APOE and Parkinson disease: This association between PDD and APOE4 is further supported by multiple studies demonstrating that those with PD and at least one APOE4 allele have a greater likelihood in developing PDD when compared to those without the allele (Pankratz et al., 2006; Monsell et al., 2014; Huertas et al., 2017; Chung et al., 2021).