Second, we did not perform apolipoprotein E (APOE) genotyping; the APOE ε4 allele has been associated with AD conversion and accelerated hippocampal atrophy,55 although hippocampal atrophy has been associated with both AD and vascular cognitive impairment.56 Novel variants associated with dementia have been continuously reported,57 and genome-based medicine is a major challenge in future studies. Here, APOE is linked to Alzheimer disease.