MAPT and Alzheimer disease: Neurotoxic metals such as Pb, Hg, Al, Cd, and As, as well as certain pesticides and metal-based nanoparticles, have been involved in AD, due to their ability to increase beta-amyloid peptide and the phosphorylation of Tau protein, causing the senile amyloid plaques and neurofibrillary tangles that are characteristic of AD.