APOE and Alzheimer disease: It has been also shown that the loss of GABAergic interneurons in the hippocampal hilus of mice carrying the AD risk factor apolipoprotein E4 (APOE4 knock-in mice) leads to severe age-dependent learning and memory deficits [41,42,43], an effect that can be rescued by transplanting medial ganglionic eminence-derived inhibitory interneuron progenitors into the hilus [43].