APOE4 is inversely associated with hippocampal volume in a dose-dependent manner both in a pooled sample that includes a DLB group and in an analysis stratifying the DLB group; (1) APOE4+/+ = smaller hippocampal volume, (2) APOE4+/− = intermediate hippocampal volume, (3) APOE4−/− = larger hippocampal volumeReduced hippocampal volume associated with reduced scores in California Verbal Learning Total Recall Test. The gene discussed is APOE; the disease is Lewy body dementia.