For instance, the APOE ε4 allele, as the strongest AD risk gene (Yu et al., 2014), was found to be associated with brain atrophy and amyloid deposition involving the hippocampus and temporoparietal regions (Li et al., 2017), as well as decreased functional connectivity in the default mode network (DMN) (Machulda et al., 2011). Here, APOE is linked to Alzheimer disease.