Aberrant splicing of HTT generates the pathogenic exon 1 protein in Huntington disease

Proc Natl Acad Sci U S A. 2013 Feb 5;110(6):2366-70. doi: 10.1073/pnas.1221891110. Epub 2013 Jan 22.


Huntington disease (HD) is a devastating, late-onset, inherited neurodegenerative disorder that manifests with personality changes, movement disorders, and cognitive decline. It is caused by a CAG repeat expansion in exon 1 of the HTT gene that translates to a polyglutamine tract in the huntingtin protein (HTT). The formation of HTT fragments has been implicated as an essential step in the molecular pathogenesis of HD and several proteases that cleave HTT have been identified. However, the importance of smaller N-terminal fragments has been highlighted by their presence in HD postmortem brains and by the fact that nuclear inclusions are only detected by antibodies to the N terminus of HTT. Despite an intense research effort, the precise length of these fragments and the mechanism by which they are generated remains unknown. Here we show that CAG repeat length-dependent aberrant splicing of exon 1 HTT results in a short polyadenylated mRNA that is translated into an exon 1 HTT protein. Given that mutant exon 1 HTT proteins have consistently been shown to be highly pathogenic in HD mouse models, the aberrant splicing of HTT mRNA provides a mechanistic basis for the molecular pathogenesis of HD. RNA-targeted therapeutic strategies designed to lower the levels of HTT are under development. Many of these approaches would not prevent the production of exon 1 HTT and should be reviewed in light of our findings.

Publication types

  • Research Support, Non-U.S. Gov't

MeSH terms

  • Animals
  • Base Sequence
  • Brain / metabolism
  • Disease Models, Animal
  • Exons
  • Humans
  • Huntingtin Protein
  • Huntington Disease / genetics*
  • Huntington Disease / metabolism
  • Mice
  • Mice, Inbred C57BL
  • Mice, Inbred CBA
  • Mice, Transgenic
  • Molecular Sequence Data
  • Mutant Proteins / genetics*
  • Mutant Proteins / metabolism
  • Nerve Tissue Proteins / genetics*
  • Nerve Tissue Proteins / metabolism
  • Nuclear Proteins / genetics*
  • Nuclear Proteins / metabolism
  • RNA Splicing*
  • RNA, Messenger / genetics
  • RNA, Messenger / metabolism
  • RNA-Binding Proteins / metabolism
  • Trinucleotide Repeats


  • Htt protein, mouse
  • Huntingtin Protein
  • Mutant Proteins
  • Nerve Tissue Proteins
  • Nuclear Proteins
  • RNA, Messenger
  • RNA-Binding Proteins