APOE and Alzheimer disease: Genome-wide association studies (GWASs) have revealed thatapproximately 40% of AD patients carry the apolipoprotein E (APOE) ε4 allele and that APOEε4-positive, but cognitively intact, individuals over 50 years of age aresignificantly more likely to have brain amyloid deposits than individuals free ofthat polymorphism [55]; reviewed in[56].