These adverse PM2.5 effects varied by APOE allele, with ɛ3/3<ɛ3/4<ɛ4/4 for both global cognitive decline (ɛ3/3: HR=1.65; ɛ3/4: HR=1.93; ɛ4/4: HR=3.95) and all-cause dementia (ɛ3/3: HR=1.68; ɛ3/4: HR=1.91; ɛ4/4: HR=2.95). The gene discussed is APOE; the disease is dementia.