APOE and major depressive disorder: Carrying the ε3/ε4 genotype of the APOE gene increased the odds of developing high levels of depression by 2.167 (95% CI 1.100–4.266) times compared to the carrier of the ε3/ε3 genotype of the APOE gene (χ2 = 5.120 df = 1 p = 0.024).