APOE and Cognitive impairment: Studies that did not find an association between APOE4 and cognitive impairment in their cohorts have emphasized the need for longitudinal studies to further evaluate the effect of APOE4 and cognitive function in PD, which are currently limited (Ezquerra et al., 2008; Collins and Williams-Gray, 2016; Mengel et al., 2016; Zhu et al., 2024).