Genetics and Molecular Biology (May 2021)

A novel mutation in ext2 caused hereditary multiple exostoses through reducing the synthesis of heparan sulfate

  • Caixia Xian,
  • Mingwei Zhu,
  • Tianying Nong,
  • Yiqiang Li,
  • Xingmei Xie,
  • Xia Li,
  • Jiangui Li,
  • Jingchun Li,
  • Jianping Wu,
  • Weizhe Shi,
  • Ping Wei,
  • Hongwen Xu,
  • Ya-ping Tang

DOI
https://doi.org/10.1590/1678-4685-gmb-2020-0334
Journal volume & issue
Vol. 44, no. 2

Abstract

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Abstract Hereditary multiple exostoses (HME) is a rare skeletal disorder characterized by the formation of multiple benign cartilage-capped tumors, usually in the metaphyseal region of the long bones. Over 70% of HME cases arise from monoallelic mutations in either of the two genes encoding the heparan sulfate (HS) synthesis enzymes, ext1 and ext2. To identify more HME-associated mutations, genomic DNA from members of five independent consanguineous families with HME was sequenced with whole exome sequencing (WES). A novel heterozygous splice site mutation (c.1173+2T>A) in ext2 was detected in all three affected members of family V. Further study showed that the novel mutation caused exon 7 of ext2 mRNA to be skipped during splicing and caused a frameshift after the codon for Arg360, which results in the appearance of new 43 codons, followed by a termination codon. Although the resulting truncated protein was still localized to the Golgi, similar to the full-length EXT2, its HS synthesis activity decreased by 40%. In this study, a novel splice site mutation in ext2 was identified and suggested to be a pathogenic mutation of HME, which may expand the genetic etiology spectrum of HME and may be helpful for clinical genetic counseling and prenatal diagnosis.

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