APOE and major depressive disorder: Once MCI due to AD is detected, the risk of progression to AD dementia is increased at older ages, in women, in those with low-level education, in people with at least one copy of the apolipoprotein E ε4 (APOE ε4) allele, in those with impaired cognition, and/or in those with comorbidities such as depression, diabetes, or hypertension [18, 22, 25, 26].