ABCG1 and Alzheimer disease: Aqueous diffusion cholesterol efflux capacity of plasma was higher in AD patients that in controls, but the two active CEC pathways, mediated by the transporters ABCA1 and ABCG1, were reduced in AD patients (Table 2), in agreement with the reduced content of discoidal pre-β HDL particles (Table 2), the major cholesterol acceptor via these pathways.