plates. In HMO, multiple osteochondromas can form, causing pain, limited joint movement, nerve compression, or deformity, especially as they grow. They can also interfere with normal bone development.
Yes, HMO is an inherited condition. It is typically passed down in an autosomal dominant pattern, meaning that a person only needs to inherit one copy of the mutated EXT1 gene from an affected parent to develop the condition. There is a 50% chance of an affected parent passing the mutation to each child.
While both conditions involve osteochondromas due to EXT1 gene changes, HMO primarily causes multiple benign bone tumors. TRPS II, however, results from a larger deletion on chromosome 8 that includes the EXT1 gene and other neighboring genes. This leads to osteochondromas along with additional features like distinctive facial characteristics, intellectual disabilities, and abnormalities of the skin, hair, and nails.
Source: MedlinePlus, National Library of Medicine

MedlinePlus brings together authoritative health information from the National Library of Medicine (NLM), the National Institutes of Health (NIH), and other government agencies and health-related organizations.

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