APOE and Alzheimer disease: Linard et al. (2020) recently assessed the impact of HSV-1 infection on AD incidence based on a genetic susceptibility factor, apolipoprotein E (APOE). The author found that HSV1 reactivation was more frequent in APOE4 carriers than in APOE4-negative subjects, which suggests that HSV1 has a higher risk of developing AD in subjects with the APOE4 allele (Linard et al., 2020).