Race, APOEɛ4, and Long-Term Cognitive Trajectories in a Biracial Population Sample.

Background: The association of the APOEɛ4 allele with incident Alzheimer's dementia is higher among European Americans (EAs) than African Americans (AAs), but similar for the rate of cognitive decline.

Objective: To examine the racial differences in the association of the APOEɛ4 allele with incident Alzheimer's dementia and cognitive decline.

Methods: Using a population-based sample of 5,117 older adults (66% AAs and 63% females), we identified cognitive trajectory groups from a latent class mixed model and examined the association of the APOEɛ4 allele with these groups.

Results: The frequency of the APOEɛ4 allele was higher among AAs than EAs (37% versus 26%). Four cognitive trajectories were identified: slow, mild, moderate, and rapid. Overall, AAs had a lower baseline global cognition than EAs, and a higher proportion had rapid (7% versus 5%) and moderate (20% versus 15%) decline, but similar mild (44% versus 46%), and lesser slow (29% versus 34%) decline compared to EAs. Additionally, 25% of AAs (13% of EAs) with mild and 5% (<1% of EAs) with slow decline were diagnosed with incident Alzheimer's dementia. The APOEɛ4 allele was associated with higher odds of rapid and moderate decline compared to slow decline among AAs and EAs, but not with mild decline.

Conclusions: AAs had lower cognitive levels and were more likely to meet the cognitive threshold for Alzheimer's dementia among mild and slow decliners, explaining the attenuated association of the ɛ4 allele with incident Alzheimer's dementia among AAs.