The hippocampal percentage of CD68 activated microglia/macrophages burden was lowest in hippocampal sparing AD (median [IQR], 0.54% [0.39%-0.79%]) but plateaued in typical AD (median [IQR], 1.2% [0.96%-1.8%; post hoc P < .001) and limbic predominant AD (median [IQR], 1.3% [0.94%-1.5%]; post hoc P < .001). This evidence concerns the gene CD68 and Alzheimer disease.