Background: Interleukin-6 (IL-6) is an important mediator of atherosclerotic disease and is also associated with coronary artery disease (CAD). The growing evidences suggest that polymorphisms in the IL-6 promoter region influence the progression of CAD. This study was performed to update the systematic results of association of IL-6 gene polymorphisms with CAD.
Methods: PubMed, Embase, and China Biology Medicine were searched systematically for English and Chinese articles published up to October 31, 2014. Data were extracted using standardized forms. Odds ratios (ORs) with 95 % confidence intervals (CIs) were used to assess the strength of associations. Subgroup analyses were made on ethnicity.
Results: A total of 42 studies including 15,145 cases and 21,496 controls were combined in this meta-analysis. IL-6 gene -174G/C polymorphism was associated with an increased risk of CAD (for C allele versus G allele: OR = 1.11, 95 % CI 1.02-1.20; for C/C versus G/G: OR = 1.21, 95 % CI 1.03-1.42; for C/C + C/G versus G/G: OR = 1.14, 95 % CI 1.03-1.27). In the subgroup analyses based on ethnicity, a significant association was found between -174 G/C polymorphism and CAD in Caucasians (for C allele versus G allele: OR = 1.12, 95 % CI 1.03-1.22; for C/C versus G/G: OR = 1.21, 95 % CI 1.02-1.42; for C/C + C/G versus G/G: OR = 1.16, 95 % CI 1.05-1.29). In order to reduce heterogeneity, we removed the outlier studies by a Galbraith plot analysis. As a result, the pooled ORs demonstrated no association of -174G/C polymorphism and CAD (C allele versus G allele: OR = 1.02, 95 % CI 0.97-1.06, p = 0.48; C/C versus G/G: OR = 0.1.03, 95 % CI 0.94-1.13, p = 0.48; C/G + C/C versus G/G: OR = 1.03, 95 % CI 0.96-1.09, p = 0.41; C/C versus C/G + G/G: OR = 1.02, 95 % CI 0.94-1.10, p = 0.70, respectively). The polymorphism of -572 G/C was not associated with CAD significantly (for C allele versus G allele: OR = 0.86, 95 % CI 0.74-1.01; C/C versus G/G: OR = 0.99, 95 % CI 0.43-2.27; C/G + C/C versus G/G: OR = 0.96, 95 % CI 0.80-1.15, respectively). In addition, subgroup analyses showed an association between -572 G/C polymorphism and CAD risk among Chinese (C allele versus G allele: OR = 0.64, 95 % CI 0.48-0.85; C/C versus G/G: OR = 0.38, 95 % CI 0.18-0.81; C/G + C/C versus G/G: OR = 0.47, 95 % CI 0.22-1.00; C/C versus C/G + G/G: OR = 0.58, 95 % CI 0.42-0.81).
Conclusion: The C allele of -174G/C polymorphism may associate with increased sensibility to CAD among Caucasians in overall analysis. Nevertheless, the effect is interfered by heterogeneity across the included studies. The C allele of -572G/C polymorphism may decrease the risk of CAD in Chinese.