APOE and Alzheimer disease: The results showed that frequency of HSV-1 reactivation was very high in APOE4 carriers manifested as raised an HSV-1 IgG antibody accompanied by increased risk of AD (Linard et al., 2020), suggesting a role of HSV-1 in the pathogenesis of AD in populations with a genetic susceptible factor, the APOE4 allele.