While several studies have linked APOE4 to cognitive impairment in PD individuals (Pankratz et al., 2006; Monsell et al., 2014; Samat et al., 2017; Tropea et al., 2018; Szwedo et al., 2022), others found no association (Ezquerra et al., 2008; Kurz et al., 2009; Williams-Gray et al., 2009; Federoff et al., 2012). The gene discussed is APOE; the disease is Parkinson disease.