Cognitive function and apolipoprotein E in very old adults: Findings from the Nun Study

Abstract

Objectives. The ε4 allele of apolipoprotein E (APOE) has been associated with Alzheimer's disease and with milder forms of cognitive impairment. We investigated the possibility that the absence of the ε4 allele may predict the maintenance of high cognitive function among very old individuals. Methods. Our data are from the Nun Study, a longitudinal study of aging and Alzheimer's disease in 678 Catholic sisters. All sisters participate in annual functional exams that include the Consortium to Establish a Registry for Alzheimer's Disease (CERAD) battery of cognitive tests. High cognitive function was defined as intact scores on five of the CERAD tests. A total of 241 participants aged 75 to 98 met this criterion at the first exam. Results. Findings showed that 62% of the 241 participants maintained intact scores on the five CERAD tests throughout their participation in the study. Life table analyses indicated that those without the APOE ε4 allele spent more time with intact cognitive function than those with the ε4 allele (p = .007). Cox regression analyses indicated that those without the ε4 allele had half the risk of losing their intact status during the study when compared with those with the ε4 allele (p < .01). Discussion. Our findings suggest that the APOE ε4 allele may be included among the variables that predict high cognitive function in cognitively intact, very old adults. Although the presence or absence of the ε4 allele is known to be related to the risk of dementia, it also appears to be related to maintaining high levels of cognitive function in old age.