ERN1 and prion disease: In the AD brains, the immunoreactivity of the ER stress markers, such as pPERK, eIF2α and IRE‐1α, was observed in hippocampal neurons associated with granulovacuolar degeneration, and the pPERK‐immunoreactive neurons were increased.21 Moreover, ER stress features are prominent in the brain of AD patients but not in Prion diseases,22 suggesting a specific role of ER stress in the pathophysiological process of AD.