APOE and Alzheimer disease: The apolipoprotein E (APOE) gene lies in chromosome 19 containing three polymorphic alleles, namely ɛ2, ɛ3, and ɛ4 [18] and the ɛ4 allele (APOE4) is involved in amyloid plaque deposition playing a major role for AD and other neurological disorders [19].