We further examined whether APOE and age showed comparable associations with total gray matter volume as they did with total hippocampal volume. We found that total gray matter volume decreased with age, but there was no effect of APOE nor evidence of an interactive effect between APOE and age (Tables S9 and S10, and Figures S5 and S6 in supporting information). This finding supports the notion that the interactive effect of the APOE genotype we observed is specific to hippocampal volume loss and is independent of overall brain atrophy associated with aging.
