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TGM6 identified as a novel causative gene of spinocerebellar ataxias using exome sequencing

Jun Ling Wang, Xu Yang, Kun Xia, Zheng Mao Hu, Ling Weng, Xin Jin, Hong Jiang, Peng Zhang, Lu Shen, Ji Feng Guo, Nan li, Ying Rui Li, Li Fang Lei, Jie Zhou, Juan Du, Ya Fang Zhou, Qian Pan, Jian Wang, Jun Wang, Rui Qiang Li, Bei Sha Tang
DOI: http://dx.doi.org/10.1093/brain/awq323 First published online: 24 November 2010

Summary

Autosomal-dominant spinocerebellar ataxias constitute a large, heterogeneous group of progressive neurodegenerative diseases with multiple types. To date, classical genetic studies have revealed 31 distinct genetic forms of spinocerebellar ataxias and identified 19 causative genes. Traditional positional cloning strategies, however, have limitations for finding causative genes of rare Mendelian disorders. Here, we used a combined strategy of exome sequencing and linkage analysis to identify a novel spinocerebellar ataxia causative gene, TGM6. We sequenced the whole exome of four patients in a Chinese four-generation spinocerebellar ataxia family and identified a missense mutation, c.1550T–G transition (L517W), in exon 10 of TGM6. This change is at a highly conserved position, is predicted to have a functional impact, and completely cosegregated with the phenotype. The exome results were validated using linkage analysis. The mutation we identified using exome sequencing was located in the same region (20p13–12.2) as that identified by linkage analysis, which cross-validated TGM6 as the causative spinocerebellar ataxia gene in this family. We also showed that the causative gene could be mapped by a combined method of linkage analysis and sequencing of one sample from the family. We further confirmed our finding by identifying another missense mutation c.980A–G transition (D327G) in exon seven of TGM6 in an additional spinocerebellar ataxia family, which also cosegregated with the phenotype. Both mutations were absent in 500 normal unaffected individuals of matched geographical ancestry. The finding of TGM6 as a novel causative gene of spinocerebellar ataxia illustrates whole-exome sequencing of affected individuals from one family as an effective and cost efficient method for mapping genes of rare Mendelian disorders and the use of linkage analysis and exome sequencing for further improving efficiency.

  • whole-exome sequencing
  • spinocerebellar ataxia
  • linkage analysis
  • TGM6
  • Abbreviations
    NS/SS/Indel
    non-synonymous/splice acceptor and donor site/insertions or deletions
    SCA
    autosomal-dominant spinocerebellar ataxias
    SNP
    single-nucleotide polymorphism
    TGM6
    transglutaminase 6
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