MAPT and Alzheimer disease: This is a classic ‘fortuitous’ example for which, by doing research—in this specific case, investigating the toxicity of the tau fragment—we came across the mitochondrion, further validating what was a hypothesis at the time—but now it is a certainty—that among the most serious and important neuropathological alterations of AD, mitochondrial dysfunction is among the timely events in the onset of the disease itself as well as in its progression.