In the context of Parkinsonisms, the APOE4 allele is prominently found in individuals with PD-MCI, PDD, and DLB, when compared to cognitively unimpaired healthy controls (HCs) and/or PD patients with normal cognition (PD-NC) (Parsian et al., 2002; Lashley et al., 2008; Tsuang et al., 2013; Outeiro et al., 2019). Here, APOE is linked to Parkinsonism.