A patient's inheritance of alleles for apolipoprotein E (APOE) affects his or her risk of developing Alzheimer's disease (AD).
APOE alleles (designated "epsilon") are on chromosome 19:
(1) epsilon 2
(2) epsilon 3
(3) epsilon 4
The allelic dose of epsilon 4 determines the risk for Alzheimer's disease. Approximately 40% of Alzheimer's cases have been linked to the APOE genotype (Martin, 1999).
Impact: on senile dementia (onset after age 60), not early onset
Influences:
(1) hazard ratio for developing Alzheimer's disease
(2) age of onset
Number of Epsilon 4 Alleles
Odds Ratio (Tsai)
Odds Ratio (Corder)
0
1
1
1
4.4
2.8
2
19.3
8
where:
• The odds ratios for 2 alleles = (odds ratio for 1 allele) * (odds ratio for 1 allele)
Number of Epsilon 4 Alleles
Median Age of AD Onset (Tsai)
Median Age of AD Onset (Corder)
0
74 years
67 years
1
78 years
74 years
2
83 years
88 years
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