noted that APOE‐ε4 carriers show a greater propensity for developing age‐related cognitive impairment, a decrease in the synapse‐neuron ratio, and an increased susceptibility to exogenous neurotoxins and hippocampal atrophy independent of head trauma (Nathoo, Chetry, van Dellen, Connolly, & Naidoo, 2003). This evidence concerns the gene APOE and hippocampal atrophy.