APOE and Alzheimer disease: By considering only those cases and controls positive for APOE4 allele, a massive increase in the risk was observed (OR3), reaching more than five-fold risk association among AD patients (OR = 5.11; 2.74–5.52; P<0.0001) which was higher than that obtained in the single analysis (OR = 4.49; 3.32–6.08; S2 Table).