APOE and depressive disorder: The few existing studies have produced mixed findings, with some finding that APOE e4 carriers have greater depressive symptoms and higher risk of later-life depression (Skoog et al., 2015) and others finding less substantial (Burns, Andrews, Cherbuin, & Anstey, 2020) or non-significant (Locke et al., 2013; Tully, Péres, Berr, & Tzourio, 2016) associations.