We found that APOE-ε4 exerts a significant direct effect on delirium in a dose-dependent way: OR direct effect (0vs1) 1.14, 95% CI 1.08–1.2; P = 4.5 × 10−7; for one APOE-ε4 copy, and OR direct effect (0vs2) 1.29, 95% CI 1.15–1.45; P = 1.7 × 10−5 for two APOE-ε4 copies. This evidence concerns the gene APOE and delirium.