In keeping with a prominent effect of APOE4 in endosomal-lysosomal trafficking, we previously showed increased expression levels of Rab GTPase genes, such as Rab5b, Rab7 and Rab9, in the EC of aged APOE4 mice [33], similar to that observed in cholinergic basal forebrain neurons in MCI and AD [63]. Here, RAB9A is linked to Alzheimer disease.