Many risk factors were proposed to be significant contributors for the AD onset such as senescence, autophagy defects, genetic factors [i.e., ApolipoproteinaE-allele4 (APOE4), Triggering receptor expressed on myeloid cells 2 (Trem2)], microbiota alterations, lifestyle choices, cardiovascular and traumatic brain injury, as well as environmental factors (level of education, hypertension, obesity, diabetes, smoking, hearing loss, depression, physical inactivity, social isolation) (Livingston et al., 2017). Here, TREM2 is linked to depressive disorder.