The association between particulate matter air pollutants and incident dementia was stronger in non-APOE4 carriers (quintile 5 versus quintile 1: 1.41 (1.22–1.61)) than in APOE4 carriers (1.17 (1.03–1.32), P-value for interaction = 0.0141). The gene discussed is APOE; the disease is dementia.