APOE and Alzheimer disease: Given our existing knowledge of the exquisite region-specific patterns of brain atrophy, glucose hypometabolism, spread of tau and amyloid burden in AD progression, we asked whether the ApoE ε4 allele, as the largest genetic determinant of AD risk, also elicits similar brain-region specific changes in MCI which often precedes Alzheimer's (Chan et al., 2003; Cope et al., 2018; Drzezga et al., 2005; Grijalva-Eternod et al., 2012; Knopman et al., 2014; Mecca et al., 2018; Misra et al., 2009; Mosconi et al., 2009).