APOE and major depressive disorder: In a study in healthy adult women, Gallagher-Thompson, O'Hara, Simmons, Kraemer, and Murphy (2001) found increased levels of self-reported stress to be associated with increased levels of depression in APOE-ε4 carriers, but not in non-carriers, suggesting that APOE-ε4 carriers have stronger responses to stress than non-carriers.