Association between apolipoprotein E polymorphism and Alzheimer disease in Tehran, Iran

Epsilon 4 allele of apolipoprotein E (APOE-ɛ4) is a major risk factor for Alzheimer's disease (AD). The association of APOE allele frequencies with AD remains unknown in developing countries. We examined the frequency of APOE alleles in 105 patients with AD and 129 cognitively normal subjects of similar age and sex (control group), in Tehran, Iran. The APOE-ɛ4 allele frequency was significantly higher in the AD subjects than in the control group (21% versus 6.2%, p < 0.001). In addition, the OR for APOE-ɛ4 heterozygous and homozygous subjects were 3.2 (p = 0.001) and 12.75 (p = 0.01), respectively. The OR was not uniform across age groups. The AD subjects carrying one or two APOE-ɛ4 allele showed earlier age-at-onset (p < 0.001). These data suggest that the APOE-ɛ4 allele increase the risk for AD in Tehran population in a dose and age-dependent manner. Although the APOE-ɛ2 allele frequency was lower in the AD subjects than in the control group (0.95% versus 2.7%, p = 0.15), APOE-ɛ2 was not associated with the onset of AD in Tehran's population. The OR for ɛ2 allele in AD subjects was 0.34 (p = 0.21). The genotype frequencies for ɛ3, ɛ4, and ɛ2 alleles in control subjects were 91.2, 6.1, and 2.7%, respectively. These values were similar to that reported for Turkish, Greece, Japanese, Spanish, and Moroccan populations, but they were significantly different from the reported values for the other ethnic populations. This observation emphasizes the importance of geographical location and ethnical background of the subjects in the study of APOE genotypes and their association with AD.