Ethnic difference in patients with type 2 diabetes mellitus in inter-East Asian populations: A systematic review and meta-analysis focusing on gene polymorphism

Background: We previously reported that the fasting serum insulin level was significantly lower in Japanese patients than in Korean and Chinese patients, and showed evidence that a difference in the dietary component would be one of the most influential factors for the ethnic difference. However, it is well known that type 2 diabetes mellitus (T2DM) results from the interaction between genetic predispositions and environmental risk factors. Therefore, we investigated ethnic differences by focusing on gene polymorphism, possibly related to T2DM in Japanese, Korean, and Chinese subjects. Methods: Data sources included MEDLINE and EMBASE between January 2001 and October 2008. We conducted a search for articles containing minor allele frequency (MAF) in the gene polymorphisms of peroxisome proliferator-activated receptor-gamma (PPARG), inward-rectifying potassium channel Kir6.2 (KCNJ11), Calpain 10 (CAPN10), and transcription factor 7-like 2 (TCF7L2). The pooled odds ratio was calculated by using a fixed-effects model with the Mantel-Haenszel method after confirming statistical evidence of homogeneity across the ethnicities using the Breslow-Day test. Results: The Breslow-Day test revealed that there were no statistically significant differences between ethnicities in pooled odds ratios for the gene polymorphisms in PPARG (P = 0.828), KCNJ11 (P = 0.194), CAPN10 (P = 0.090), and TCF7L2 (P = 0.376). Also, pooled odds ratios of each gene polymorphism in East Asians were 0.645 for PPARG (P = 0.000), 1.168 for KCNJ11 (P = 0.000), 0.967 for CAPN10 (P = 0.759), and 1.386 for TCF7L2 (P = 0.000). Conclusion: The results of this study and our previous studies suggest that behavioral and environmental risk factors have a more significant impact on ethnic difference in East Asian patients with T2DM compared with genetic predispositions.