APOE and Alzheimer disease: The APOE ε4 allele (APOE4), a minor allele of the APOE gene, is associated with a higher risk for AD (>2-fold increased risk for heterozygotes, >9-fold risk for homozygotes) and an elevated risk for VCID (2-fold increased risk for heterozygotes, 3-fold risk for homozygotes) (Rasmussen et al., 2018).