APOE and Alzheimer disease: The apolipoprotein E (APOE) gene consists of polymorphic ε2, ε3 and ε4 alleles, with worldwide frequencies of 8.4, 77.9 and 13.7%, respectively, in cognitive normal subjects; AD patients show a 40% increase in ε4 allele frequency (Farrer et al., 1997) with gender independence (Neu et al., 2017).