APOE and Alzheimer disease: Efforts to find the genetic factors contributing to AD have led to the discovery of Amyloid precursorprotein (APP), Presenilin 1 (PSEN1), and Presenilin 2 (PSEN2) as a cause of autosomal dominant AD, and ε4 allele of Apolipoprotein E (APOE) has been identified as a strong genetic risk factor for AD[3], in addition to at least 21 additional genetic risk loci[3].