Hence, we particularly focused on the association between APOE ε4 and Aβ1–42 level in CSF in AD patients, and found that APOE ε4 was markedly and negatively correlated with the significantly decreased Aβ1–42 level in CSF, and innovatively demonstrated that quantitative dependence of APOE ε4 on Aβ1–42 level in CSF. This evidence concerns the gene APOE and Alzheimer disease.