BDNF and Alzheimer disease: A study that reviewed several biomarkers of Alzheimer's disease, including brain-derived neurotrophic factor (BDNF) and tumor necrosis factor α (TNF-α), resulted in significantly lower BDNF levels in the early-onset Alzheimer's disease (EOAD) and the late-onset Alzheimer's disease (LOAD) groups compared with the control group (p < 0.05) [27].