APOE and Alzheimer disease: Thus, all the foregoing data suggest that one of the several mechanisms accounting for the association between APOE4 and AD, is that APOE4 detrimentally affects the functions of astrocytes, oligodendrocytes, synapses, neurons, endothelial cells, and microglia, which supports the thesis of this article, that treatments should be directed to improving the functions of affected brain cell-types.