Association of apolipoprotein E epsilon 4 allele with sporadic late onset Alzheimer`s disease. A meta-analysis.

OBJECTIVE To obtain a better insight into the effect of the epsilon (e) 4 allele of the apolipoprotein E gene (APOE) on the risk of late onset Alzheimer`s disease (LOAD), and assess its heterogeneity in geographic regions. METHODS We performed a systemic review and meta-analysis of available studies. An electronic and manual search of international and local databases was conducted to identify relevant studies between January 1991 and December 2011 in the Central Library of Tabriz University of Medical Sciences, Tabriz, Iran. All articles related to patients with LOAD that evaluated APOE genotype were included in our study. Two reviewers assessed the inclusion/exclusion criteria, summarized, and analyzed the extracted data. We assessed 21 separate studies overall involving 1480 subjects; the total sample size was 6777. RESULTS According to the results, there was no heterogeneity among the included studies. The total APOE e4 allele frequency was significantly higher in AD cases compared with control subjects (35% versus 11.43%, p<0.001). The odds ratio (OR) for APOE e4 frequency in AD and control groups was 3.98 (95% confidence interval [CI]: 3.44-4.61). This factor in various geographic regions was different. CONCLUSION This meta-analysis is strongly supportive of the hypothesis that the APOE e4 allele increases the risk of sporadic LOAD, and determination of the e4 allele in populations may be a useful tool for monitoring demented patients and planning healthcare policies.