APOE and Alzheimer disease: In addition, neuroimaging studies have showed shrinkage in hippocampal volume in APOE ε4 carriers with mild cognitive impairment (MCI) and AD compared to APOE ε4 non-carriers (Plassman et al., 1997; Liu et al., 2013), which correlated with reduced cognition memory performance (Lind et al., 2006).