In the current study, we found significantly smaller right hippocampus volumes in carriers of two APOE ε4 alleles relative to non-carriers, which is in line with previous work linking the APOE ε4 genotype to greater rates of hippocampal atrophy in non-demented and Alzheimer’s disease samples (Saeed et al., 2021; Gorbach et al., 2020). This evidence concerns the gene APOE and early-onset autosomal dominant Alzheimer disease.