A splice mutation and mRNA decay of EXT2 provoke hereditary multiple exostoses.

Chen Tian,Shuzhen Wen,Tianfeng Li,Zhenming Cai,Hong Du,Xueling Li,Rengna Yan,Huimei Chen,Xinxiu Li,Henry H Roehl

doi:10.1371/journal.pone.0094848

Abstract

BackgroundHereditary multiple exostoses (HME) is an autosomal dominant disease. The classical paradigm of mutation screening seeks to relate alterations in the exostosin glycosyltransferase genes, EXT1 and EXT2, which are responsible for over 70% of HME cases. However, the pathological significance of the majority of these mutations is often unclear.MethodsIn a Chinese family with HME, EXT1 and EXT2 genes were screened by direct sequencing. The consequence of a detected mutant was predicted by in silico analysis and confirmed by mRNA analysis. The EXT1 and EXT2 mRNA and protein levels and the HS patterns in the HME patients were compared with those in healthy controls.ResultsA heterozygous transition (c.743+1G>A) in the EXT2 gene, which co-segregated with the HME phenotype in this family, was identified. The G residue at position +1 in intron 4 of EXT2 was predicted to be a 5′ donor splice site. The mRNA analysis revealed an alternative transcript with a cryptic splice site 5 bp downstream of the wild-type site, which harbored a premature stop codon. However, the predicted truncated protein was not detected by western blot analysis. Decay of the mutant mRNA was shown by clone sequencing and quantification analysis. The corresponding downregulation of the EXT2 mRNA will contribute to the abnormal EXT1/EXT2 ratio and HS pattern that were detected in the patients with HME.ConclusionThe heterozygous mutation c.743+1G>A in the EXT2 gene causes HME as a result of abnormal splicing, mRNA decay, and the resulting haploinsufficiency of EXT2.

Highlights

Hereditary multiple exostosis (HME, OMIM 133700 and OMIM 133701) is an autosomal dominant disorder characterized by the presence of cartilage-capped multiple exostoses [1]
Mutations in the EXT1 and EXT2 genes have been reported to be involved in the pathogenesis of Hereditary multiple exostoses (HME) and are responsible for about twothirds and one-third of HME cases, respectively [10,11]
Clinical description of the family with HME According to the anamnesis of some family members, at least ten individuals in the whole family were severely affected with multiple large exostoses

Summary

Introduction

Hereditary multiple exostosis (HME, OMIM 133700 and OMIM 133701) is an autosomal dominant disorder characterized by the presence of cartilage-capped multiple exostoses (osteochondromas) [1]. HME is a genetically heterogeneous disease that is associated with at least two chromosomal loci: EXT1 (exostosin 1, 8q24.1, OMIM 133700) and EXT2 (exostosin 2, 11p11-p13, OMIM 133701) [5,6,7,8]. Mutations in the EXT1 and EXT2 genes have been reported to be involved in the pathogenesis of HME and are responsible for about twothirds and one-third of HME cases, respectively [10,11]. Hereditary multiple exostoses (HME) is an autosomal dominant disease. The classical paradigm of mutation screening seeks to relate alterations in the exostosin glycosyltransferase genes, EXT1 and EXT2, which are responsible for over 70% of HME cases. The pathological significance of the majority of these mutations is often unclear

Methods

Results

Conclusion