PSEN2 and familial Alzheimer disease: Whereas, the early-onset AD, also called familial AD (FAD), occurs at onset ages ranging from 30–65 years old, and its rarely hereditary involving the amyloid precursor protein, presenilin-1 (PS1), presenilin-2 (PS2) and apolipoprotein E (APOE) ɛ4 allele genes [3, 4].