Different population constitutions may also account for this inconsistency between the Asian and Caucasian populations. It is hypothesized that the lack of association between IL-1β polymorphisms and gastritis severity in the Indian population may be due to the comparatively lower level of cytokines secreted in the mucosa than the Caucasian population. As the IL-1β polymorphisms lack association with gastritis risk in the Asian population entirely, the cytokines expression level may also influence the epidemiology study results of the whole Asian population.
For a sound meta-analysis, 1 major concern is publication bias. No publication bias for the 2 polymorphisms was found by Begg funnel plot or Egger test. The shapes of the funnel plot were symmetrical in all the comparison models. Heterogeneity between studies is another major concern. In our study, there was no heterogeneity in IL-1β-511 polymorphism by Q test. However, there is heterogeneity between studies in the allele model, homozygous model, and recessive model of IL-1β-31 polymorphism. The heterogeneity disappeared in subgroup analysis by “ethnicity.” The “sample size” and “ethnicity” could only explain part of the τ2 by logistic meta-regression analyses. There may be other reasons accounting for the heterogeneity in IL-1β-31 polymorphism. Nevertheless, sensitivity analysis proved that our meta-analysis results were statistically reliable.
Different ethnic groups, especially a mixed population such as the Mexican and the Brazilian, have their own migration history, genetic drift, allele-frequency-affecting mating status, lifestyle, and disease susceptibility. Therefore, in epidemiology investigation, ethnic differences may induce discrepancies in these studies. In our study, the ethnicity could induce heterogeneity and affect the meta-analysis results. In the future, the ethnicity should be paid more attention to when designing the study method and explaining study results in epidemiology investigation of IL-1β polymorphisms.
In conclusion, the current meta-analysis provides data to support the existence of association between IL-1β-31 polymorphism and gastritis risk in the Caucasian population. It is necessary to conduct more studies with larger sample sizes and various ethnic populations to provide further evidence of the results. In addition, further studies evaluating the gene–environment interaction effects may provide a more comprehensive explanation for the association between IL-1β promoter polymorphisms and gastritis risk.
The authors thank Ms Grace Tan for the help on English language editing.
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