APP and Alzheimer disease: Conversely, a significant reduction of class I HDACs (HDACs 1, 2, and 3) was recently reported in brains from MCI and AD patients, as evaluated by PET analysis using [11C]Martinostat tracer, as well as in transgenic rats with both amyloid and tau pathology, but not in aged transgenic rats (McGill‐R‐Thy1‐APP rats with the APP Swedish and Indiana mutations) expressing single amyloid pathology (Pascoal et al., 2022).