No association between the ApoE ε2 and ε4 alleles and the risk of obstructive sleep apnea: A systematic review and meta-analysis.

Apolipoprotein E (ApoE) gene ε2 and ε4 alleles have been reported to be associated with the risk of obstructive sleep apnea (OSA); however, the results are controversial. Thus, we performed a meta-analysis to obtain a more precise estimate of the associations by pooling sporadic, inconsistent and small-sample-size studies. Electronic databases such as PubMed and Embase were searched to identify eligible studies focusing on the association between ApoE polymorphisms and susceptibility to OSA before April 2014. The associations were assessed by odds ratio (ORs) with 95% confidence intervals (CIs). The Begg and Egger's test was used to evaluate publication bias. Ten eligible studies (1,696 cases/2,216 controls for the ε2 allele and 2,449 cases/5,592 controls for the ε4 allele) were included in the meta-analysis. An association between the ApoE ε2 and ε4 alleles and OSA was not found in the overall population (OR=0.97, 95% CI: 0.75-1.25; OR=1.09, 95% CI: 0.86-0.38 for ApoE ε2 and ε4, respectively). Significant heterogeneity (ε2: I2=36.6%, P=0.16; ε4: I2=69.7%, P=0.001) was observed across studies, however, heterogeneity could not be explained by variations in mean age, body mass index, apnea hypopnea index, gender, ethnic background, or the ApoE ε2 and ε4 alleles. No evidence of publication bias was found according to the Begg and Egger's test. In conclusion, our findings show that the ApoE ε2 and ε4 alleles have no significant associations with OSA susceptibility based on available data.