Early studies have illustrated that APOE ε4 carriers exacerbated gray matter atrophy in the medial temporal lobe and hippocampus in patients with MCI (Schuff et al., 2009; Racine et al., 2018; Abushakra et al., 2020; Zhang et al., 2020) and AD (Li et al., 2016; Saeed et al., 2018; Bilgel and Jedynak, 2019). Here, APOE is linked to Alzheimer disease.