APOE and Alzheimer disease: In AD, most pharmacogenetic studies used apolipoprotein E (APOE) and cytochrome P450 (CYP) variants, as a reference, since the presence of the APOE-4 allele is a major pathogenic risk factor for dementia and most acetylcholinesterase inhibitors are metabolized via CYP enzymes, with the exception of rivastigmine [2,4,6,18,34,35].