APOE and Alzheimer disease: APOE ε4 also influences the clinical course of AD [29–31], causing earlier onset of dementia [25–27, 32–35], higher degrees of brain atrophy [36], lower temporal [19, 37], hippocampal [2, 36–40], amygdala volumes [38, 41] and significant thinner cortices [42], and faster cognitive decline [30].