Variations in KCNQ1 are associated with type 2 diabetes and beta cell function in a Chinese population

Diabetes in China: epidemiology, pathophysiology and multi-omics

Although diabetes is now a global epidemic, China has the highest number of affected people, presenting profound public health and socioeconomic challenges. In China, rapid ecological and lifestyle shifts have dramatically altered diabetes epidemiology and risk factors. In this Review, we summarize the epidemiological trends and the impact of traditional and emerging risk factors on Chinese diabetes prevalence. We also explore recent genetic, metagenomic and metabolomic studies of diabetes in Chinese, highlighting their role in pathogenesis and clinical management. Although heterogeneity across these multidimensional areas poses major analytic challenges in classifying patterns or features, they have also provided an opportunity to increase the accuracy and specificity of diagnosis for personalized treatment and prevention. National strategies and ongoing research are essential for improving diabetes detection, prevention and control, and for personalizing care to alleviate societal impacts and maintain quality of life.

DNA methylation and type 2 diabetes: a systematic review

OBJECTIVE

DNA methylation influences gene expression and function in the pathophysiology of type 2 diabetes mellitus (T2DM). Mapping of T2DM-associated DNA methylation could aid early detection and/or therapeutic treatment options for diabetics.

DESIGN

A systematic literature search for associations between T2DM and DNA methylation was performed. Prospero registration ID: CRD42020140436.

METHODS

PubMed and ScienceDirect databases were searched (till October 19, 2023). Preferred Reporting Items for Systematic Reviews and Meta-Analyses (PRISMA) guidelines and New Castle Ottawa scale were used for reporting the selection and quality of the studies, respectively.

RESULT

Thirty-two articles were selected. Four of 130 differentially methylated genes in blood, adipose, liver or pancreatic islets (TXNIP, ABCG1, PPARGC1A, PTPRN2) were reported in > 1 study. TXNIP was hypomethylated in diabetic blood across ethnicities. Gene enrichment analysis of the differentially methylated genes highlighted relevant disease pathways (T2DM, type 1 diabetes and adipocytokine signaling). Three prospective studies reported association of methylation in IGFBP2, MSI2, FTO, TXNIP, SREBF1, PHOSPHO1, SOCS3 and ABCG1 in blood at baseline with incident T2DM/hyperglycemia. Sex-specific differential methylation was reported only for HOOK2 in visceral adipose tissue (female diabetics: hypermethylated, male diabetics: hypomethylated). Gene expression was inversely associated with methylation status in 8 studies, in genes including ABCG1 (blood), S100A4 (adipose tissue), PER2 (pancreatic islets), PDGFA (liver) and PPARGC1A (skeletal muscle).

CONCLUSION

This review summarizes available evidence for using DNA methylation patterns to unravel T2DM pathophysiology. Further validation studies in diverse populations will set the stage for utilizing this knowledge for identifying early diagnostic markers and novel druggable pathways.

Perspectives on genetic studies of type 2 diabetes from the genome-wide association studies era to precision medicine

Genome-wide association studies (GWAS) have facilitated a substantial and rapid increase in the number of confirmed genetic susceptibility variants for complex diseases. Approximately 700 variants predisposing individuals to the risk for type 2 diabetes have been identified through GWAS until 2023. From 2018 to 2022, hundreds of type 2 diabetes susceptibility loci with smaller effect sizes were identified through large-scale GWAS with sample sizes of 200,000 to >1 million. The clinical translation of genetic information for type 2 diabetes includes the development of novel therapeutics and risk predictions. Although drug discovery based on loci identified in GWAS remains challenging owing to the difficulty of functional annotation, global efforts have been made to identify novel biological mechanisms and therapeutic targets by applying multi-omics approaches or searching for disease-associated coding variants in isolated founder populations. Polygenic risk scores (PRSs), comprising up to millions of associated variants, can identify individuals with higher disease risk than those in the general population. In populations of European descent, PRSs constructed from base GWAS data with a sample size of approximately 450,000 have predicted the onset of diseases well. However, European GWAS-derived PRSs have limited predictive performance in non-European populations. The predictive accuracy of a PRS largely depends on the sample size of the base GWAS data. The results of GWAS meta-analyses for multi-ethnic groups as base GWAS data and cross-population polygenic prediction methodology have been applied to establish a universal PRS applicable to small isolated ethnic populations.

An early prediction model for type 2 diabetes mellitus based on genetic variants and nongenetic risk factors in a Han Chinese cohort

Aims

We aimed to construct a prediction model of type 2 diabetes mellitus (T2DM) in a Han Chinese cohort using a genetic risk score (GRS) and a nongenetic risk score (NGRS).

Methods

A total of 297 Han Chinese subjects who were free from type 2 diabetes mellitus were selected from the Tianjin Medical University Chronic Disease Cohort for a prospective cohort study. Clinical characteristics were collected at baseline and subsequently tracked for a duration of 9 years. Genome-wide association studies (GWASs) were performed for T2DM-related phenotypes. The GRS was constructed using 13 T2DM-related quantitative trait single nucleotide polymorphisms (SNPs) loci derived from GWASs, and NGRS was calculated from 4 biochemical indicators of independent risk that screened by multifactorial Cox regressions.

Results

We found that HOMA-IR, uric acid, and low HDL were independent risk factors for T2DM (HR >1; P<0.05), and the NGRS model was created using these three nongenetic risk factors, with an area under the ROC curve (AUC) of 0.678; high fasting glucose (FPG >5 mmol/L) was a key risk factor for T2DM (HR = 7.174, P< 0.001), and its addition to the NGRS model caused a significant improvement in AUC (from 0.678 to 0.764). By adding 13 SNPs associated with T2DM to the GRS prediction model, the AUC increased to 0.892. The final combined prediction model was created by taking the arithmetic sum of the two models, which had an AUC of 0.908, a sensitivity of 0.845, and a specificity of 0.839.

Conclusions

We constructed a comprehensive prediction model for type 2 diabetes out of a Han Chinese cohort. Along with independent risk factors, GRS is a crucial element to predicting the risk of type 2 diabetes mellitus.

Visceral fat correlates with insulin secretion and sensitivity independent of BMI and subcutaneous fat in Chinese with type 2 diabetes

AIM

Clinical heterogeneity exists in overall obesity and abdominal obesity in terms of insulin secretion and sensitivity. Further, the impact of visceral fat (VF) on the first- and second-phase insulin secretion (FPIS and SPIS) is controversial. We aim to investigate insulin secretion and sensitivity in Chinese patients with T2DM according to different BMI and VF levels.

METHODS

This study enrolled 300 participants. A dual bioelectrical impedance analyzer was used to assess the visceral and subcutaneous fat area (VFA and SFA). VF levels were categorized as normal or high, with the cutoff value of 100 cm². FPIS and SPIS were evaluated by arginine stimulation test and standardized steamed bread meal tolerance test, respectively. β-cell function (HOMA2-β), insulin resistance (HOMA2-IR), and Gutt's insulin sensitivity index (Gutt-ISI) were also calculated. Spearman's correlation analysis and multivariate linear regression analysis were adopted for statistical analysis.

RESULTS

Participants were categorized into four groups: normal weight-normal VF, normal weight-high VF, overweight/obese-normal VF and overweight/obese-high VF. Multivariate linear regression showed that both VFA and SFA were correlated with FPIS, HOMA2-IR and Gutt-ISI after controlling for gender and diabetes duration. After further adjustment for BMI and VFA, some associations of SFA with insulin secretion and sensitivity disappeared. After adjustment for gender, diabetes duration, BMI and SFA, VFA was positively correlated with FPIS, SPIS and HOMA2-IR. Subjects with overweight/obese-high VF were more likely to have higher FPIS, HOMA2-IR and lower Gutt-ISI (all p < 0.05).

CONCLUSION

VF affects both FPIS and SPIS, and worsens insulin sensitivity independent of BMI and subcutaneous fat in Chinese patients with T2DM.

CLINICAL TRIAL REGISTRATION

http://www.chictr.org.cn, identifier ChiCTR2200062884.

Associations between KCNQ1 and ITIH4 gene polymorphisms and infant weight gain in early life

BACKGROUND

An earlier meta-analysis of genome-wide association studies in Asian populations detected five novel body mass index-associated single-nucleotide polymorphisms (SNPs), including potassium voltage-gated channel subfamily Q member 1 (KCNQ1) (rs2237892), ALDH2/MYL2 (rs671, rs12229654), ITIH4 (rs2535633), and NT5C2 (rs11191580). Whether these SNPs take effect in early life, for example, affect infant rapid weight gain (RWG), is unclear.

METHODS

We obtained genomic DNA from 460 term infants with normal birth weight. RWG was defined as the change of weight-for-age standardized Z-score, calculated according to the Children Growth Standard released by the World Health Organization, from birth to 3 months of age >0.67. Using genetic models, associations between the candidate SNPs and infant RWG were examined, along with the interaction between the SNPs and the potential risk factors.

RESULTS

RWG was presented in 225 of 460 infants. SNP rs2535633 and rs2237892 were associated with the risk of RWG. Both additive and multiplicative interaction effects were found between infant delivery mode and rs2237892. The negative association between the rs2237892 T allele and infant RWG was only observed in vaginally delivered infants.

CONCLUSIONS

Obesity-related loci rs2535633 and rs2237892 are associated with infant RWG in the first 3 months of infancy. The relationship between rs2237892 and infant RGW might be moderated by cesarean delivery.

IMPACT

Genetic predisposition is an essential aspect to understand infant weight gain. Obesity-related SNPs, rs2535633 and rs2237892, are associated with RWG in very early years of life. The negative association between rs2237892 T allele and RWG is only observed in infants delivered vaginally instead of cesarean section.

Relationship Between KCNQ1 Polymorphism and Type 2 Diabetes Risk in Northwestern China

Purpose

This study aimed to explore the relationship between KCNQ1 polymorphism and type 2 diabetes mellitus (T2DM) risk in the population of Northwest China.

Patients and Methods

Case-control strategy was used to reveal the correlation between KCNQ1 polymorphism and T2DM risk, and MDR analysis clarified the influence of KCNQ1 polymorphism interaction on T2DM risk. The related proteins, functions, and signal pathways of KCNQ1 were further explored through bioinformatics methods. PCR was used to explore the relative expression of KCNQ1 in T2DM patients and the controls.

Results

Studies showed that rs163177, rs163184, rs2237895 and rs2283228 on the KCNQ1 gene are closely related to the risk of T2DM in Northwest China. MDR results showed that the three-locus model is the best model for T2DM risk assessment, which increases the risk of T2DM. The bioinformatics results showed that KCNQ1 closely-acted proteins are mainly involved in signal pathways such as gastric acid secretion and renin secretion. The PCR results showed that, compared with the controls, the expression of KCNQ1 was up-regulated in T2DM patients.

Conclusion

The results revealed that KCNQ1 polymorphism is related to the risk of T2DM in the population of Northwest China and provide a scientific basis for the early screening and prevention of T2DM high-risk populations.

KCNQ1 rs2237895 polymorphism is associated with the therapeutic response to sulfonylureas in Iranian type 2 diabetes mellitus patients

Background and Aims

Sulfonylureas are the most secondary prescribed oral anti-diabetic drug. Understanding its genetic role in pharmacodynamics can elucidate a considerable knowledge about personalized treatment in type 2 diabetes patients. This study aimed to assess the impact of KCNQ1 variants on sulfonylureas response among type 2 diabetes Iranian patients.

Methods and Results

100 patients were recruited who were under sulfonylureas therapy for six months. 50 responder and 50 non-responder patients were selected. KCNQ1 variants were determined by the RFLP method, and their role in treatment response was assessed retrospectively. Patients with rs2237895 CC and AC genotypes demonstrated a significant decrement in FBS and HbA1c after treatment over patients with AA genotypes (All P < 0.001). Compared to the A allele, the odds ratio for treatment success between carriers with rs2237895 C allele was 4.22-fold (P < 0.001). Patients with rs2237892 CT heterozygous genotype exhibit a higher reduction rate in HbA1c and FBS than CC homozygotes (P=0.064 and P=0.079, respectively). The rs2237892 T allele carriers showed an odds ratio equals to 2.83-fold over C allele carriers in the responder group compared to the non-responder group (p=0.081).

Conclusion

Findings suggest that the KCNQ1 rs2237895 polymorphism is associated with the sulfonylureas response on Iranian type 2 diabetes patients.

Regulation of Pancreatic β-Cell Mass by Gene-Environment Interaction

The main pathogenic mechanism of diabetes consists of an increase in insulin resistance and a decrease in insulin secretion from pancreatic β-cells. The number of diabetic patients has been increasing dramatically worldwide, especially in Asian people whose capacity for insulin secretion is inherently lower than that of other ethnic populations. Causally, changes of environmental factors in addition to intrinsic genetic factors have been considered to have an influence on the increased prevalence of diabetes. Particular focus has been placed on "gene-environment interactions" in the development of a reduced pancreatic β-cell mass, as well as type 1 and type 2 diabetes mellitus. Changes in the intrauterine environment, such as intrauterine growth restriction, contribute to alterations of gene expression in pancreatic β-cells, ultimately resulting in the development of pancreatic β-cell failure and diabetes. As a molecular mechanism underlying the effect of the intrauterine environment, epigenetic modifications have been widely investigated. The association of diabetes susceptibility genes or dietary habits with gene-environment interactions has been reported. In this review, we provide an overview of the role of gene-environment interactions in pancreatic β-cell failure as revealed by previous reports and data from experiments.

[Association of polymorphisms of genes TCF7L2, FABP2, KCNQ1, ADIPOQ with the prognosis of the development of type 2 diabetes mellitus]

AIM

To study the possibility of using polymorphisms of genesTCF7L2,FABP2,KCNQ1,ADIPOQas markers for predicting the development of type 2 diabetes mellitus (T2D) in the population of Novosibirsk.

MATERIALS AND METHODS

On the basis of prospective observation of a representative population sample of residents of Novosibirsk (HAPIEE), 2 groups were formed according to the case-control principle (case people who had diabetes mellitus 2 over 10 years of observation, and control people who did not developed disorders of carbohydrate metabolism). T2D group (n=443, mean age 56.26.7 years, men 29.6%, women 70.4%), control group (n=532, mean age 56.17.1 years, men 32.7%, women 67.3%). DNA was isolated by phenol-chloroform extraction. Genotyping was performed by the method of polymerase chain reaction with subsequent analysis of restriction fragment length polymorphism, polymerase chain reaction in real time. Statistical processing was carried out using the SPSS 16.0 software package.

RESULTS AND DISCUSSION

No significant effect of rs1799883 of theFABP2gene, rs2237892 of theKCNQ1gene, and rs6773957 of theADIPOQgene on the risk of developing T2D was found. Genotypes TT and TC rs7903146 of theTCF7L2gene are genotypes for the risk of developing T2D (relative risk RR 3.90, 95% confidence interval CI 2.316.61,p0.001; RR 1.86, 95% CI 1.422.43,p0.001, respectively). The CC genotype rs7903146 of theTCF7L2gene is associated with a protective effect against T2D (RR 0.37, 95% CI 0.290.49,p0.001). When theTCF7L2gene is included in the model for assessing the risk of developing T2D rs7903146, it retains its significance in both men and women.

CONCLUSION

The rs7903146 polymorphism of theTCF7L2gene confirmed its association with the prognosis of the development of T2D, which indicates the possibility of considering it as a candidate for inclusion in a diabetes risk meter. Variants of risk meters have been developed to assess the prognosis of the development of diabetes mellitus 2 in men and women aged 4569 years during 10 years of follow-up. The association with the prognosis of the development of T2D polymorphisms rs1799883 of theFABP2gene, rs2237892 of theKCNQ1gene and rs6773957 of theADIPOQgene was not found.

KCNQ1 common genetic variant and type 2 diabetes mellitus risk

Background

Type 2 diabetes mellitus (T2DM) is a multifactorial trait that both environmental and genetic factors contribute to its pathogenesis. The most common single nucleotide polymorphism (SNP) of the potassium voltage-gated channel subfamily Q member 1 (KCNQ1) gene, rs2237892, is highly associated with the risk of T2DM. The aim of the present study was to examine any association between KCNQ1 gene rs2237892 variant and risk of T2DM in a group of Iranian patients.

Methods

Genotyping was carried out in 100 type 2 diabetic patients and 100 non-diabetic subjects using the Sanger sequencing method.

Results

The CC genotype caused more than 30% reduction in the risk of T2DM in compared with CT. Nonetheless, this association was not statistically significant and this variant had no protective effect for T2DM. A significant difference was not found in genotypes (CC, CT, and TT) and alleles (C and T) frequency of KCNQ1 rs2237892 SNP between T2DM and control groups (P = 0.475 and P = 0.470, respectively).

Conclusions

Our investigations did not show enough evidence for the presence of an association between KCNQ1 gene rs2237892 polymorphism and risk of T2DM among a group of Iranian patients.

Impact of acute-phase insulin secretion on glycemic variability in insulin-treated patients with type 2 diabetes

AIMS

The association between β-cell function and glycemic variability remains to be clarified in insulin-treated patients with type 2 diabetes. Therefore, the study sought to examine the association of various indices of β-cell function with glycemic variability in Chinese insulin-treated patients with type 2 diabetes.

METHODS

Glycemic variability was assessed by the coefficient of variation (CV) of glucose levels with the use of continuous glucose monitoring (CGM). Basal β-cell function was evaluated by fasting C-peptide (FCP) and the homeostasis model assessment 2 for β-cell function (HOMA2-%β). Postload β-cell function was measured by 2-hour C-peptide (2hCP) and the acute C-peptide response (ACPR) to arginine.

RESULTS

When a cutoff value of CV ≥ 36% was used to define unstable glucose, the multivariable-adjusted odds ratios for labile glycemic control were 0.34 (95% CI 0.18-0.64) for each 1 ng/mL increase in ACPR, 0.47 (95% CI 0.27-0.81) for each 1 ng/mL increase in FCP, 0.77 (95% CI 0.61-0.97) for each 1 ng/mL increase in 2hCP, and 1.00 (95% CI 0.98-1.01) for each 1% increase in HOMA2-%β. When we further adjusted for 2hCP and HOMA2-%β in the ACPR and FCP analyses, and adjusted for ACPR or FCP in the 2hCP analyses, only ACPR but not FCP or 2hPC remained to be a significant and inverse predictor for labile glycemic control.

CONCLUSIONS

ACPR evaluated by the arginine stimulation test may be superior to other commonly used β-cell function parameters to reflect glycemic fluctuation in insulin-treated patients with type 2 diabetes.

Associations of KCNQ1 Polymorphisms with the Risk of Type 2 Diabetes Mellitus: An Updated Meta-Analysis with Trial Sequential Analysis

BACKGROUND

Previous studies have examined the role of the KQT-like subfamily Q member1 (KCNQ1) gene polymorphisms on the risk of type 2 diabetes mellitus (T2DM), but the findings are inconclusive.

OBJECTIVE

To examine the association between the KCNQ1 gene polymorphisms and the risk of T2DM using an updated meta-analysis with an almost tripled number of studies.

METHODS

Five electronic databases, such as PubMed and Embase, were searched thoroughly for relevant studies on the associations between seven most studied KCNQ1 gene polymorphisms, including rs2237892, rs2237897, rs2237895, rs2283228, rs231362, rs151290, and rs2074196, and T2DM risk up to September 14, 2019. The summary odds ratios (ORs) with their 95% confidence intervals (CIs) were applied to assess the strength of associations in the random-effects models. We used the trial sequential analysis (TSA) to measure the robustness of the evidence.

RESULTS

49 publications including 55 case-control studies (68,378 cases and 66,673 controls) were finally enrolled. In overall analyses, generally, increased T2DM risk was detected for rs2237892, rs2237895, rs2283228, rs151290, and rs2074196, but not for rs231362 under all genetic models. The ORs and 95% CIs for allelic comparison were 1.23 (1.14-1.33) for rs2237892, 1.21 (1.16-1.27) for rs2237895, 1.27 (1.11-1.46) for rs2237897, 1.25 (1.09-1.42) for rs2283228, 1.14 (1.03-1.27) for rs151290, 1.31 (1.23-1.39) for rs2074196, and 1.16 (0.83, 1.61) for rs231362. Stratified analyses showed that associations for rs2237892, rs2237895, rs2283228, and rs151290 were more evident among Asians than Caucasians. TSA demonstrated that the evidence was sufficient for all polymorphisms in this study. The genotypes of the three SNPs (rs2237892, rs2283228, and rs231362) were significantly correlated with altered KCNQ1 gene expression.

CONCLUSION

This meta-analysis suggested that KCNQ1 gene polymorphisms (rs2237892, rs2283228, rs2237895, rs151290, and rs2074196) might be the susceptible factors for T2DM, especially among Asian population.

Whole-exome sequencing identifies a novel INS mutation causative of maturity-onset diabetes of the young 10

Monogenic diabetes is often misdiagnosed with type 2 diabetes due to overlapping characteristics. This study aimed to discover novel causative mutations of monogenic diabetes in patients with clinically diagnosed type 2 diabetes and to explore potential molecular mechanisms. Whole-exome sequencing was performed on 31 individuals clinically diagnosed with type 2 diabetes. One novel heterozygous mutation (p.Ala2Thr) in INS was identified. It was further genotyped in an additional case-control population (6523 cases and 4635 controls), and this variant was observed in 0.09% of cases. Intracellular trafficking of insulin proteins was assessed in INS1-E and HEK293T cells. p.Ala2Thr preproinsulin-GFP was markedly retained in the endoplasmic reticulum (ER) in INS1-E cells. Activation of the PERK-eIF2α-ATF4, IRE1α-XBP1, and ATF6 pathways as well as upregulated ER chaperones were detected in INS1-E cells transfected with the p.Ala2Thr mutant. In conclusion, we identified a causative mutation in INS responsible for maturity-onset diabetes of the young 10 (MODY10) in a Chinese population and demonstrated that this mutation affected β cell function by inducing ER stress.

Impact of KCNQ1, CDKN2A/2B, CDKAL1, HHEX, MTNR1B, SLC30A8, TCF7L2, and UBE2E2 on risk of developing type 2 diabetes in Thai population

BACKGROUND

Several type 2 diabetes (T2D) susceptibility loci identified via genome-wide association studies were found to be replicated among various populations. However, the influence of these loci on T2D in Thai population is unknown. The aim of this study was to investigate the influence of eight single nucleotide polymorphisms (SNPs) reported in GWA studies on T2D and related quantitative traits in Thai population.

METHODS

Eight SNPs in or near the KCNQ1, CDKN2A/2B, SLC30A8, HHEX, CDKAL1, TCF7L2, MTNR1B, and UBE2E2 genes were genotyped. A case-control association study comprising 500 Thai patients with T2D and 500 ethnically-matched control subjects was conducted. Associations between SNPs and T2D were examined by logistic regression analysis. The impact of these SNPs on quantitative traits was examined by linear regression among case and control subjects.

RESULTS

Five SNPs in KCNQ1 (rs2237892), CDK2A/2B (rs108116610, SLC30A8 (rs13266634), TCF7L2 (rs7903146) and MTNR1B (rs1387153) were found to be marginally associated with risk of developing T2D, with odds ratios ranging from 1.43 to 2.02 (p = 0.047 to 3.0 × 10-4) with adjustments for age, sex, and body mass index. Interestingly, SNP rs13266634 of SLC30A8 gene reached statistical significance after correcting for multiple testing (p = 0.0003) (p < 0.006 after Bonferroni correction). However, no significant association was detected between HHEX (rs1111875), CDKAL1 (rs7756992), or UBE2E2 (rs7612463) and T2D. We also observed association between rs10811661 and both waist circumference and waist-hip ratio (p = 0.007 and p = 0.023, respectively). In addition, rs13266634 in SLC30A8 was associated with glycated hemoglobin (p = 0.018), and rs7903146 in TCF7L2 was associated with high-density lipoprotein cholesterol level (p = 0.023).

CONCLUSION

Of the eight genes included in our analysis, significant association was observed between KCNQ1, CDKN2A/2B, SLC30A8, TCF7L2, and MTNR1B loci and T2D in our Thai study population. Of these, CDKN2A/2B, SLC30A8, and TCF7L2 genes were also significantly associated with anthropometric, glycemic and lipid characteristics. Larger cohort studies and meta-analyses are needed to further confirm the effect of these variants in Thai population.

Pharmacogenetics of Antidiabetic Drugs

Pharmacogenetic studies of antidiabetic drugs have so far focused largely on response to metformin, which is the first-line therapy for treatment of type 2 diabetes (T2D). The first studies of metformin pharmacogenetics were focused on candidate genes that were implicated in metformin pharmacokinetics and transport. Since 2011, genome-wide association studies have been conducted in large cohorts of individuals with T2D identifying genes that are associated with glycemic response to metformin. There have been fewer pharmacogenetic studies of other antidiabetic drugs, and those have been largely limited to candidate gene studies with small sample sizes. Understanding the pharmacogenetics of antidiabetes medications is important for the integration of genetic screening into therapeutic decision making, and to achieve the goal of "precision medicine" for patients with T2D. In this chapter, we provide a review of the pharmacogenetics investigations of metformin and other antidiabetes medications. In addition, we highlight the importance of collaborative efforts with large sample size and representation from multiple ethnic groups in pharmacogenetics studies.

Diabetes in China: Epidemiology and Genetic Risk Factors and Their Clinical Utility in Personalized Medication

The incidence of type 2 diabetes (T2D) has rapidly increased over recent decades, and T2D has become a leading public health challenge in China. Compared with European descents, Chinese patients with T2D are diagnosed at a relatively young age and low BMI. A better understanding of the factors contributing to the diabetes epidemic is crucial for determining future prevention and intervention programs. In addition to environmental factors, genetic factors contribute substantially to the development of T2D. To date, more than 100 susceptibility loci for T2D have been identified. Individually, most T2D genetic variants have a small effect size (10-20% increased risk for T2D per risk allele); however, a genetic risk score that combines multiple T2D loci could be used to predict the risk of T2D and to identify individuals who are at a high risk. Furthermore, individualized antidiabetes treatment should be a top priority to prevent complications and mortality. In this article, we review the epidemiological trends and recent progress in the understanding of T2D genetic etiology and further discuss personalized medicine involved in the treatment of T2D.

Type 2 diabetes associated variants of KCNQ1 strongly confer the risk of cardiovascular disease among the Saudi Arabian population

Genome-wide association studies have identified several loci associated with an increased risk for cardiovascular disease (CVD) and type 2 diabetes (T2D). Polymorphisms within the KCNQ1 (potassium voltage-gated channel, KQT-like subfamily, member 1) gene are consistently associated with T2D in a number of populations. The current study was undertaken to evaluate the association of 3 polymorphisms of KCNQ1 (rs2237892, rs151290 and rs2237895) with T2D and/or CVD. Patients diagnosed with either T2D (320 patients), CVD (250 patients) or both (60 patients) and 516 healthy controls were genotyped by TaqMan assay run on a real time PCR thermocycler. A statistically significant association was found for SNPs rs151290 (OR = 1.76; 95%CI = 1.02-3.05; p = 0.0435) and rs2237895 (OR = 2.49; 95%CI = 1.72-3.61; p < 0.0001) with CVD. SNP rs151290 (OR = 7.43; 95%CI = 1.00-55.22; p = 0.0499) showed a strong association in patients with both T2D and CVD. None of the SNPs showed any significant association with T2D. Haploview analysis showed that the ACC (rs151290, rs2237892 and rs2237895) haplotype is the most significant risk allele combination for CVD, while CCA is the most significant risk haplotype for co-morbidity with T2D. KCNQ1 polymorphism at SNPs rs151290 and rs2237895 is strongly associated with CVD in this population, but presented no association with T2D.

Polymorphisms associated with a tropical climate and root crop diet induce susceptibility to metabolic and cardiovascular diseases in Solomon Islands

The people of the Solomon Islands represent an Austronesian (AN)-speaking population's adaptation to a humid tropical environment and subsistence of tuberous crops. Genome-wide association studies (GWASs) of other populations (e.g. the Human Genome Diversity Project [HGDP]) have suggested the existence of genotypes adaptive to ecoregion, diet, and subsistence, and that those genotypes are also associated with metabolic and cardiovascular diseases. Recently, the incidence of non-communicable diseases has been increasing in the Solomon Islands. In the present study, we explored the association of genotypes adaptive to a tropical environment and tuberous crop diet with metabolic and cardiovascular conditions in rural and urban AN-speaking Melanesian and Micronesian populations of the Solomon Islands. A total of 561 participants were genotyped for single nucleotide polymorphisms (SNPs) potentially associated with a tropical environment (rs174570 and rs2237892) and a tuberous crop diet (rs162036, rs185819, and rs2722425). The results showed that the allele frequencies of the Solomon Islands populations adopted patterns similar to those in populations from other hot, tropical areas with a tuberous crop diet in previous studies. Furthermore, rs162036, rs185819, rs2237892, and rs2722425 were all strongly associated with one or more metabolic and cardiovascular conditions. The derived allele of rs2722425 (i.e. rs2722425-G) was significantly associated with an elevated LDL level (P = 0.000264) even after the significance level was adjusted for multiple testing (i.e., α = 0.0005). Our results suggest that the inhabitants of the Solomon Islands exhibit the effects of the tropical environment and tuberous crop diet on their allele frequencies, and that their susceptibility to metabolic and cardiovascular diseases is therefore considered to be associated with their environment and diet.

Polymorphisms of the KCNQ1 gene are associated with the therapeutic responses of sulfonylureas in Chinese patients with type 2 diabetes

KCNQ1 channel is a member of the voltage-gated potassium channel KQT-like subfamily. The KCNQ1 gene has recently been identified as a susceptibility locus for type 2 diabetes mellitus (T2DM). In the present study, we examined the effects of KCNQ1 variants on the therapeutic response to modified-release gliclazide (gliclazide MR) treatment in Chinese patients newly diagnosed with T2DM. A total of 100 newly diagnosed T2DM patients without a history of any anti-diabetic medications were treated with gliclazide MR for 16 weeks, but 91 patients completed the entire study. The anthropometric parameters were determined at baseline and at the final visit, while clinical laboratory tests were performed at baseline and on weeks 2, 4, 6, 12, 16. Two SNPs, rs2237892 and rs2237895, in the region of the KCNQ1 gene were genotyped in all the participants. All calculations and statistical analyses were conducted using SPSS. The rs2237892 TT homozygotes exhibited significantly higher 2-h glucose levels at baseline (P<0.05) and a lower cumulative attainment rate of the target 2-h glucose level (Plog-rank=0.020) than the C allele carriers. Patients with greater numbers of rs2237892 T alleles exhibited larger augmentations (Δ) in the 2-h glucose levels (P=0.027); and patients with the rs2237892 TT genotype exhibited a higher Δ homeostasis model assessment of β-cell function (HOMA-β) than CC and CT genotype carriers (P=0.021 and P=0.043, respectively). Moreover, the rs2237895 C allele was associated with a greater decrement in Δ glycated hemoglobin (HbA1c) (P=0.024); and patients with the CC genotype exhibited greater variance than those with the AA and AC genotypes (P=0.005 and 0.021, respectively). Compared with the C allele, the odds ratio for treatment success among carriers of the rs2237892 T allele was 2.533 (P=0.007); and the rs2237895 C allele was associated with a 2.360-fold decrease in HbA1c compared with the A allele (P=0.009). KCNQ1 polymorphisms are associated with gliclazide MR efficacy in Chinese patients with type 2 diabetes.

Gene-environment interaction in type 2 diabetes

Type 2 diabetes is a typical multifactorial disease, but the causes can largely be divided into genetic and environmental factors. In recent years, focus has shifted to the interaction between these factors (i.e., gene-environment interactions). It has become widely known that changes in the intrauterine environment such as intrauterine growth restriction result in gene expression changes in various tissues, which ultimately lead to the onset of diabetes. Epigenetic modification is considered to be a particularly important mechanism in these effects, as it is easily affected by environmental changes that occur during the fetal and neonatal periods. Moreover, recent reports have revealed that epigenetic modifications are passed down through generations. Although genome-wide association studies have identified many type 2 diabetes susceptibility genes, these genes do not pose a significantly high risk when isolated as single factors. In particular, it has been suggested that the interaction of the FTO or KCNQ1 genes with environmental factors increases the incidence of diabetes. These findings suggest that detailed analyses of individual gene-environment interactions hold promise for gaining new insight into the mechanisms and risk factors contributing to type 2 diabetes, with application to personalized diagnoses and treatments. We look forward to future developments in this regard.

Prevalence and risk of diabetes based on family history in the Shanghai High-Risk Diabetic Screen (SHiDS) study

AIMS

To evaluate the prevalence and risk of diabetes based on family history in high-risk subjects and also to evaluate insulin sensitivity and insulin secretion in these subjects.

METHODS

Data were analysed from 9756 participants in the Shanghai High-Risk Diabetic Screen (SHiDS) Project. Family history of diabetes was classified according to parental and sibling diabetes status. The prevalence and odds ratios were calculated for each grouping after adjusting for other risk factors. Insulin resistance and sensitivity were evaluated using oral glucose tolerance test-derived indices that were validated by hyperinsulinaemic-euglycaemic and hyperglycaemic clamps.

RESULTS

A total of 30.4% of the subjects had a family history of diabetes in a first-degree relative. The proportions of subjects with a father, mother or sibling with diabetes were 7.5, 11.9 and 5.5%, respectively. The prevalence rates of diabetes in subjects with sibling history, maternal history or paternal history of diabetes were 39.3, 38.3 and 36.4%, respectively. Sibling history was a strong risk factor for diabetes (odds ratio 1.53, 95% CI 1.27-1.84; P < 0.05). Insulin secretion was significantly lower in those with a maternal or sibling history of diabetes; however, insulin sensitivity was not significantly different among subjects with a family history of diabetes.

CONCLUSIONS

Sibling history of diabetes was more strongly associated with diabetes risk than parental history among high-risk subjects. Subjects with a sibling or maternal history of diabetes had significantly lower insulin secretion. Sibling history is an important and independent risk factor for diabetes even among multi-risk populations. Those with a sibling history of diabetes warrant intensive care and follow-up screening.

A variation in KCNQ1 gene is associated with repaglinide efficacy on insulin resistance in Chinese Type 2 Diabetes Mellitus Patients

Repaglinide is an insulin secretagogue that often exhibits considerable interindividual variability in therapeutic efficacy. The current study was designed to investigate the impact of KCNQ1 genetic polymorphism on the efficacy of repaglinide and furthermore to identify the potential mechanism of action in patients with type 2 diabetes. A total of 305 patients and 200 healthy subjects were genotyped for the KCNQ1 rs2237892 polymorphism, and 82 patients with T2DM were randomized for the oral administration of repaglinide for 8 weeks. HepG2 cells were incubated with repaglinide in the absence or presence of a KCNQ1 inhibitor or the pcDNA3.1-hKCNQ1 plasmid, after which the levels of Akt, IRS-2 and PI(3)K were determined. Our data showed that repaglinide significantly decreased HOMA-IR in patients with T2DM. Furthermore, the level of HOMA-IR was significantly reduced in those patients with CT or TT genotypes than CC homozygotes. The KCNQ1 inhibitor enhanced repaglinide efficacy on insulin resistance, with IRS-2/PI(3)K/Akt signaling being up-regulated markedly. As in our clinical experiment, these data strongly suggest that KCNQ1 genetic polymorphism influences repaglinide response due to the pivotal role of KCNQ1 in regulating insulin resistance through the IRS-2/PI(3)K/Akt signaling pathway. This study was registered in the Chinese Clinical Trial Register on May 14, 2013. (No. ChiCTR-CCC13003536).

Association of type 2 diabetes susceptibility loci with peripheral nerve function in a Chinese population with diabetes

Aims/Introduction

Previous studies have suggested a possible relationship between type 2 diabetes mellitus susceptibility loci and diabetic complications. The present study aimed to investigate the associations between type 2 diabetes mellitus loci with peripheral nerve function in a Chinese population with type 2 diabetes mellitus.

Materials and Methods

A total of 1,900 type 2 diabetes mellitus patients were recruited in the study. We selected ten single nucleotide polymorphisms (SNPs) from ten type 2 diabetes mellitus susceptibility genes previously confirmed in Chinese patients. Genotyping was carried out by using a MassARRAY Compact Analyzer. Peripheral nerve function was evaluated by nerve conduction studies in all participants. The composite Z‐scores for nerve conduction parameters including conduction velocity (CV), amplitude and latency were calculated, respectively.

Results

Rs5219 of KCNJ11 (E23K, G→A) was identified to be associated with all the parameters obtained from nerve conduction studies (Z‐score of CV: β = 0.113, P = 0.01; Z‐score of amplitude: β = 0.133, P = 0.01; Z‐score of latency: β = −0.116, P = 0.01) after adjustment for covariates including age, duration and glycated hemoglobin. Specifically, each copy of the A allele was related to better outcomes. CDKAL1 rs7756992 and TCF7L2 rs7903146 correlated with the composite Z‐score of amplitude (P = 0.028 and P = 0.016, respectively), but not CV (P = 0.393 and P = 0.281, respectively) or latency (P = 0.286 and P = 0.273, respectively). There were no significant associations between the other seven SNPs and peripheral nerve function.

Conclusions

Rs5219 at KCNJ11 (E23K) was associated with peripheral nerve function in a Chinese population with type 2 diabetes mellitus, suggesting shared genetic factors for type 2 diabetes mellitus and diabetic polyneuropathy in this population.

Type 2 Diabetes Risk Allele UBE2E2 Is Associated With Decreased Glucose-Stimulated Insulin Release in Elderly Chinese Han Individuals

Recently, rs163182 in KCNQ1, rs7612463 in UBE2E2, rs7119 in HMG20A, and rs6815464 in MAEA were discovered as type 2 diabetes (T2D) loci unique to Asians, and rs13342692 in SLC16A11 were newly reported as T2D loci in multiethnicities by genome-wide association (GWA) studies. The aim of the present study is to ascertain the potential associations between these variants and T2D risk in the Chinese population, and characterize diabetic-related quantitative traits underlying these variants.A total of 4268 Chinese Han individuals (1754 patients with T2D and 2514 glucose-tolerant health subjects, age ≥40 years) were genotyped for these 5 variants. All the health individuals underwent an oral glucose tolerance test (OGTT), and measures of insulin release and sensitivity were estimated from insulinogenic, BIGTT, Matsuda, and disposition indices. The associations were determined by using logistic regression analysis.After adjustment for age, sex, and BMI, rs163182 in KCNQ1 (P = 0.002) and rs7612463 in UBE2E2 (P = 0.024) were found to be associated with T2D risk in Chinese Han population. The risk C allele of rs7612463 in UBE2E2 is associated with decreased IGI (P = 0.001), BIGTT-AIR (P = 0.002), CIR (P = 0.002), and DI (P = 0.006). The other 4 variants did not associate with insulin release or sensitivity.UBE2E2 rs7612463 may mediate its diabetogenic impact on insulin response, which highly depends on the impairment of β-cell function.

Association of KCNQ1 polymorphisms with gliclazide efficacy in Chinese type 2 diabetic patients

OBJECTIVES

To investigate the effects of KCNQ1 polymorphisms on the efficacy of gliclazide in type 2 diabetic patients.

MATERIALS AND METHODS

A total of 443 newly diagnosed type 2 diabetic patients were included in this study. After enrollment, patients went on an 8-week gliclazide monotherapy. Fasting plasma glucose (FPG) was measured before and after the treatment. Life-style information was collected by weekly follow-up. Genotyping of the two single-nucleotide polymorphisms was performed using the single base primer extension method. T-test, one-way analysis of variance, and Pearson χ-test were used to evaluate the effects of rs2237892 and rs2237897 on the FPG reduction and treatment success rate.

RESULTS

After 8 weeks of gliclazide therapy, the FPG decreased significantly from 10.9±2.8 to 7.4±2.2 mmol/l (P<0.001). Compared with the CC genotype, patients with CT or TT genotypes of rs2237897 achieved greater reduction in FPG (3.9±2.6 vs. 3.2±2.4 mmol/l, P=0.003; 33.9±19.0 vs. 27.7±17.4%, P<0.001) and a higher rate of treatment success (74.1 vs. 65.2%, P=0.042 for criterion 1; 61.1 vs. 44.5%, P<0.001 for criterion 2, respectively), whereas no significant difference was found in the FPG reduction and treatment success rate among different genotypes of rs2237892.

CONCLUSION

Our results indicated that a common variant of KCNQ1, rs2237897, was associated with the efficacy of gliclazide after 8-week monotherapy in Chinese newly diagnosed type 2 diabetic patients. The FPG reduction and treatment success rate were significantly higher in carriers of CT and TT genotypes.

Joint effects of diabetic-related genomic loci on the therapeutic efficacy of oral anti-diabetic drugs in Chinese type 2 diabetes patients

Previous pharmacogenomic studies of oral anti-diabetic drugs have primarily focused on the effect of a single site. This study aimed to examine the joint effects of multiple loci on repaglinide or rosiglitazone efficacy in newly diagnosed type 2 diabetes mellitus (T2DM) patients. A total of 209 newly diagnosed T2DM patients were randomly assigned to treatment with repaglinide or rosiglitazone for 48 weeks. The reductions in fasting glucose (ΔFPG), 2h glucose (Δ2hPG) and glycated hemoglobin (ΔHbA1c) levels were significantly associated with genetic score that was constructed using the sum of the effect alleles both in the repaglinide (P = 0.0011, 0.0002 and 0.0067, respectively) and rosiglitazone cohorts (P = 0.0002, 0.0014 and 0.0164, respectively) after adjusting for age, gender, body mass index and dosage. Survival analyses showed a trend towards a greater attainment rate of target HbA1c level in individuals with a high genetic score in the repaglinide cohort and rosiglitazone cohort (P_log-rank = 0.0815 and 0.0867, respectively) when the attainment of treatment targets were defined as more than 20% decrease of FPG, 2hPG, and HbA1c levels after treatment. In conclusion, we identified the joint effects of several T2DM-related loci on the efficacy of oral anti-diabetic drugs; moreover, we built a model to predict the drug efficacy.

Variant rs2237892 of KCNQ1 Is Potentially Associated with Hypertension and Macrovascular Complications in Type 2 Diabetes Mellitus in A Chinese Han Population

KCNQ1 has been identified as a susceptibility gene of type 2 diabetes mellitus (T2DM) in Asian populations through genome-wide association studies. However, studies on the association between gene polymorphism of KCNQ1 and T2DM complications remain unclear. To further analyze the association between different alleles at the single nucleotide polymorphism (SNP) rs2237892 within KCNQ1 and TD2M and its complications, we conducted a case-control study in a Chinese Han population. The C allele of rs2237892 variant contributed to susceptibility to T2DM (odds ratio [OR], 1.45; 95% confidence interval [CI], 1.20-1.75). Genotypes CT (OR, 1.97; 95% CI, 1.24-3.15) and CC (OR, 2.49; 95% CI, 1.57-3.95) were associated with an increased risk of T2DM. Multivariate regression analysis was performed with adjustment of age, gender, and body mass index. We found that systolic blood pressure (P=0.015), prevalence of hypertension (P=0.037), and risk of macrovascular disease (OR, 2.10; CI, 1.00-4.45) were significantly higher in subjects with the CC genotype than in the combined population with genotype either CT or TT. Therefore, our data support that KCNQ1 is associated with an increased risk for T2DM and might contribute to the higher incidence of hypertension and macrovascular complications in patients with T2DM carrying the risk allele C though it needs further to be confirmed in a larger population.

Association Between KCNQ1 Genetic Variants and Type 2 Diabetes in the Uyghur Population

OBJECTIVE

To investigate the association between KCNQ1 gene polymorphisms and type 2 diabetes (T2D) in an admixed ethnic minority, Uyghur population, living in the Northwest region of China.

MATERIALS AND METHODS

We genotyped three tagging single-nucleotide polymorphisms rs2283171, rs11023485, and rs2283208 of the KCNQ1 gene in 1006 T2D participants and 1004 controls and conducted association analysis.

RESULTS

The frequencies of the AG and GG genotypes and the G allele of rs2283171 were higher in the control group (51.4%, 22%, and 47.7%, respectively) than in the case group (49%, 17.6%, and 42.1%, respectively). The minor G allele decreased the risk of T2D with a per-allele odds ratio of 0.79 (95% CI: 0.70-0.90) for the additive genetic model in univariate analysis (p = 0.0001). After adjustment for the covariates of age, gender, smoking, alcohol use, systolic blood pressure (SBP), diastolic blood pressure (DBP), body mass index (BMI), triglyceride (TG), and total cholesterol (TC), the diabetic protective effect of the rs2283171-G allele remained. No difference was observed in the frequency distributions of the rs11023485 and rs2283208 genotypes between the two groups.

CONCLUSION

We identified a novel association between rs2283171 of KCNQ1 and T2D in the Uyghur population. Further association and functional studies are required to identify the causal functional variant that is in linkage disequilibrium with this polymorphism.

Role of high-risk variants in the development of impaired glucose metabolism was modified by birth weight in Han Chinese

BACKGROUND

The aim of this study was to investigate the role of common variants in the genes SLC30A8, KCNQ1, and TCF7L2 in the association between birth weight and increased risk of type 2 diabetes in Han Chinese.

METHODS

Seven variants (SLC30A8-rs13266634 and rs2466293; KCNQ1-rs2237895 and rs2074196; and TCF7L2-rs11196218, rs7903146, and rs290487) were genotyped in 1181 individuals born in Peking Union Medical College Hospital from 1921 to 1954 by Taqman allelic discrimination assay. All the subjects were stratified by birth weight into groups of ≥3000 g and <3000 g. Associations of genetic variants with birth weight and with risk of type 2 diabetes and impaired glucose tolerance (together as impaired glucose metabolism) were analysed.

RESULTS

After adjustment for sex, gestational weeks, parity, and maternal age, the G allele of KCNQ1-rs2074196 was associated with higher birth weight (p = 0.032). KCNQ1-rs2074196, rs2234895, and TCF7L2-rs290487 were associated with increased risk of impaired glucose metabolism. However, the associations were modified by size at birth. The associations above were only found in subjects with birth weights greater than (or equal to) 3000 g. In subjects with birth weights less than 3000 g, impaired glucose metabolism was associated with variants SLC30A8-rs2466293 and TCF7L2-rs11196218.

CONCLUSIONS

The role of common variants in susceptible genes in the development of impaired glucose metabolism was modified by birth weight in Han Chinese. This provides evidence that genetic variants influence birth weight and are involved in development of type 2 diabetes.

TOX and CDKN2A/B Gene Polymorphisms Are Associated with Type 2 Diabetes in Han Chinese

To study associations between type 2 diabetes (T2DM) candidate genes and microvascular complications of diabetes (MVCDs), we performed case-control association studies for both T2DM and MVCDs in Han Chinese subjects. We recruited 1,939 unrelated Han Chinese T2DM patients and 918 individuals with normal blood glucose levels as nondiabetic controls. Among T2DM patients, 1116 have MVCDs, 266 have a history of T2DM of >10 years but never developed MVCDs. Eighty-two single-nucleotide polymorphisms (SNPs) in 54 candidate genes were genotyped. Discrete association studies were performed by the PLINK program for T2DM and MVCDs. Significant associations were found among candidate gene SNPs and T2DM, including rs1526167 of the TOX gene (allele A, P = 2.85 × 10⁻⁹, OR = 1.44). The SNP rs10811661 of the CDKN2A/B gene was also associated with T2DM (allele T, P = 4.09 × 10⁻⁷, OR = 1.36). When we used control patients with >10 years of T2DM history without MVCD, we found that the G allele of SNP rs1526167 of the TOX gene was associated with MVCD (nominal P = 4.33 × 10⁻⁴). In our study, significant associations were found between TOX and CDKN2A/B gene SNPs and T2DM. The TOX polymorphism might account for the higher risk of T2DM and the lower risk of MVCDs in the Han Chinese population.

Paternal allelic mutation at the Kcnq1 locus reduces pancreatic β-cell mass by epigenetic modification of Cdkn1c

Genetic factors are important determinants of the onset and progression of diabetes mellitus. Numerous susceptibility genes for type 2 diabetes, including potassium voltage-gated channel, KQT-like subfamily Q, member1 (KCNQ1), have been identified in humans by genome-wide analyses and other studies. Experiments with genetically modified mice have also implicated various genes in the pathogenesis of diabetes. However, the possible effects of the parent of origin for diabetes susceptibility alleles on disease onset have remained unclear. Here, we show that a mutation at the Kcnq1 locus reduces pancreatic β-cell mass in mice by epigenetic modulation only when it is inherited from the father. The noncoding RNA KCNQ1 overlapping transcript1 (Kcnq1ot1) is expressed from the Kcnq1 locus and regulates the expression of neighboring genes on the paternal allele. We found that disruption of Kcnq1 results in reduced Kcnq1ot1 expression as well as the increased expression of cyclin-dependent kinase inhibitor 1C (Cdkn1c), an imprinted gene that encodes a cell cycle inhibitor, only when the mutation is on the paternal allele. Furthermore, histone modification at the Cdkn1c promoter region in pancreatic islets was found to contribute to this phenomenon. Our observations suggest that the Kcnq1 genomic region directly regulates pancreatic β-cell mass and that genomic imprinting may be a determinant of the onset of diabetes mellitus.

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.

Effect of body mass index on insulin secretion or sensitivity and diabetes

BACKGROUND

Although the association between obesity and diabetes is well known, the factors predisposing to diabetes in non-obese Asians are less clearly characterized.

PURPOSE

To investigate the effects of impaired insulin secretion (IIS) and insulin resistance (IR) according to BMI on the incidence of diabetes in the Saku Study.

METHODS

This 4-year cohort study involved 3,083 participants aged 30-69 years without diabetes at baseline (2006-2007). Participants were stratified by BMI (<23.0, 23.0-24.9, and ≥25). Based on insulinogenic index and homeostasis model of IR values, participants were classified into four categories: normal; isolated IIS (i-IIS); isolated IR (i-IR); and IIS plus IR. All data were collected in 2006-2011 and analyzed in 2013-2014.

RESULTS

For participants with BMI <23.0, the risk of developing diabetes was higher in the i-IIS (adjusted hazard ratio=6.6; 95% CI=3.7, 11.6) and IIS plus IR groups (9.4; 3.1, 28.4) than in the normal group. For participants with BMI 23.0-24.9, risk was higher in the i-IIS (9.9; 4.4, 22.1); i-IR (3.4; 1.2, 9.5); and IIS plus IR (23.4; 9.3, 58.9) groups. Among participants with BMI ≥25, risk was higher in the i-IIS (16.9; 6.0, 47.7); i-IR (7.9; 2.8, 22.6); and IIS plus IR (26.9; 9.0, 80.8) groups. BMI was negatively associated with incidence of IIS but positively associated with IR incidence.

CONCLUSIONS

Individuals with normal BMI may develop diabetes mainly through IIS, whereas individuals with high BMI may develop diabetes primarily through IR.

Cumulative effect and predictive value of genetic variants associated with type 2 diabetes in Han Chinese: a case-control study

Background

Genome-wide association studies (GWAS) have identified dozens of single nucleotide polymorphisms (SNPs) associated with type 2 diabetes risk. We have previously confirmed the associations of genetic variants in HHEX, CDKAL1, VEGFA and FTO with type 2 diabetes in Han Chinese. However, the cumulative effect and predictive value of these GWAS identified SNPs on the risk of type 2 diabetes in Han Chinese are largely unknown.

Methodology/Principal Findings

We conducted a two-stage case-control study consisting of 2,925 cases and 3,281controls to examine the association of 30 SNPs identified by GWAS with type 2 diabetes in Han Chinese. Significant associations were found for proxy SNPs at KCNQ1 [odds ratio (OR) = 1.41, P = 9.91 × 10–16 for rs2237897], CDKN2A/CDKN2B (OR = 1.30, P = 1.34 × 10–10 for rs10811661), CENTD2 (OR = 1.28, P = 9.88 × 10-4 for rs1552224) and SLC30A8 (OR = 1.19, P = 1.43 × 10-5 for rs13266634). We further evaluated the cumulative effect on type 2 diabetes of these 4 SNPs, in combination with 5 SNPs at HHEX, CDKAL1, VEGFA and FTO reported previously. Individuals carrying 12 or more risk alleles had a nearly 4-fold increased risk for developing type 2 diabetes compared with those carrying less than 6 risk alleles [adjusted OR = 3.68, 95% confidence interval (CI): 2.76–4.91]. Adding the genetic factors to clinical factors slightly improved the prediction of type 2 diabetes, with the area under the receiver operating characteristic curve increasing from 0.76 to 0.78. However, the difference was statistically significant (P < 0.0001).

Conclusions/Significance

We confirmed associations of SNPs in KCNQ1, CDKN2A/CDKN2B, CENTD2 and SLC30A8 with type 2 diabetes in Han Chinese. The utilization of genetic information may improve the accuracy of risk prediction in combination with clinical characteristics for type 2 diabetes.

Pharmacogenomics of glinides

Glinides, including repaglinide, nateglinide and mitiglinide, are a type of fasting insulin secretagogue that could help to mimic early-phase insulin release, thus providing improved control of the postprandial glucose levels. Glinides stimulate insulin secretion by inhibiting ATP-sensitive potassium channels in the pancreatic β-cell membrane. Although glinides have been widely used clinically and display excellent safety and efficacy, the response to glinides varies among individuals, which is partially due to genetic factors involved in drug absorption, distribution, metabolism and targeting. Several pharmacogenomic studies have demonstrated that variants of genes involved in the pharmacokinetics or pharmacodynamics of glinides are associated with the drug response. Polymorphisms of genes involved in drug metabolism, such as CYP2C9, CYP2C8 and SLCO1B1, may influence the efficacy of glinides and the incidence of adverse effects. In addition, Type 2 diabetes mellitus susceptibility genes, such as KCNQ1, PAX4 and BETA2, also influence the efficacy of glinides. In this article, we review and discuss current pharmacogenomics researches on glinides, and hopefully provide useful data and proof for clinical application.

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.

Increase in homeostasis model assessment of insulin resistance (HOMA-IR) had a strong impact on the development of type 2 diabetes in Japanese individuals with impaired insulin secretion: the Saku study

Our aim was to assess the impact of increase in homeostasis model assessment of insulin resistance (HOMA-IR) on the development of type 2 diabetes in Japanese individuals with impaired insulin secretion (IIS). This study included 2,209 participants aged 30–69 without diabetes at baseline who underwent comprehensive medical check-ups between April 2006 and March 2007 at Saku Central Hospital. Participants were classified into eight groups according to the combination of baseline IIS status (non-IIS and IIS) and category of HOMA-IR change between the baseline and follow-up examinations (decrease, no change/small increase, moderate increase, and large increase). Type 2 diabetes was determined from fasting and 2 h post-load plasma glucose concentrations at the follow-up examination between April 2009 and March 2011. At baseline, 669 individuals (30.3%) were classified as having IIS. At follow-up, 74 individuals developed type 2 diabetes. After adjusting for confounding factors including baseline HOMA-IR values, the multivariable-adjusted odds ratios (95% confidence intervals) for type 2 diabetes in the non-IIS with a decrease (mean change in HOMA-IR: −0.47), non-IIS with a moderate increase (mean change in HOMA-IR: 0.28), non-IIS with a large increase (mean change in HOMA-IR: 0.83), IIS with a decrease (mean change in HOMA-IR: −0.36), IIS with no change/small increase (mean change in HOMA-IR: 0.08), IIS with a moderate increase (mean change in HOMA-IR: 0.27), and IIS with a large increase (mean change in HOMA-IR: 0.73) groups, relative to the non-IIS with no change/small increase (mean change in HOMA-IR: 0.08) group were 0.23 (0.04, 1.11), 1.22 (0.26, 5.72), 2.01 (0.70, 6.46), 1.37 (0.32, 4.28), 3.60 (0.83, 15.57), 5.24 (1.34, 20.52), and 7.01 (1.75, 24.18), respectively. Moderate and large increases in HOMA-IR had a strong impact on the development of type 2 diabetes among individuals with IIS in this Japanese population.

Genetic association study with metabolic syndrome and metabolic-related traits in a cross-sectional sample and a 10-year longitudinal sample of chinese elderly population

Background

The metabolic syndrome (MetS) has been known as partly heritable, while the number of genetic studies on MetS and metabolic-related traits among Chinese elderly was limited.

Methods

A cross-sectional analysis was performed among 2 014 aged participants from September 2009 to June 2010 in Beijing, China. An additional longitudinal study was carried out among the same study population from 2001 to 2010. Biochemical profile and anthropometric parameters of all the participants were measured. The associations of 23 SNPs located within 17 candidate genes (MTHFR, PPARγ, LPL, INSIG, TCF7L2, FTO, KCNJ11, JAZF1, CDKN2A/B, ADIPOQ, WFS1, CDKAL1, IGF2BP2, KCNQ1, MTNR1B, IRS1, ACE) with overweight and obesity, diabetes, metabolic phenotypes, and MetS were examined in both studies.

Results

In this Chinese elderly population, prevalence of overweight, central obesity, diabetes, dyslipidemia, hypertension, and MetS were 48.3%, 71.0%, 32.4%, 75.7%, 68.3% and 54.5%, respectively. In the cross-sectional analyses, no SNP was found to be associated with MetS. Genotype TT of SNP rs4402960 within the gene IGF2BP2 was associated with overweight (odds ratio (OR)  = 0.479, 95% confidence interval (CI): 0.316-0.724, p = 0.001) and genotype CA of SNP rs1801131 within the gene MTHFR was associated with hypertension (OR = 1.560, 95% CI: 1.194–2.240, p = 0.001). However, these associations were not observed in the longitudinal analyses.

Conclusions

The associations of SNP rs4402960 with overweight as well as the association of SNP rs1801131 with hypertension were found to be statistically significant. No SNP was identified to be associated with MetS in our study with statistical significance.

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.

KCNQ1 rs2237892 C→T gene polymorphism and type 2 diabetes mellitus in the Asian population: a meta-analysis of 15,736 patients

The KCNQ1 rs2237892 C→T gene polymorphism is reportedly associated with T2DM susceptibility, but various studies show conflicting results. To explore this association in the Asian population, a meta-analysis of 15,736 patients from 10 individual studies was performed. The pooled odds ratios (ORs) and their 95% confidence intervals (CIs) were evaluated using random-effect or fixed-effect models. A significant relationship between the KCNQ1 rs2237892 C→T gene polymorphism and T2DM was observed in the Asian population under the allelic (OR, 1.350; 95% CI, 1.240-1.480; P < 0.00001), recessive (OR: 0.650; 95% CI: 0.570-0.730; P < 0.00001), dominant (OR: 1.450; 95% CI: 1.286-1.634; P < 0.00001), and additive (OR: 1.346; 95% CI: 1.275-1.422; P < 0.00001) genetic models. In the subgroup analysis by race, a significant association was found in Chinese, Korean and Malaysia population, but not in Indian population. KCNQ1 rs2237892 C→T gene polymorphism was found to be significantly associated with increased T2DM risk in the Asian population, except Indian population. The C allele of the KCNQ1 rs2237892 C→T gene polymorphism may confer susceptibility to T2DM.

Association between KCNQ1 genetic variants and QT interval in a Chinese population

AIM

There is a close link between electrocardiographic ventricular repolarization QT parameters and Type 2 diabetes. The aim of the present study was to assess the effects of QT-related and diabetes-related variants in KCNQ1 on QT interval in a Chinese population.

METHODS

We recruited 2415 patients with Type 2 diabetes and 1163 subjects with normal glucose regulation in the present study. QT interval was obtained and the heart rate-corrected QT interval (QTc) was calculated using Bazett's formula. Four single nucleotide polymorphisms in KCNQ1 were selected (rs12296050, rs12576239, rs2237892 and rs2237895) and genotyped.

RESULTS

In participants with normal glucose regulation, the minor allele T of rs12296050 was associated with a 3.46-ms QTc prolongation under an additive model (P = 0.0109, empirical P = 0.0498). In patients with Type 2 diabetes, we did not find any association for the single nucleotide polymorphisms.

CONCLUSIONS

Our findings indicate that KCNQ1 is associated with QT interval in a Chinese population with normal glucose regulation.

Association of genetic variants with isolated fasting hyperglycaemia and isolated postprandial hyperglycaemia in a Han Chinese population

BACKGROUND

Though multiple single nucleotide polymorphisms (SNPs) associated with type 2 diabetes have been identified, the genetic bases of isolated fasting hyperglycaemia (IFH) and isolated postprandial hyperglycaemia (IPH) were still unclear. In present study, we aimed to investigate the association of genome-wide association study-validated genetic variants and IFH or IPH in Han Chinese.

METHODS/PRINCIPAL FINDINGS

We genotyped 27 validated SNPs in 6,663 unrelated individuals comprising 341 IFH, 865 IPH, 1,203 combined fasting hyperglycaemia and postprandial hyperglycaemia, and 4,254 normal glycaemic subjects of Han ancestry. The distributions of genotype frequencies of FTO, CDKAL1 and GCKR were significant different between individuals with IFH and those with IPH (SNP(ptrend ): rs8050136(0.0024), rs9939609(0.0049), rs7756992(0.0122), rs780094(0.0037)). Risk allele of FTO specifically increased the risk of IFH (rs8050136: OR 1.403 [95% CI 1.125-1.750], p = 0.0027; rs9939609: 1.398 [1.120-1.744], p = 0.0030). G allele of CDKAL1 specifically increased the risk of IPH (1.217 [1.092-1.355], p = 0.0004). G allele of GCKR increased the risk of IFH (1.167 [0.999-1.362], p = 0.0513), but decreased the risk of IPH (0.891 [0.801-0.991], p = 0.0331). In addition, TCF7L2 and KCNQ1 increased the risk of both IFH and IPH. When combined, each additional risk allele associated with IFH increased the risk for IFH by 1.246-fold (p<0.0001), while each additional risk allele associated with IPH increased the risk for IPH by 1.190-fold (p<0.0001).

CONCLUSION/SIGNIFICANCE

Our results indicate that genotype distributions of variants from FTO, GCKR, CDKAL1 were different between IPH and IFH in Han Chinese. Variants of genes modulating insulin sensitivity (FTO, GCKR) contributed to the risk of IFH, while variants of genes related to beta cell function (CDKAL1) increase the risk of IPH.

Impact of impaired insulin secretion and insulin resistance on the incidence of type 2 diabetes mellitus in a Japanese population: the Saku study

AIMS/HYPOTHESIS

To assess the impact of impaired insulin secretion (IIS) and insulin resistance (IR) on type 2 diabetes incidence in a Japanese population.

METHODS

This 4 year cohort study included 3,059 participants aged 30-69 without diabetes at baseline who underwent comprehensive medical check-ups between April 2006 and March 2007 at Saku Central Hospital. Based on their insulinogenic index and HOMA-IR values, participants were classified by the criteria of the Japan Diabetes Society into four categories: normal; isolated IIS (i-IIS); isolated IR (i-IR); and IIS plus IR. They were followed up until March 2011. The incidence of type 2 diabetes was determined from fasting and 2 h post-load plasma glucose concentrations and from receiving medical treatment for diabetes.

RESULTS

At baseline, 1,550 individuals (50.7%) were classified as normal, 900 (29.4%) i-IIS, 505 (16.5%) i-IR, and 104 (3.4%) IIS plus IR. During 10,553 person-years of follow-up, 219 individuals developed type 2 diabetes, with 126 (57.5%) having i-IIS at baseline. Relative to the normal group, the multivariable-adjusted HRs for type 2 diabetes in the i-IIS, i-IR and IIS plus IR groups were 8.27 (95% CI 5.33, 12.83), 4.90 (95% CI 2.94, 8.17) and 16.93 (95% CI 9.80, 29.25), respectively. The population-attributable fractions of type 2 diabetes onset due to i-IIS, i-IR, and IIS plus IR were 50.6% (95% CI 46.7%, 53.0%), 14.2% (95% CI 11.8%, 15.6%) and 12.9% (95% CI 12.3%, 13.2%), respectively.

CONCLUSIONS/INTERPRETATION

Compared with IR, IIS had a greater impact on the incidence of type 2 diabetes in a Japanese population.

Strong parent-of-origin effects in the association of KCNQ1 variants with type 2 diabetes in American Indians

Parent-of-origin effects were observed in an Icelandic population for several genetic variants associated with type 2 diabetes, including those in KLF14 (rs4731702), MOB2 (rs2334499), and KCNQ1 (rs2237892, rs231362). We analyzed parent-of-origin effects for these variants, along with two others in KCNQ1 identified in previous genome-wide association studies (rs2237895, rs2299620), in 7,351 Pima Indians from 4,549 nuclear families; 34% of participants had diabetes. In a subset of 287 normoglycemic individuals, acute insulin secretion was measured by an intravenous glucose tolerance test. Statistically significant (P < 0.05) parent-of-origin effects were seen for association with type 2 diabetes for all variants. The strongest effect was seen at rs2299620 in KCNQ1; the C allele was associated with increased diabetes when maternally derived (odds ratio [OR], 1.92; P = 4.1 × 10(-12)), but not when paternally derived (OR, 0.93; P = 0.47; P = 9.9 × 10(-6) for difference in maternal and paternal effects). A maternally derived C allele also was associated with a 28% decrease in insulin secretion (P = 0.002). This study confirms parent-of-origin effects in the association with type 2 diabetes for variants in KLF14, MOB2, and KCNQ1. In Pima Indians, the effect of maternally derived KCNQ1 variants appears to be mediated through decreased insulin secretion and is particularly strong, accounting for 4% of the variance in liability to diabetes.

Common variants in KCNQ1 confer increased risk of type 2 diabetes and contribute to the diabetic epidemic in East Asians: a replication and meta-analysis

We aimed to evaluate the effect of four common variants (rs2237892, rs2283228, rs2237895, and rs2237897) in KCNQ1 on susceptibility of type 2 diabetes (T2D) by performing a case-control study as well as a comprehensive meta-analysis. We genotyped these four variants in two sets of Chinese Han population, comprising a total of 2533 type 2 diabetic patients and 2643 nondiabetic controls. We also performed a meta-analysis of our results with published studies in East Asians, meanwhile assessing the population attributable risk (PAR) of these variants. By combining our case-control sets, a total of 45,204 T2D cases and 42,832 controls were included in the meta-analyses. The per-allele ORs ranged from 1.24 to 1.33, and the PARs ranged from 15.8% to 31.8%, with SNP rs2237892 being the most widely studied (16 articles containing a total of 38,338 cases and 35,907 controls), showing strongest association (per-allele OR: 1.33, 95% CI: 1.28-1.39) and indicating the highest PAR (31.8%). This study confirmed the strong association between common variants in KCNQ1 and risk of T2D. Variants in KCNQ1 were among the leading genetic factors contributing to the overall burden of T2D in East Asians.

Association study of genetic variants of 17 diabetes-related genes/loci and cardiovascular risk and diabetic nephropathy in the Chinese She population

BACKGROUND

Genetic determinations are important in type 2 diabetes (T2DM) pathology. We investigated associations between genetic variants of 17 diabetes-related genes/loci, T2DM and diabetic complications in Chinese She subjects.

METHODS

A comprehensive gene-based association study was conducted using 17 single nucleotide polymorphisms in Chinese She subjects with normal glucose tolerance (n = 1119), impaired glucose regulation (n = 1767), and T2DM (n = 443). We applied major abnormal Minnesota Code findings to predict cardiovascular risk and estimated glomerular filtration rate to assess kidney function.

RESULTS

Nine variants in FTO rs8050136, WFS1 rs10010131, CDKN2A/B rs10811661, KCNJ11 rs5219, CDC123/CAMK1D rs12779790, JAZF1 rs864745, SLC30A8 rs13266634, CDKAL1 rs10946398, and HHEX/IDE rs5015480 were significantly associated with T2DM (P < 0.05). Single nucleotide polymorphisms in WFS1 rs10010131, CDKN2A/B rs10811661, CDC123/CAMK1D rs12779790, JAZF1 rs864745, FTO rs8050136, and HHEX/IDE rs5015480 were associated with T2DM and impaired glucose regulation. Risk alleles in WFS1 rs10010131, IGF2BP2 rs4402960, CDKAL1 rs10946398, FTO rs8050136, KCNQ1 rs2237897, and ADAMTS9 rs4607103 were significantly associated with decreased homeostatic model assessment (HOMA)-β (P < 0.05). After adjusting for age, gender and body mass index, genetic variants JAZF1 rs864745, FTO rs8050136, and HHEX/IDE rs5015480 were significantly related to reduced estimated glomerular filtration rate (P < 0.05). Genetic variants in WFS1 rs10010131, CDKN2A/B rs10811661, CDC123/CAMID rs12779790, JAZF1 rs864745, FTO rs80501360, CDKAL1 rs10946398, and HHEX/IDE rs5015480 correlated with abnormal major Minnesota Code findings (P < 0.05).

CONCLUSION

Variants in WFS1, CDKN2A/B, KCNJ11, CDC123/CAMK1D, JAZF1, SLC30A8, FTO, CDKAL1, and HHEX/IDE genes are significantly associated with T2DM in She Chinese subjects. JAZF1, FTO, CDKAL1, and HHEX/IDE are associated with diabetic nephropathy. WFS1, CDKN2A/B, CDC123/CAMK1D, JAZF1, FTO, CDKAL1, and HHEX/IDE are associated with cardiovascular risk.

Genome-wide association study in a Chinese population identifies a susceptibility locus for type 2 diabetes at 7q32 near PAX4

AIMS/HYPOTHESIS

Most genetic variants identified for type 2 diabetes have been discovered in European populations. We performed genome-wide association studies (GWAS) in a Chinese population with the aim of identifying novel variants for type 2 diabetes in Asians.

METHODS

We performed a meta-analysis of three GWAS comprising 684 patients with type 2 diabetes and 955 controls of Southern Han Chinese descent. We followed up the top signals in two independent Southern Han Chinese cohorts (totalling 10,383 cases and 6,974 controls), and performed in silico replication in multiple populations.

RESULTS

We identified CDKN2A/B and four novel type 2 diabetes association signals with p < 1 × 10(-5) from the meta-analysis. Thirteen variants within these four loci were followed up in two independent Chinese cohorts, and rs10229583 at 7q32 was found to be associated with type 2 diabetes in a combined analysis of 11,067 cases and 7,929 controls (p meta = 2.6 × 10(-8); OR [95% CI] 1.18 [1.11, 1.25]). In silico replication revealed consistent associations across multiethnic groups, including five East Asian populations (p meta = 2.3 × 10(-10)) and a population of European descent (p = 8.6 × 10(-3)). The rs10229583 risk variant was associated with elevated fasting plasma glucose, impaired beta cell function in controls, and an earlier age at diagnosis for the cases. The novel variant lies within an islet-selective cluster of open regulatory elements. There was significant heterogeneity of effect between Han Chinese and individuals of European descent, Malaysians and Indians.

CONCLUSIONS/INTERPRETATION

Our study identifies rs10229583 near PAX4 as a novel locus for type 2 diabetes in Chinese and other populations and provides new insights into the pathogenesis of type 2 diabetes.