Our findings revealed an association of T2DM and the risk allele C and CC genotype of the SNP rs290487 (IVS3C/T) of TCF7L2 and the haplotype CC in Han Chinese in Henan province in China. We found no association of clinical and metabolic characteristics and the distribution of the 2 SNPs in controls. As well, we found no interactions between behavioral risk factors and distribution of the SNPs in Han Chinese in Henan province, China.
We found an association of the CC genotype (adjusted OR 1.364, 1.137–1.636, p
0.001) and the recessive model (adjusted OR 1.457, 1.156–1.838, p
0.001) of rs290487 (IVS3C/T) and T2DM, and the power of our study was 100% to detect association based on the prevalence of T2DM in China is 9.7%. This founding is familiar to our previous meta-analysis findings for southern China (OR 1.54, 1.22–1.94, I2
<0.001) and studies by H. Zhu et al. (1.73, 1.04–2.87) 
and Ren et al. (1.73, 1.00–2.25) 
. However, results from other studies were opposite, such as the results of YC. Chan et. al 
, M. Yu et. al 
, and Q. Huang et. al 
. The main reason might due to the complex of the composition of the Chinese population and the great differences among ethnic groups in genetics and living environment.
We found no association of any genotypes for rs7903146 (IVS3C/T) and T2DM. This founding was similar to that form almost all studies performed in China, except for Z. Wang et al 
and X.Tang et al study 
in Chongqing and Chengdu. China is divided into north and south section with the Yangtze River as the approximate boundary, and Chongqing and Chengdu belong to southern China, whereas Henan belongs to northern China. The environment, diet, and lifestyles greatly differ which might explain the inconsistent results. Because of the low frequency of the risk allele T in rs7903146 (IVS3C/T) in the NCBI database, the sample sizes are important for detecting associations.
Both our previous meta-analysis and present meta-analysis indicated the strong association of rs7903146 (IVS3C/T) and T2DM, with the power of the meta-analysis is 100% for the risk allele of rs7903146 (IVS3C/T). This result is inconsistent with our study findings. The reasons for this discrepancy may be because first, the meta-analysis pooled all results from China, and the Han Chinese are not a genetically homogenous group, so regional diversity may contribute to the discrepancy. Second, because of the lack of full information about some potential confounders such as gender, age, and BMI of subjects included in the meta-analysis, we could not perform a stratified or interaction analysis based on these factors. However, in our study, we attempted to adjust findings for the potential confounders.
In the Bodhini. D et al 
and Lehman et al studies 
, rs7903146 (IVS3C/T) variants were associated with increased 2-hr plasma glucose levels in Asian Indians and Caucasians, respectively, and in Liu PH et al study 
, the C allele of rs290487 (IVS3C/T) was associated with 60-, 90-, and 120-min glucose concentrations#. However, because we lacked this information, we did not analyze these indexes. We assessed other clinical and metabolic characteristics of normal glucose-tolerant participants and found no associations between the indexes and the 2 SNPs.
Henan is the most populated province in China, but data were lacking on the association of rs7903146 (IVS3C/T) and rs290487 (IVS3C/T) polymorphisms and T2DM. Our study is the first to assess the associations with SNPs in Han Chinese in Henan province. As well, we analyzed the associations of metabolic measurements and genotypes of the 2 loci in Han Chinese population for the first time. In addition, our meta-analysis, by combining our data and published data, provides strong evidence for the association of the risk alleles of these 2 SNPs and T2DM in Han Chinese. Finally, the power of our study to detect the association of rs290487 (IVS3C/T) and T2DM in our study population was 100% by PGA.
In conclusion, our findings suggest that the genotypes of rs7903146 (IVS3C/T) in TCF7L2 have no major impact on T2DM; however, the CC genotype and the recessive model of rs290487 (IVS3C/T) and the haplotype CC of rs7903146 (IVS3C/T) and rs290487 (IVS3C/T) in TCF7L2 gene are associated with T2DM. We found no association of behavioral risk factors and distribution of rs7903146 (IVS3C/T) and rs290487 (IVS3C/T) in Han Chinese in Henan province, China. However, more representative and comprehensive studies of people with different ethnic backgrounds are needed to clarify the mechanisms and underlying genetic effects of T2DM in the Chinese population.