title: Variability of familial risk of Alzheimer disease across the late life span.
abstract: BACKGROUND
  The role of genetic factors in Alzheimer disease (AD) varies across the late life span, complicating efforts to quantify the risk of AD for relatives of probands with AD.
  
  
  OBJECTIVE
  To visualize the changing levels of familial risk according to proband onset age and the age of the at-risk relative and to determine the familiality of age at onset in AD.
  
  
  METHODS
  A retrospective, informant-based family study. SETTING, PATIENTS, AND OTHER PARTICIPANTS: Siblings and parents of probands with AD (relatives = 4687; probands = 904), ascertained at geriatric clinic and nursing home settings, and of elderly probands without dementia (relatives = 7649; probands = 1525) who were spouses of probands, participants at senior centers, or nursing home residents without dementia.
  
  
  METHODS
  Informant-based assessments of AD in the relatives were used to generate 3-dimensional surfaces representing the patterns of risk of AD across the late life span depending on the specific onset age of the proband with AD (or assessment age of the elderly proband without dementia). We then constructed a 3-dimensional, age-specific, 10-year hazard rate ratio (HRR) surface representing the relative risk of AD in relatives of probands with AD with smoothly shifting levels of onset age compared with relatives of elderly probands without dementia.
  
  
  RESULTS
  The HRR surface peaked (HRR, 13.0) for younger sexagenarian relatives related to probands with AD with onset age in their early 60s. The HRRs dropped sharply both as the proband age at onset and the age of the relative increased. For relatives aged in their late 80s, the HRR fell lower than 2.0 regardless of proband onset age and their lower-limit 95% confidence intervals were less than 1.0.
  
  
  CONCLUSIONS
  The role of genetic risk factors decreases with increasing onset age of the proband with AD regardless of the age of the relatives themselves. The familiality of onset age is greatly reduced at later ages. The role of environmental risk factors in AD likely increases with onset age.
authors.affiliation: Department of Psychiatry, Mount Sinai School of Medicine, New York, NY 10029, USA. jeremy.silverman@mssm.edu
authors.forename: Jeremy M
authors.initials: JM
authors.lastname: Silverman
authors.forename: Gregory
authors.initials: G
authors.lastname: Ciresi
authors.forename: Christopher J
authors.initials: CJ
authors.lastname: Smith
authors.forename: Deborah B
authors.initials: DB
authors.lastname: Marin
authors.forename: Michal
authors.initials: M
authors.lastname: Schnaider-Beeri
mesh_terms: D000367:Age Factors; D017668:Age of Onset; D000368:Aged; D000544:Alzheimer Disease / Q000175:diagnosis / Q000453:epidemiology / Q000235:genetics*; D005190:Family; D005260:Female; D020022:Genetic Predisposition to Disease / Q000453:epidemiology / Q000235:genetics; D006801:Humans; D007407:Interviews as Topic; D008297:Male; D010375:Pedigree; D016016:Proportional Hazards Models; D012189:Retrospective Studies; D012307:Risk Factors; D011795:Surveys and Questionnaires