APOE and Alzheimer disease: Given that hippocampal asymmetry might be due to genetic, developmental and environmental factors (Verstynen et al., 2001; Tang et al., 2008), hippocampal asymmetry in AD has been suggested to be influenced by the dose effect of the APOE4 allele; the R > L asymmetry is progressively reduced and even reversed in APOE4/4 carriers affected by AD (Geroldi et al., 2000).