title: Genotype and phenotype in Alzheimer's disease.
abstract: BACKGROUND
  Patients with Alzheimer's disease show a wide variation in clinical phenotype. Genetic research has been largely concerned with the role of mutations or common variants as risk factors for the disease. Do genetic factors also influence clinical phenotype?
  
  
  OBJECTIVE
  To examine the evidence that genetic factors influence the clinical expression of the disease in addition to influencing risk.
  
  
  METHODS
  A selective review was made of the key literature.
  
  
  RESULTS
  Mutations in three genes, coding for amyloid precursor protein, presenilin-1 and presenilin-2, and a common variation (epsilon4) in another gene, APOE, have been shown to lead to an earlier development of the disease. More recently, genetic association and twin studies have suggested a role for genetic factors in the development of other aspects of clinical phenotype, notably the appearance of non-cognitive symptoms.
  
  
  CONCLUSIONS
  In Alzheimer's disease genetic variation influences a number of aspects of clinical phenotype.
authors.affiliation: Thornhill Research Unit, University of Southampton, Moorgreen Hospital, Botley Road, West End, Southampton SO30 3JB, UK.
authors.forename: Clive
authors.initials: C
authors.lastname: Holmes
mesh_terms: D000368:Aged; D000544:Alzheimer Disease / Q000235:genetics*; D020022:Genetic Predisposition to Disease; D005838:Genotype; D006801:Humans; D010641:Phenotype; D012307:Risk Factors