APOE and Alzheimer disease: AD can also result from the genetic impairment of presenilin 1 (PSEN1), mainly variants rs63750306 and rs63751235, the presenilin 2 (PSEN2) rs63750215 variant, the apolipoprotein E epsilon 4 (APOE-ε4) allele, and/or the amyloid precursor protein (APP) rs63751263, rs63750264, and rs63750671 variants [4].