APOE and Alzheimer disease: In infants and toddlers, gray matter volume (GMV) and myelin water fractionation are decreased in the precuneus, temporal, and occipitotemporal regions, areas vulnerable to AD, and increased in the parietal, occipital, and frontal regions in APOE4 carriers (Dean et al., 2014; Knickmeyer et al., 2014).