title: APOE and AD concordance in twin pairs as predictors of AD in first-degree relatives.
abstract: OBJECTIVE
  To examine the independent effects of the APOE genotype (APOE) and concordance for AD in twin pairs on the occurrence of AD in first-degree relatives.
  
  
  BACKGROUND
  Studies of twins have been undertaken to investigate the influence of genes in a variety of conditions, including AD. A previous study, performed before reports linking APOE to AD, demonstrated an increase in AD among first-degree relatives of twins concordant for AD compared with relatives of discordant twins.
  
  
  METHODS
  In a sample of 94 twin pairs the authors examined the association between concordance for AD within the twin pair and family history of AD among first-degree relatives of twins. They then examined the extent to which the presence of the APOE epsilon4 allele in the twin pair explains the association between concordance for AD within the twin pair and family history of AD.
  
  
  RESULTS
  Concordance among twins was associated with increased risk of AD among relatives (logrank test, chi2 = 12.558; p = 0.0004), and the presence of at least one APOE epsilon4 allele in each member of the twin pair is also associated with increased risk of AD among family members (logrank test, chi2 = 7.712; p = 0.0055).
  
  
  CONCLUSIONS
  APOE genotype explains much but not all of the association between concordance among twins and increased familial risk of AD.
authors.affiliation: Department of Psychiatry and Behavioral Sciences, Duke University Medical Center, Durham, NC 27710, USA.
authors.forename: D C
authors.initials: DC
authors.lastname: Steffens
authors.forename: B L
authors.initials: BL
authors.lastname: Plassman
authors.forename: M J
authors.initials: MJ
authors.lastname: Helms
authors.forename: K A
authors.initials: KA
authors.lastname: Welsh-Bohmer
authors.forename: T T
authors.initials: TT
authors.lastname: Newman
authors.forename: J C
authors.initials: JC
authors.lastname: Breitner
mesh_terms: D017668:Age of Onset; D000368:Aged; D000369:Aged, 80 and over; D000483:Alleles; D000544:Alzheimer Disease / Q000235:genetics*; D001057:Apolipoproteins E / Q000235:genetics*; D004200:Diseases in Twins; D005838:Genotype; D006801:Humans; D008875:Middle Aged; D011237:Predictive Value of Tests
chemical_list: D001057:Apolipoproteins E