APOE and early-onset autosomal dominant Alzheimer disease: However, the subsystem-specific effects of <i>APOE ε4</i> and the cognitive mechanisms through which they operate in MCI remain unclear.<h4>Methods</h4>We enrolled 176 participants from the Alzheimer's Disease Neuroimaging Initiative (ADNI), including 116 patients with MCI and 60 cognitively normal (CN) individuals, with balanced APOE ε4 carrier status within each diagnostic group.