Pathological hallmarks of both types of AD are neurofibrillary tangles formed by hyperphosphorylated tau, a protein belonging to microtubule associated proteins (MAPs), and extracellular plaques containing the amyloid beta 1-42 (Aβ42) fragment of APP, generated by aberrant activity of PS1/PS2. Here, PSEN2 is linked to Alzheimer disease.