title: Apolipoprotein E: depressive illness, depressive symptoms, and Alzheimer's disease.
abstract: BACKGROUND
  The apolipoprotein E (ApoE) epsilon 4 and epsilon 2 alleles may influence the age of onset of depressive illness. Depressive illness of late onset is also a risk factor for Alzheimer's disease (AD), and there is some evidence that the ApoE epsilon 2 allele is associated with depressive symptomatology in AD. Depressive symptomatology in AD may thus share common genetic risk factors with late-onset depressive illness.
  
  
  METHODS
  The frequency of the epsilon 2 and epsilon 4 alleles of ApoE and their effects on age of onset of disease in three independent groups of subjects, with depressive illness, with AD, and controls, were compared in a defined population from Southeast London.
  
  
  RESULTS
  The frequency of the ApoE epsilon 2 allele was significantly lower in the depressive illness group compared with the control group and was associated with a later mean age at onset. Subjects with depressive symptomatology in AD had a higher frequency of the ApoE epsilon 2 allele and had a significantly later age of onset of depressive illness compared with the nondepressed AD group.
  
  
  CONCLUSIONS
  The presence of the ApoE epsilon 2 allele in AD is found to be highly associated with depressive symptomatology, and it is proposed that this subgroup represents the presence of delayed depressive illness and that there are common genetic risk factors between AD and depressive illness.
authors.affiliation: Department of Neurosciences, Institute of Psychiatry, London, United Kingdom.
authors.forename: C
authors.initials: C
authors.lastname: Holmes
authors.forename: C
authors.initials: C
authors.lastname: Russ
authors.forename: G
authors.initials: G
authors.lastname: Kirov
authors.forename: K J
authors.initials: KJ
authors.lastname: Aitchison
authors.forename: J F
authors.initials: JF
authors.lastname: Powell
authors.forename: D A
authors.initials: DA
authors.lastname: Collier
authors.forename: S
authors.initials: S
authors.lastname: Lovestone
mesh_terms: D017668:Age of Onset; D000368:Aged; D000369:Aged, 80 and over; D000483:Alleles; D000544:Alzheimer Disease / Q000235:genetics* / Q000523:psychology; D001057:Apolipoproteins E / Q000235:genetics*; D003866:Depressive Disorder / Q000235:genetics* / Q000523:psychology; D005260:Female; D005787:Gene Frequency; D005838:Genotype; D006801:Humans; D008297:Male; D008875:Middle Aged; D011569:Psychiatric Status Rating Scales
chemical_list: D001057:Apolipoproteins E