Hereditary multiple osteochondromas is a condition in which people develop multiple benign (noncancerous) bone tumors called osteochondromas. The number of osteochondromas and the bones on which they are located vary greatly among affected individuals. The osteochondromas are not present at birth, but approximately 96 percent of affected people develop multiple osteochondromas by the time they are 12 years old. Osteochondromas typically form at the end of long bones and on flat bones such as the hip and shoulder blade.

Mutations in the EXT1 and EXT2 genes cause hereditary multiple osteochondromas. The EXT1 gene and the EXT2 gene provide instructions for producing the proteins exostosin-1 and exostosin-2, respectively. The two exostosin proteins bind together and form a complex found in a cell structure called the Golgi apparatus, which modifies newly produced enzymes and other proteins. In the Golgi apparatus, the exostosin-1 and exostosin-2 complex modifies a protein called heparan sulfate so it can be used by the cell.

The incidence of hereditary multiple osteochondromas is estimated to be 1 in 50,000 individuals. This condition occurs more frequently in some isolated populations: the incidence is approximately 1 in 1,000 in the Chamorro population of Guam and 1 in 77 in the Ojibway Indian population of Manitoba, Canada.

This condition is inherited in an autosomal dominant pattern, which means one copy of the altered gene in each cell is sufficient to cause the disorder.

Published Date: March 01, 2016
Published By: National Institutes of Health