For example, in a meta-analysis of primarily candidate gene studies, Tsang and colleagues reported that APOE e4 carriers had significantly higher odds of later-life depression (clinical diagnosis or high symptom scores) (Tsang, Mather, Sachdev, & Reppermund, 2017), although this was only relative to e3 allele carriers and was largely driven by a single candidate gene study, with several other reviewed studies reporting no significant association. Here, APOE is linked to major depressive disorder.