Current meta-analyses were performed among 48,148 cases and 56,738 controls from 72 studies, covering a total of 6 populations, including Caucasian, Asian, Japanese-American, European-American, African-American, South American, and African. Among the tested 18 polymorphisms, there were two (SH2B1 rs7498665 and FAIM2 rs7138803) with significant association results (P < 0.05). Power analysis also showed large power existed in our meta-analyses of two significant polymorphisms including SH2B1 rs7498665 (100%) and FAIM2 rs7138803 (100%).
SH2B1 encodes an adaptor protein associated with leptin and insulin signaling in the lipid metabolism . SH2B1 is an enhancer that may influence the phenotype of obesity through JAK-STAT pathway , which is important in the development and function of adipocytes . SH2B1 acts as a mediator through PI3-kinase pathway which is correlated with the biological actions of leptin . Many animal studies have shown that SH2B1 is involved in the development of obesity. SH2B1 through its participation in the regulation of leptin sensitivity, energy metabolism and body weight . SH2B1 has been identified to be related to obesity through genome-wide association studies (GWAS) . Our meta-analysis of SH2B1 rs7498665 was performed among 6,652 cases and 4,814 controls with four studies. Among the tested populations, no heterogeneity was observed (I2 = 0). Our results confirmed the relationship between SH2B1 and the risk of overweight/obesity (overall OR = 1.21, 95% CI = 1.09-1.34, P = 0.0004, Figure 1).
FAIM2 is an anti-apoptotic gene that provides protection from Fas-mediated cell death  that is associated with extreme overweight by GWAS . FAIM2 rs7138803 polymorphism is associated with increased risk of obesity in Japanese . But there is no relationship between FAIM2 rs7138803 and obesity in Chinese . Minor allele frequency of rs7138803 in Chinese populations ranges from 0.28 to 0.29, while FAIM2 rs7138803 is monomorphic in Japanese and Caucasian populations. Our meta-analysis among 3477 cases and 4676 controls demonstrated that FAIM2 rs7138803 was associated with the risk of overweight/obesity (overall OR = 1.11, 95% CI = 1.01-1.22, P = 0.04, Figure 1).
Although meta-analysis is an important method to improve the precision and accuracy, to analyze and quantify the published results [61–63], some disadvantages exist in the meta-analysis. For the current meta-analyses, several limitations need to be taken with cautions. Firstly, obesity is always accompanied by other complications such as coronary artery diseases and hypertension. These confounding factors needed to be adjusted in the original case–control studies. We were unable to obtain the related information. Therefore we can’t exclude a chance of the positive findings confounded by these obesity-related factors. Secondly, the significant result of FAIM2 rs7138803 needs to be validated in the future. However, after Bonferroni’s correction by the number of testing, the association of FAIM2 rs7138803 was unable to retain significant. Thirdly, power analysis suggested moderate power in the meta-analyses of MTHFR rs1801133 (power = 78.2%) and SERPINE1 rs1799768 (power = 69.4%) The negative results of them might be caused by a lack of power in our meta-analyses. Future studies with larger samples may help clarify the contribution of these biomarkers to the risk of overweight/obesity.
Our results identified significant associations between 2 polymorphisms (SH2B1 rs7498665 and FAIM2 rs7138803) and overweight/obesity. Moreover, overweight/obesity is a complicated disease influenced by both genetic and environmental factors. The potential mechanism of interaction between gene and environment could be taken into consideration in the future study. Well-designed studies with large samples could help elucidate the contribution of above polymorphisms to overweight/obesity.