Montagne et al. (2020) found APOE ε4 carriers (ε3/ε4 and ε4/ε4) had obvious BBB breakdown in the hippocampus and medial temporal lobe compared with non-carriers (ε3/ε3) and suggested the breakdown of the BBB contributes to APOE ε4-associated cognitive decline independently of AD pathology. The gene discussed is APOE; the disease is Alzheimer disease.