Executive function asymmetry in older adults genetically at-risk for Alzheimer's disease: verbal versus design fluency.

Recent studies have reported cognitive asymmetries in patients with Alzheimer's disease (AD) and in individuals with apolipoprotein E epsilon4 (APOE epsilon4) genotype who are in the preclinical phase of AD. This increased frequpncy of cognitive asymmetry, typically defined as a significant discrepancy (in either direction) between verbal and spatial abilities, often occurs despite an absence of differences on traditional measures of central tendency (i.e., mean test scores). We prospectively studied the relationship between APOE genotype and two modality-specific executive-function tasks: The Verbal Fluency and Design Fluency tests of the Delis-Kaplan Executive Function System (D-KEFS) in 52 normal functioning older adult participants who were grouped according to the presence (n=24) or absence (n=28) of the APOE e4 allele. Nondemented older adults with the APOE epsilon4 allele demonstrated a greater frequency of cognitive asymmetric profile on the new switching conditions of the Verbal and Design Fluency measures than the APOE non-epsilon4 individuals. This study further supports the utility of assessing cognitive asymmetry for the detection of subtle cognitive differences in individuals at-risk for AD, and suggests that dual-task executive function tests (i.e., fluency plus switching) may serve as a useful preclinical marker of AD.