Several factors are involved in the pathogenesis of AD including genetic predisposition, decreased synthesis of acetylcholine neurotransmitter, extracellular accumulation of amyloid beta (Aβ) in the brain, and abnormalities in tau protein and oxidative stress.   26  Cleavage of amyloid precursor protein (APP) can produce Aβ peptide which activates microglia through toll-like receptors (TLRs). Here, APP is linked to Alzheimer disease.