APOE and Parkinson disease: By far the greatest risk factor of Alzheimer’s disease, but also implicated in some forms of Parkinson’s disease (Tsuang et al., 2013; Pang et al., 2018; Shi and Holtzman, 2018; Belloy et al., 2019), is the gene Apolipoprotein E (APOE), which is involved in the transport of cholesterol and other fatty acids or compounds (Urosevic and Martins, 2008; Shi and Holtzman, 2018; Belloy et al., 2019).