The APOE ε4 allele is associated with the risk of late-onset Alzheimer's disease. The age at which memory decline diverges among persons who are homozygous for the APOE ε4 allele, those who are heterozygous for the allele, and noncarriers is unknown. Using local advertisements, we recruited cognitively normal subjects between the ages of 21 and 97 years, who were grouped according to their APOE ε4 status. We then followed the subjects with longitudinal neuropsychological testing. Anyone in whom mild cognitive impairment or dementia developed during follow-up was excluded. We compared the rates of decline in predetermined cognitive measures between carriers and noncarriers of the APOE ε4 allele, using a mixed model for longitudinal change with age. We analyzed 815 subjects: 317 APOE ε4 carriers (79 who were homozygous for the APOE ε4 allele and 238 who were heterozygous) and 498 noncarriers. Carriers, as compared with noncarriers, were generally younger (mean age, 58.0 vs. 61.4 years; P<0.001) and were followed for a longer period (5.3 vs. 4.7 years, P=0.01), with an equivalent duration of formal education (15.4 years) and proportion of women (69%). Longitudinal decline in memory in carriers began before the age of 60 years and showed greater acceleration than in noncarriers (P=0.03), with a possible allele–dose effect (P=0.008). We observed similar although weaker effects on measures of visuospatial awareness and general mental status. Age-related memory decline in APOE ε4 carriers diverges from that of noncarriers before the age of 60 years, despite ongoing normal clinical status.

Apolipoprotein E (APOE) ε4 reduces the median age at Alzheimer disease (AD) onset by gene dose from 84 years in APOE ε4 noncarriers to 68 years in APOE ε4 homozygotes.^1-6 Breitner et al,⁴ for example, found a disproportionately high number of APOE ε4 homozygotes in a population with AD onset between the ages of 55 and 75 years. Since 1994 we have been enrolling and following up a cohort of healthy APOE ε4 homozygotes aged 50 to 69 years at entry, demographically matched to APOE ε3/4 heterozygotes and APOE ε4 noncarriers. As a group, these APOE ε4 carriers have reduced cerebral metabolism in the same brain regions as patients with probable AD, which correlates with the APOE ε4 gene dose⁷ and is progressive.⁸ Memory declines more rapidly with age in APOE ε4 carriers than in APOE ε4 noncarriers,⁹ and the APOE ε4 homozygotes' cognitive performances correlate with stressors, including fatigue¹⁰ and anxiety.¹¹ These changes could represent presymptomatic disease in some, despite their youth. We postulated, therefore, that cognitively healthy APOE ε4 homozygotes must be at greater risk for neuropsychological decline than APOE ε4 heterozygotes and noncarriers preceding clinical conversion to mild cognitive impairment (MCI) and AD as they age into their 60s.

Background: Fibrillar amyloid deposition preferentially affects the frontal lobes, temporal pole/neocortex, and posterior cingulate by age 65 years in APOE ε4 carriers prior to the diagnosis of mild cognitive impairment (MCI) and Alzheimer disease (AD), but is it impairing frontally mediated neuropsychological performance? Methods: A total of 71 ε4 homozygotes (HMZ), 194 ε4 heterozygotes (HTZ), and 356 ε4 noncarriers (NC) who did not differ significantly in mean age (56.6 years), years of education (15.6), gender (70% women), or follow-up duration (6.3 years) had neuropsychological testing every 2 years including the Auditory Verbal Learning Test (AVLT) and frontal/executive tasks sensitive to psychomotor speed, working memory, problem solving, and activity. A subset also received the Iowa Gambling Task (IGT). Findings were then tested in a clinical sample of 27 patients with incident MCI and AD. Results: APOE ε4 carriers had greater acceleration of decline (quadratic effect) than NC on the AVLT (p = 0.04) but not on any frontal test. APOE ε4 HMZ had greater velocity of decline (linear effects) than NC on all mental arithmetic tests: paced auditory serial attention task (PASAT) 3 second (p = 0.01) and 2 second (p = 0.004) versions; and Wechsler Adult Intelligence Scale–Revised arithmetic (p = 0.048). IGT performance did not differ between 12 ε4 HMZ, 27 ε4 HTZ, and 44 NC. Among 27 patients with incident MCI and AD, the PASAT showed progressive decline preceding diagnosis in 50%. Conclusions: No frontal cognitive effects were as robust as memory decline. APOE ε4 HMZ declined more quickly than NC on mental arithmetic tests related to frontal lobe–mediated working memory ability.

Objective: To characterize the effects of cerebrovascular (CV) risk factors on preclinical memory decline in cognitively normal individuals at 3 levels of genetic risk for Alzheimer disease (AD) based on APOE genotype. Methods: We performed longitudinal neuropsychological testing on an APOE ε4 enriched cohort, ages 21–97. The long-term memory (LTM) score of the Auditory Verbal Learning Test (AVLT) was the primary outcome measure. Any of 4 CV risk factors (CVany), including hypercholesterolemia (CHOL), prior cigarette use (CIG), diabetes mellitus (DM), and hypertension (HTN), was treated as a dichotomized variable. We estimated the longitudinal effect of age using statistical models that simultaneously modeled the cross-sectional and longitudinal effects of age on AVLT LTM by APOE genotype, CVany, and the interaction between the two. Results: A total of 74 APOE ε4 homozygotes (HMZ), 239 ε4 heterozygotes (HTZ), and 494 ε4 noncarriers were included. APOE ε4 carrier status showed a significant quadratic effect with age-related LTM decline in all models as previously reported. CVany was associated with further longitudinal AVLT LTM decline in APOE ε4 carriers (p = 0.02), but had no effect in noncarriers. When ε4 HTZ and HMZ were considered separately, there was a striking effect in HMZ (p < 0.001) but not in HTZ. In exploratory analyses, significant deleterious effects were found for CIG (p = 0.001), DM (p = 0.03), and HTN (p = 0.05) in APOE ε4 carriers only that remained significant only for CIG after correction for multiple comparisons. Conclusion: CV risk factors influence age-related memory decline in APOE ε4 HMZ.