Mutation Screening Of EXT Genes In A Chinese Hereditary Multiple Exostoses Family

Objective:To investigate gene mutation of a Chinese family with hereditary multiple exostoses (HME) by analyzing clinical data and sequencing the gene EXT1locus on18q23-24.1, EXT2locus on11p11-12, in order to identify the causative mutation in the pedigree, and to explain the cause of the huge osteochondroma. Also to provide evidence for the future genetic research and clinical consulting in HME.Methods:A five-generation family with MO from Loudi city in Hunan was studied. Out of33family members, there were13affected individuals. A pedigree was constructed based on physical examination, radiographical evaluations, clinical data and DNA analysis of all family members, and all patients provided informed consent prior to participation in the study. DNA samples were subjected to mutation screening by amplification of the coding regions and intron-exon boundaries of EXT1and EXT2genes using26pairs of primers synthesizedon the basis of these two genes. RNA isolation and reverse-transcription polymerase chain reaction (RT-PCR) were performed to prove the site of mutation caused splicing variant.Results:Hereditary multiple exostoses in this family is an autosomal dominant inherited disorder. The disease causing gene of the family was linked to the EXT2locus on chromosome11, which was unreported before.A mutation c.939+1G>T was detected and located at EXT2gene, which was co-segregated with the disease phenotype. The proband had no other mutation on EXT1or EXT2except the mutation c.939+1G>T. The consequence of this mutation was exon5being spliced out, and the resulted in losing the codon-reading frame from codon744to933, and then frameshift leading to a premature termination codon and truncated protein of266amino acids. Loss of the EXT expression results in disordered synthesis ofheparan sulfate and therefore results in HME. Combined with splice-site mutations which leads to HME proved in other study, it is the mutation c.939+1G>T causing HME in this pedigree.Conclusions:Mutation c.939+1G>T on EXT2is the disease causing gene of the family with HME. Splice-site mutation can cause HME. Mutation in gene EXT1or EXT2is not the cause of the huge osteochondroma of proband. Phenotypic diversity of HME may be correlated with other modifier gene.