title: Plasma Abeta(1-40) and Abeta(1-42) and the risk of dementia: a prospective case-cohort study.
abstract: BACKGROUND
  Amyloid beta peptides (Abeta) are important components of plaques in Alzheimer's disease. Plasma concentrations of Abeta(1-40) and Abeta(1-42) rise with age and are increased in people with mutations that cause early-onset Alzheimer's disease. However, Abeta(1-42) concentrations may decrease early in the dementia process. We postulated that concentrations of Abeta(1-40) and Abeta(1-42) in plasma are associated with risk of dementia.
  
  
  METHODS
  We did a case-cohort study embedded in the prospective, population-based Rotterdam Study. Of 6713 participants at risk for dementia, a random sample of 1756 people was drawn. During follow-up (mean 8.6 years), 392 incident dementia cases were identified. We investigated the association between plasma Abeta concentrations and risk of dementia and its subtypes using Cox proportional hazard models.
  
  
  RESULTS
  High concentrations of Abeta(1-40) but not Abeta(1-42) at baseline were associated with an increased risk of dementia. Compared with the first quartile of Abeta(1-40), age and sex-adjusted hazard ratios for dementia for the second, third, and fourth quartiles were 1.07 (95% CI 0.72-1.58), 1.16 (0.78-1.70), and 1.46 (1.01-2.12). People with an increased Abeta(1-42)/Abeta(1-40) ratio had a reduced risk of dementia. Compared with the first quartile of the Abeta(1-42)/Abeta(1-40) ratio, hazard ratios for the second, third, and fourth quartiles were 0.74 (0.53-1.02), 0.62 (0.44-0.88), and 0.47 (0.33-0.67). Associations were similar for Alzheimer's disease and vascular dementia.
  
  
  CONCLUSIONS
  High plasma concentrations of Abeta(1-40), especially when combined with low concentrations of Abeta(1-42), indicate an increased risk of dementia. A potential role of plasma Abeta concentrations as a marker of incipient dementia warrants further investigation.
authors.affiliation: Department of Epidemiology and Biostatistics, Erasmus Medical Centre, Rotterdam, The Netherlands.
authors.forename: Marieke
authors.initials: M
authors.lastname: van Oijen
authors.forename: Albert
authors.initials: A
authors.lastname: Hofman
authors.forename: Holly D
authors.initials: HD
authors.lastname: Soares
authors.forename: Peter J
authors.initials: PJ
authors.lastname: Koudstaal
authors.forename: Monique M B
authors.initials: MM
authors.lastname: Breteler
mesh_terms: D000368:Aged; D016229:Amyloid beta-Peptides / Q000097:blood*; D015331:Cohort Studies; D016001:Confidence Intervals; D003704:Dementia / Q000097:blood* / Q000453:epidemiology; D004797:Enzyme-Linked Immunosorbent Assay / Q000379:methods; D005260:Female; D006801:Humans; D008297:Male; D008609:Mental Status Schedule; D008875:Middle Aged; D009483:Neuropsychological Tests / Q000706:statistics & numerical data; D010446:Peptide Fragments / Q000097:blood*; D016016:Proportional Hazards Models; D012306:Risk; D013997:Time Factors
chemical_list: D016229:Amyloid beta-Peptides; D010446:Peptide Fragments; C078592:amyloid beta-protein (1-40); C075222:amyloid beta-protein (1-42)