To examine the association of the APOE 24 genotype with incident Alzheimer disease (AD), mild cognitive impairment (MCI), cognitive decline, and AD pathology in older adults.
We used data from 2,151 older adults of European ancestry who were free of dementia at baseline and underwent structured annual clinical evaluation in a longitudinal study for incident AD and MCI, and cognitive decline. Postmortem examination in decedents documented pathologic AD and quantified β-amyloid and neurofibrillary tangles. Participants were stratified into 4 groups based on APOE genotyping: 24, 4 (44, 43), 2 (22, 23), with 33 carriers serving as the reference group. We used Cox proportional hazards models to examine the association of APOE genotype with incident AD and MCI. Linear mixed-effect models were used to examine the association with cognitive decline. Logistic and linear regression models were used to examine AD pathology. All the models controlled for age, sex, and education.
Of the 2,151 participants included in this study, 24 accounted for 2.1%, 3/4 and 4/4 21.8%, 2/3 and 2/2 14.0%, and 33 62.1%. We did not observe a difference in the risk of AD for 24 compared to 33. In cases without cognitive impairment at baseline, 24 carriers had an increased risk of incident MCI (hazard ratio 2.13, 95% confidence interval 1.34–3.39, p = 0.002) and a faster rate of cognitive decline (estimate –0.047, SE 0.018, p = 0.008) compared to 33 carriers. In decedents (n = 1,100), 24 showed a 3-fold increased odds of pathologic AD and a higher β-amyloid load than 33.
APOE 24 genotype in older adults is associated with risk of MCI, cognitive decline, and a greater burden of AD pathology, especially β-amyloid.