Replication and identification of novel variants at TCF7L2 associated with type 2 diabetes in Hong Kong Chinese

Genome-Wide Association Studies for Albuminuria of Nondiabetic Taiwanese Population

INTRODUCTION

Chronic kidney disease, which is defined by a reduced estimated glomerular filtration rate and albuminuria, imposes a large health burden worldwide. Ethnicity-specific associations are frequently observed in genome-wide association studies (GWAS). This study conducts a GWAS of albuminuria in the nondiabetic population of Taiwan.

METHODS

Nondiabetic individuals aged 30-70 years without a history of cancer were enrolled from the Taiwan Biobank. A total of 6,768 subjects were subjected to a spot urine examination. After quality control using PLINK and imputation using SHAPEIT and IMPUTE2, a total of 3,638,350 single-nucleotide polymorphisms (SNPs) remained for testing. SNPs with a minor allele frequency of less than 0.1% were excluded. Linear regression was used to determine the relationship between SNPs and log urine albumin-to-creatinine ratio.

RESULTS

Six suggestive loci are identified in or near the FCRL3 (p = 2.56 × 10-6), TMEM161 (p = 4.43 × 10-6), EFCAB1 (p = 2.03 × 10-6), ELMOD1 (p = 2.97 × 10-6), RYR3 (p = 1.34 × 10-6), and PIEZO2 (p = 2.19 × 10-7). Genetic variants in the FCRL3 gene that encode a secretory IgA receptor are found to be associated with IgA nephropathy, which can manifest as proteinuria. The PIEZO2 gene encodes a sensor for mechanical forces in mesangial cells and renin-producing cells. Five SNPs with a p-value between 5 × 10-6 and 5 × 10-5 are also identified in five genes that may have a biological role in the development of albuminuria.

CONCLUSION

Five new loci and one known suggestive locus for albuminuria are identified in the nondiabetic Taiwanese population.

The correlation between transcription factor 7-like 2 gene polymorphisms and susceptibility of gestational diabetes mellitus in the population of central China: A case-control study

OBJECTIVE

To investigate the correlation between transcription factor 7-like 2 (TCF7L2) gene polymorphisms and gestational diabetes mellitus (GDM) risk in the central Chinese population.

METHODS

This case-control study examined the association of seven TCF7L2 gene single-nucleotide polymorphisms (SNPs) (rs11196218, rs4506565, rs7895340, rs7901695, rs11196205, rs12243326, and rs290487) with GDM risk in the central Chinese population (843 GDM and 877 controls). The clinical information and blood samples were collected by trained interviewers and nurses. Genotyping of SNPs was conducted on the Sequenom MassARRAY platform. Statistical analyses including t-test, ANOVA, chi-square test, Fisher's exact test, and logistic regression were performed.

RESULTS

Differences in age, pre-pregnant body mass index (BMI), and family history of type 2 diabetes mellitus (T2DM) between the case and control groups were significant (p < 0.05). Compared with the wild-type genotype, pregnant women with genotypes of rs4506565-AT (OR = 1.89, 95%CI: 1.18-3.02), rs7895340 GA (OR = 1.93, 95%CI: 1.06-3.54), rs7901695-TC (OR = 1.79, 95%CI: 1.11-2.88), and rs11196205-GC (OR = 2.15, 95%CI: 1.16-3.98) had a significantly higher risk of GDM, adjusted by age, pre-pregnant BMI, and family history of T2DM. Functional annotation showed that all these four SNPs fell in the functional elements of human pancreatic islets. Further cumulative effects analysis concluded that when participants carried all these four risk genotypes, the risk of GDM was 3.51 times (OR = 3.51, 95%CI: 1.38-8.90) than that of those without any risk genotypes.

CONCLUSIONS

The findings of this study suggested that rs4506565, rs7895340, rs7901695, and rs11196205 were the genetic susceptibility SNPs of GDM in the central Chinese population. Further studies are needed to validate our findings and clarify the underlying mechanisms.

Anticipation of Precision Diabetes and Promise of Integrative Multi-Omics

Precision diabetes is a concept of customizing delivery of health practices based on variability of diabetes. The authors reviewed recent research on type 2 diabetes heterogeneity and -omic biomarkers, including genomic, epigenomic, and metabolomic markers associated with type 2 diabetes. The emerging multiomics approach integrates complementary and interconnected molecular layers to provide systems level understanding of disease mechanisms and subtypes. Although the multiomic approach is not currently ready for routine clinical applications, future studies in the context of precision diabetes, particular in populations from diverse ethnic and demographic groups, may lead to improved diagnosis, treatment, and management of diabetes and diabetic complications.

The Role of TCF7L2 in Type 2 Diabetes

TCF7L2 is the most potent locus for type 2 diabetes (T2D) risk and the first locus to have been robustly reported by genomic linkage studies. TCF7L2 is a transcription factor that forms a basic part of the Wnt signaling pathway. This gene has highly conserved sequence regions that correspond to functional domains. The association of TCF7L2 with T2D is one of the most powerful genetically discovered in studies of complex diseases, as it has been consistently replicated in multiple populations with diverse genetic origins. The mechanisms over which TCF7L2 exerts its effect on T2D are still not well understood. In this article, we describe the main molecular mechanisms of how TCF7L2 is related to T2D. TCF7L2 variants associated with T2D risk exert an influence on the initial therapeutic success of the hypoglycemic oral agent sulfonylurea. Thus, it is important to know whether there are other TCF7L2 variants associated with T2D that can influence treatment with oral hypoglycemic agents. Resequencing of the TCF7L2 gene in diverse ethnic groups is required to reveal common and rare variations and their role in different pathologies and in adverse reactions to drugs. Identification of TCF7L2-susceptibility disease variants will permit, at a given moment, offering of therapies to patients according to their genotype.

The role of transcription factor 7-like 2 in metabolic disorders

Transcription factor 7-like 2 (TCF7L2), a member of the T cell factor/lymphoid enhancer factor family, generally forms a complex with β-catenin to regulate the downstream target genes as an effector of the canonical Wnt signalling pathway. TCF7L2 plays a vital role in various biological processes and functions in many organs and tissues, including the liver, islet and adipose tissues. Further, TCF7L2 down-regulates hepatic gluconeogenesis and promotes lipid accumulation. In islets, TCF7L2 not only affects the insulin secretion of the β-cells but also has an impact on other cells. In addition, TCF7L2 influences adipogenesis in adipose tissues. Thus, an out-of-control TCF7L2 expression can result in metabolic disorders. The TCF7L2 gene is composed of 17 exons, generating 13 different transcripts, and has many single-nucleotide polymorphisms (SNPs). The discovery that these SNPs have an impact on the risk of type 2 diabetes (T2D) has attracted thorough investigations in the study of TCF7L2. Apart from T2D, TCF7L2 SNPs are also associated with type 1, posttransplant and other types of diabetes. Furthermore, TCF7L2 variants affect the progression of other disorders, such as obesity, cancers, metabolic syndrome and heart diseases. Finally, the interaction between TCF7L2 variants and diet also needs to be investigated.

Lack of association between single nucleotide polymorphisms in TCF7L2 and T2DM in the Chinese Yao population: A case-control study

Single-nucleotide polymorphisms (SNPs) in the transcription factor 7-like 2 (TCF7L2) gene have been identified to be associated with the susceptibility to type 2 diabetes mellitus (T2DM) in various populations worldwide, but the results in Chinese are conflicting, and no data are available about the Liannan Yao population. Therefore, this study aimed to investigate the association of the TCF7L2 gene polymorphisms (rs12255372, rs7903146, rs7901695, rs11196205, and rs7895340) with T2DM in the Yao population living in the rural areas in the Liannan Yao Autonomous County.This was a case-control study of 28 subjects with T2DM or prediabetes and 52 non-T2DM controls, all from the Chinese Yao population and recruited between January 2019 and June 2020. Patients with T2DM and prediabetes were grouped as the case group. The five SNPs (rs12255372, rs7903146, rs7901695, rs11196205, and rs7895340) were examined by polymerase chain reaction and direct genomic DNA sequencing in case and control groups.The subjects in case group were older than the controls (55±14 vs 48 ± 15 years, P = .047), had higher FBG levels (9.31 ± 5.43 vs 4.09 ± 0.81, P < .001), higher TC (5.79 ± 1.29 vs 5.13 ± 1.18 mmol/L, P = .025), and higher triglycerides (2.94 ± 2.04 vs 1.86 ± 1.39 mmol/L, P = .003). The genotypic distribution for each of the SNPs was in agreement with the Hardy-Weinberg equilibrium. There were no statistically significant differences in the distributions of genotypes or alleles at all five SNPs of the TCF7L2 gene between the case and control groups (all P > .05).TCF7L2 SNPs were not associated with T2DM in the Liannan Yao population.

Impact of type 2 diabetes variants identified through genome-wide association studies in early-onset type 2 diabetes from South Indian population

The prevalence of early-onset type 2 diabetes (EOT2D) is increasing in Asian countries. Genome-wide association studies performed in European and various other populations have identified associations of numerous variants with type 2 diabetes in adults. However, the genetic component of EOT2D which is still unexplored could have similarities with late-onset type 2 diabetes. Here in the present study we aim to identify the association of variants with EOT2D in South Indian population. Twenty-five variants from 18 gene loci were genotyped in 1,188 EOT2D and 1,183 normal glucose tolerant subjects using the MassARRAY technology. We confirm the association of the HHEX variant rs1111875 with EOT2D in this South Indian population and also the association of CDKN2A/2B (rs7020996) and TCF7L2 (rs4506565) with EOT2D. Logistic regression analyses of the TCF7L2 variant rs4506565(A/T), showed that the heterozygous and homozygous carriers for allele ‘T’ have odds ratios of 1.47 (95% confidence interval [CI], 1.17 to 1.83; p = 0.001) and 1.65 (95% CI, 1.18 to 2.28; p = 0.006) respectively, relative to AA homozygote. For the HHEX variant rs1111875 (T/C), heterozygous and homozygous carriers for allele ‘C’ have odds ratios of 1.13 (95% CI, 0.91 to 1.42; p = 0.27) and 1.58 (95% CI, 1.17 to 2.12; p = 0.003) respectively, relative to the TT homozygote. For CDKN2A/2B variant rs7020996, the heterozygous and homozygous carriers of allele ‘C’ were protective with odds ratios of 0.65 (95% CI, 0.51 to 0.83; p = 0.0004) and 0.62 (95% CI, 0.27 to 1.39; p = 0.24) respectively, relative to TT homozygote. This is the first study to report on the association of HHEX variant rs1111875 with EOT2D in this population.

Interaction between dietary patterns and TCF7L2 polymorphisms on type 2 diabetes mellitus among Uyghur adults in Xinjiang Province, China

PURPOSE

This study aimed to characterize dietary patterns in the Uyghur population and examined the relationship between dietary pattern, TCF7L2 single-nucleotide polymorphisms (SNPs), and the risk of type 2 diabetes mellitus (T2DM).

PATIENTS AND METHODS

Dietary patterns were defined using factor analysis, and associations between dietary patterns were evaluated using multivariate logistic regression analyses. Genotyping of seven SNPs of TCF7L2 (rs11196205, rs12255372, rs12573128, rs4506565, rs7895340, rs7901695, and rs7903146) was conducted, and the association between these seven SNPs and the risk of T2DM was evaluated. Interactions between SNPs, homeostasis model assessment-insulin resistance, and dietary patterns were also analyzed.

RESULTS

A total of 828 participants were enrolled in this study, including 491 people with T2DM and 337 healthy controls. Five dietary patterns were defined, and the results indicated that the "fruit" and "vegetables" dietary patterns were associated with a significant decrease in the risk of T2DM, whereas the "meats" and "grains" dietary patterns were associated with an increased risk of T2DM. Moreover, the "dairy product" dietary pattern showed no association with the risk of T2DM. Furthermore, our results revealed that the TCF7L2 SNP, rs12573128, is associated with an increased risk of T2DM. SNPs rs4506565 and rs7903146 significantly interacted with dietary pattern.

CONCLUSION

Our studies suggest that dietary pattern and genetic polymorphisms of TCF7L2 are associated with the development of T2DM in the Uyghur population of China.

Precision medicine in diabetes prevention, classification and management

Diabetes has become a major burden of healthcare expenditure. Diabetes management following a uniform treatment algorithm is often associated with progressive treatment failure and development of diabetic complications. Recent advances in our understanding of the genomic architecture of diabetes and its complications have provided the framework for development of precision medicine to personalize diabetes prevention and management. In the present review, we summarized recent advances in the understanding of the genetic basis of diabetes and its complications. From a clinician's perspective, we attempted to provide a balanced perspective on the utility of genomic medicine in the field of diabetes. Using genetic information to guide management of monogenic forms of diabetes represents the best-known examples of genomic medicine for diabetes. Although major strides have been made in genetic research for diabetes, its complications and pharmacogenetics, ongoing efforts are required to translate these findings into practice by incorporating genetic information into a risk prediction model for prioritization of treatment strategies, as well as using multi-omic analyses to discover novel drug targets with companion diagnostics. Further research is also required to ensure the appropriate use of this information to empower individuals and healthcare professionals to make personalized decisions for achieving the optimal outcome.

TCF7L2 gene variants predispose to the development of type 2 diabetes mellitus among individuals with metabolic syndrome

INTRODUCTION

Transcription factor 7-like 2 (TCF7L2) gene variants rs12255372 and rs7903146 have been consistently shown to raise genetic risk for type 2 diabetes mellitus (T2DM). The aim of this study was to investigate the possible role of these variants in the development of impaired glucose metabolism (IGM), including impaired fasting glucose (IFG) or T2DM, in patients with metabolic syndrome (MS).

PATIENTS AND METHODS

The study population consisted of 228 patients with MS who were divided into two groups. The first group consisted of 148 patients with MS and IGM [39M/109F, 59.8 ± 14.6 (mean ± SD) years] and the second group of 80 patients with MS and normoglycemia (NGM) (16M/64F, 56.1 ± 15.8 years). The diagnosis of MS was based on the criteria proposed by the American Heart Association/National Heart, Lung, and Blood Institute (AHA/NHLBI) Scientific Statement. Anthropometric parameters including BMI and waist circumference were recorded and blood samples were obtained after overnight fasting for biochemical tests. The rs12255372 and rs7903146 TCF7L2 polymorphisms were genotyped in peripheral blood leucocytes.

RESULTS

Analysis of the distribution of the TCF7L2 polymorphic alleles revealed that the frequency of the T allele of the TCF7L2 variant rs12255372 was 38.2% in the study population, while the frequency of the T allele of the TCF7L2 rs7903146 variant was 35.3%. The T allele of the rs12255372 variant was more frequently present in patients with MS and IGM (48.3%) compared to patients with MS and NGM (19.4%, p < 0.001). Also, the T allele of rs7903146 was more frequently present in patients with MS and IGM (44.6%) compared to patients with MS and NGM (18.1%, p < 0.001). Logistic regression analysis followed and revealed that the presence of the T allele for both rs12255372 and rs7903146 TCF7L2 gene variants is a very powerful predictor of the presence of glucose disorders, increasing the risk more than fourfold in patients with MS and after adjustment for potential confounders, such as age, gender, BMI, and waist circumference (TCF7L2 rs12255372: Exp(B) 4.917, p < 0.001 and TCF7L2 rs7903146: Exp(B) 5.460, p < 0.001).

CONCLUSION

The presence of the rs12255372 and rs7903146 TCF7L2 gene variants plays an important role in the development of T2DM among individuals with MS. These findings support the notion that among subjects with MS, those who finally develop T2DM have a genetic predisposition to β-cell dysfunction.

Diabetic macular oedema: under-represented in the genetic analysis of diabetic retinopathy

Diabetic retinopathy, a complication of both type 1 and type 2 diabetes, is a complex disease and is one of the leading causes of blindness in adults worldwide. It can be divided into distinct subclasses, one of which is diabetic macular oedema. Diabetic macular oedema can occur at any time in diabetic retinopathy and is the most common cause of vision loss in patients with type 2 diabetes. The purpose of this review is to summarize the large number of genetic association studies that have been performed in cohorts of patients with type 2 diabetes and published in English-language journals up to February 2017. Many of these studies have produced positive associations with gene polymorphisms and diabetic retinopathy. However, this review highlights that within this large body of work, studies specifically addressing a genetic association with diabetic macular oedema, although present, are vastly under-represented. We also highlight that many of the studies have small patient numbers and that meta-analyses often inappropriately combine patient data sets. We conclude that there will continue to be conflicting results and no meaningful findings will be achieved if the historical approach of combining all diabetic retinopathy disease states within patient cohorts continues in future studies. This review also identifies several genes that would be interesting to analyse in large, well-defined cohorts of patients with diabetic macular oedema in future candidate gene association studies.

TCF7L2 polymorphisms and the risk of schizophrenia in the Chinese Han population

Single nucleotide polymorphisms (SNPs) in TCF7L2 (Transcription Factor 7-Like 2) reportedly affect susceptibility to schizophrenia (SCZ). We examined the association between TCF7L2 polymorphisms and SCZ susceptibility in a Chinese Han population. Six SNPs were genotyped in 499 SCZ patients and 500 healthy individuals, after which their associations with SCZ were evaluated using the Chi-squared test and genetic model analyses. We observed that the allele A of rs12573128 is associated with an increased SCZ risk (odds ratio [OR] = 1.33, 95% confidence interval [CI]: 1.08-1.63, P = 0.006, adjusted P = 0.030). The AA genotype of rs12573128 was associated with a higher SCZ risk than the GG genotype, before and after adjustment for sex and age (adjusted OR = 2.97, 95% CI: 1.49-5.92, P = 0.002). In addition, SNP rs12573128 was associated with 1.47-fold, 2.64-fold and 1.50-fold increases in SCZ risk of in dominant, recessive and additive model, respectively (adjusted OR = 1.47, 95% CI = 1.09-1.99, P = 0.012; Bonferroni adjusted P = 0.030). adjusted OR = 2.64, 95% CI = 1.34-5.18, P = 0.005 and adjusted OR = 1.50, 95% CI = 1.17-1.93, P = 0.002, respectively). These results suggest rs12573128 is significantly associated with an increased risk of SCZ in the Chinese Han population.

A candidate functional SNP rs7074440 in TCF7L2 alters gene expression through C-FOS in hepatocytes

The SNP rs7903146 at the transcription factor 7-like 2 (TCF7L2) locus is established as the strongest known genetic marker for type 2 diabetes via genome-wide association studies. However, the functional SNPs regulating TCF7L2 expression remain unclear. Here, we show that the SNP rs7074440 is a candidate functional SNP highly linked with rs7903146. A reporter plasmid with rs7074440 normal allele sequence exhibited 15-fold higher luciferase activity compared with risk allele sequence in hepatocytes, demonstrating a strong enhancer activity at rs7074440. Additionally, we identified C-FOS as an activator binding to the rs7074440 enhancer using a TFEL genome-wide screen method. Consistently, knockdown of C-FOS significantly reduced TCF7L2 expression in hepatocytes. Collectively, a novel enhancer regulating TCF7L2 expression was revealed through searching for functional SNPs.

A tale of agriculturalists and hunter-gatherers: Exploring the thrifty genotype hypothesis in native South Americans

OBJECTIVES

To determine genetic differences between agriculturalist and hunter-gatherer southern Native American populations for selected metabolism-related markers and to test whether Neel's thrifty genotype hypothesis (TGH) could explain the genetic patterns observed in these populations.

MATERIALS AND METHODS

375 Native South American individuals from 17 populations were genotyped using six markers (APOE rs429358 and rs7412; APOA2 rs5082; CD36 rs3211883; TCF7L2 rs11196205; and IGF2BP2 rs11705701). Additionally, APOE genotypes from 39 individuals were obtained from the literature. AMOVA, main effects, and gene-gene interaction tests were performed.

RESULTS

We observed differences in allele distribution patterns between agriculturalists and hunter-gatherers for some markers. For instance, between-groups component of genetic variance (F_CT ) for APOE rs429358 showed strong differences in allelic distributions between hunter-gatherers and agriculturalists (p = 0.00196). Gene-gene interaction analysis indicated that the APOE E4/CD36 TT and APOE E4/IGF2BP2 A carrier combinations occur at a higher frequency in hunter-gatherers, but this combination is not replicated in archaic (Neanderthal and Denisovan) and ancient (Anzick, Saqqaq, Ust-Ishim, Mal'ta) hunter-gatherer individuals.

DISCUSSION

A complex scenario explains the observed frequencies of the tested markers in hunter-gatherers. Different factors, such as pleotropic alleles, rainforest selective pressures, and population dynamics, may be collectively shaping the observed genetic patterns. We conclude that although TGH seems a plausible hypothesis to explain part of the data, other factors may be important in our tested populations.

Using genetics to inform new therapeutics for diabetes

The genetic architecture of diabetes has been extensively studied. Numerous genetic markers for diabetes have been reported. However, the translation of such knowledge into clinical interventions has been inadequate. Areas covered: We performed a literature search on various frontiers in diabetes treatment that could be improved using genetic information: (1) understanding the mechanisms of existing antidiabetic drugs, (2) repurposing existing drugs for the treatment of diabetes, (3) complementing clinical trial findings; (4) finding novel treatment approaches; (5) better estimation of the efficacy of metabolic surgery. Expert commentary: The translation of genetic information to clinical intervention requires further study, including the development of an appropriate genetic risk score algorithm for type 2 diabetes. Genomic studies provide empirical explanations for clinical trial findings. Moreover, the mechanisms of antidiabetic drugs should be thoroughly investigated to enable clinical trials and pharmacogenomics studies of these drugs. As metabolic surgery becomes more prevalent for the treatment of diabetes, genetic approaches may improve patient prioritization.

Evaluation of Transcription Factor 7 like 2 polymorphisms and haplotypes in risk of Type 2 Diabetes

Type 2 diabetes (T2D) is a chronic disorder with different genetics and environmental factors. It is one of growing diseases in the world. Previous studies show association between Transcription Factor 7 Like2 (TCF7L2) and T2D. The current study set to evaluate the relation between TCF7L2 polymorphisms and T2D in Southeast Iran. The present case-control study was done on 250 T2D and 250 healthy controls (HCs). For genotyping polymorphisms TCF7L2 (rs11196205) and (rs4132670) Amplification-Refractory Mutation System-Polymers Chain Reaction (ARMS-PCR) was used. The results showed frequency rates of GC and CC genotypes increased in patients compared to controls (31% vs. 6% and 55% vs. 8%, respectively), showing a statistically significant difference (OR=2.67(1.37-5.21), P<0.05 and OR=3.31(1.92-5.71), P< 0.05, respectively). The C allele was associated with an increased risk of T2D, with the frequency of 28% and 11% in patients and controls, respectively (OR=3.11 (2.22-4.37), P< 0.05). Another Polymorphism of this gene TCF7L2 (rs4132670) was not associated with T2D. Furthermore, the haplotype analysis revealed that rs11196205C/rs4132670C and rs11196205C/rs4132670T are risk factors against T2D (OR=2.08 (1.49-2.86, P<0.05 and OR=1.72 (1.06-2.78) P<0.05, respectively). The findings demonstrated that TCF7L2 (rs11196205) genotypes GC, CC, and allele (C) confer risk for susceptibility to T2D.

Replication of genome-wide association signals in Asian Indians with early-onset type 2 diabetes

AIMS

To evaluate the association of 87 genetic variants previously associated with type 2 diabetes mellitus (T2DM) in genome-wide association studies of populations of European ancestry in an Asian Indian population with early-onset type 2 diabetes mellitus (EOT2DM).

METHODS

The study groups comprised of 877 type 2 diabetes individuals, 436 individuals with EOT2DM (age at diagnosis below 35 years), 441 individuals with older T2DM (diagnosis at 35 years or greater) and controls with normal glucose tolerance (NGT) (n = 400 younger than 35 years; n = 438 older than 35 years). The participants were genotyped for 87 SNPs from 44 genes and 27 intergenic loci. Associations were tested using logistic regression.

RESULTS

All the variants in TCF7L2 and CDKN2A/2B showed study-wide significance (p < 1.4 × 10^-4) with T2DM, but only rs7903146, rs12243326, rs12255372 of TCF7L2 and rs7020996 of CDKN2A/2B showed study-wide significance (p < 1.4 × 10^-4) with EOT2DM in this population. In addition, an intergenic SNP on chromosome 1 (rs10493685) was also shown to be study-wide significant (p = 7.1 × 10^-6). Several additional SNPs previously associated with T2DM reached borderline significance in this study, but may have been limited by relatively low sample numbers. Various other SNPs of T2DM were not associated with EOT2DM.

CONCLUSIONS

Some of the variants in TCF7L2 and CDKN2A/2B associated with T2DM are associated with EOT2DM as well. An intergenic SNP on chromosome 1p31 showed association only with early-onset T2DM in this Asian Indian population. The lack of association with many other SNPs of T2DM may be a reflection of the lack of power of the study, sample size, differences in the frequencies of genetic polymorphisms in different ethnic groups, effect sizes, as well as ancestral differences in pattern of LD between the genetic variants involved in early- and late-onset T2DM.

Role of GNB3, NET, KCNJ11, TCF7L2 and GRL genes single nucleotide polymorphism in the risk prediction of type 2 diabetes mellitus

Type 2 diabetes (T2DM) is a polygenic metabolic disorder characterized by hyperglycemia occurring as a result of impaired insulin secretion or insulin resistance. Various environmental and genetic factors interact and increase the risk of T2DM and its complications. Among the various genetic factors associated with T2DM, single nucleotide polymorphism in different candidate genes have been studied intensively and the resulting genetic variants have been found to have either positive or negative association with T2DM thereby increasing or decreasing the risk of T2DM, respectively. In this review, we will focus on Guanine nucleotide-binding protein subunit beta 3 (GNB3), Norepinephrine Transporter (NET), Potassium Channel gene (KCNJ11), Transcription Factor 7-Like 2 (TCF7L2) and Glucocorticoid receptor (GRL) genes and their association with T2DM studied in different ethnic groups. The products of these genes are involved in the biochemical pathway leading to T2DM. Polymorphisms in these genes have been intensively studied in individuals of different ethnic origins. Results show that genetic variants of TCF7L2 and KCNJ11 genes have potential to emerge as a risk biomarker for T2DM whereas results of GNB3, GRL and NET genes have been controversial when studied in individuals of different ethnicities. We have tried to summarize the results generated globally in context to the selected genes which could possibly help researchers working in this field and would eventually help in understanding the mechanistic pathways of T2DM leading early diagnosis and prevention.

Common variants in TCF7L2 and CDKAL1 genes and risk of type 2 diabetes mellitus in Egyptians

In this work we studied association of common variants in transcription factor 7-like 2 (TCF7L2) and cyclin-dependent kinase 5 regulatory subunit-associated protein 1-like 1 (CDKAL1) genes with type 2 diabetes mellitus (T2DM) in Egyptians.

SUBJECTS AND METHODS

This is a case-control study; 180 T2DM patients and 210 control subjects were genotyped for TCF7L2 rs7903146 and rs12255372 and CDKAL1 rs7756992 single nucleotide polymorphisms (SNPs) by TaqMan method on real time polymerase chain reaction system (real time-PCR).

RESULTS

TCF7L2 rs12255372 and rs7903146 associated with T2DM (p = 0.0001 and 0.003; respectively). The rs12255372 variant T allele associated with 2-fold increased risk for T2DM and TT genotype carriers were at 3.58-folds higher risk to develop T2DM than wild genotype (GG) carriers. Meanwhile, rs7903146 variant T allele associated with 1.6-fold increased risk for T2DM and TT genotype carriers were at 2.3-folds higher risk than wild genotype (CC) carriers. Both TCF7L2 SNPs significantly associated with T2DM under additive and dominant models and after adjustment for other covariates. On the other hand, CDKAL1 rs7756992 showed no significant association with T2DM under any genetic model. Both TCF7L2 SNPs were in strong LD (P = 0.02; D' = 0.85). Taking common TCF7L2 rs12255372/rs7903146 GC haplotype as reference, multivariate analysis confirmed the association of rs12255372 T allele-containing haplotypes (TC and TT) with T2DM. Haplotype TC associated with 6.32 times-higher risk for T2DM (95%CI = 0.55-76.17, Pc = 0.04) followed by haplotype TT which associated with 3.88 times-higher risk for the disease (95%CI = 1.09-13.76, Pc = 0.03).

CONCLUSION

TCF7L2 rs12255372 and rs7903146 common variants associate with T2DM risk in Egyptians.

Polymorphisms in TCF7L2 gene are associated with gestational diabetes mellitus in Chinese Han population

This study aimed to investigate the possible association between diabetes susceptibility gene transcription factor 7-like 2 (TCF7L2) and gestational diabetes mellitus (GDM) in a Chinese Han population. A total of 556 GDM patients and 500 Non-GDM were included. Eighteen single nucleotide polymorphisms (SNPs) were evaluated. Fifteen tag SNPs were selected from HapMap CHB database with a minor allele frequency of >0.2 and r² of >0.8. Three additional SNPs were also chosen because these SNPs are associated with type 2 diabetes in East Asians. TCF7L2 rs290487, rs6585194, and rs7094463 polymorphisms were found to be significantly associated with GDM. In multivariate analysis, rs290487 genetic variation (OR = 2.686 per each C allele, P = 0.002), pre-BMI > 24 kg/m² (OR = 1.592, P = 0.018), age > 25 years (OR = 1.780, P = 0.012) and LDL-C > 3.6 mmol/L (OR = 2.034, P = 0.009) were identified as independent risk factors of GDM, rs7094463 genetic variation (OR = 0.429 per each G allele, P = 0.005) was identified as independent protect factor of GDM. This finding suggests that TCF7L2 rs290487, and rs7094463 were a potential clinical value for the prediction of GDM.

Current Understanding on Role of the Wnt Signaling Pathway Effector TCF7L2 in Glucose Homeostasis

The role of the Wnt signaling pathway in metabolic homeostasis has drawn our intensive attention, especially after the genome-wide association study discovery that certain polymorphisms of its key effector TCF7L2 are strongly associated with the susceptibility to type 2 diabetes. For a decade, great efforts have been made in determining the function of TCF7L2 in various metabolic organs, which have generated both considerable achievements and disputes. In this review, I will briefly introduce the canonical Wnt signaling pathway, focusing on its effector β-catenin/TCF, including emphasizing the bidirectional feature of TCFs and β-catenin post-translational modifications. I will then summarize the observations on the association between TCF7L2 polymorphisms and type 2 diabetes risk. The main content, however, is on the intensive functional exploration of the metabolic role of TCF7L2, including the disputes generated on determining its role in the pancreas and liver with various transgenic mouse lines. Finally, I will discuss those achievements and disputes and present my future perspectives.

Rare intronic variants of TCF7L2 arising by selective sweeps in an indigenous population from Mexico

Background

Genetic variations of the TCF7L2 gene are associated with the development of Type 2 diabetes (T2D). The associated mutations have demonstrated an adaptive role in some human populations, but no studies have determined the impact of evolutionary forces on genetic diversity in indigenous populations from Mexico. Here, we sequenced and analyzed the variation of the TCF7L2 gene in three Amerindian populations and compared the results with whole-exon-sequencing of Mestizo populations from Sigma and the 1000 Genomes Project to assess the roles of selection and recombination in diversity.

Results

The diversity in the indigenous populations was biased to intronic regions. Most of the variation was low frequency. Only mutations rs77961654 and rs61724286 were located on exon 15. We did not observe variation in intronic region 4–6 in any of the three indigenous populations. In addition, we identified peaks of selective sweeps in the mestizo samples from the Sigma Project within this region. By replicating the analysis of association with T2D between case-controls from the Sigma Project, we determined that T2D was most highly associated with the rs7903146 risk allele and to a lesser extent with the other six variants. All associated markers were located in intronic region 4–6, and their r² values of linkage disequilibrium were significantly higher in the Mexican population than in Africans from the 1000 Genomes Project. We observed reticulations in both the haplotypes network analysis from seven marker associates and the neighborNet tree based on 6061 markers in the TCF7L2 gene identified from all samples of the 1000 Genomes Project. Finally, we identified two recombination hotspots in the upstream region and 3’ end of the TCF7L2 gene.

Conclusions

The lack of diversity in intronic region 4–6 in Indigenous populations could be an effect of selective sweeps generated by the selection of neighboring rare variants at T2D-associated mutations. The survivors’ variants make the intronic region 4–6 the area of the greatest population differentiation within the TCF7L2 gene. The abundance of selective peak sweeps in the downstream region of the TCF7L2 gene suggests that the TCF7L2 gene is part of a region that is in constant recombination between populations.

Electronic supplementary material

The online version of this article (doi:10.1186/s12863-016-0372-7) contains supplementary material, which is available to authorized users.

Affection of single-nucleotide polymorphisms in miR-27a, miR-124a, and miR-146a on susceptibility to type 2 diabetes mellitus in Chinese Han people

BACKGROUND

Polymorphisms of microRNA (miRNA), as a novel mechanism, are closely associated with disease states by interfering with miRNA function. Direct correlations have been identified between single-nucleotide polymorphisms (SNPs) in miRNA, but the effect on type 2 diabetes mellitus (T2DM) onset among Chinese population remains unclear. Therefore, the aim of this study was to identify correlations between common SNPs in miR-27a, miR-146a, and miR-124a with T2DM among a Chinese population, as well as to explore diabetic pathological mechanisms and the impact of environmental factors.

METHODS

SNPscan technology was used to genotype 995 patients newly diagnosed with T2DM and 967 controls. Logistic regression analysis was performed to compare mutation frequencies between cases and controls.

RESULTS

We found no significant correlations between all genotypes of these miRNAs and T2DM in our research. However, stratification analysis identified a lower risk of T2DM associated with the rs531564GC genotype among younger subjects (age < 45 years) (adjusted P = 0.043; odds ratio [OR] = 0.73; 95% confidence interval [CI] = 0.54-0.99). Furthermore, the rs895819CC genotype in overweight people (24 ≤ body mass index [BMI] < 28) was significantly associated with an increased risk of T2DM (adjusted P = 0.042; OR = 1.73; 95% CI = 1.02-2.94), while the rs2910164 genotype in miR-146a was not significantly correlated with T2DM. The genetic risk score was calculated based on the number of risk alleles of the three SNPs and was found to be correlated to total cholesterol (adjusted P = 0.021).

CONCLUSIONS

The rs531564GC genotype acted as a protective factor to decrease the risk of T2DM in younger subjects (age < 45 years), while the presence of the rs895819CC genotype increased the risk of illness among overweight subjects (24 ≤ BMI < 28 kg/m 2 ). The presence of SNPs in miRNA might promote disease by affecting miRNA expression and gene function. Thus, miRNA mimics or inhibitors that directly regulate miRNA expression present novel and promising therapeutic targets.

Association of TCF7L2 Genetic Polymorphisms with Type 2 Diabetes Mellitus in the Uygur Population of China

BACKGROUND

Genetic polymorphisms of the transcription factor 7-like 2 (TCF7L2) gene have been reported to be strongly associated with type 2 diabetes mellitus (T2DM) in Icelandic, Danish and American populations and further replicated in other European populations, African Americans, Mexican Americans, and Asian populations. The aim of the present study was to investigate the association of TCF7L2 gene polymorphisms with T2DM in a Uygur population of China.

METHODS

877 T2DM patients and 871 controls were selected for the present study. Two single nucleotide polymorphisms (SNPs) (rs12255372 and rs7901695) were genotyped by using matrix-assisted laser desorption/ionization time-of-flight (MALDI-TOF) mass spectrometry. The associations of SNPs and haplotypes with T2DM and linkage disequilibrium (LD) structure of the TCF7L2 gene were analyzed.

RESULTS

For total participants and male, the distribution of rs12255372 alleles and the dominant model (Guanine Guanine (GG) genotype vs. Guanine Thymine (GT) genotype + Thymine Thymine (TT) genotype) showed significant difference between T2DM and control subjects (for allele: p = 0.013 and p = 0.002, respectively; for dominant model: p = 0.028 and p = 0.008, respectively). The distribution of rs7901695 alleles and the dominant model (TT genotype vs. Thymine Cytosine (TC) genotype + Cytosine Cytosine (CC) genotype) for total participants and male showed significant difference between T2DM and control subjects (for allele: both p = 0.001; for dominant model: p = 0.006 and p = 0.008, respectively).

CONCLUSIONS

Our data suggested that the genetic polymorphisms of the TCF7L2 gene were associated with T2DM in the Uygur population of China.

The association between the rs11196218A/G polymorphism of the TCF7L2 gene and type 2 diabetes in the Chinese Han population: a meta-analysis

Transcription factor 7-like 2 has been shown to be associated with type 2 diabetes mellitus in multiple ethnic groups in recent years. In the Chinese Han population in particular, numerous studies have evaluated the association between the rs11196218A/G polymorphism of the transcription factor 7-like 2 gene and type 2 diabetes mellitus. However, the results have been inconsistent, so we performed a meta-analysis to assess the association. Odds ratio and 95% confidence interval values were calculated using a random-effects model or a fixed-effects model based on heterogeneity analysis. The quality of the included studies was evaluated using the Newcastle-Ottawa Scale. Subgroup analyses were conducted based on conformity with Hardy-Weinberg equilibrium in the control group as well as on other variables, such as age, sex and body mass index. Sensitivity analysis was also performed to detect heterogeneity and to assess the stability of the results. In total, 10 case-control studies comprising 7,491 cases and 12,968 controls were included in this meta-analysis. The combined analysis indicated that the rs11196218A/G polymorphism was not associated with type 2 diabetes mellitus (G vs. A, OR=1.04, 95% CI=0.97-1.13, p=0.28). The subgroup analyses also did not show any association between the rs11196218A/G polymorphism and the risk of type 2 diabetes mellitus. Furthermore, the results of the subgroup analyses indicated that the absence of an association was not influenced by age, sex or body mass index. The results of the sensitivity analysis verified the reliability and stability of this meta-analysis. In conclusion, this study indicated that there is no significant association between the rs11196218A/G polymorphism and the risk of type 2 diabetes mellitus in the Chinese Han population.

Association of Canonical Wnt/β-Catenin Pathway and Type 2 Diabetes: Genetic Epidemiological Study in Han Chinese

We aimed to investigate the associations of polymorphisms in Canonical Wnt/β-catenin pathway (WNT) signaling genes (including low-density lipoprotein-related protein 5 [LRP5] and transcription factor 7-like 2 [TCF7L2] gene) and the downstream gene glucagon (GCG) and risk of type 2 diabetes mellitus (T2DM) in a Han Chinese population. We genotyped the single nucleotide polymorphisms (SNPs) for LRP5, TCF7L2 and GCG gene were genotyped in 1842 patients with T2DM and 7777 normal glucose-tolerant healthy subjects. We used multifactor dimensionality reduction (MDR) and multiplicative logistic regression adjusting for sex, age, anthropometric measurements and lipid levels to investigate the gene-gene interactions for the risk of T2DM. Among the five SNPs in LRP5, the recessive model of rs7102273 and the haplotype GCTCC were associated with T2DM risk; the haplotype GCTTC was associated with decreased risk. For TCF7L2, the rs11196218 genotype GA and the haplotype CCG, TTG, TTA were associated with T2DM risk; whereas, the haplotype CTG and TCG were associated with decreased risk. Both MDR and multiplicative logistic regression revealed potential gene–gene interactions among LRP5, TCF7L2, and GCG associated with T2DM. The WNT signaling pathway may play a significant role in risk of T2DM in Han Chinese people.

The gene polymorphisms of UCP1 but not PPAR γ and TCF7L2 are associated with diabetic retinopathy in Chinese type 2 diabetes mellitus cases

PURPOSE

This study was designed to investigate the association between the polymorphisms in three insulin resistance-related genes, uncoupling protein-1 (UCP1), peroxisome proliferator-activated receptor γ (PPARγ) and transcription factor 7-like 2 (TCF7L2) and the susceptibility to diabetic retinopathy (DR) in a Chinese type 2 diabetes mellitus (T2DM) cohort.

METHODS

A total of 792 patients with T2DM were enrolled and categorized into two groups: (1) the DR group consisted of 448 patients, which was further subclassified into a proliferative DR (PDR) group with 220 patients and a non-proliferative DR (NPDR) group with 228 patients; (2) the diabetes without retinopathy (DNR) group, comprised 344 patients who had no signs of DR. Single-nucleotide polymorphisms (SNPs), rs1800592 in the UCP1 gene, rs1801282, rs3856806 and rs1249719 in the PPARγ gene and rs11196205 in the TCF7L2 gene were genotyped in this study.

RESULTS

For SNP rs1800592 of the UCP1 gene, the frequency of allele G and genotype GG was significantly higher in the PDR group than in the DNR group (allele OR: 1.32, 95% CI: 1.03-1.68, p = 0.03; genotype OR: 1.72, 95%CI: 1.06-2.79, p = 0.03). No evident association was found between the allele frequencies and genotype distributions of any individual SNP in the PPARγ or TCF7L2 genes and DR, PDR or NPDR. Haplotype analyses of the PPARγ gene did not provide any evidence for an association with DR, PDR or NPDR in this Chinese T2DM cohort.

CONCLUSIONS

This study suggests that the SNP rs1800592 in the UCP1 gene is associated with increased risk of PDR in the Chinese T2DM population.

Association of LRP5, TCF7L2, and GCG variants and type 2 diabetes mellitus as well as fasting plasma glucose and lipid metabolism indexes

Recent data puts WNT signaling pathway in a pivotal role in regulating pancreas development as well as islet function, insulin production and secretion. The key effectors in the WNT signaling pathway are low-density lipoprotein receptor-related protein 5 (LRP5), transcription factor 7-like 2 (TCF7L2), and downstream-regulated glucagon (GCG). Our previous studies suggest that the WNT signaling pathway plays a significant role in risk of type 2 diabetes mellitus (T2DM) in Chinese population. The main purpose of the present study was to investigate the associations of single nucleotide polymorphisms (SNPs) in LRP5, TCF7L2 and glucagon (GCG) and quantitative traits in a healthy population. We used tag SNP to screen candidate SNPs for LRP5 and GCG; for TCF7L2, used the confirmed SNP rs11196218. A total of 1842 patients with T2DM and 7777 healthy controls underwent genotyping for the SNPs. We found a significant association of rs3758644 in LRP5 and fasting plasma glucose (p=0.006), and rs11196218 in TCF7L2 and triglycerides level (p=0.004). Among the SNPs in LRP5, TCF7L2, and GCG analyzed, only rs3758644 of LRP5 and rs11196218 of TCF7L2 were significantly associated with fasting plasma glucose and triglycerides index, respectively, in a healthy population.

Association of gene variants with susceptibility to type 2 diabetes among Omanis

AIM: To investigate the association of 10 known common gene variants with susceptibility to type 2 diabetes mellitus (T2D) among Omanis.

METHODS: Using case-control design, a total of 992 diabetic patients and 294 normoglycemic Omani Arabs were genotyped, by an allelic discrimination assay-by-design TaqMan method on fast real time polymerase chain reaction system, for the following gene variants: KCNJ11 (rs5219), TCF7L2 (rs7903146), CDKAL1 (rs10946398), CDKN2A/B (rs10811661), FTO (rs9939609 and rs8050136), IGF2BP2 (rs4402960), SLC30A8 (rs13266634) CAPN10 (rs3792267) and HHEX (rs1111875). T2D patients were recruited from the Diabetes Clinic (n = 243) and inpatients (n = 749) at Sultan Qaboos Univesity Hospital (SQUH), Muscat, Oman. Adult control participants (n = 294) were volunteers from the community and from those visiting Family Medicine Clinic at SQU, for regular medical checkup. The difficulty in recruiting Omani participants with no family history of diabetes was the main reason behind the small number of control participants in this study. Almost all volunteers questioned had a relative with diabetes mellitus. Inspite of the small number of normoglycemic controls in this study, this sample was sufficient for detection of genes and loci for common alleles influencing T2D with an odds ratio of ≥ 1.3 reaching at least 80% power. Data was collected from June 2010 to February 2012.

RESULTS: Using binary logistic regression analysis, four gene variants showed significant association with T2D risk: KCNJ11 (rs5219, P = 5.8 × 10^-6, OR = 1.74), TCF7L2 (rs7903146, P = 0.001, OR = 1.46), CDKAL1 (rs10946398, P = 0.002, OR = 1.44) and CDKN2A/B (rs10811661, P = 0.020, OR = 1.40). The fixation index analysis of these four gene variants indicated significant genetic differentiation between diabetics and controls {[KCNJ11 (rs5219), P < 0.001], [TCF7L2 (rs7903146), P < 0.001], [CDKAL1 (rs10946398), P < 0.05], [CDKN2A/B (rs10811661), P < 0.05]}. The highest genotype variation % between diabetics and controls was found at KCNJ11 (2.07%) and TCF7L2 (1.62%). This study was not able to detect an association of T2D risk with gene variants of IGF2BP2 (rs4402960), SLC30A8 (rs13266634), CAPN10 (rs3792267) and HHEX (rs1111875). Moreover, no association was found between FTO gene variants (rs9939609 and rs8050136) and T2D risk. However, T2D risk was found to be significantly associated with obesity (P = 0.002, OR = 2.22); and with the Waist-to-Hip ratio (n = 532, P = 1.9 ×10^-7, OR = 2.4), [among males (n = 234, P = 1.2 × 10^-4, OR = 2.0) and females (n = 298, P = 0.001, OR = 6.3)].

CONCLUSION: Results confirmed the association of KCNJ11 (rs5219), TCF7L2 (rs7903146), CDKAL1 (rs10946398) and CDKN2A/B (rs10811661) gene variants with susceptibility to T2D among Omani Arabs.

Genetic Determinants of Type 2 Diabetes in Asians

Type 2 diabetes (T2D) has become a major health problem throughout the world and the epidemic is particularly severe in Asian countries. Compared with European populations, Asians tend to develop diabetes at a younger age and at much higher incidence rates given the same amount of weight gain. Genome-wide association studies (GWAS) have identified over 70 loci associated with T2D. Although the majority of GWAS results were conducted in populations of European ancestry, recent GWAS in Asians have made important contributions to the identification of T2D susceptibility loci. These studies not only confirmed T2D susceptibility loci initially identified in European populations, but also identified novel susceptibility loci that provide new insights into the pathophysiology of diseases. In this article, we review GWAS results of T2D conducted in East and South Asians and compare them to those of European populations. Currently identified T2D genetic variants do not appear to explain the phenomenon that Asians are more susceptible to T2D than European populations, suggesting further studies in Asian populations are needed.

Causes of type 2 diabetes in China

The prevalence of diabetes in China has increased substantially over recent decades, with more than 100 million people estimated to be affected by the disease presently. During this period there has been an increase in the rates of obesity and a reduction in physical activity. Many of the changes in lifestyle and diet are a result of increased economic development and urbanisation. In addition to an increasingly westernised diet, the traditional Chinese diet also plays a part, with the quantity and quality of rice intake linked to the risk of type 2 diabetes. Familial factors including inherited genetic variants are important, although differences in the genetic architecture suggest a different combination of genetic variants could be most relevant in Chinese when compared with Europeans. Recent advances have also emphasised the role of early life factors in the epidemic of diabetes and non-communicable diseases: maternal undernutrition, maternal obesity, and gestational diabetes are all linked to increased risk of diabetes in offspring. A mismatch between developmentally programmed biology and the modern environment is relevant for countries like China where there has been rapid economic transformation. Multisectoral efforts to address the risks will be needed at different stages throughout the lifecourse to reduce the burden of diabetes.

The incidence and prevalence of diabetes mellitus and related atherosclerotic complications in Korea: a National Health Insurance Database Study

AIMS/INTRODUCTION

The incidence and prevalence of type 2 diabetes mellitus (T2DM) and related macrovascular complications in Korea were estimated using the Health Insurance Review and Assessment (HIRA) database from 2007-2011, which covers the claim data of 97.0% of the Korean population.

MATERIALS AND METHODS

T2DM, coronary artery disease (CAD), cerebrovascular disease (CVD), and peripheral artery disease (PAD) were defined according to ICD-10 codes. We used the Healthcare Common Procedure Coding System codes provided by HIRA to identify associated procedures or surgeries. When calculating incidence, we excluded cases with preexisting T2DM within two years before the index year. A Poisson distribution was assumed when calculating 95% confidence intervals for prevalence and incidence rates.

RESULTS

The prevalence of T2DM in Korean adults aged 20-89 years was 6.1-6.9% and the annual incidence rates of T2DM ranged from 9.5-9.8/1,000 person-year (PY) during the study period. The incidence rates of T2DM in men and women aged 20-49 years showed decreasing patterns from 2009 to 2011 (P<0.001); by contrast, the incidence in subjects aged 70-79 years showed increased patterns from 2009 to 2011 (P<0.001). The incidence rates of CAD and CVD in patients newly diagnosed with T2DM were 18.84/1,000 PY and 11.32/1,000 PY, respectively, in the year of diagnosis. Among newly diagnosed individuals with T2DM who were undergoing treatment for PAD, 14.6% underwent angioplasty for CAD during the same period.

CONCLUSIONS

Our study measured the national incidences of T2DM, CAD, CVD, and PAD, which are of great concern for public health. We also confirmed the relatively higher risk of CAD and CVD newly detected T2DM patients compared to the general population in Korea.

Association of the rs11196218 polymorphism in TCF7L2 with type 2 diabetes mellitus in Asian population

OBJECTIVE

To clarify the association of rs11196218 polymorphism in transcription factor 7-like 2 (TCF7L2) and type 2 diabetes mellitus (T2DM) in Asian population by a case-control study and meta-analysis.

METHODS

In the case-control study, 1842 patients with T2DM and 7777 normal glucose-tolerant controls in the Henan province of China were genotyped for rs11196218 in TCF7L2 by PCR-ligase detection reaction. We used allele, co-dominant, dominant and recessive models to evaluate the risk association and performed a meta-analysis of the results of different genetic models in previous studies and the current study.

RESULTS

The AG genotype of rs11196218 was associated with risk of T2DM in the Henan population (odds ratio 1.37, 95% confidence interval 1.06-1.78), and dominant model showed marginal significant association (1.28, 0.99-1.67). Meta-analysis of 10 studies revealed the dominant model associated with T2DM in the overall population (1.20, 1.05-1.36). When stratified by region (southern and northern China and Japan), both the AG genotype and the dominant model were associated with risk of T2DM in southern Chinese (1.31, 1.03-1.66; 1.27, 1.01-1.60, respectively).

CONCLUSION

The rs11196218 polymorphism in TCF7L2 is associated with risk of T2DM in Asian population.

Genetics of type 2 diabetes: insights into the pathogenesis and its clinical application

With rapidly increasing prevalence, diabetes has become one of the major causes of mortality worldwide. According to the latest studies, genetic information makes substantial contributions towards the prediction of diabetes risk and individualized antidiabetic treatment. To date, approximately 70 susceptibility genes have been identified as being associated with type 2 diabetes (T2D) at a genome-wide significant level (P < 5 × 10⁻⁸). However, all the genetic loci identified so far account for only about 10% of the overall heritability of T2D. In addition, how these novel susceptibility loci correlate with the pathophysiology of the disease remains largely unknown. This review covers the major genetic studies on the risk of T2D based on ethnicity and briefly discusses the potential mechanisms and clinical utility of the genetic information underlying T2D.

Validation of type 2 diabetes risk variants identified by genome-wide association studies in Han Chinese population: a replication study and meta-analysis

BACKGROUND

Several genome-wide association studies (GWAS) involving European populations have successfully identified risk genetic variants associated with type 2 diabetes mellitus (T2DM). However, the effects conferred by these variants in Han Chinese population have not yet been fully elucidated.

METHODS

We analyzed the effects of 24 risk genetic variants with reported associations from European GWAS in 3,040 Han Chinese subjects in Taiwan (including 1,520 T2DM cases and 1,520 controls). The discriminative power of the prediction models with and without genotype scores was compared. We further meta-analyzed the association of these variants with T2DM by pooling all candidate-gene association studies conducted in Han Chinese.

RESULTS

Five risk variants in IGF2BP2 (rs4402960, rs1470579), CDKAL1 (rs10946398), SLC30A8 (rs13266634), and HHEX (rs1111875) genes were nominally associated with T2DM in our samples. The odds ratio was 2.22 (95% confidence interval, 1.81-2.73, P<0.0001) for subjects with the highest genetic score quartile (score>34) as compared with subjects with the lowest quartile (score<29). The incoporation of genotype score into the predictive model increased the C-statistics from 0.627 to 0.657 (P<0.0001). These estimates are very close to those observed in European populations. Gene-environment interaction analysis showed a significant interaction between rs13266634 in SLC30A8 gene and age on T2DM risk (P<0.0001). Further meta-analysis pooling 20 studies in Han Chinese confirmed the association of 10 genetic variants in IGF2BP2, CDKAL1, JAZF1, SCL30A8, HHEX, TCF7L2, EXT2, and FTO genes with T2DM. The effect sizes conferred by these risk variants in Han Chinese were similar to those observed in Europeans but the allele frequencies differ substantially between two populations.

CONCLUSION

We confirmed the association of 10 variants identified by European GWAS with T2DM in Han Chinese population. The incorporation of genotype scores into the prediction model led to a small but significant improvement in T2DM prediction.

Genetic susceptibility to type 2 diabetes and obesity: follow-up of findings from genome-wide association studies

Elucidating the underlying genetic variations influencing various complex diseases is one of the major challenges currently facing clinical genetic research. Although these variations are often difficult to uncover, approaches such as genome-wide association studies (GWASs) have been successful at finding statistically significant associations between specific genomic loci and disease susceptibility. GWAS has been especially successful in elucidating genetic variants that influence type 2 diabetes (T2D) and obesity/body mass index (BMI). Specifically, several GWASs have confirmed that a variant in transcription factor 7-like 2 (TCF7L2) confers risk for T2D, while a variant in fat mass and obesity-associated protein (FTO) confers risk for obesity/BMI; indeed both of these signals are considered the most statistically associated loci discovered for these respective traits to date. The discovery of these two key loci in this context has been invaluable for providing novel insight into mechanisms of heritability and disease pathogenesis. As follow-up studies of TCF7L2 and FTO have typically lead the way in how to follow up a GWAS discovery, we outline what has been learned from such investigations and how they have implications for the myriad of other loci that have been subsequently reported in this disease context.

Association of TCF7L2 gene polymorphisms with T2DM in the population of Hyderabad, India

We attempt to evaluate the nature of association of TCF7L2 gene variants with T2DM, for the first time in the population of Hyderabad, which is considered to be diabetic capital of India. It is a case-control study of the three SNPs of TCF7L2, rs7903146, rs12255372 and rs11196205, genotyped on Sequenom Massarray platform, in a sample of 758 patients and 621 controls. The risk allele frequency of the three SNPs was found to be significantly higher in the T2DM cases than controls, implicating susceptibility for diabetes (p<0.01). The greatest risk of developing the disease was conferred by rs7903146. Further, the logistic regression of genotypes of each SNP under log additive model, and the haplotypes constituted by at least one of the three risk alleles also show significantly greater risk of developing T2DM when compared to the wild type haplotype. Further, BMI and WHR emerge as significant covariates with confounding effects. The strong association of the TCF7L2 SNPs with T2DM is consistent with the findings among other Indian and Non-Indian populations, suggesting universal phenomena of its association across ethnic groups globally, both within and outside the Indian subcontinent, albeit the functional relevance of these SNPs needs yet to be established.

Impacts of TCF7L2 gene polymorphisms on the susceptibility of hepatogenous diabetes and hepatocellular carcinoma in cirrhotic patients

BACKGROUND

Hepatogenous diabetes (HD) occurs as a complication of cirrhosis. Whether genetic factors, rather than only liver damage, play roles in the development of HD is unknown. TCF7L2 gene has been reported to be associated with type 2 diabetes and also cancer risks. We aim to evaluate the impact of TCF7L2 gene on the susceptibility of HD and hepatocellular carcinoma (HCC) in a Chinese Han population.

PATIENTS AND METHODS

A total of 367 adult liver transplant candidates with liver cirrhosis were included. Fifteen tag single nucleotide polymorphisms (SNPs) were selected from HapMap CHB database with a minor allele frequency of >0.2 and r(2) of >0.8. Another three SNPs were also chosen because of their close association with type 2 diabetes in East Asian.

RESULTS

Patients with HD presented significantly poorer liver function, higher incidence of cirrhotic complications and higher insulin resistance compared with non-HD patients. Three SNPs were differentially distributed between HD patients and non-HD patients. In multivariate logistic analysis, TCF7L2 rs290487 and rs6585194 polymorphisms were independently associated with HD after adjustment of clinical factors. The TCF7L2 rs290487 C/C variant homozygote showed much higher insulin resistance and significantly increased HD risk comparing with T/T and T/C genotypes, while the genetic variant of rs6585194 was protectively against HD. Three SNPs (rs290481, rs290487 and rs290489) located near the 3' end of TCF7L2 gene were associated with HCC risk with marginal significance. Patients carrying G-C-A haplotype had a significantly higher HCC risk than those with A-T-G.

CONCLUSIONS

TCF7L2 polymorphisms were associated with HD and maybe cancer risk as well. Further studies with large samples are needed to verify these results.

Association of rs7903146 (IVS3C/T) and rs290487 (IVS3C/T) polymorphisms in TCF7L2 with type 2 diabetes in 9,619 Han Chinese population

AIMS

We aimed to replicate the association of the rs290487 (IVS3C/T) and rs7903146 (IVS3C/T) polymorphisms of transcription factor 7-like 2 (TCF7L2) and type 2 diabetes mellitus (T2DM) in Han Chinese people in Henan province, China.

METHODS

In all, 1,842 patients with T2DM and 7,777 normal glucose-tolerant controls underwent genotyping for the T2DM-associated variants rs7903146 (IVS3C/T) and rs290487 (IVS3C/T). W performed a meta-analysis of the association of the risk alleles of rs7903146 (IVS3C/T) and rs290487 (IVS3C/T) in TCF7L2 and T2DM in Han Chinese by combining previous studies with the present study.

RESULTS

We found that T2DM was associated with the CC genotype (1.364, 1.137-1.636, p  = 0.001), the recessive model (1.457, 1.156-1.838, p  = 0.001) of rs290487 (IVS3C/T) and haplotype CC (1.116, 1.034-1.204, p  = 0.004) in Han Chinese. Moreover, our meta-analyses supported the association of the T allele (IVS3C/T) of rs7903146 (1.36, 1.24-1.48; p  = 6.404×10(-12)) and T2DM but not the C allele of rs290487 (IVS3C/T) (0.99, 0.85-1.15, p  = 0.890) in Han Chinese. We found no interactions between behavioral risk factors (smoking, alcohol drinking, and physical activity) and rs7903146 (IVS3C/T) and rs290487 (IVS3C/T) polymorphisms.

CONCLUSIONS

The CC genotype and the recessive model of the variant rs290487 (IVS3C/T) and CC haplotype of rs7903146 (IVS3C/T) and rs290487 (IVS3C/T) in TCF7L2 may be associated with T2DM in Han Chinese people in Henan province, China.

The association between gene polymorphism of TCF7L2 and type 2 diabetes in Chinese Han population: a meta-analysis

In recent years, it has been widely accepted that transcription factor 7-like 2 (TCF7L2) is associated with type 2 diabetes mellitus (T2DM) in multiple ethnic groups, especially its single nucleotide polymorphisms of rs7903146C/T, rs12255372G/T and rs290487T/C. However, the results previously obtained in Chinese Han population are often inconsistent. For clearing this issue, herein we performed meta-analysis based on the reports that can be found to assess the association. In the meta-analysis, Odds ratio (OR) and 95% confidence interval (95% CI) were calculated with random-effect model or fixed-effect model based on the heterogeneity analysis. The quality of included studies was evaluated by using the Newcastle-Ottawa Scale. The sensitivity analysis was used to confirm the reliability and stability of the meta-analysis. In total, 20 case-control studies with 9122 cases of T2DM and 8017 controls were included. Among these case-control studies, we selected 13 ones on rs7903146 C/T, 5 ones on rs12255372 G/T, 8 ones on rs290487 T/C. The results indicated that rs7903146C/T polymorphism was significantly associated with T2DM (T vs. C, OR = 1.73, 95% CI = 1.39-2.16). There was no evidence that rs12255372G/T and rs290487T/C polymorphisms increased T2DM risk (T vs. G, OR = 1.77, 95% CI = 0.88-3.56; C vs. T, OR = 1.08, 95% CI = 0.93-1.25). Subgroup analysis of different regions proved the relationship between rs7903146C/T polymorphism and T2DM risk in both the northern and the southern China. The association of rs290487 with T2DM was affected by body mass index, whereas the association of rs7903146 and rs290487 with T2DM was influenced neither by age nor by sex. In conclusion, this study indicated that the rs7903146C/T polymorphism of the TCF7L2 gene had a significant effect on T2DM risk in Chinese Han population, with rs12255372G/T and rs290487T/C polymorphisms showing no significant effect.

Meta-analysis of associations between TCF7L2 polymorphisms and risk of type 2 diabetes mellitus in the Chinese population

Background

Associations between transcription factor 7-like 2 (TCF7L2) polymorphisms and type 2 diabetes mellitus (T2DM) have been evaluated extensively in multiple ethnic groups. TCF7L2 has emerged as the strongest T2DM susceptibility gene in Europeans, but the findings have been inconsistent in the Chinese population. The purpose of this meta-analysis was to evaluate the associations between TCF7L2 single nucleotide polymorphisms (SNPs) and T2DM risk in the Chinese population.

Methods

We performed searches in the PubMed, EMBASE, Cochrane, and Chinese databases (CNKI, CQVIP and Wanfang databases) for literature published from January 2007 to February 2012. We reviewed all relevant articles on TCF7L2 polymorphisms and susceptibility to T2DM in the Chinese population written in English and Chinese. Two reviewers extracted data independently using a standardized protocol, and any discrepancies were adjudicated by a third reviewer. Fixed-effects and random-effects meta-analyses were performed to pool the odds ratios (ORs). Publication bias and heterogeneity were examined.

Results

A total of 21 articles were confirmed to be eligible for and included in this meta-analysis: 7 (with 3942 cases and 3502 controls) concerning rs11196218 (IVS−/+4G>A), 8 (with 3377 cases and 2975 controls) concerning rs290487 (IVS3−/+C>T), and 14 (with 7902 cases and 7436 controls) concerning rs7903146 (IVS3−/+C>T). Overall, the results showed a significant association between rs7903146 and T2DM risk. The pooled ORs were 1.54 for the comparison of T and C alleles (95% CI [confidence interval]: 1.37–1.74, p = 1.47 × 10^-12, I² = 25.20%) and 1.56 for TC heterozygotes and CC homozygotes (95% CI : 1.38–1.76, p = 8.25 × 10^-9, I² = 21.00%). The rs11196218(IVS4G>A) and rs290487 (IVS3C>T) SNPs were not associated with T2DM risk.

Conclusions

The rs7903146 SNP of the TCF7L2 gene is associated with increased susceptibility to T2DM in the Chinese population as a whole as well as northern Chinese and southern Chinese as subgroups.

Transcription factor-7-like 2 gene variants are strongly associated with type 2 diabetes in Lebanese subjects

We tested the association of TCF7L2 variants with type 2 diabetes (T2DM) in 691 Lebanese people and 919 controls. rs7901695, rs4506565, rs7903146, rs12243326, rs7895340, and rs12255372 minor allele frequencies were higher in T2DM. Haplotype analysis (rs7901695-rs4506565-rs7903146-rs12243326-rs7895340-rs11196205-rs12255372) identified positively- (2122112, 2222222) and negatively- (1111111) T2DM-associated haplotypes. TCF7L2 is a common T2DM candidate gene in Lebanese people.

TCF7L2 gene polymorphisms and type 2 diabetes risk: a comprehensive and updated meta-analysis involving 121,174 subjects

Recently, many new loci associated with type 2 diabetes have been uncovered by genetic association studies and genome-wide association studies. As more reports are made, particularly with respect to varying ethnicities, there is a need to determine more precisely the effect sizes in each major racial group. In addition, some reports have claimed ethnic-specific associations with alternative single-nucleotide polymorphisms (SNPs), and to that end there has been a degree of confusion. We conducted a meta-analysis using an additive genetic model. Eight polymorphisms in 155 studies with 121174 subjects (53385 cases and 67789 controls) were addressed in this meta-analysis. Significant associations were found between type 2 diabetes and rs7903146, rs12255372, rs11196205, rs7901695, rs7895340 and rs4506565, with summary odds ratios (ORs) (95% confidence interval) of 1.39 (1.34-1.45), 1.33 (1.27-1.40), 1.20 (1.14-1.26), 1.32 (1.25-1.39), 1.21 (1.13-1.29) and 1.39 (1.29-1.49), respectively. In addition, no significant associations were found between the two polymorphisms (rs290487 and rs11196218) and type 2 diabetes. The summary ORs for the six statistically significant associations (P < 0.05) were further evaluated by estimating the false-positive report probability, with results indicating that all of the six significant associations were considered noteworthy, and may plausibly be true associations. Significant associations were found between the six polymorphisms (rs7903146, rs12255372, rs11196205, rs7901695, rs7895340 and rs4506565) in the TCF7L2 gene and type 2 diabetes risk, and the other two polymorphisms (rs11196218 and rs290487) were not found to be significantly associated with type 2 diabetes. Subgroups analyses show that significant associations are not found between the six SNPs (rs7903146, rs12255372, rs11196205, rs7901695, rs7895340, and rs4506565) and the type 2 diabetes in some ethnic populations.

Transcription factor-7-like 2 gene variants are strongly associated with type 2 diabetes in Tunisian Arab subjects

Genome-wide association studies validated transcription factor 7-like 2 (TCF7L2) gene as confirmed type 2 diabetes (T2DM) susceptibility locus, and an ethnic contribution of TCF7L2 variants to T2DM risk was indicated. The aim of this study was to replicate in a Tunisian Arab population identified associations of common TCF7L2 variants with T2DM. We tested the association of TCF7L2 variants: rs4506565, rs7903146, rs12243326, and rs12255372, with T2DM in 900 Tunisian patients and 875 control subjects. TCF7L2 genotyping was done by allelic discrimination/real-time PCR method. Minor allele frequencies of rs4506565 (P=2.4×10(-8)), rs7903146 (P=1.2×10(-6)), rs12243326 (P=8.4×10(-8)) and rs12255372 (P=1.1×10(-5)) were significantly higher in cases. The four tested TCF7L2 variants were in linkage disequilibrium, and 4-locus (rs4506565, rs7903146, rs12243326, rs12255372) haplotype analysis demonstrated that haplotype 1111 was negatively associated (Pc<0.001), while haplotypes 2222 (Pc=0.008) and 2211 (Pc=0.020) were positively associated with T2DM risk, after controlling for a number of covariates. The strong contribution of TCF7L2 gene variants to T2DM among Tunisians is in line with similar findings in other ethnic groups, confirming TCF7L2 as a common T2DM candidate gene.

Association of TCF7L2 gene polymorphisms with type 2 diabetes mellitus in Han Chinese population: a meta-analysis

Variants of transcription factor 7-like 2 (TCF7L2) gene have been reported to be associated with type 2 diabetes mellitus (T2DM), but the available data on this relationship are inconsistent in Han Chinese populations. A meta-analysis was performed to quantitatively analyze the association of TCF7L2 gene polymorphisms with T2DM using previous case-control studies in Chinese Han populations. Several electronic databases were searched for relevant articles up to May 2012. After data collection and gene loci selection, a meta-analysis was performed to assess heterogeneity, combine results and evaluate variations. Publication bias was examined by the Egger's linear regression test. Hardy-Weinberg equilibrium (HWE) test and by omitting one study at a time were employed for the sensitivity analysis. Eighteen studies from sixteen eligible papers were included in the meta-analysis. Ten eligible studies were analyzed for rs7903146, and eight were analyzed for rs290487. We found that the rs7903146 T allele was associated with an increased risk for T2DM under a dominant model, a co-dominant model and an allele contrast model, with an OR of 1.54 (1.32, 1.79), an OR of 1.53 (1.31, 1.79) and an OR of 1.52 (1.31, 1.76), respectively. The rs290487 C allele showed no significant overall association with T2DM, yielding ORs of 1.08 (0.88, 1.32) under a dominant model, with strong evidence of heterogeneity. Similar results were also obtained in other genetic models. Sensitivity analysis confirmed the reliability and stability of this meta-analysis. The accumulated evidence suggested that the rs7903146 T allele was associated with an increased risk for T2DM, but the rs290487 C allele is not associated with T2DM in the Chinese Han population. More well-designed large studies are required for the validation of this association.

Genetic advances of type 2 diabetes in Chinese populations

In recent decades, the prevalence of type 2 diabetes in China has increased significantly, underscoring the importance of investigating the etiological mechanisms, including genetic determinants, of the disease in Chinese populations. Numerous loci conferring susceptibility to type 2 diabetes (T2D) have been identified worldwide, with most having been identified in European populations. In terms of ethnic heterogeneity in pathogenesis as well as disease predisposition, it is imperative to explore the specific genetic architecture of T2D in Han Chinese. Replication studies of European-derived susceptibility loci have been performed, validating 11 of 32 loci in Chinese populations. Genetic investigations into heritable traits related to glucose metabolism are expected to provide new insights into the pathogenesis of T2D, and such studies have already inferred some new susceptibility loci. Other than replication studies of European-derived loci, efforts have been made to identify specific susceptibility loci in Chinese populations using methods such as genome-wide association studies. These efforts have identified additional new loci for the disease. Genetic studies can facilitate the prediction of risk for T2D and also promote individualized anti-diabetic treatment. Despite many advances in the field of risk prediction and pharmacogenetics, the pace of clinical application of these findings is rather slow. As a result, more studies into the practical utility of these findings remain necessary.

Common variants of transcription factor 7-like 2 (TCF7L2) are associated with reduced insulin secretion in women with polycystic ovary syndrome

Common variants of the transcription factor 7-like 2 (TCF7L2) gene were identified as one of the few genetic polymorphisms with powerful effects on the risk of type 2 diabetes (T2D). Given the genetic overlap between polycystic ovary syndrome (PCOS) and T2D, the present study was undertaken to investigate whether the TCF7L2 variants are also associated with PCOS. We analyzed single nucleotide polymorphisms (SNPs) rs11196218 and rs290487 of the TCF7L2 gene, which showed robust associations with T2D in Chinese population, in 430 PCOS patients and 360 control subjects by pyrosequencing, and also assessed the effect of genotype on clinical and biochemical traits in the PCOS group. We found no evidence for association between SNP rs11196218 and PCOS. The SNP rs290487 showed marginal differences in genotype frequencies between the PCOS and control group, with the minor C allele being the at-risk allele for PCOS. In PCOS women, the C allele carriers of rs290487 had higher levels of 2h blood glucose but lower insulinogenic index than noncarriers, suggesting impaired insulin secretion. Our data suggested that the TCF7L2 variants may confer an increased risk for early impairment of glucose homeostasis in PCOS.

Association of genetic variation in FTO with risk of obesity and type 2 diabetes with data from 96,551 East and South Asians

AIMS/HYPOTHESIS

FTO harbours the strongest known obesity-susceptibility locus in Europeans. While there is growing evidence for a role for FTO in obesity risk in Asians, its association with type 2 diabetes, independently of BMI, remains inconsistent. To test whether there is an association of the FTO locus with obesity and type 2 diabetes, we conducted a meta-analysis of 32 populations including 96,551 East and South Asians.

METHODS

All studies published on the association between FTO-rs9939609 (or proxy [r (2) > 0.98]) and BMI, obesity or type 2 diabetes in East or South Asians were invited. Each study group analysed their data according to a standardised analysis plan. Association with type 2 diabetes was also adjusted for BMI. Random-effects meta-analyses were performed to pool all effect sizes.

RESULTS

The FTO-rs9939609 minor allele increased risk of obesity by 1.25-fold/allele (p = 9.0 × 10(-19)), overweight by 1.13-fold/allele (p = 1.0 × 10(-11)) and type 2 diabetes by 1.15-fold/allele (p = 5.5 × 10(-8)). The association with type 2 diabetes was attenuated after adjustment for BMI (OR 1.10-fold/allele, p = 6.6 × 10(-5)). The FTO-rs9939609 minor allele increased BMI by 0.26 kg/m(2) per allele (p = 2.8 × 10(-17)), WHR by 0.003/allele (p = 1.2 × 10(-6)), and body fat percentage by 0.31%/allele (p = 0.0005). Associations were similar using dominant models. While the minor allele is less common in East Asians (12-20%) than South Asians (30-33%), the effect of FTO variation on obesity-related traits and type 2 diabetes was similar in the two populations.

CONCLUSIONS/INTERPRETATION

FTO is associated with increased risk of obesity and type 2 diabetes, with effect sizes similar in East and South Asians and similar to those observed in Europeans. Furthermore, FTO is also associated with type 2 diabetes independently of BMI.

Genetic variants of TCF7L2 are associated with type 2 diabetes in a northeastern Chinese population

Variants in the gene encoding transcription factor 7-like 2 (TCF7L2) are associated with type 2 diabetes mellitus (T2D) in several ethnic groups. Two intronic variants, rs290487 and rs11196218, were originally identified as T2D modifiers in Hong Kong Chinese and Taiwan Chinese populations, respectively. However, discrepancies were noted in subsequent replicated studies. In this study, an association of these two loci with T2D was investigated in a Harbin Chinese population. Whereas the two populations in the initial studies were southern Han Chinese, Harbin Chinese are from northeastern China. The SNPs rs290487 and rs11196218 were genotyped by ligase detection reactions in 700 T2D patients and 570 unrelated non-diabetic controls. Association analyses, which were carried out using the case-control sample set, yielded a significant association between rs290487 and T2D, with a trend opposite to that described in a previous report. Specifically, rs290487T was found to be significantly associated with disease susceptibility (p=0.039), and the allelic OR of rs290487T carriers was 1.184 (95% CI 1.008-1.391). There was no significant association between rs11196218 and T2D. Taken together, TCF7L2 may be an important susceptibility gene for T2D in some Chinese populations. The discrepancies in the allelic associations determined for northern vs. southern Chinese allude to the presence of genetic variation among the Han Chinese.