Association between Val66Met polymorphisms in brain-derived neurotrophic factor gene and asthma risk: a meta-analysis

Objective: The Val66Met polymorphisms in brain-derived neurotrophic factor (BDNF) gene have been reported to be associated with asthma risk, while the results are inconclusive. Considering a single study may lack the power to provide reliable conclusion, we performed a meta-analysis to investigate the association between the Val66Met polymorphisms and asthma susceptibility. Methods: A comprehensive literature search of PubMed, Embase, China National Knowledge Infrastructure (CNKI) and Wanfang databases was conducted before February 12, 2015. The pooled odds ratio (OR) with 95 % confidence intervals (CIs) were calculated. Results: Six eligible studies with a total of 3501 subjects were finally included in this meta-analysis. Overall, a significantly increased risk was detected in the Val66Met G allele (G vs. A: OR 1.33, 95 % CI 1.19–1.49, P = 5.61E−07; GG vs. GA + AA: OR 1.48, 95 % CI 1.20–1.83, P = 3.14E−04; GG vs. GA: OR 1.48, 95 % CI 1.17–1.89, P = 0.001; GG vs. AA: OR 1.62, 95 % CI 1.20–2.19, P = 0.002). Moreover, stratification by ethnicity indicated marked association between the Val66Met G allele and asthma risk in Caucasians (G vs. A: OR 1.29, 95 % CI 1.12–1.49, P = 0.001; GG + GA vs. AA: OR 1.59, 95 % CI 1.03–2.46, P = 0.039; GG vs. GA + AA: OR 1.32, 95 % CI 1.11–1.57, P = 0.001; GG vs. GA: OR 1.28, 95 % CI 1.07–1.53, P = 0.007; GG vs. AA: OR 1.72, 95 % CI 1.11–2.68, P = 0.015). Conclusion: Our present meta-analysis suggests that the Val66Met polymorphisms in BDNF gene are potentially associated with asthma risk in Caucasians. Further well-designed case–control studies with larger sample size and more ethnic groups are needed to confirm these conclusions.