In the present study, an ordered trend in the frequency of the APOE e4 allele was observed: AD (30.8%), L-aMCI (24.0%), E-aMCI (15.1%), SMI (11.7%), and control (9.1%) groups, suggesting that there is an increasing trend in the frequency of APOE e4 alleles in the AD spectrum. The gene discussed is APOE; the disease is Alzheimer disease.