Deletion of AEP from human α‐SNCA transgenic mice alleviates dopaminergic neuronal loss and diminishes motor deficits.[6] In addition to α‐Syn, we have reported that AEP acts as δ‐secretase that truncates both APP N585 and Tau N368 in Alzheimer's disease (AD), promoting AD pathogenesis.[7] Most recently, we report that AEP cleaves both α‐Syn at N103 and Tau at N368 in the enteric nervous system (ENS), and mediates their fibrillization and retrograde propagation from the gut to the brain, triggering nigra dopaminergic neuronal death associated with Lewy bodies and motor dysfunction. The gene discussed is MAPT; the disease is Alzheimer disease.