title: How do C9ORF72 repeat expansions cause amyotrophic lateral sclerosis and frontotemporal dementia:  can we learn from other noncoding repeat expansion disorders?
abstract: OBJECTIVE
  The aim of this review is to describe disease mechanisms by which chromosome 9 open reading frame 72 (C9ORF72) repeat expansions could lead to amyotrophic lateral sclerosis (ALS) and frontotemporal dementia (FTD) and to discuss these diseases in relation to other noncoding repeat expansion disorders.
  
  
  RESULTS
  ALS and FTD are complex neurodegenerative disorders with a considerable clinical and pathological overlap, and this overlap is further substantiated by the recent discovery of C9ORF72 repeat expansions. These repeat expansions are currently the most important genetic cause of familial ALS and FTD, accounting for approximately 34.2 and 25.9% of the cases. Clinical phenotypes associated with these repeat expansions are highly variable, and combinations with mutations in other ALS-associated and/or FTD-associated genes may contribute to this pleiotropy. It is challenging, however, to diagnose patients with C9ORF72 expansions, not only because of large repeat sizes, but also due to somatic heterogeneity. Most other noncoding repeat expansion disorders share an RNA gain-of-function disease mechanism, a mechanism that could underlie the development of ALS and/or FTD as well.
  
  
  CONCLUSIONS
  The discovery of C9ORF72 repeat expansions provides novel insights into the pathogenesis of ALS and FTD and highlights the importance of noncoding repeat expansions and RNA toxicity in neurodegenerative diseases.
authors.affiliation: Department of Neuroscience, Mayo Clinic, Jacksonville, Florida 32224, USA.
authors.forename: Marka
authors.initials: M
authors.lastname: van Blitterswijk
authors.forename: Mariely
authors.initials: M
authors.lastname: DeJesus-Hernandez
authors.forename: Rosa
authors.initials: R
authors.lastname: Rademakers
mesh_terms: D000690:Amyotrophic Lateral Sclerosis / Q000235:genetics*; D000073885:C9orf72 Protein; D042622:DNA Repeat Expansion; D057180:Frontotemporal Dementia / Q000235:genetics*; D005838:Genotype; D006801:Humans; D010641:Phenotype; D011506:Proteins / Q000235:genetics*
chemical_list: D000073885:C9orf72 Protein; C568651:C9orf72 protein, human; D011506:Proteins