title: Global investigation and meta-analysis of the C9orf72 (G4C2)n repeat in Parkinson disease.
abstract: OBJECTIVE
  The objective of this study is to clarify the role of (G4C2)n expansions in the etiology of Parkinson disease (PD) in the worldwide multicenter Genetic Epidemiology of Parkinson's Disease (GEO-PD) cohort.
  
  
  METHODS
  C9orf72 (G4C2)n repeats were assessed in a GEO-PD cohort of 7,494 patients diagnosed with PD and 5,886 neurologically healthy control individuals ascertained in Europe, Asia, North America, and Australia.
  
  
  RESULTS
  A pathogenic (G4C2)n>60 expansion was detected in only 4 patients with PD (4/7,232; 0.055%), all with a positive family history of neurodegenerative dementia, amyotrophic lateral sclerosis, or atypical parkinsonism, while no carriers were detected with typical sporadic or familial PD. Meta-analysis revealed a small increase in risk of PD with an increasing number of (G4C2)n repeats; however, we could not detect a robust association between the C9orf72 (G4C2)n repeat and PD, and the population attributable risk was low.
  
  
  CONCLUSIONS
  Together, these findings indicate that expansions in C9orf72 do not have a major role in the pathogenesis of PD. Testing for C9orf72 repeat expansions should only be considered in patients with PD who have overt symptoms of frontotemporal lobar degeneration/amyotrophic lateral sclerosis or apparent family history of neurodegenerative dementia or motor neuron disease.
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authors.affiliation: Authors' affiliations are listed at the end of the article. christine.vanbroeckhoven@molgen.vib-ua.be.
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mesh_terms: D000073885:C9orf72 Protein; D015331:Cohort Studies; D042622:DNA Repeat Expansion / Q000235:genetics*; D005260:Female; D006801:Humans; D038622:Internationality; D008297:Male; D008875:Middle Aged; D010300:Parkinson Disease / Q000175:diagnosis* / Q000453:epidemiology / Q000235:genetics*; D011506:Proteins / Q000235:genetics*
chemical_list: D000073885:C9orf72 Protein; C568651:C9orf72 protein, human; D011506:Proteins