The etiology of sporadic AD is currently unclear, but the following hypotheses have been proposed: Aβ toxicity hypothesis, tau protein phosphorylation hypothesis, oxidative stress hypothesis, neuroinflammation hypothesis, mitochondrial dysfunction hypothesis, cholinergic damage hypothesis, and apolipoprotein E (ApoE) hypothesis (Zetterberg and Mattsson, 2014). The gene discussed is MAPT; the disease is Alzheimer disease.