The cause of Aβ aggregation is not fully understood, but genetic factors such as missense mutations in the genes encoding amyloid precursor protein (APP), presenilin 1 (PSEN 1), presenilin 2 (PSEN 2), and apolipoprotein E (APOE) are known to increase the risk of AD [13,115]. Here, APOE is linked to Alzheimer disease.