APP and Alzheimer disease: Even though clinical classification for probable AD (McKhann et al., 1984) and research frameworks as the definition of AD by dementia with A+T+N+ biomarkers exist (Jack et al., 2018), only examination of invasively obtained tissue samples either from living individuals by biopsy or post-mortem at autopsy can provide a definitive diagnosis of AD—by proving the presence of neuritic plaques (with Abeta) or neurofibrillary tangles (with Tau).