APOE and Mental deterioration: In stratified analysis by APOE ε4, the association between olfactory impairment and cognitive decline over time was present in both APOE ε4 carries (β = −0.07, 95% confidence interval [CI] −0.12 to −0.02) and ε4 noncarriers (β = −0.04, 95% CI −0.06 to −0.02).