APOE and early-onset autosomal dominant Alzheimer disease: High-risk populations are defined as individuals with a family history of Alzheimer’s disease (Honea et al., 2012), the ε4 allele of the APOE gene (Bonham et al., 2016), or the presence of biomarkers, like elevated τ and a high Aβ1-42/Aβ1-40 ratio (Holland et al., 2012).