MAPT and Alzheimer disease: Starting with age as the main cause and primary risk factor, AD is being explained by the oligomeric amyloid beta (Aβ) cascade hypothesis, which includes hyperphosphorylated and dysregulated tau [1], the intoxication hypothesis [2–4], chronic infections [5–7], microbiome composition [8], neuronal insulin resistance [9, 10], physical and functional breakdown of the blood–brain-barrier (BBB) [11, 12], chronic neuroinflammation, due to multiple causes [13], impaired neuronal rejuvenation (NRJ) [14], synaptic failure [15], and a growing list of many others.