Compared to the MCI and CN group, patients in the AD group had the highest frequency of the ε4 allele within the APOE gene as well as the lowest cognitive function based on the scores of the five neuropsychological scales (ADAS11, MMSE, ADAS13, RAVLT, FAQ), lower CSF Aβ1−42 levels, higher CSF T-tau and P-tau levels, and the most severe atrophy in the hippocampus. The gene discussed is APOE; the disease is Alzheimer disease.