↓ in temporoparietal and occipital cortex and in SMA in PD-MCI vs. cognitively normal PD. Diffuse atrophy in occipital, temporal, right frontal and left parietal lobe; and in putamen, hippocampus, parahippocampal region, anterior cingulate gyrus, nucleus accumbens and thalamic nuclei in PDD vs. NC. Atrophy in occipital lobe and entorhinal cortex in PDD vs. PD; in temporoparietal and occipital cortex in DLB vs. PDD. Preserved hippocampal volume (mainly cornu ammonis-1 subfield) in DLB vs. AD. APOE-ε4 may influence hippocampal atrophy in PDD/DLB. The gene discussed is APOE; the disease is Lewy body dementia.