ApoE ε4 appears to be a risk factor common to both AD and COVID-19-related outcomes, since symptom severity (Kuo et al., 2020a) and mortality rates (Kuo et al., 2020b) have been found to be significantly worse in ε4 homozygotes, independently of any common comorbidities (i.e., coronary heart disease, dementia, diabetes, and hypertension). This evidence concerns the gene APOE and diabetes mellitus.