Genetics of type 2 diabetes mellitus: status and perspectives

Impaired postprandial adipose tissue microvascular blood flow responses to a mixed-nutrient meal in first-degree relatives of adults with type 2 diabetes

Adipose tissue microvascular blood flow (MBF) is stimulated postprandially to augment delivery of nutrients and hormones to adipocytes. Adipose tissue MBF is impaired in type 2 diabetes (T2D). Whether healthy individuals at-risk of T2D show similar impairments is unknown. We aimed to determine whether adipose tissue MBF is impaired in apparently healthy individuals with a family history of T2D. Overnight-fasted individuals with no family history of T2D for two generations (FH-, n = 13), with at least one parent with T2D (FH+, n = 14) and clinically diagnosed T2D (n = 11) underwent a mixed meal challenge (MMC). Metabolic responses [blood glucose, plasma insulin, plasma nonesterified fatty acids (NEFAs), and fat oxidation] were measured before and during the MMC. MBF in truncal subcutaneous adipose tissue was assessed by contrast ultrasound while fasting and 60 min post-MMC. FH+ had normal blood glucoses, increased adiposity, and impaired post-MMC adipose tissue MBF (Δ0.70 ± 0.22 vs. 2.45 ± 0.60 acoustic intensity/s, P = 0.007) and post-MMC adipose tissue insulin resistance (Adipo-IR index; Δ45.5 ± 13.9 vs. 7.8 ± 5.1 mmol/L × pmol/L, P = 0.007) compared with FH-. FH+ and T2D had an impaired ability to suppress fat oxidation post-MMC. Fat oxidation incremental area under the curve (iAUC) (35-55 min post-MMC, iAUC) was higher in FH+ and T2D than in FH- (P = 0.005 and 0.009, respectively). Postprandial MBF was negatively associated with postprandial fat oxidation iAUC (P = 0.01). We conclude that apparently healthy FH+ individuals display blunted postprandial adipose tissue MBF that occurs in parallel with adipose tissue insulin resistance and impaired suppression of fat oxidation, which may help explain their heightened risk for developing T2D.NEW & NOTEWORTHY Adipose tissue blood flow plays a key role in postprandial nutrient storage. People at-risk of type 2 diabetes have impaired postmeal adipose tissue blood flow. Impaired adipose tissue blood flow is associated with altered fat oxidation. Risk of type 2 diabetes may be elevated by poor adipose tissue blood flow.

Circulating glucose levels inversely correlate with Drosophila larval feeding through insulin signaling and SLC5A11

In mammals, blood glucose levels likely play a role in appetite regulation yet the mechanisms underlying this phenomenon remain opaque. Mechanisms can often be explored from Drosophila genetic approaches. To determine if circulating sugars might be involved in Drosophila feeding behaviors, we scored hemolymph glucose and trehalose, and food ingestion in larvae subjected to various diets, genetic mutations, or RNAi. We found that larvae with glucose elevations, hyperglycemia, have an aversion to feeding; however, trehalose levels do not track with feeding behavior. We further discovered that insulins and SLC5A11 may participate in glucose-regulated feeding. To see if food aversion might be an appropriate screening method for hyperglycemia candidates, we developed a food aversion screen to score larvae with abnormal feeding for glucose. We found that many feeding defective larvae have glucose elevations. These findings highlight intriguing roles for glucose in fly biology as a potential cue and regulator of appetite.

Rupali Ugrankar et al. show that Drosophila larvae with high levels of circulating glucose, but not trehalose, don’t eat much. This study suggests that circulating glucose communicates with insulin signaling and the sodium/solute co-transporter SLC5A11 in the brain to suppress larval appetite.

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.

Drosophila glucome screening identifies Ck1alpha as a regulator of mammalian glucose metabolism

Circulating carbohydrates are an essential energy source, perturbations in which are pathognomonic of various diseases, diabetes being the most prevalent. Yet many of the genes underlying diabetes and its characteristic hyperglycaemia remain elusive. Here we use physiological and genetic interrogations in D. melanogaster to uncover the ‘glucome', the complete set of genes involved in glucose regulation in flies. Partial genomic screens of ∼1,000 genes yield ∼160 hyperglycaemia ‘flyabetes' candidates that we classify using fat body- and muscle-specific knockdown and biochemical assays. The results highlight the minor glucose fraction as a physiological indicator of metabolism in Drosophila. The hits uncovered in our screen may have conserved functions in mammalian glucose homeostasis, as heterozygous and homozygous mutants of Ck1alpha in the murine adipose lineage, develop diabetes. Our findings demonstrate that glucose has a role in fly biology and that genetic screenings carried out in flies may increase our understanding of mammalian pathophysiology.

Diabetes is associated with aberrations in glucose metabolism. Here the authors perform a genomic screen in fruit flies to identify new regulators of fly glucose metabolism, and show that mice lacking the murine homologue of one of their hits, the protein kinase CK1alpha, in the adipose lineage develop diabetes.

Genetic Associations of PPARGC1A with Type 2 Diabetes: Differences among Populations with African Origins

The aim of this study was to assess the differences in correlation of PPARGC1A polymorphisms with type 2 diabetes (T2D) risk in adults of African origins: African Americans and Haitian Americans. The case-control study consisted of >30 years old, self-identified Haitian Americans (n = 110 cases and n = 116 controls) and African Americans (n = 124 cases and n = 122 controls) living in South Florida with and without T2D. Adjusted logistic regression indicated that both SNP rs7656250 (OR = 0.22, P = 0.005) and rs4235308 (OR = 0.42, P = 0.026) showed protective association with T2D in Haitian Americans. In African Americans, however, rs4235308 showed significant risk association with T2D (OR = 2.53, P = 0.028). After stratification with sex, in Haitian Americans, both rs4235308 (OR = 0.38, P = 0.026) and rs7656250 (OR = 0.23, P = 0.006) showed protective association with T2D in females whereas in African American males rs7656250 had statistically significant protective effect on T2D (OR = 0.37, P = 0.043). The trends observed for genetic association of PPARGC1A SNPs, rs4235308, and rs7656250 for T2D between Haitian Americans and African Americans point out differences in Black race and warrant replicative study with larger sample size.

Nutrigenetics and nutrigenomics insights into diabetes etiopathogenesis

Diabetes mellitus (DM) is considered a global pandemic, and the incidence of DM continues to grow worldwide. Nutrients and dietary patterns are central issues in the prevention, development and treatment of this disease. The pathogenesis of DM is not completely understood, but nutrient-gene interactions at different levels, genetic predisposition and dietary factors appear to be involved. Nutritional genomics studies generally focus on dietary patterns according to genetic variations, the role of gene-nutrient interactions, gene-diet-phenotype interactions and epigenetic modifications caused by nutrients; these studies will facilitate an understanding of the early molecular events that occur in DM and will contribute to the identification of better biomarkers and diagnostics tools. In particular, this approach will help to develop tailored diets that maximize the use of nutrients and other functional ingredients present in food, which will aid in the prevention and delay of DM and its complications. This review discusses the current state of nutrigenetics, nutrigenomics and epigenomics research on DM. Here, we provide an overview of the role of gene variants and nutrient interactions, the importance of nutrients and dietary patterns on gene expression, how epigenetic changes and micro RNAs (miRNAs) can alter cellular signaling in response to nutrients and the dietary interventions that may help to prevent the onset of DM.

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.

Peroxisome proliferator-activated receptor delta (PPARD) genetic variation and type 2 diabetes in middle-aged Chinese women

Animal studies have shown that the peroxime proliferator-activated receptor delta (PPARD) gene regulates glucose metabolism and insulin sensitivity. Genetic variation in the PPARD gene might affect physical endurance and has been associated with obesity. We investigated the independent and modifying effect of variants in the PPARD gene with exercise participation and body mass index (BMI) on type 2 diabetes (T2D), using data from a genome-wide association study (GWAS) of middle-aged women living in Shanghai, China, with 1019 T2D cases and 1709 controls. The genotyping was performed using the Affymetrix Genome-Wide Human SNP Array 6.0 platform. Imputation was used to determine missing genotypes. Participation in exercise was assessed by a questionnaire. Anthropometric variables were measured by trained interviewers. The association between polymorphisms and T2D was assessed by logistic regression analyses. The combined effects of polymorphisms in the PPARD gene with exercise participation and BMI on T2D risk was assessed by conducting stratified analysis with exercise participation and BMI categories. No significant associations between PPARD and T2D were found in either genotyped or imputed SNPs and no effect modification between exercise participation and PPARD genetic variation was found, suggesting that PPARD is not a risk factor for T2D in this population.

Association of a common variant in TCF7L2 gene with type 2 diabetes mellitus in a Persian population

Diabetes is one of the most common and challenging health problems. Studies in several nations show that polymorphisms within the transcription factor 7-like 2 genes could be associated with type 2 diabetes (T2D). Therefore, a case-control study was conducted to find the association between SNP rs7903146 and T2D in our population. The study consists of 110 patients referring to clinic and 80 healthy controls randomly selected based on WHO guideline. DNA was extracted from blood and genotyped by PCR-RFLP with specific primers to amplify a fragment for restriction enzyme (RsaI). A chi-square test was calculated to compare the proportions of genotypes or alleles. Using a logistic regression model, the odds ratio for risk of developing T2D was calculated with and without adjustment for age, sex, and BMI. The frequency of the T allele of rs7903146 (C/T) polymorphism was significantly higher in diabetic subjects (47.3%) compared to that in normal subjects (34.4%). Logistic regression analysis of the rs7903146 polymorphism showed that the odds ratio was 3.71(95% CI: 1.43-9.56; P: 0.008) for the TT genotype and 1.26 (95% CI: 0.67-2.39; P: 0.516) for the CT genotype when compared with the CC genotype. Odds ratio adjusted for age, sex, and BMI have shown similar results. The results show that rs7903146 of TCF7L2 gene is an important susceptibility gene for T2D mellitus in the province of Isfahan, Iran. Our results support the recent findings that rs7903146 of TCF7L2 gene is an important genetic risk factor for the development of T2D in multiple ethnic groups.

In vitro-targeted gene identification in patients with hepatitis C using a genome-wide microarray technology

Iron in association with reactive oxygen species (ROS) is highly toxic, aggravating oxidative stress reactions. Increased iron not only plays an important role in the progression of hereditary hemochromatosis (HH) but also in common liver diseases such as chronic hepatitis C. The underlying mechanisms of hepatitis C virus (HCV)-mediated iron accumulation, however, are poorly understood. We introduce an in vitro-targeted approach to identify ROS/iron-regulated genes in patients with HCV using a genome-wide DNA microarray. The sensitivity of the 32,231 complementary DNA clone-carrying microarray was approximately 20% as estimated by detecting target genes of the genome-wide transcription factor hypoxia inducible factor 1alpha. Upon in vitro challenge to iron and oxidative stress, 265 iron-related and 1326 ROS-related genes could be identified in HepG2 cells; 233 significantly regulated genes were found in patients with mild (HCV) or severe (HH) iron deposition. Notably, 17 of the in vitro-selected genes corresponded to the genes identified in patients with HCV or HH. Among them, natriuretic peptide precursor B (NPPB) was the only iron-regulated gene identified in vitro that was differentially regulated between HCV and HH. Reverse-transcription polymerase chain reaction confirmed most of the microarray-identified genes in an even larger group of patients (n = 12). In patients with HCV, these included genes that are associated with RNA processing (MED9/NFAT, NSUN2), proliferation, differentiation, hypoxia, or iron metabolism (ISG20, MIG6, HIG2, CA9, NDRG1), whereas none of the nine known iron-related genes showed significant differences between HCV and HH.

CONCLUSION

Although high-density microarray technology is less suitable for routine liver diagnosis, its use in combination with prior in vitro selection is a powerful approach to identify candidate genes relevant for liver disease.

The TRIB3 Q84R polymorphism and risk of early-onset type 2 diabetes

CONTEXT

The prevalence of type 2 diabetes (T2D), particularly among young adults, has been rising steadily during the past 2 decades. T2D, especially in its early-onset subtype, is under genetic control. TRIB3 inhibits insulin-stimulated Akt phosphorylation and subsequent insulin action. A TRIB3 gain-of-function polymorphism, Q84R (rs2295490), impairs insulin signaling.

OBJECTIVE

The objective of the study was to verify the association of TRIB3 Q84R with: 1) T2D, either subtyped or not according to age at diagnosis (early-onset, <45 yr, or >or= 45 yr); 2) insulin secretion and sensitivity in nondiabetic individuals; or 3) in vitro insulin secretion from isolated human islets.

DESIGN

Four different case-control samples comprising a total of 5,469 whites were examined. Insulinogenic and insulin sensitivity indexes and their interplay (disposition index) were assessed in 645 nondiabetic individuals at oral glucose tolerance test, glucose (16.7 mmol/liter)-induced in vitro insulin secretion was assessed in islets isolated from 54 nondiabetic donors.

RESULTS

In the whole sample, the R84 variant was nominally associated with T2D (odds ratio 1.17, 95% confidence interval 1.00-1.36, P = 0.04). When stratifying according to age of diabetes onset, R84 carriers had an increased risk of early-onset T2D (odds ratio 1.32, 95% confidence interval 1.10-1.58, P = 0.002). Among 645 nondiabetic subjects, R84 carriers had higher glucose levels (P = 0.005) and lower insulinogenic (P = 0.03) and disposition index (P = 0.02) during the oral glucose tolerance test. R84 islets were more likely to display relatively low glucose-stimulated insulin release (P = 0.04).

CONCLUSIONS

The TRIB3 R84 variant is associated with early-onset T2D in whites. Alteration in the insulin secretion/insulin sensitivity interplay appears to underlie this association.

The emerging genetic architecture of type 2 diabetes

Type 2 diabetes is a genetically heterogeneous disease, with several relatively rare monogenic forms and a number of more common forms resulting from a complex interaction of genetic and environmental factors. Previous studies using a candidate gene approach, family linkage studies, and gene expression profiling uncovered a number of type 2 genes, but the genetic basis of common type 2 diabetes remained unknown. Recently, a new window has opened on defining potential type 2 diabetes genes through genome-wide SNP association studies of very large populations of individuals with diabetes. This review explores the pathway leading to discovery of these genetic effects, the impact of these genetic loci on diabetes risk, the potential mechanisms of action of the genes to alter glucose homeostasis, and the limitations of these studies in defining the role of genetics in this important disease.

Genetic links between diabetes mellitus and coronary atherosclerosis

Diabetes mellitus is one of the most common endocrine disorders. It affects almost 6% of the world's population, and its prevalence continues to increase. The causes of diabetes mellitus are multifactorial, and in the general population both genetic and environmental factors contribute evenly to its development. Several genes have been consistently associated with type 2 diabetes mellitus; however, it is not clear how many of those translate into increased cardiovascular disease risk. Recent evidence suggests that genetic variation at the CALPN10, FABP4, GK, GST, PPARA, and PPARG loci may confer higher cardiovascular disease risk in patients with type 2 diabetes mellitus. However, the evidence is scattered and inconclusive and its translation into practical clinical testing will require studies properly designed to examine not only simple genetic associations but also gene-gene and gene-environment interactions.

Insulin structure and function

Throughout much of the last century insulin served a central role in the advancement of peptide chemistry, pharmacology, cell signaling and structural biology. These discoveries have provided a steadily improved quantity and quality of life for those afflicted with diabetes. The collective work serves as a foundation for the development of insulin analogs and mimetics capable of providing more tailored therapy. Advancements in patient care have been paced by breakthroughs in core technologies, such as semisynthesis, high performance chromatography, rDNA-biosynthesis and formulation sciences. How the structural and conformational dynamics of this endocrine hormone elicit its biological response remains a vigorous area of study. Numerous insulin analogs have served to coordinate structural biology and biochemical signaling to provide a first level understanding of insulin action. The introduction of broad chemical diversity to the study of insulin has been limited by the inefficiency in total chemical synthesis, and the inherent limitations in rDNA-biosynthesis and semisynthetic approaches. The goals of continued investigation remain the delivery of insulin therapy where glycemic control is more precise and hypoglycemic liability is minimized. Additional objectives for medicinal chemists are the identification of superagonists and insulins more suitable for non-injectable delivery. The historical advancements in the synthesis of insulin analogs by multiple methods is reviewed with the specific structural elements of critical importance being highlighted. The functional refinement of this hormone as directed to improved patient care with insulin analogs of more precise pharmacology is reported.

Pathogenesis, risk assessment and prevention of type 2 diabetes mellitus

Type 2 diabetes mellitus is a complex, polygenic disease with a heterogeneous pathophysiology, mainly characterised by obesity-associated insulin resistance and a progressive failure of pancreatic beta-cells. Predominant risk factors for its development are abdominal obesity and age; other factors that augment the individual disease risk independent of obesity are the nutritional pattern (low consumption of fibres, high consumption of red meat, saturated and trans fat), lifestyle (smoking, low physical activity), and biomarkers such as blood pressure, HbA1c, serum adiponectin and inflammatory cytokines. These variables can provide the basis for a precise risk assessment and a personalised prevention. Genotyping for the presently known gene variants conferring an increased disease risk adds relatively little to the information provided by the phenotypic risk factors and biomarkers. However, genetic information is necessary for a personalised risk assessment and intervention that begins before phenotypic risk factors are detectable. The incidence of type 2 diabetes can significantly be lowered by reduction of the intraabdominal fat mass (by nutritional intervention and exercise), and by pharmacological control of post-prandial blood glucose excursions. Because of the high portion of non-responders to a preventive intervention, current efforts aim at the identification of phenotypic and genetic variables predicting the success of the intervention.

The Pro12Ala variant at the peroxisome proliferator-activated receptor gamma gene and change in obesity-related traits in the Diabetes Prevention Program

AIMS/HYPOTHESIS

Peroxisome proliferator-activated receptor gamma (PPARgamma), encoded by the PPARG gene, regulates insulin sensitivity and adipogenesis, and may bind polyunsaturated fatty acids (PUFA) and thiazolidinediones in a ligand-dependent manner. The PPARG proline for alanine substitution at position 12 (Pro12Ala polymorphism) has been related with obesity directly and via interaction with PUFA.

METHODS

We tested the effect-modifying role of Pro12Ala on the 1 year change in obesity-related traits in a randomised clinical trial of treatment with metformin (n = 989), troglitazone (n = 363) or lifestyle modification (n = 1,004) vs placebo (n = 1,000) for diabetes prevention in high-risk individuals.

RESULTS

At baseline, Ala12 carriers had larger waists (p < 0.001) and, in a subset, more subcutaneous adipose tissue (SAT; lumbar 2/3; p = 0.04) than Pro12 homozygotes. There was a genotype-by-intervention interaction on 1-year weight change (p = 0.01); in the placebo arm, Pro12 homozygotes gained weight and Ala12 carriers lost weight (p = 0.001). In the metformin and lifestyle arms, weight loss occurred across genotypes, but was greatest in Ala12 carriers (p < 0.05). Troglitazone treatment induced weight gain, which tended to be greater in Ala12 carriers (p = 0.08). In the placebo group, SAT (lumbar 2/3, lumbar 4/5) decreased in Ala12 allele carriers, but was unchanged in Pro12 homozygotes (p < or = 0.005). With metformin treatment, SAT decreased independently of genotype. In the lifestyle arm, SAT (lumbar 2/3) reductions occurred across genotypes, but were greater in Ala12 carriers (p = 0.03). A genotype-by-PUFA intake interaction on reduction in visceral fat (lumbar 4/5; p = 0.04) was also observed, which was most evident with metformin treatment (p < 0.001).

CONCLUSIONS/INTERPRETATION

Within the Diabetes Prevention Program, the Ala12 allele influences central obesity, an effect which may differ by treatment group and dietary PUFA intake (ClinicalTrials.gov ID no: NCT00004992).

Do we inherit or acquire mitochondrial dysfunction in the metabolic syndrome and Type 2 diabetes?

The rapid increase in the incidence of Type 2 diabetes mellitus as part of the metabolic syndrome in our current societies is largely the result of an increased caloric intake in combination with a sedentary lifestyle. Mitochondria are the organelles within our body that oxidize the constituents of our food, furthermore, they provide the energy for physical activity. An imbalance between energy supply and energy consumption at the mitochondrial level may be at the basis of the current epidemics of Type 2 diabetes. This review discusses underlying pathogenic mechanisms. In particular, it will focus on the contribution of mitochondrial dysfunction in muscle and adipose tissue and the issue to what extent genetic factors are primary determinants for a mitochondrial dysfunction.

Type 2 diabetes whole-genome association study in four populations: the DiaGen consortium

Type 2 diabetes (T2D) is a common, polygenic chronic disease with high heritability. The purpose of this whole-genome association study was to discover novel T2D-associated genes. We genotyped 500 familial cases and 497 controls with >300,000 HapMap-derived tagging single-nucleotide-polymorphism (SNP) markers. When a stringent statistical correction for multiple testing was used, the only significant SNP was at TCF7L2, which has already been discovered and confirmed as a T2D-susceptibility gene. For a replication study, we selected 10 SNPs in six chromosomal regions with the strongest association (singly or as part of a haplotype) for retesting in an independent case-control set including 2,573 T2D cases and 2,776 controls. The most significant replicated result was found at the AHI1-LOC441171 gene region.

Alcohol consumption and type 2 diabetes among older adults: the Cardiovascular Health Study

OBJECTIVE

The objective was to examine the role of total and beverage-specific alcohol consumption on the incidence of type 2 diabetes mellitus (DM) among elderly men and women.

RESEARCH METHODS AND PROCEDURES

We studied prospectively 4655 participants of the Cardiovascular Health Study who were free of DM at baseline. Alcohol consumption was obtained at baseline and during follow-up examinations. DM was defined using fasting glucose and/or use of hypoglycemic medications. We used Cox proportional hazard models to estimate adjusted relative risks of diabetes across alcohol categories.

RESULTS

During a mean follow-up of 6.3 years, 234 incident cases of DM were documented. Compared with never drinkers, hazard ratios [95% confidence interval (CI)] for DM were 0.7 (0.3 to 1.4), 0.5 (0.3 to 0.9), 0.6 (0.4 to 1.1), and 0.8 (0.4 to 1.3) for former drinkers and current drinkers of <1, 1 to 6, and 7+ drinks per week, respectively, for men after adjustment for age, BMI, education, and smoking. Corresponding values for women were 1.2 (0.6 to 2.3), 0.7 (0.4 to 1.1), 0.6 (0.3 to 1.1), and 0.4 (0.2 to 1.0), respectively. A reduced risk of DM was observed with all types of beverage consumed. Similar findings were observed when we repeated the above analyses using simple or weighted cumulative alcohol update and covariates over time.

DISCUSSION

Light to moderate alcohol consumption was associated with a lower incidence of DM among elderly people, irrespective of the type of beverage consumed.

Past and future of genetic research in thrombosis

Genetic studies in thrombosis started with coining of the term thrombophilia by Jordan and Nandorff in 1956. Next, antithrombin deficiency was identified in 1965 as a simple genetic entity that increased thrombotic risk, albeit in a small subset of patients. This subset was enlarged when, in the 1980s, family studies showed that deficiency of protein C (PC) or its co-factor protein S (PS) increased thrombotic risk. Ten years later activated PC resistance and the underlying genetic trait of factor V Leiden were discovered in a family setting. This genetic risk factor was the first prothrombotic defect in a procoagulant protein and was also more prevalent than abnormalities in anticoagulant proteins. The high incidence induced a shift from family studies to case-control studies. Case-control studies became even more popular after the common prothrombin 20,210 mutation was discovered in 1996. In fact, in the last decade common genetic variations in almost all coagulation proteins were tested in association studies. These common variants impart a small risk, if any risk at all, thereby limiting their usefulness in furthering insight into the pathophysiology of thrombosis. Moreover, common risk factors for venous thrombosis fail to improve prediction models for thrombosis on which prophylactic treatment can be tailored. Now that large-scale sequencing techniques are becoming available that enable many genes to be studied in a single individual, one can expect a revival of the identification of private mutations that are associated with large risks, in particular in genes that have been only poorly studied.

[Gene-environment interactions in the pathogenesis and prevention of type 2 diabetes mellitus]

Type 2 diabetes mellitus is a chronic progressive disease characterized by impaired insulin secretion of the beta cell and impaired insulin sensitivity of different tissues. The incidence of type 2 diabetes mellitus is increasing worldwide, and the disease has reached epidemic proportions. Lifestyle intervention programs are able to delay or possibly prevent the manifestation of type 2 diabetes mellitus. This review summarizes the genetic and environmental factors which influence the risk for type 2 diabetes and their interactions, and determine the success of prevention programs.

Complexity of type 2 diabetes mellitus data sets emerging from nutrigenomic research: a case for dimensionality reduction?

Nutrigenomics promises personalized nutrition and an improvement in preventing, delaying, and reducing the symptoms of chronic diseases such as diabetes. Nutritional genomics is the study of how foods affect the expression of genetic information in an individual and how an individual's genetic makeup affects the metabolism and response to nutrients and other bioactive components in food. The path to those promises has significant challenges, from experimental designs that include analysis of genetic heterogeneity to the complexities of food and environmental factors. One of the more significant complications in developing the knowledge base and potential applications is how to analyze high-dimensional datasets of genetic, nutrient, metabolomic (clinical), and other variables influencing health and disease processes. Type 2 diabetes mellitus (T2DM) is used as an illustration of the challenges in studying complex phenotypes with nutrigenomics concepts and approaches.

Calpains and their multiple roles in diabetes mellitus

Type 2 diabetes mellitus (T2DM) can lead to death without treatment and it has been predicted that the condition will affect 215 million people worldwide by 2010. T2DM is a multifactorial disorder whose precise genetic causes and biochemical defects have not been fully elucidated, but at both levels, calpains appear to play a role. Positional cloning studies mapped T2DM susceptibility to CAPN10, the gene encoding the intracellular cysteine protease, calpain 10. Further studies have shown a number of noncoding polymorphisms in CAPN10 to be functionally associated with T2DM while the identification of coding polymorphisms, suggested that mutant calpain 10 proteins may also contribute to the disease. Here we review recent studies, which in addition to the latter enzyme, have linked calpain 5, calpain 3, and its splice variants, calpain 2 and calpain 1 to T2DM-related metabolic pathways along with T2DM-associated phenotypes, such as obesity and impaired insulin secretion, and T2DM-related complications, such as epithelial dysfunction and diabetic cataract.

Dissecting the heterogeneity of rheumatoid arthritis through linkage analysis of quantitative traits

OBJECTIVE

To dissect the heterogeneity of rheumatoid arthritis (RA) through linkage analysis of quantitative traits, specifically, IgM rheumatoid factor (IgM-RF) and anti-cyclic citrullinated peptide (anti-CCP) autoantibody titers.

METHODS

Subjects, 1,002 RA patients from 491 multiplex families recruited by the North American RA Consortium, were typed for 379 microsatellite markers. Anti-CCP titers were determined based on a second-generation enzyme-linked immunosorbent assay, and IgM-RF levels were quantified by immunonephelometry. We used the Merlin statistical package to perform nonparametric quantitative trait linkage analysis.

RESULTS

For each of the quantitative traits, evidence of linkage, with logarithm of odds (LOD) scores of >1.0, was found in 9 regions. For both traits, the strongest evidence of linkage was for marker D6S1629 on chromosome 6p (LOD 14.02 for anti-CCP and LOD 12.09 for RF). Six other regions with LOD scores of >1.0 overlapped between the 2 traits, on chromosomes 1p21.1, 5q15, 8p23.1, 16p12.1, 16q23.1, and 18q21.31. Evidence of linkage to anti-CCP titer but not to RF titer was found in 2 regions (chromosomes 9p21.3 and 10q21.1), and evidence of linkage to RF titer but not to anti-CCP titer was found in 2 regions (chromosomes 5p15.2 and 1q42.3). Several covariates were significantly associated with 1 or both traits, and linkage analysis exploring the covariate effects revealed striking effects of sex in modulating linkage signals for several chromosomal regions. For example, sex had a striking impact on the linkage results for both quantitative traits on chromosome 6p (P = 0.0007 for anti-CCP titer and P = 0.0012 for RF titer), suggesting a sex-HLA region interaction.

CONCLUSION

Analysis of quantitative components of RA is a promising approach for dissecting the genetic heterogeneity of this complex disorder. These results highlight the potential importance of sex or other covariates that may modulate some of the genetic effects that influence the risk of specific disease manifestations.

Application of nutrigenomic concepts to Type 2 diabetes mellitus

The genetic makeup that individuals inherit from their ancestors is responsible for variation in responses to food and susceptibility to chronic diseases such as Type 2 diabetes mellitus (T2DM). Common variations in gene sequences, such as single nucleotide polymorphisms, produce differences in complex traits such as height or weight potential, food metabolism, food-gene interactions, and disease susceptibilities. Nutritional genomics, or nutrigenomics, is the study of how foods affect the expression of genetic information in an individual and how an individual's genetic makeup affects the metabolism and response to nutrients and other bioactive components in food. Since both diet and genes alter one's health and susceptibility to disease, identifying genes that are regulated by diet and that cause or contribute to chronic diseases could result in the development of diagnostic tools, individualized intervention, and eventually strategies for maintaining health. Translating this research through clinical studies promises contributions to the development of personalized medicine that includes nutritional as well as drug interventions. Reviewed here are the key nutrigenomic concepts that help explain aspects of the development and complexity of T2DM.

Effect of genotype on success of lifestyle intervention in subjects at risk for type 2 diabetes

Lifestyle intervention programs including increased physical activity and healthy nutrition have been proven to delay the onset of type 2 diabetes. This is achieved mainly by reducing body weight and improving insulin sensitivity. However, response to lifestyle or dietary interventions does differ between individuals, and the genetic or environmental factors that may account for these differences are not yet precisely characterized. Identification of these factors would be desirable in order to provide an individually tailored preventive strategy for patients at risk of developing diabetes. This review summarizes the so far known genetic variations, which determine responders and nonresponders to a lifestyle intervention. In addition, general methodological approaches to study gene-lifestyle interactions are described.

Polymorphism in the transcription factor 7-like 2 (TCF7L2) gene is associated with reduced insulin secretion in nondiabetic women

Recently, the transcription factor 7-like 2 (TCF7L2) gene on chromosome 10q25.2 has been linked with type 2 diabetes among Caucasians, with disease associations noted for single nucleotide polymorphisms (SNPs) rs12255372 and rs7903146. To investigate mechanisms by which TCF7L2 could contribute to type 2 diabetes, we examined the effects of these SNPs on clinical and metabolic traits affecting glucose homeostasis in 256 nondiabetic female subjects (138 European Americans and 118 African Americans) aged 7-57 years. Outcomes included BMI, percent body fat, insulin sensitivity (S(i)), acute insulin response to glucose (AIR(g)), and the disposition index (DI). Homozygosity for the minor allele (TT) of SNP rs12255372 occurred in 9% of individuals and was associated with a 31% reduction in DI values in a recessive model. The at-risk allele TT was also associated with lower AIR(g) adjusted for S(i) in both ethnic groups, whereas rs12255372 genotype was not associated with measures of adiposity or with S(i). The T allele of rs12255372 was also associated with increased prevalence of impaired fasting glucose. Genotypes at rs7903146 were not associated with any metabolic trait. Lower S(i) and higher AIR(g) observed in the African-American compared with the European-American subgroup could not be explained by the TCF7L2 genotype. Our data suggest that the TCF7L2 gene is an important factor regulating insulin secretion, which could explain its association with type 2 diabetes.

Variation in CAPN10 in relation to type 2 diabetes, obesity and quantitative metabolic traits: studies in 6018 whites

The first type 2 diabetes (T2D) gene to be identified in a genome wide scan followed by positional cloning was CAPN10 encoding the cysteine protease calpain-10. Subsequently, a large number of studies have investigated variation in CAPN10 in relation to T2D. Two CAPN10 single nucleotide polymorphisms (SNPs), the SNP43 (rs3792267) and the SNP44 (rs2975760), have been associated with T2D in some, but not all studies conducted in a wide range of ethnicities. We investigated the two SNPs for association with T2D in a relatively large, homogenous population of Danish whites (n = 1359 T2D cases, n = 4659 normoglycemic and glucose-tolerant control subjects), however, no significant associations of the SNP43 or the SNP44 variant with T2D were found. Neither were the two variants associated with obesity, and no association of either variant with diabetes-related quantitative traits was found in a study involving a population-based sample of 5698 middle-aged subjects. Meta-analyses, however, of the present and previously published studies involving 15,368 (SNP43) or 13,628 (SNP44) subjects yielded odds ratios of 1.09 (95% CI 1.02-1.16, p = 0.007) and 1.15 (1.07-1.23, p = 0.0002), respectively, for association with T2D. In conclusion, in a relatively large study sample of whites we found no consistent evidence of association of the CAPN10 SNP43 or SNP44 with T2D, obesity, or related quantitative traits, although meta-analyses of these two CAPN10 SNPs demonstrated an association with T2D.

IL6 gene promoter polymorphisms and type 2 diabetes: joint analysis of individual participants' data from 21 studies

Several lines of evidence indicate a causal role of the cytokine interleukin (IL)-6 in the development of type 2 diabetes in humans. Two common polymorphisms in the promoter of the IL-6 encoding gene IL6, -174G>C (rs1800795) and -573G>C (rs1800796), have been investigated for association with type 2 diabetes in numerous studies but with results that have been largely equivocal. To clarify the relationship between the two IL6 variants and type 2 diabetes, we analyzed individual data on >20,000 participants from 21 published and unpublished studies. Collected data represent eight different countries, making this the largest association analysis for type 2 diabetes reported to date. The GC and CC genotypes of IL6 -174G>C were associated with a decreased risk of type 2 diabetes (odds ratio 0.91, P = 0.037), corresponding to a risk modification of nearly 9%. No evidence for association was found between IL6 -573G>C and type 2 diabetes. The observed association of the IL6 -174 C-allele with a reduced risk of type 2 diabetes provides further evidence for the hypothesis that immune mediators are causally related to type 2 diabetes; however, because the association is borderline significant, additional data are still needed to confirm this finding.

Prevention and treatment of type 2 diabetes in youth

Parallel to the increase in obesity worldwide, there has been a rise in the prevalence of type 2 diabetes mellitus (T2DM) in children and adolescents. The etiology of T2DM in youth, similar to adults, is multifactorial including genetic and environmental factors, among them obesity, sedentary lifestyle, family history of the disease, high-risk ethnicity and insulin resistance phenotype playing major roles. Treatment of T2DM should not have a glucocentric approach; it should rather target improving glycemia, dyslipidemia, hypertension, weight management and the prevention of short- and long-term complications. Prevention strategies, especially in high-risk groups, should focus on environmental change involving participation of families, schools, the food and entertainment industries and governmental agencies. Presently, limited pharmacotherapeutic options need to be expanded both for childhood T2DM and obesity. The coming decades will prove very challenging for healthcare providers battling socioeconomic waves conducive to obesity and T2DM. Evidence-based research and clinical experience in pediatrics, possibly modeled after adult trials, need to be developed if this public health threat is to be contained.

Molecular approaches to study control of glucose homeostasis

Type 2 diabetes is a polygenic disease that can lead to severe complications in multiple tissues. Rodent models have been used widely for investigating the pathophysiology underlying type 2 diabetes and for examining the potential link with obesity, largely due to the limitations of invasive testing and of studying detailed molecular mechanisms in human tissues. Among rodents, the mouse model is especially popular because mice are easy to manipulate genetically, have a short generation time, and are relatively inexpensive. The most commonly used inbred mouse strains are reviewed in addition to several genetically engineered mouse models that have been generated to study type 2 diabetes in the context of obesity, with a focus on insulin, leptin, and peroxisome proliferator-activated receptor (PPAR) signaling pathways.

ENPP1 K121Q polymorphism is not related to type 2 diabetes mellitus, features of metabolic syndrome, and diabetic cardiovascular complications in a Chinese population

BACKGROUND

Ectoenzyme nucleotide pyrophosphate phosphodiesterase 1 (ENPP1) is known to influence insulin sensitivity by inhibiting insulin receptor signaling. A DNA polymorphism in the ENPP1 gene at exon 4 (K121Q) was demonstrated to be associated with insulin resistance, type 2 diabetes mellitus (T2DM), and a risk of early myocardial infarction, albeit with controversy. Our aim was to investigate any association of ENPP1 K121Q alleles with T2DM, features of the metabolic syndrome, and diabetic cardiovascular complications in a Chinese population of Han origin.

METHODS

The ENPP1 K121Q polymorphism was determined by a restriction fragment-length polymorphism-polymerase chain reaction in 1,862 patients with T2DM and 844 non-diabetic subjects.

RESULTS

The genotype distributions or Q-allele frequency were not statistically different between the diabetic and non-diabetic groups. The anthropometric parameters, systolic and diastolic blood pressures, lipid profiles, and serum creatinine levels of subjects with different ENPP1 K121Q polymorphisms were not statistically different in the two groups or even in the pooled data. When sub-group analyses of diabetic subjects were stratified according to BMI levels (greater or less than 27), gender, age of diabetes onset (older or younger than 60 years), and the presence or absence of a diabetic family history; this polymorphism was still not associated with T2DM. Nor was the ENPP1 K121Q polymorphism associated with the prevalence of coronary artery disease and ischemic cerebrovascular disease in patients with T2DM.

CONCLUSION

The ENPP1 K121Q polymorphism is not related to T2DM, features of the metabolic syndrome, or diabetic macrovascular complications in a Chinese population.

Association of single-nucleotide polymorphisms in the suppressor of cytokine signaling 2 (SOCS2) gene with type 2 diabetes in the Japanese

Several previous linkage scans in type 2 diabetes (T2D) families indicated a putative susceptibility locus on chromosome 12q15-q22, while the underlying gene for T2D has not yet been identified. We performed a region-wide association analysis on 12q15-q22, using a dense set of >500 single-nucleotide polymorphisms (SNPs), in 1492 unrelated Japanese individuals enrolled in this study. We identified an association between T2D and a haplotype block spanning 13.6 kb of genomic DNA that includes the entire SOCS2 gene. Evolutionary-based haplotype analysis of haplotype-tagging SNPs followed by a "sliding window" haplotypic analysis indicated SNPs that mapped to the 5' region of the SOCS2gene to be associated with T2D with high statistical significance. The SOCS2 gene was expressed ubiquitously in human and murine tissues, including pancreatic beta-cell lines. Adenovirus-mediated expression of the SOCS2 gene in MIN6 cells or isolated rat islets significantly suppressed glucose-stimulated insulin secretion. Our data indicate that SOCS2 may play a role in susceptibility to T2D in the Japanese.

Type 2 Diabetes--An Introduction to the Development and Use of Animal Models

Although the epidemiology of type 2 diabetes (T2D) has been well described, there is much about the disease that remains unclear. For example, lifestyle factors-including increased body weight with visceral fat deposition and insufficient physical activity-are thought to be primary contributors to the adverse changes in the metabolism of muscle and fat cells that comprise the first stage of the disease. However, the precise mechanisms underlying these initial alterations are incompletely understood. Other, less obvious questions relate to the presence of sex differences in the development and health consequences of T2D, the etiological role of the central nervous system ("stress"), and the potential evolutionary origins of T2D susceptibility. Some of these issues can be resolved by further study of human populations. However, many questions can be answered only through the kinds of controlled prospective studies that are conducted with appropriate animal models. The use of such models can be an invaluable part of an overall strategy designed to elucidate the mechanisms underlying the development of T2D, understand the natural history of the disease, identify targets for therapy, and evaluate interventions. Current evidence indicates that no single animal model replicates the development of human T2D in all of its details. Nonetheless, the existing models (e.g., naturally occurring and genetically modified rodents, cats, pigs, and nonhuman primates) offer researchers a rich array of opportunities to investigate the myriad complexities of T2D. The individual contributions comprising this issue of ILAR Journal review the research that has been conducted on many of these animals.

Type 2 diabetes mellitus in youth: the complete picture to date

Type 2 diabetes mellitus is a heterogeneous condition in which the clinical manifestation of hyperglycemia is a reflection of the impaired balance between insulin sensitivity and insulin secretion. Clinical experience and research in youth type 2 diabetes mellitus are in an early stage because of the relative novelty of the condition in pediatrics. This article discusses the amassed information in type 2 diabetes mellitus of youth to date with respect to the epidemiology, pathophysiology, risk factors, clinical presentation, screening, and management strategies.

The K121Q polymorphism of the ENPP1/PC-1 gene is associated with insulin resistance/atherogenic phenotypes, including earlier onset of type 2 diabetes and myocardial infarction

Insulin resistance (IR) is pathogenic for type 2 diabetes and coronary artery disease (CAD). The K121Q polymorphism of the ENPP1/PC-1 gene is associated with IR. Our aim was to investigate the role of the 121Q variant on the risk of type 2 diabetes and CAD. Nondiabetic control subjects (n = 638), type 2 diabetic patients without CAD (n = 535), and type 2 diabetic patients with CAD (n = 434) from Italy and the U.S. were studied. The proportion of 121Q carriers progressively increased in the three groups (27.4, 28.8, and 33.2%, respectively; adjusted P value = 0.027). Among diabetic patients (n = 969), 121Q carriers had an increased risk of developing type 2 diabetes before the age of 65 years (adjusted odds ratio [OR] 2.26, 95% CI 1.26-4.03; P = 0.006) and having a myocardial infarction (MI) (n = 156) by 50 years of age (3.17, 1.46-6.88, P = 0.007). The 121Q variant was also associated with an increased risk for CAD (1.47, 1.01-2.18; P = 0.049) in diabetic patients who did not smoke (n = 546). In conclusion, the ENPP1/PC-1 121Q variant is associated with a progressive deterioration of the IR-atherogenic phenotype; among diabetic individuals, it is also associated with earlier onset of type 2 diabetes and MI.