Contribution of APOE promoter polymorphisms to Alzheimer's disease risk

Objective: To determine whether the effects of APOE promoter polymorphisms on AD are independent of the APOE-ε4 allele. Background: Recently, the -491 A→T and -219 G→T polymorphisms located in the APOE promoter have been suggested to be risk factors for AD. However, the effects of these polymorphisms have not always been reproduced in case-control studies, possibly because of the strong linkage disequilibrium existing at this locus or the characteristics of the populations studied. Methods: Data collection was performed from six independent samples (1,732 patients with AD and 1,926 control subjects) genotyped for APOE exon 4 and the two APOE promoter polymorphisms. The risks associated with the APOE polymorphisms for developing AD were estimated using logistic regression procedures and calculation of odds ratios with 95% CI adjusted by age, sex, and collection center. Independence of the APOE promoter polymorphisms was tested by stratification for APOE-ε4 and tertile design was used for age stratification. Results: The independence of the -491 AA genotype was observed in the whole sample whereas the independence of the -219 TT genotype was observed only in the oldest population. Conclusion: The -491 and -219 APOE promoter polymorphisms incur risk for AD in addition to risk associated with the APOE-ε4 allele, with age accentuating the effect of the -219 TT genotype. Because these polymorphisms appear to influence apoE levels, these results suggest that APOE expression is an important determinant of AD pathogenesis.