PSEN2 and Alzheimer disease: More in detail, Alzheimer’s disease (AD) is characterized by deposition of brain amyloid plaques and neurofibrillary tangles, which rise in consequence of amyloid precursor protein (APP), presenilin 1 (PS1), presenilin 2 (PS2), tau protein deposition and apolipoprotein E (APO E) gene mutations or altered processing.