Mutation Screening of the EXT Genes in Patients with Hereditary Multiple Exostoses in Taiwan

Hereditary multiple exostoses (HME) is an autosomal dominant disorder characterized by growth of benign bone tumors. This genetically heterozygous disease comprises three chromosomal loci: the EXT1 gene on chromosome 8q23-q24, EXT2 on 11p11-p13, and EXT3 on 19p. Both EXT1 and EXT2 have been cloned and defined as a new family of potential tumor suppressor genes in previous work. However, no studies have been conducted in the Taiwanese population. To determine if previous results can also be applied to the Taiwanese, we analyzed 5 Taiwanese probands with clinical features of HME: 1 of them is a sporadic case, and the others are familial cases. Linkage studies were performed in the familial cases before the mutation analysis to determine to which of the three EXT chromosomes these cases could be assigned. Our results showed that one proband is linked to the EXT1 locus and three are linked to the EXT2 locus; the sporadic case was subsequently found to involve EXT1. We then identified four new mutations that have not been found in other races: two in EXT1--frameshift (K218fsX247) and nonsense (Y468X) mutations and two in EXT2-missense (R223P) and nonsense (Y394X) mutations. Our results indicate that in familial cases, linkage analysis can prove useful for preimplantation genetic diagnosis.