APOE and Alzheimer disease: For the current study we examined a large cohort (n = 662) of subjects drawn from a publicly available database, made up of cognitively normal (CN) controls, subjects with mild-cognitive impairment (MCI), and subjects with AD, in order to investigate the differential effects of the APOE ε4 and ε2 alleles on hippocampal volume across the cognitive spectrum–and in particular whether any such effects are dose-dependent.