APOE and depressive disorder: Among non-modifiable risk factors, advanced age, female sex and various apolipoprotein E (ApoE) and amyloid precursor protein (APP) alleles have been associated with developing AD, while metabolic syndrome (i.e., hypertension, high fasting plasma glucose, elevated cholesterol, obesity) and associated atherosclerosis, inadequate physical activity, excessive alcohol consumption, hearing loss and other co-morbidities (e.g., depression) are among the modifiable risk factors for developing the disease [23,24].