Early-onset Alzheimer's disease (EOAD) is thought to be associated with greater clinical heterogeneity than late-onset Alzheimer's disease (LOAD), with up to one third of patients displaying an atypical, nonamnestic cognitive profile. While this heterogeneity has been recognized in the existing literature, past studies have been plagued by small sample sizes and potentially inaccurate clinical diagnoses. A recent dissertation study sought to characterize cognitive differences between patients with EOAD and those with LOAD in a large autopsy-confirmed sample. Participants included 1,567 individuals with autopsy-confirmed Alzheimer's disease (AD) pathology who completed a battery of neuropsychological tests during their initial presentation to a memory clinic. Participants were divided into two groups for primary analyses: the EOAD group included patients aged 65 and younger; the LOAD group included patients over the age of 65. Secondary analyses investigated the role of apolipoprotein E (APOE) genotype on retentive memory abilities in patients with EOAD. For this analysis, participants with EOAD were divided into two groups based on APOE genotype: one group was composed of those with one or two ε4 alleles; the other group included those with no ε4 alleles. Results indicate significant differences in overall neuropsychological profile between EOAD and LOAD, F(10, 1554) = 34.938, p < .0005, Wilks's Λ = .816, partial η2 = .184. Follow-up logistic regression identified two measures of attention (Digit Span Forward, Digit Span Backward), two measures of processing speed (Trail Making Test Part A, WAIS Coding), and two measures of language (Vegetables, Boston Naming Test) as significant predictors of group membership. Secondary analyses examining differences in retentive memory performance between ε4 carriers and noncarriers within the EOAD group were notable for significantly better memory performance in ε4 noncarriers, t(229) = 2.291, p = .023, Cohen's d = 0.30. These findings are consistent with past literature that describes a unique neurocognitive profile in EOAD. Further, these findings suggest that some of the heterogeneity in EOAD may be related to APOE genotype. (PsycInfo Database Record (c) 2020 APA, all rights reserved)
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