Research article

APOE ε4 lowers age at onset and is a high risk factor for Alzheimer's disease; A case control study from central Norway

Sigrid B Sando^1,2 , Stacey Melquist³ , Ashley Cannon³ , Michael L Hutton³ , Olav Sletvold^1,5 , Ingvild Saltvedt^1,5 , Linda R White^1,2 , Stian Lydersen⁴ and Jan O Aasly^1,2

¹Department of Neuroscience, Norwegian University of Science and Technology, (NTNU), Trondheim, Norway

²Department of Neurology, St Olav's Hospital, Trondheim, Norway

³Department of Neuroscience, Mayo Clinic College of Medicine, Jacksonville, Florida, USA

⁴Unit for Applied Clinical Research, Department of Cancer Research and Molecular Medicine, The Norwegian University of Science and Technology (NTNU), Trondheim, Norway

⁵Department of Geriatric medicine, St Olav's Hospital, Trondheim, Norway

author email corresponding author email

BMC Neurology 2008, 8:9doi:10.1186/1471-2377-8-9

Published:	16 April 2008

Abstract

Background

The objective of this study was to analyze factors influencing the risk and timing of Alzheimer's disease (AD) in central Norway. The APOE ε4 allele is the only consistently identified risk factor for late onset Alzheimer's disease (LOAD). We have described the allele frequencies of the apolipoprotein E gene (APOE) in a large population of patients with AD compared to the frequencies in a cognitively-normal control group, and estimated the effect of the APOE ε4 allele on the risk and the age at onset of AD in this population.

Methods

376 patients diagnosed with AD and 561 cognitively-normal control individuals with no known first degree relatives with dementia were genotyped for the APOE alleles. Allele frequencies and genotypes in patients and control individuals were compared. Odds Ratio for developing AD in different genotypes was calculated.

Results

Odds Ratio (OR) for developing AD was significantly increased in carriers of the APOE ε4 allele compared to individuals with the APOE ε3/ε3 genotype. Individuals carrying APOE ε4/ε4 had OR of 12.9 for developing AD, while carriers of APOE ε2/ε4 and APOE ε3/ε4 had OR of 3.2 and 4.2 respectively. The effect of the APOE ε4 allele was weaker with increasing age. Carrying the APOE ε2 allele showed no significant protective effect against AD and did not influence age at onset of the disease. Onset in LOAD patients was significantly reduced in a dose dependent manner from 78.4 years in patients without the APOE ε4 allele, to 75.3 in carriers of one APOE ε4 allele and 72.9 in carriers of two APOE ε4 alleles. Age at onset in early onset AD (EOAD) was not influenced by APOE ε4 alleles.

Conclusion

APOE ε4 is a very strong risk factor for AD in the population of central Norway, and lowers age at onset of LOAD significantly.