Definition

Hereditary multiple osteochondromatosis type 1 is an autosomal dominant skeletal disorder caused by heterozygous loss-of-function variants in the EXT1 gene, which is responsible for chain elongation in heparan sulfate biosynthesis. It is characterized by the formation of numerous cartilage-capped bony outgrowths (osteochondromas) on the long bones, ribs, and vertebrae; in about 2% of cases, osteochondromas can transform into chondrosarcoma/osteosarcoma.

Gene/region examined

EXT1 - Whole Gene

Method

Sequence analysis

Accepted sample types

EDTA blood, AF, CVS

Inheritance

Hereditary, autosomal dominant (additional somatic second-hit mutations play a role in malignant transformation).

Related Tests

Inheritance Patterns

Describes how a genetic condition is passed on within a family. There are five main patterns

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Carrier (Heterozygous / Homozygous)

Why it matters: In autosomal recessive inheritance, when each parent is a carrier (while both appear healthy), the chance of their child being born with the disease is 25% in each

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VUS (Variant of Uncertain Significance)

This is the situation where the test has detected a change in the DNA, but the role of this change in the development of disease is unconfirmed.

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How to Read a Genetic Test Result (Positive / Negative / VUS)

A genetic test result falls into three main categories

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Types of Genetic Tests

A genetic test is a type of medical test that detects changes in genes, chromosomes or proteins. Today there are more than 77,000 genetic tests available.

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