title: APOE ε4 and the risk for Alzheimer disease and cognitive decline in African Americans and Yoruba.
abstract: BACKGROUND
  There is little information on the association of the APOEe4 allele and AD risk in African populations. In previous analyses from the Indianapolis-Ibadan dementia project, we have reported that APOE ε4 increased the risk for Alzheimer's disease (AD) in African Americans but not in Yoruba. This study represents a replication of this earlier work using enriched cohorts and extending the analysis to include cognitive decline.
  
  
  METHODS
  In this longitudinal study of two community dwelling cohorts of elderly Yoruba and African Americans, APOE genotyping was conducted from blood samples taken on or before 2001 (1,871 African Americans & 2,200 Yoruba). Mean follow up time was 8.5 years for African Americans and 8.8 years for Yoruba. The effects of heterozygosity or homozygosity of ε4 and of the possession of e4 on time to incident AD and on cognitive decline were determined using Cox's proportional hazards regression and mixed effects models.
  
  
  RESULTS
  After adjusting for covariates, one or two copies of the APOE ε4 allele were significant risk factors for incident AD (p < 0.0001) and cognitive decline in the African-American population (p < 0001). In the Yoruba, only homozygosity for APOE ε4 was a significant risk factor for AD (p = 0.0002) but not for cognitive decline (p = 0.2346), however, possession of an e4 allele was significant for both incident AD (p = 0.0489) and cognitive decline (p = 0.0425).
  
  
  CONCLUSIONS
  In this large longitudinal comparative study, APOE ε4 had a significant, but weaker, effect on incident AD and on cognitive decline in Yoruba than in African Americans. The reasons for these differences remain unclear.
authors.affiliation: Indiana University Center for Aging Research, Indianapolis, Indiana, USA.
authors.forename: Hugh C
authors.initials: HC
authors.lastname: Hendrie
authors.affiliation: Department of Pathology and Laboratory Medicine, Indiana University School of Medicine, Indianapolis, Indiana, USA.
authors.forename: Jill
authors.initials: J
authors.lastname: Murrell
authors.affiliation: Department of Psychiatry, College of Medicine, University of Ibadan, Ibadan, Nigeria.
authors.forename: Olusegun
authors.initials: O
authors.lastname: Baiyewu
authors.affiliation: Department of Biostatistics, Indiana University School of Medicine, Indianapolis, Indiana, USA.
authors.forename: Kathleen A
authors.initials: KA
authors.lastname: Lane
authors.affiliation: Regenstrief Institute, Inc., Indianapolis, Indiana, USA.
authors.forename: Christianna
authors.initials: C
authors.lastname: Purnell
authors.affiliation: Department of Medicine, College of Medicine, University of Ibadan, Ibadan, Nigeria.
authors.forename: Adesola
authors.initials: A
authors.lastname: Ogunniyi
authors.affiliation: Department of Psychiatry, Indiana University School of Medicine, Indianapolis, Indiana, USA.
authors.forename: Frederick W
authors.initials: FW
authors.lastname: Unverzagt
authors.affiliation: Department of Psychiatry, Indiana University School of Medicine, Indianapolis, Indiana, USA.
authors.forename: Kathleen
authors.initials: K
authors.lastname: Hall
authors.affiliation: Indiana University Center for Aging Research, Indianapolis, Indiana, USA.
authors.forename: Christopher M
authors.initials: CM
authors.lastname: Callahan
authors.affiliation: Department of Radiology and Imaging Services, Indiana University School of Medicine, Indianapolis, Indiana, USA.
authors.forename: Andrew J
authors.initials: AJ
authors.lastname: Saykin
authors.affiliation: Department of Psychiatry, College of Medicine, University of Ibadan, Ibadan, Nigeria.
authors.forename: Oye
authors.initials: O
authors.lastname: Gureje
authors.affiliation: Department of Neurology, Indiana University School of Medicine, Indianapolis, Indiana, USA.
authors.forename: Ann
authors.initials: A
authors.lastname: Hake
authors.affiliation: Department of Medical and Molecular Genetics, Indiana University School of Medicine, Indianapolis, Indiana, USA.
authors.forename: Tatiana
authors.initials: T
authors.lastname: Foroud
authors.affiliation: Department of Biostatistics, Indiana University School of Medicine, Indianapolis, Indiana, USA.
authors.forename: Sujuan
authors.initials: S
authors.lastname: Gao
mesh_terms: D001741:Black or African American / Q000235:genetics*; D000368:Aged; D000483:Alleles; D000544:Alzheimer Disease / Q000235:genetics*; D053327:Apolipoprotein E4 / Q000235:genetics*; D044383:Black People / Q000235:genetics*; D003072:Cognition Disorders / Q000235:genetics*; D005260:Female; D020022:Genetic Predisposition to Disease / Q000235:genetics*; D060005:Genotyping Techniques; D006801:Humans; D053208:Kaplan-Meier Estimate; D008297:Male; D009483:Neuropsychological Tests; D009549:Nigeria / Q000453:epidemiology; D016016:Proportional Hazards Models; D012307:Risk Factors
chemical_list: D053327:Apolipoprotein E4