According to this study, APOE-ε4 allele is a risk factor for developing late onset AD in Iranian population like many other populations.[24][25][26][27][28][29] Although ε2ε3 genotype seems to play a protective role against AD but the protective role of APOE- ε2 allele has not demonstrated in this study and it may be proved by a larger sample size. Here, APOE is linked to Alzheimer disease.