Our finding of a more pronounced main effect of ApoE4 genotype on right hippocampal volume also extends the literature regarding laterality which has focused to date on older subjects where greater atrophy in the right hippocampus in E4 carriers has also been consistently reported [18], [37]–[39], [41], [80], [81] as well as among AD patients [8], [40], [66], [82]. The gene discussed is APOE; the disease is Alzheimer disease.