Although a larger cohort study has not supported the APOE ε4 allele as a risk factor for depression as a prodrome in AD (Locke et al., 2013), another study has found an interaction between APOE ε4 genotype and depression, as well as a higher risk of incident mild cognitive impairment in male depressed patients (Geda et al., 2006). This evidence concerns the gene APOE and major depressive disorder.