Multiple Hereditary Exostosis, EXT Genes, and Skeletal Development

Abstract

Multiple hereditary exostosis is an autosomal dominant inherited disease in which osteochondral growths occur on the periphery of bones. These growths are comprised of bone surrounded by a cap of cartilage. A small number of these exostoses proceed to a low-grade chondrosarcoma1,2. Although the disease can occur spontaneously, it has been estimated that 80% of affected individuals have a positive family history2. Research on the genetics of multiple hereditary exostosis over the past thirty years has been productive. Advances in the understanding of the disease have paralleled the methodological advances that have occurred in the field of molecular genetics. Initially, it was recognized that multiple hereditary exostosis is often inherited and that large families were available for genetic mapping. As techniques for gene mapping improved, regions of the chromosomes involved were identified, localized, and eventually subjected to DNA sequencing. The genes identified, the exostosins, were found to encode known enzymes whose function within the disease could be reasonably predicted. Mouse models were created, and the hypothesized function of these genes was verified. Many surprises were encountered along the way, which served to uncover important biological principles. The understanding of human multiple hereditary exostosis is a paradigm for the power of combining modern molecular biology, genetics, and clinical science. In the early 1990s, the clearly autosomal dominant inheritance of multiple hereditary exostosis was recognized by clinicians and DNA techniques became available to localize the inheritance patterns in the DNA. By genetic linkage analysis, Hecht et al. and Le Merrer et al. were able to localize the inheritance patterns of these families to three chromosomal locations: 8q24.1, 11p11-13, and 19p2,3. These genes were identified as tumor-suppressor genes, and loss of heterozygosity in these regions was associated with transformation into chondrosarcoma2, …