APOE and Alzheimer disease: This pattern has been observed in carriers of the apolipoprotein ε4 (APOE4) allele7,8,13,14 which is the most well-known genetic risk factor for sporadic AD conferring a 4- fold (single copy) to 8–12 fold (two copies) increase in risk for future AD,15,16 as well as in people with subtle cognitive decline.17