APOE and familial Alzheimer disease: fAD is associated with the presence of some autosomal-dominant mutation in key genes, such as amyloid β precursor protein (AβPP), the γ-secretase catalytic components presenilin-1 (PSEN1) and presenilin-2 (PSEN2), or apolipoprotein E (apoE-ε4); this AD type only represents the ~2% of cases [279].