Metabolic and genetic influence on glucose metabolism in type 2 diabetic subjects--experiences from relatives and twin studies

A prospective study on physical performance of Chinese chronic obstructive pulmonary disease males with type 2 diabetes

Currently no research is available on muscle and functional performance of chronic obstructive pulmonary disease (COPD) patients with type 2 diabetes (T2DM) in China, even though both diseases have been reported to damage motor function.This single-center prospective study involves 55 males with COPD and T2DM and 46 males with COPD. Lung function, muscle strength and endurance of the upper limbs, and quadriceps strength of both legs were assessed using instruments. The 6-min walk (6MW) test was performed to evaluate physical performance.Between the two groups, respiratory function of COPD patients with T2DM was worse than in those without (P < .05). Mean handgrip strength and muscle endurance of upper limbs and mean quadriceps strength at both 60°/s and 120°/s in COPD males with T2DM was also significantly less (P < .05). Mean 6MW distances of COPD patients with T2DM were significantly worse (P < .05), and mean pulse rate (PR) increments of COPD patients with T2DM in 6MW test were significantly higher (P < .05).The combination of COPD and T2DM not only brings one more chronic disease to elderly patients but also significantly affects muscle strength and endurance as well as physical performance. Accordingly, in the management of chronic diseases, we recommend that clinicians as well as patients themselves actively control blood sugar and review them regularly with a view to reducing adverse effects on physical performance.

First-degree family history of diabetes and its relationship with serum osteocalcin levels independent of liver fat content in a non-diabetic Chinese cohort

BACKGROUND

First-degree relatives of patients with diabetes (FDR) tend to have impaired insulin activity, which lead to the alternation of circulating cytokine levels. Liver is a main target tissue of insulin action; therefore, liver fat content (LFC) has a close relationship with insulin resistance. This study aimed to find the alteration in serum osteocalcin levels in FDR and the relationship of serum osteocalcin levels with FDR and non-alcoholic fatty liver disease (NAFLD).

METHODS

In total, 1206 subjects including 413 men and 793 women from the communities, aged 59.7 (range, 54.8-64.3) years, were enrolled. An electrochemiluminescence immunoassay was performed to measure the levels of serum osteocalcin. LFC was measured using quantitative ultrasonography.

RESULTS

A significant decrease was found in serum osteocalcin levels in subjects with NAFLD (P < 0.001) as well as in FDR (19.8 ± 5.7 ng/mL versus 20.7 ± 6.8 ng/mL, P = 0.028). Furthermore, among the subjects with NAFLD, those with FDR had lower levels of osteocalcin than those without FDR (P = 0.011). The presence of FDR remained a predictor for decreased serum osteocalcin levels after adjusting for body mass index, blood glucose, blood lipids, and LFC (standardized β = - 0.057, P = 0.028).

CONCLUSIONS

FDR had lower serum osteocalcin levels than non-FDR. The inverse association between FDR and serum osteocalcin levels was independent of metabolic factors.

Neuroimaging endophenotypes of type 2 diabetes mellitus: a discordant sibling pair study

Background

Type 2 diabetes mellitus (T2DM) is characterized by notable familial aggregation involving common variants of many genes, and its heritability leads to a high prevalence in the siblings of affected individuals compared with the general population. Endophenotypes are objective, heritable, quantitative traits that appear to reflect the genetic risk for polygenic disorders at more biologically tractable levels. Based on a sibling pair design, we aimed to find the neuroimaging endophenotypes of T2DM and investigate the role of inherent neurological disorders in the pathogenesis and deterioration of T2DM.

Methods

Twenty-six pairs of diagnosed T2DM patients with unaffected siblings and 26 unrelated controls were included in this study. Both high-resolution structural MRI and three-dimensional pseudo-continuous arterial spin labelling (3D-pCASL) MRI data were acquired with a 3.0 T MRI system. Voxel-based morphometry (VBM) analysis was performed on the structural T1W images, and cerebral blood flow (CBF) maps were obtained. All data were processed with the SPM8 package under the MATLAB 7.6 operation environment.

Results

The T2DM patients and their unaffected siblings shared significant atrophy in the right inferior/middle temporal gyrus, and left insula, in addition to elevated CBF in the right prefrontal lobe. Several regions with abnormal CBF in siblings, including the right inferior/middle temporal gyrus, left insula, left operculum, right supramarginal gyrus, right prefrontal lobe, and bilateral anterior cingulate cortex, also presented significant atrophy in T2DM patients.

Conclusions

The shared brain regions with grey matter (GM) loss and CBF increases may serve as neuroimaging endophenotypes of T2DM, and the regions with abnormal CBF in siblings indicate an increased risk for T2DM.

Type 2 diabetes - An unresolved disease across centuries contributing to a public health emergency

AIMS

Type 2 diabetes mellitus (T2DM) is a global epidemic. However, T2DM is not a new, 21^stcentury disease. Different populations have been struggling with this disease across a number of centuries. The question lies as to why humanity has never succeeded in keeping it in check over the course of its history.

MATERIALS AND METHODS

In this review, the history of T2DM and its evolution throughout the ages are revisited. The review then investigates the growing burden of T2DM across the past fourteen years within the European continent, while comparing this epidemic with the obesity burden.

RESULTS

Various explanations for the emergence of this public health epidemic were explored ranging from lifestyle factors, high sugary food and drink, disrupted sleep pattern to obesity. Over a fourteen-year period, an evident steady incline in both T2DM and obesity prevalence rates across Europe was evident.

CONCLUSION

It is essential for public health officials and researchers alike to have a good grip of the past and the present diabetes epidemiology and its co-determinants. This will provide the basis for new and improved strategies to target and prevent this epidemic.

Serum levels of immunoglobulins in an adult population and their relationship with type 2 diabetes

OBJECTIVE

Some studies have found patients with diabetes had an impaired humoral immune response. Immunoglobulins provide key information on the humoral immune status. But few population-based studies comprehensively estimated the serum immunoglobulins concentration in type 2 diabetes (T2D). So we design a cross-sectional study to investigate the relationships between immunoglobulin levels and prevalence of T2D in a large-scale adult population.

METHODS

A cross-sectional assessment was performed in 10,691 participants living in Tianjin, China. Type 2 diabetes was defined in accordance with the criteria of the world health organization, and serum levels of immunoglobulins were determined by the immunonephelometric technique. Adjusted logistic models were used to assess relationships between the quintiles of immunoglobulins concentration and the prevalence of T2D.

RESULTS

In this study, the prevalence of T2D was 11.7%, and the means (standard deviation) of immunoglobulins (IgG, IgE, IgM, IgA) were 1192.3 (241.1)mg/dL, 92.3 (234.6)IU/mL, 104.8 (55.8)mg/dL, 234.1 (96.2)mg/dL, respectively. The adjusted odds ratio (95% confidence interval) of T2D for the highest immunoglobulins (IgG, IgE, IgM, IgA) quintile, when compared to the lowest quintile were 0.64 (0.52, 0.78), 1.00 (0.81, 1.22), 0.77 (0.62, 0.95) and 1.57 (1.29, 1.92), respectively.

CONCLUSIONS

Decreased IgG and IgM, and increased IgA levels were independently related to the prevalence of T2D among the adult population. Our findings indicate that the immunoglobulins might useful predictive factors for T2D in the general adult population. Further studies are needed to explore the causality and exact mechanisms of immunoglobulins in T2D.

Metabolic syndrome and nephrolithiasis

Problem

This review focuses on the association between the metabolic syndrome (MS) and nephrolithiasis.

Findings

Associations between nephrolithiasis and systemic diseases are recognized, including atherosclerosis, cardiovascular (CV) disease, hypertension (HNT), diabetes mellitus (DM)—composite risk factors grouped as the MS. Kidney stones incidence is increasing in this particularly high risk group. Those with stones are prone to the disease and those with the systemic disease are at risk for stone formation, with the highest incidence in persons with multiple traits of the MS. Pathophysiologic explanations for the increased stone risk related to MS are likely complex and dynamic.

Conclusions

Kidney stones disproportionately affect persons with some or all traits of MS. One unifying theory may be of a common systemic malfunction of inflammation and tissue damage as an underlying mechanism, but it is unlikely to be the only mechanistic explanation. Further research is needed to investigate this and other hypotheses that go beyond population based and urine physiochemical studies in order to elucidate the mechanisms behind the individual disease states themselves.

ATP-dependent potassium channels and type 2 diabetes mellitus

Diabetes mellitus is a public health problem, which affects a millions worldwide. Most diabetes cases are classified as type 2 diabetes mellitus, which is highly associated with obesity. Type 2 diabetes is considered a multifactorial disorder, with both environmental and genetic factors contributing to its development. An important issue linked with diabetes development is the failure of the insulin releasing mechanism involving abnormal activity of the ATP-dependent potassium channel, KATP. This channel is a transmembrane protein encoded by the KCNJ11 and ABCC8 genes. Furthermore, polymorphisms in these genes have been linked to type 2 diabetes because of the role of KATP in insulin release. While several genetic variations have been reported to be associated with this disease, the E23K polymorphism is most commonly associated with this pathology, as well as to obesity. Here, we review the molecular genetics of the potassium channel and discusses its most described polymorphisms and their associations with type 2 diabetes mellitus.

Impact of the gut microbiota on the development of obesity and type 2 diabetes mellitus

Obesity and its associated disorders are a major public health concern. Although obesity has been mainly related with perturbations of the balance between food intake and energy expenditure, other factors must nevertheless be considered. Recent insight suggests that an altered composition and diversity of gut microbiota could play an important role in the development of metabolic disorders. This review discusses research aimed at understanding the role of gut microbiota in the pathogenesis of obesity and type 2 diabetes mellitus (TDM2). The establishment of gut microbiota is dependent on the type of birth. With effect from this point, gut microbiota remain quite stable, although changes take place between birth and adulthood due to external influences, such as diet, disease and environment. Understand these changes is important to predict diseases and develop therapies. A new theory suggests that gut microbiota contribute to the regulation of energy homeostasis, provoking the development of an impairment in energy homeostasis and causing metabolic diseases, such as insulin resistance or TDM2. The metabolic endotoxemia, modifications in the secretion of incretins and butyrate production might explain the influence of the microbiota in these diseases.

In vivo activating transcription factor 3 silencing ameliorates the AMPK compensatory effects for ER stress-mediated β-cell dysfunction during the progression of type-2 diabetes

In obese Zucker diabetic fatty (ZDF) rats, ER stress is associated with insulin resistance and pancreatic β-cell dysfunction; however the exact mechanisms by which ER stress drives type-2 diabetes remain uncertain. Here, we investigated the role of ATF3 on the preventive regulation of AMPK against ER stress-mediated β-cell dysfunction during the end-stage progression of hyperglycemia in ZDF rats. The impaired glucose metabolism and β-cell dysfunction were significantly increased in late-diabetic phase 19-week-old ZDF rats. Although AMPK phosphorylation reduced in 6- and 12-week-old ZDF rats was remarkably increased at 19weeks, the increases of lipogenice genes, ATF3, and ER stress or ROS-mediated β-cell dysfunction were still remained, which were attenuated by in vivo-injection of chemical chaperon tauroursodeoxycholate (TUDCA), chronic AICAR, or antioxidants. ATF3 did not directly affect AMPK phosphorylation, but counteracts the preventive effects of AMPK for high glucose-induced β-cell dysfunction. Moreover, knockdown of ATF3 by delivery of in vivo-jetPEI ATF3 siRNA attenuated ER stress-mediated β-cell dysfunction and enhanced the beneficial effect of AICAR. Our data suggest that ATF3 may play as a counteracting regulator of AMPK and thus promote β-cell dysfunction and the development of type-2 diabetes and could be a potential therapeutic target in treating type-2 diabetes.

Association of the common FTO-rs9939609 polymorphism with type 2 diabetes, independent of obesity-related traits in a Vietnamese population

Type 2 diabetes (T2D) is a complex disorder resulting from both genetic and environmental factors in its pathogenesis. A case-control study was designed with subjects recruited from a general population to investigate whether the association between T2D and the common T>A polymorphism (rs9939609) in fat mass and obesity associated (FTO) gene is mediated by obesity-related measurements, considering the contribution of socio-economic status and lifestyle factors. The significant association between the FTO rs9939609 polymorphism and T2D was first observed in the model unadjusted (OR per A allele=1.61, 95% CI=1.06-2.44, P=0.024). It remained consistently replicated in the final model after adjustments for sex, age, systolic blood pressure, socio-economic status, lifestyle factors, and obesity-related measurements (body mass index, waist-hip ratio, body fat percentage, and body adiposity index), showing an increased T2D risk with an additive effect of the alleles (ORs per A allele=1.80-1.92, 95% CI=1.09-3.19, P<0.05). The FTO-rs9939609 polymorphism, systolic blood pressure, and waist-hip ratio were the most significant independent predictors for T2D, in which the power of the adjusted prediction model was 0.769. In conclusion, the study suggested that the FTO-rs9939609 polymorphism was significantly associated with the increased risk of T2D, independent of obesity-related measurements in a Vietnamese population.

Exercise training, genetics and type 2 diabetes-related phenotypes

Type 2 diabetes mellitus (T2DM) is at virtually pandemic levels world-wide. Diabetes has been referred to as 'a geneticist's nightmare'. However, dramatic advances in our understanding of the genetics of T2DM have occurred in the past 5 years. While endurance exercise training and increased habitual physical activity levels have consistently been shown to improve or be associated with improved T2DM-related phenotypes, there is substantial interindividual variation in these responses. There is some evidence that T2DM-related phenotype responses to exercise training are heritable, indicating that they might have a genetic basis. Genome-wide linkage studies have not identified specific chromosomal loci that could account for these differences, and no genome-wide association studies have been performed relative to T2DM-related phenotype responses to exercise training. From candidate gene studies, there are relatively strong and replicated data supporting a role for the PPARγ Pro12Ala variant in the interindividual differences in T2DM-related phenotype responses to training. This is a potentially important candidate locus because it affects T2DM susceptibility, has high biological plausibility and is the target for the primary pharmaceutical method for treating T2DM. Is it time to conduct a hypothesis-driven large-scale exercise training intervention trial based on PPARγ Pro12Ala genotype with T2DM-related phenotypes as the primary outcome measures, while also assessing potential mechanistic changes in skeletal muscle and adipose tissue? Or would it be more appropriate to propose a smaller trial to address the specific skeletal muscle and adipose tissue mechanisms affected by the interaction between the PPARγ Pro12Ala genotype and exercise training?

Impaired TCA cycle flux in mitochondria in skeletal muscle from type 2 diabetic subjects: marker or maker of the diabetic phenotype?

The diabetic phenotype is complex, requiring elucidation of key initiating defects. Recent research has shown that diabetic myotubes express a primary reduced tricarboxylic acid (TCA) cycle flux. A reduced TCA cycle flux has also been shown both in insulin resistant offspring of T2D patients and exercising T2D patients in vivo. This review will discuss the latest advances in the understanding of the molecular mechanisms regulating the TCA cycle with focus on possible underlying mechanism which could explain the impaired TCA flux in insulin resistant human skeletal muscle in type 2 diabetes. A reduced TCA is both a marker and a maker of the diabetic phenotype.

Strong association of common variants in the IGF2BP2 gene with type 2 diabetes in Lebanese Arabs

OBJECTIVE

Several genome-wide association studies and replication analyses have identified common variation at the insulin-like binding protein 2 (IGF2BP2) gene to be associated with type 2 diabetes (T2DM). The aim of this study was to replicate in a Lebanese Arab population identified associations of IGF2BP2 variants rs4402960 and rs1470579 with T2DM.

METHODS

This case-control study involved 544 T2DM patients and 606 control subjects. Genotyping was done by the allelic exclusion method.

RESULTS

T allele of rs440960 (P=6.5 × 10(-6)) and C allele of rs1470579 (P=5.3 × 10(-4)) were significantly associated with T2DM; both SNPs were in strong LD (D'=0.83, r(2)=0.58). While both IGF2BP2 SNPs were significantly associated with T2DM under additive and recessive models, only rs4402960 remained significantly associated with T2DM under the dominant model. Taking the common rs4402960/rs1470579 GA haplotype as reference, multivariate analysis confirmed the positive association of TC (P=0.009; OR, 1.43; 95%CI, 1.09-1.87), and TA (P<0.001; OR=5.49; 95%CI=2.09-14.39) haplotypes with increased T2DM risk. These differences remained significant after applying the Bonferroni correction for multiple testing.

CONCLUSION

We validate that IGF2BP2 susceptibility variants rs4402960 and rs1470579 associate with T2DM in Lebanese Arabs.

Immuno-microbiota cross and talk: the new paradigm of metabolic diseases

Over the last decades the rising occurrence of metabolic diseases throughout the world points to the failure of preventive and therapeutic strategies and of the corresponding molecular and physiological concepts. Therefore, a new paradigm needs to be elucidated. Very recently the intimate cross talk of the intestinal microbiota with the host immune system has opened new avenues. The large diversity of the intestinal microbes' genome, i.e. the metagenome, and the extreme plasticity of the immune system provide a unique balance which, when finely tuned, maintains a steady homeostasis. The discovery that a new microbiota repertoire is one of the causes responsible for the onset of metabolic disease suggests that the relationship with the immune system is impaired. Therefore, we here review the recent arguments that support the view that an alteration in the microbiota to host immune system balance leads to an increased translocation of bacterial antigens towards metabolically active tissues, and could result in a chronic inflammatory state and consequently impaired metabolic functions such as insulin resistance, hepatic fat deposition, insulin unresponsiveness, and excessive adipose tissue development. This imbalance could be at the onset of metabolic disease, and therefore the early treatment of the microbiota dysbiosis or immunomodulatory strategies should prevent and slow down the epidemic of metabolic diseases and hence the corresponding lethal cardiovascular consequences.

Periconceptional events perturb postnatal growth regulation in sheep

Periconceptional undernutrition and twin conception alter intrauterine growth and metabolism and are associated with later adverse metabolic outcomes. The contribution of postnatal growth to these outcomes is less well defined. We investigated whether maternal periconceptional undernutrition or twin conception altered postnatal growth regulation in ways that could lead to metabolic disease. Single and twin offspring of ewes undernourished (UN) from 61 d before until 30 d after mating, fed to achieve and maintain 10-15% weight loss (UN), were compared with offspring of maintenance-fed controls (N). At 2 h and 1, 6, and 12 wk after birth, lambs were weighed and plasma hormone and metabolite concentrations analyzed. Milk intake, measured by deuterium oxide dilution, was inversely related to birth weight only in N singles, although twins had the greatest postnatal growth velocity. Positive associations were seen between milk intake, growth velocity, and leptin concentrations in N, but not UN, offspring. We conclude that periconceptional undernutrition alters the relationships between regulators of postnatal growth, including nutrient intake and key hormonal axes, in both singles and twins without affecting size at birth or postnatal growth velocity. Dissociation of growth from its key regulators is one possible mechanism underlying adverse metabolic outcomes after periconceptional undernutrition.

Marine food pollutants as a risk factor for hypoinsulinemia and type 2 diabetes

BACKGROUND

Some persistent environmental chemicals are suspected of causing an increased risk of type 2 diabetes mellitus, a disease particularly common after the age of 70. This concern was examined in a cross-sectional study of elderly subjects from a fishing population with elevated contaminant exposures from seafood species high in the food chain.

METHODS

Clinical examinations of 713 Faroese residents aged 70-74 years (64% of eligible population) included fasting plasma concentrations of glucose and insulin, and glycosylated hemoglobin. Lifetime exposure to persistent environmental chemicals from pilot whale and other traditional food was estimated from a dietary questionnaire and by analysis of blood samples for polychlorinated biphenyls (PCBs) and related food contaminants.

RESULTS

Septuagenarians with type 2 diabetes or impaired fasting glycemia tended to have higher PCB concentrations and higher past intake of traditional foods, especially during childhood and adolescence. In nondiabetic subjects, the fasting insulin concentration decreased by 7% (95% CI = -12% to -2%) for each doubling of the PCB concentration after adjustment for sex and body mass index at age 20. Conversely, the fasting glucose concentration increased by 6% (-1% to 13%) for each doubling in PCB. Similar associations were seen in subjects without impaired fasting glycemia, while further adjustment for current body mass index and lipid metabolism parameters attenuated some of the associations.

CONCLUSIONS

Impaired insulin secretion appears to constitute an important part of the type 2 diabetes pathogenesis associated with exposure to persistent lipophilic food contaminants.

Characterization of human myotubes from type 2 diabetic and nondiabetic subjects using complementary quantitative mass spectrometric methods

Skeletal muscle is a key tissue site of insulin resistance in type 2 diabetes. Human myotubes are primary skeletal muscle cells displaying both morphological and biochemical characteristics of mature skeletal muscle and the diabetic phenotype is conserved in myotubes derived from subjects with type 2 diabetes. Several abnormalities have been identified in skeletal muscle from type 2 diabetic subjects, however, the exact molecular mechanisms leading to the diabetic phenotype has still not been found. Here we present a large-scale study in which we combine a quantitative proteomic discovery strategy using isobaric peptide tags for relative and absolute quantification (iTRAQ) and a label-free study with a targeted quantitative proteomic approach using selected reaction monitoring to identify, quantify, and validate changes in protein abundance among human myotubes obtained from nondiabetic lean, nondiabetic obese, and type 2 diabetic subjects, respectively. Using an optimized protein precipitation protocol, a total of 2832 unique proteins were identified and quantified using the iTRAQ strategy. Despite a clear diabetic phenotype in diabetic myotubes, the majority of the proteins identified in this study did not exhibit significant abundance changes across the patient groups. Proteins from all major pathways known to be important in type 2 diabetic subjects were well-characterized in this study. This included pathways like the trichloroacetic acid (TCA) cycle, lipid oxidation, oxidative phosphorylation, the glycolytic pathway, and glycogen metabolism from which all but two enzymes were found in the present study. None of these enzymes were found to be regulated at the level of protein expression or degradation supporting the hypothesis that these pathways are regulated at the level of post-translational modification. Twelve proteins were, however, differentially expressed among the three different groups. Thirty-six proteins were chosen for further analysis and validation using selected reaction monitoring based on the regulation identified in the iTRAQ discovery study. The abundance of adenosine deaminase was considerably down-regulated in diabetic myotubes and as the protein binds propyl dipeptidase (DPP-IV), we speculate whether the reduced binding of adenosine deaminase to DPP-IV may contribute to the diabetic phenotype in vivo by leading to a higher level of free DPP-IV to bind and inactivate the anti-diabetic hormones, glucagon-like peptide-1 and glucose-dependent insulintropic polypeptide.

Genetic and environmental influences on oxidative damage assessed in elderly Danish twins

Previous studies have shown an association between oxidative stress and various diseases in humans including cancer, cardiovascular disease, diabetes, and chronic respiratory disease. To what extents this damage is determined by genetic and environmental factors is unknown. In a classical twin study with 198 elderly twins we examined the contributions of genetic versus environmental factors to nucleic acid oxidation and lipid peroxidation. Urinary excretion of 8-oxo-7,8-dihydro-2'-deoxyguanosine (8-oxodG), 8-oxo-7,8-dihydroguanosine (8-oxoGuo), and dinor,dihydro F₂-isoprostane metabolites (F₂-IsoP-M) was measured using liquid chromatography-tandem mass spectrometry. The environmental influence on nucleic acid oxidation and lipid peroxidation was predominant, leaving only little influence from genetic factors, as evidenced by no differences in intraclass correlations between monozygotic (MZ) and dizygotic (DZ) twins, neither for 8-oxodG (r(MZ)=0.55, r(DZ)=0.47; P=0.43), F(2)-IsoP-M (r(MZ)=0.33, r(DZ)=0.22; P=0.42), nor 8-oxoGuo (r(MZ)=0.45, r(DZ)=0.58; P=0.21). Accordingly, heritability estimates for the three markers of oxidative damage were low (h²=0.17-0.22). The three urinary markers of oxidative stress were closely correlated (r=0.60-0.84). In conclusion, we demonstrated in a large population of elderly Danish twins that "whole-body" oxidative damage to nucleic acids and lipids is predominantly determined by potentially modifiable nongenetic factors.

The 1p13.3 LDL (C)-associated locus shows large effect sizes in young populations

Genome-wide association studies (GWASs) have identified polymorphic loci associated with coronary artery disease (CAD) risk factors (i.e. serum lipids) in adult populations (42-69 y). We hypothesized that younger populations would show a greater relative genetic component due to fewer confounding variables. We examined the influence of 20 GWAS loci associated with serum lipids and insulin metabolism, in a university student cohort (n = 548; mean age = 24 y), and replicated statistically associated results in a second study cohort of primary school students (n = 810, mean age = 11.5 y). Nineteen loci showed no relationship with studied risk factors in young adults. However, the ancestral allele of the rs646776 (SORT1) locus was strongly associated with increased LDL (C) in young adults [TT: 97.6 ± 1.0 mg/dL (n = 345) versus CT/CC: 87.3 ± 1.0 mg/dL (n = 203); p = 3 × 10(x6)] and children [TT: 94.0 ± 1.3 mg/dL (n = 551) versus CT/CC: 84.7 ± 1.4 mg/dL (n = 259); p = 4 × 10(x6)]. This locus is responsible for 3.6% of population variance in young adults and 2.5% of population variance in children. The effect size of the SORT1 locus is considerably higher in young populations (2.5-4.1%) compared with older subjects (1%).

Ancestry-informative markers on chromosomes 2, 8 and 15 are associated with insulin-related traits in a racially diverse sample of children

Type 2 diabetes represents an increasing health burden. Its prevalence is rising among younger age groups and differs among racial/ethnic groups. Little is known about its genetic basis, including whether there is a genetic basis for racial/ethnic disparities. We examined a multi-ethnic sample of 253 healthy children to evaluate associations between insulin-related phenotypes and 142 ancestry-informative markers (AIMs), while adjusting for sex, age, Tanner stage, genetic admixture, total body fat, height and socio-economic status. We also evaluated the effect of measurement errors in the estimation of the individual ancestry proportions on the regression results. We found that European genetic admixture is positively associated with insulin sensitivity (S I ), and negatively associated with the acute insulin response to glucose, fasting insulin levels and the homeostasis model assessment of insulin resistance. Our analysis revealed associations between individual AIMs on chromosomes 2, 8 and 15 and these phenotypes. Most notably, marker rs3287 at chromosome 2p21 was found to be associated with S I ( p = 5.8 × 10(-5)). This marker may be in admixture linkage disequilibrium with nearby loci ( THADA and BCL11A ) that previously have been reported to be associated with diabetes and diabetes-related phenotypes in several genome-wide association and linkage studies. Our results provide further evidence that variation in the 2p21 region containing THADA and BCL11A is associated with type 2 diabetes. Importantly, we have implicated this region in the early development of diabetes-related phenotypes, and in the genetic aetiology of population differences in these phenotypes.

Single nucleotide polymorphisms within functional regions of genes implicated in insulin action and association with the insulin resistant phenotype

Type 2 diabetes and insulin resistance (IR) are characterized by severe anomalies in genes expression rate including genes involved in insulin signal transduction. Post-transcriptional regulation of gene expression is crucial for many physiological processes and is mediated mainly by untranslated region (UTR). Present study concentrated on the search for correlation between single nucleotides polymorphisms in UTRs of the INSR, PIK3R1, PTPN1, and SLC2A4 genes and IR. 130 unrelated diabetic patients and 98 healthy controls were analyzed in present study. Genotyping was performed by multiplex minisequencing preceded by multiplex PCR. Two single nucleotide polymorphisms (SNPs) showed significant differences in genotype frequencies between analyzed groups. Statistical significance was received for rs3745551 located in 3'-UTR of the INSR and rs3756668 located in 3'-UTR of the PIK3R1 gene with higher number of G/G genotype in insulin resistant subjects. Furthermore, patients carrying G/G genotype of those SNPs displayed higher BMI value, higher fasting glucose and insulin levels and were more insulin resistant assessed by HOMA-IR and QUICKI. Present study provides evidence for association between SNPs in UTRs of the INSR and PIK3R1 genes and insulin resistant phenotype.

Integrated genetic and epigenetic analysis identifies haplotype-specific methylation in the FTO type 2 diabetes and obesity susceptibility locus

Recent multi-dimensional approaches to the study of complex disease have revealed powerful insights into how genetic and epigenetic factors may underlie their aetiopathogenesis. We examined genotype-epigenotype interactions in the context of Type 2 Diabetes (T2D), focussing on known regions of genomic susceptibility. We assayed DNA methylation in 60 females, stratified according to disease susceptibility haplotype using previously identified association loci. CpG methylation was assessed using methylated DNA immunoprecipitation on a targeted array (MeDIP-chip) and absolute methylation values were estimated using a Bayesian algorithm (BATMAN). Absolute methylation levels were quantified across LD blocks, and we identified increased DNA methylation on the FTO obesity susceptibility haplotype, tagged by the rs8050136 risk allele A (p = 9.40×10⁻⁴, permutation p = 1.0×10⁻³). Further analysis across the 46 kb LD block using sliding windows localised the most significant difference to be within a 7.7 kb region (p = 1.13×10⁻⁷). Sequence level analysis, followed by pyrosequencing validation, revealed that the methylation difference was driven by the co-ordinated phase of CpG-creating SNPs across the risk haplotype. This 7.7 kb region of haplotype-specific methylation (HSM), encapsulates a Highly Conserved Non-Coding Element (HCNE) that has previously been validated as a long-range enhancer, supported by the histone H3K4me1 enhancer signature. This study demonstrates that integration of Genome-Wide Association (GWA) SNP and epigenomic DNA methylation data can identify potential novel genotype-epigenotype interactions within disease-associated loci, thus providing a novel route to aid unravelling common complex diseases.

Does skeletal muscle oxidative stress initiate insulin resistance in genetically predisposed individuals?

Reactive oxygen species (ROS) are postulated to be a common trigger of insulin resistance. For example, treatment of adipocytes with either tumor-necrosis factor-alpha or dexamethasone increases ROS before impairing glucose uptake. Similarly, treatment with mitochondria-specific antioxidants preserves insulin sensitivity in animal models of insulin resistance. However, it remains unclear whether ROS contribute to insulin resistance in humans. First-degree relatives (FDRs) of type 2 diabetes subjects are at increased risk of developing insulin resistance and type 2 diabetes. Here we review the documented metabolic impairments in FDRs that could contribute to insulin resistance via increased oxidative stress. We propose that lipotoxic intermediates and lipid peroxides in skeletal muscle interfere with insulin signaling and might cause insulin resistance in these 'at risk' individuals.

Genetic influences on the insulin response of the beta cell to different secretagogues

AIMS/HYPOTHESIS

The aim of the present study was to estimate the heritability of the beta cell insulin response to glucose and to glucose combined with glucagon-like peptide-1 (GLP-1) or with GLP-1 plus arginine.

METHODS

This was a twin-family study that included 54 families from the Netherlands Twin Register. The participants were healthy twin pairs and their siblings of the same sex, aged 20 to 50 years. Insulin response of the beta cell was assessed by a modified hyperglycaemic clamp with additional GLP-1 and arginine. Insulin sensitivity index (ISI) was assessed by the euglycaemic-hyperinsulinaemic clamp. Multivariate structural equation modelling was used to obtain heritabilities and the genetic factors underlying individual differences in BMI, ISI and secretory responses of the beta cell.

RESULTS

The heritability of insulin levels in response to glucose was 52% and 77% for the first and second phase, respectively, 53% in response to glucose + GLP-1 and 80% in response to an additional arginine bolus. Insulin responses to the administration of glucose, glucose + GLP-1 and glucose + GLP-1 + arginine were highly correlated (0.62< r <0.79). Heritability of BMI and ISI was 74% and 60% respectively. The genetic factors that influenced BMI and ISI explained about half of the heritability of insulin levels in response to the three secretagogues. The other half was due to genetic factors specific to the beta cell.

CONCLUSIONS/INTERPRETATION

In healthy adults, genetic factors explain most of the individual differences in the secretory capacity of the beta cell. These genetic influences are partly independent from the genes that influence BMI and ISI.

m.3243A>G mutation in mitochondrial DNA leads to decreased insulin sensitivity in skeletal muscle and to progressive beta-cell dysfunction

OBJECTIVE

To study insulin sensitivity and perfusion in skeletal muscle together with the beta-cell function in subjects with the m.3243A>G mutation in mitochondrial DNA, the most common cause of mitochondrial diabetes.

RESEARCH DESIGN AND METHODS

We measured skeletal muscle glucose uptake and perfusion using positron emission tomography and 2-[18F]fluoro-2-deoxyglucose and [15O]H2O during euglycemic hyperinsulinemia in 15 patients with m.3243A>G. These patients included five subjects with no diabetes as defined by the oral glucose tolerance test (OGTT) (group 1), three with GHb <6.1% and newly found diabetes by OGTT (group 2), and seven with a previously diagnosed diabetes (group 3). Control subjects consisted of 13 healthy individuals who were similar to the carriers of m.3243A>G with respect to age and physical activity. Beta-cell function was assessed using the OGTT and subsequent mathematical modeling.

RESULTS

Skeletal muscle glucose uptake was significantly lower in groups 1, 2, and 3 than in the control subjects. The glucose sensitivity of beta-cells in group 1 patients was similar to that of the control subjects, whereas in group 2 and 3 patients, the glucose sensitivity was significantly lower. The insulin secretion parameters correlated strongly with the proportion of m.3243A>G mutation in muscle.

CONCLUSIONS

Our findings show that subjects with m.3243A>G are insulin resistant in skeletal muscle even when beta-cell function is not markedly impaired or glucose control compromised. We suggest that both the skeletal muscle insulin sensitivity and the beta-cell function are affected before the onset of the mitochondrial diabetes caused by the m.3243A>G mutation.

Regulation of muscle glycogen synthase phosphorylation and kinetic properties by insulin, exercise, adrenaline and role in insulin resistance

In mammals, excess carbohydrate is stored as glycogen and glycogen synthase is the enzyme that incorporates glucose units into the glycogen particle. Glycogen synthase activity is regulated by phosphorylation and allosterically activated by glucose 6-phosphate. Phosphorylation of nine serines by different kinases regulates glycogen synthase affinity for glucose 6-phosphate and its substrate UDP-glucose. Glucose 6-phosphate increases both enzyme activity and substrate affinity. Insulin and exercise increase glycogen synthase affinity for glucose 6-phosphate and activity whereas high glycogen content and adrenaline decrease affinity for glucose 6-phosphate and activity. However, insulin, exercise and adrenaline also regulate intracellular concentration of glucose 6-phosphate which will influence in vivo glycogen synthase activity. Importantly, type 2 diabetes is associated with reduced insulin-stimulated glycogen synthase activation. The nine phosphorylation sites theoretically allow 512 combinations of phosphorylation configurations of glycogen synthase with different kinetic properties. However, due to hierarchal phosphorylation, the number of configurations in vivo is most likely much lower. Unfortunately, many studies only report data on glycogen synthase activity measured with high concentration of UDP-glucose which holds back information about changes in substrate affinity. In this paper we discuss the physiological regulation of glycogen synthase phosphorylation and how the phosphorylation pattern regulates glycogen synthase kinetic properties.

Mitochondrial fitness and insulin sensitivity in humans

Human mitochondria can be studied either in biopsies or by measuring flux through ATP synthase and phosphocreatine recovery using magnetic resonance spectroscopy. Myocellular ATP production (flux through ATP synthase [fATP]) increases by up to 90% during 8 h of insulin stimulation. Fasting mitochondrial function is 14-40% lower than in controls in the presence of insulin resistance, as seen in those with type 2 diabetes, their insulin-resistant relatives or the obese. Insulin-stimulated fATP is abolished in insulin-resistant relatives and patients with type 2 diabetes, and patients frequently show decreased mitochondrial size/density. Age, fat mass, physical activity, plasma NEFA and glucose all correlate negatively with mitochondrial function, but it is for methodological reasons difficult to determine whether reduced mitochondrial content or function account for reduced ATP production in insulin resistance. Experimental plasma NEFA elevation appears to inhibit mitochondrial function by interfering with the metabolic actions of insulin, which might explain impaired mitochondrial function in obesity. Alternatively, primary mitochondrial abnormalities, as seen in those with inherited risk of type 2 diabetes, could decrease lipid oxidation, thereby raising circulating and intracellular NEFA levels. In type 2 diabetes, chronic hyperglycaemia and dyslipidaemia could first diminish the function, and subsequently reduce the size or density of mitochondria via oxidative stress and apoptosis. Many questions remain unsolved, including (1) which mechanisms regulate mitochondrial adaptation to nutrient overload; (2) what factors control the expression of genes encoding mitochondrial proteins and other signals involved in mitochondrial biogenesis; (3) which geno/phenotypes are associated with both insulin resistance and mitochondrial abnormalities; and (4) which are the most promising targets for improving mitochondrial fitness in insulin resistance?

Transcriptional profiling of myotubes from patients with type 2 diabetes: no evidence for a primary defect in oxidative phosphorylation genes

AIMS/HYPOTHESIS

Microarray-based studies of skeletal muscle from patients with type 2 diabetes and high-risk individuals have demonstrated that insulin resistance and reduced mitochondrial biogenesis co-exist early in the pathogenesis of type 2 diabetes independently of hyperglycaemia and obesity. It is unknown whether reduced mitochondrial biogenesis or other transcriptional alterations co-exist with impaired insulin responsiveness in primary human muscle cells from patients with type 2 diabetes.

METHODS

Using cDNA microarray technology and global pathway analysis with the Gene Map Annotator and Pathway Profiler (GenMapp 2.1) and Gene Set Enrichment Analysis (GSEA 2.0.1), we examined transcript levels in myotubes established from obese patients with type 2 diabetes and matched obese healthy participants, who had been extensively metabolically characterised both in vivo and in vitro. We have previously reported reduced basal lipid oxidation and impaired insulin-stimulated glycogen synthesis and glucose oxidation in these diabetic myotubes.

RESULTS

No single gene was differently expressed after correction for multiple testing, and no biological pathway was differently expressed using either method of global pathway analysis. In particular, we found no evidence for differential expression of genes involved in mitochondrial oxidative metabolism. Consistently, there was no difference in mRNA levels of genes known to mediate the transcriptional control of mitochondrial biogenesis (PPARGC1A and NRF1) or in mitochondrial mass between diabetic and control myotubes.

CONCLUSIONS/INTERPRETATION

These results support the hypothesis that impaired mitochondrial biogenesis is not a primary defect in the sequence of events leading to insulin resistance and type 2 diabetes.

Impaired glucose regulation and type 2 diabetes in children and adolescents

Diabetes mellitus in paediatric patients used to be almost exclusively type 1, but in recent years, case series as well as hospital-based and population-based studies indicated that the number of children and adolescents with type 2 diabetes (T2DM) has been increasing. This development is alarming since T2DM in youth is usually not an isolated condition, but accompanied by other cardiovascular risk factors such as obesity, dyslipidaemia, hypertension and low-grade inflammation. In adults, numerous studies provided detailed data on prevalence, incidence and risk factors for the development of T2DM, but for children and adolescents clinical and experimental data are still rather limited. This review provides an overview about the epidemiology and pathogenesis of T2DM in youth and about impaired glucose regulation as major risk factor for diabetes development with a special focus on the recent literature on clinical and lifestyle-related risk factors. Differences in incidence and prevalence across different populations indicate that ethnic background and genetic pre-disposition may be important risk determinants. In addition, epigenetic factors and foetal programming appear to confer additional risk before birth. Among the environmental and lifestyle-related risk factors there is evidence that obesity, hypercaloric diet, physical inactivity, socio-economic position (SEP), smoking, low-grade inflammation, psychosocial stress and sleeping patterns contribute to the risk for T2DM. However, the assessment of the relevance of risk factors and of incidence or prevalence estimates in youth is complicated by methodological issues that are also discussed.

Mitochondrial dysfunction in type 2 diabetes and obesity

Insulin resistance in skeletal muscle is a major hallmark of type 2 diabetes mellitus (T2D) and obesity that is characterized by impaired insulin-mediated glucose transport and glycogen synthesis and by increased intramyocellular content of lipid metabolites. Several studies have provided evidence for mitochondrial dysfunction in skeletal muscle of type 2 diabetic and prediabetic subjects, primarily due to a lower content of mitochondria (mitochondrial biogenesis) and possibly to a reduced functional capacity per mitochondrion. This article discusses the latest advances in the understanding of the molecular mechanisms underlying insulin resistance in human skeletal muscle in T2D and obesity, with a focus on possible links between insulin resistance and mitochondrial dysfunction.

Glycogen content and contraction regulate glycogen synthase phosphorylation and affinity for UDP-glucose in rat skeletal muscles

Glycogen content and contraction strongly regulate glycogen synthase (GS) activity, and the aim of the present study was to explore their effects and interaction on GS phosphorylation and kinetic properties. Glycogen content in rat epitrochlearis muscles was manipulated in vivo. After manipulation, incubated muscles with normal glycogen [NG; 210.9 +/- 7.1 mmol/kg dry weight (dw)], low glycogen (LG; 108.1 +/- 4.5 mmol/ kg dw), and high glycogen (HG; 482.7 +/- 42.1 mmol/kg dw) were contracted or rested before the studies of GS kinetic properties and GS phosphorylation (using phospho-specific antibodies). LG decreased and HG increased GS K(m) for UDP-glucose (LG: 0.27 +/- 0.02 < NG: 0.71 +/- 0.06 < HG: 1.11 +/- 0.12 mM; P < 0.001). In addition, GS fractional activity inversely correlated with glycogen content (R = -0.70; P < 0.001; n = 44). Contraction decreased K(m) for UDP-glucose (LG: 0.14 +/- 0.01 = NG: 0.16 +/- 0.01 < HG: 0.33 +/- 0.03 mM; P < 0.001) and increased GS fractional activity, and these effects were observed independently of glycogen content. In rested muscles, GS Ser(641) and Ser(7) phosphorylation was decreased in LG and increased in HG compared with NG. GSK-3beta Ser(9) and AMPKalpha Thr(172) phosphorylation was not modulated by glycogen content in rested muscles. Contraction decreased phosphorylation of GS Ser(641) at all glycogen contents. However, contraction increased GS Ser(7) phosphorylation even though GS was strongly activated. In conclusion, glycogen content regulates GS affinity for UDP-glucose and low affinity for UDP-glucose in muscles with high glycogen content may reduce glycogen accumulation. Contraction increases GS affinity for UDP-glucose independently of glycogen content and creates a unique phosphorylation pattern.

Mitochondrial respiration is decreased in skeletal muscle of patients with type 2 diabetes

We tested the hypothesis of a lower respiratory capacity per mitochondrion in skeletal muscle of type 2 diabetic patients compared with obese subjects. Muscle biopsies obtained from 10 obese type 2 diabetic and 8 obese nondiabetic male subjects were used for assessment of 3-hydroxy-Acyl-CoA-dehydrogenase (HAD) and citrate synthase activity, uncoupling protein (UCP)3 content, oxidative stress measured as 4-hydroxy-2-nonenal (HNE), fiber type distribution, and respiration in isolated mitochondria. Respiration was normalized to citrate synthase activity (mitochondrial content) in isolated mitochondria. Maximal ADP-stimulated respiration (state 3) with pyruvate plus malate and respiration through the electron transport chain (ETC) were reduced in type 2 diabetic patients, and the proportion of type 2X fibers were higher in type 2 diabetic patients compared with obese subjects (all P < 0.05). There were no differences in respiration with palmitoyl-l-carnitine plus malate, citrate synthase activity, HAD activity, UCP3 content, or oxidative stress measured as HNE between the groups. In the whole group, state 3 respiration with pyruvate plus malate and respiration through ETC were negatively associated with A1C, and the proportion of type 2X fibers correlated with markers of insulin resistance (P < 0.05). In conclusion, we provide evidence for a functional impairment in mitochondrial respiration and increased amount of type 2X fibers in muscle of type 2 diabetic patients. These alterations may contribute to the development of type 2 diabetes in humans with obesity.

Prevention of diet-induced obesity and impaired glucose tolerance in rats following administration of leptin to their mothers

Absence of leptin is known to disrupt the development of energy balance regulatory mechanisms. We investigated whether administration of leptin to normally nourished rats affects energy balance in their offspring. Leptin (2 mg·kg−1·day−1) was administered from day 14 of pregnancy and throughout lactation. Male and female offspring were fed either on chow or on high-fat diets that elicited similar levels of obesity in the sexes from 6 wk to 15 mo of age. Treatment of the dams with leptin prevented diet-induced increases in the rate of weight gain, retroperitoneal fat pad weight, area under the intraperitoneal glucose tolerance curve, and fasting plasma insulin concentration in female offspring. In the male offspring, the diet-induced increase in weight gain was prevented and increased fat pad weight was reduced. Energy intake per rat was higher in response to the obesogenic diet in male offspring of saline-treated but not leptin-treated dams. A similar trend was seen in 3-mo-old female offspring. Energy expenditure at 3 mo of age was higher for a given body weight in female offspring of leptin-treated compared with saline-treated dams when these animals were fed on the obesogenic diet. A similar trend was seen for male rats fed on the obesogenic diet. Thus leptin levels during pregnancy and lactation can affect the development of energy balance regulatory systems in their offspring.

The effect of exercise, training, and inactivity on insulin sensitivity in diabetics and their relatives: what is new?

Insulin resistance is a hallmark characteristic of type 2 diabetes. However, in healthy first-degree relatives of type 2 diabetics, insulin resistance is often present years before glucose intolerance or diabetes becomes clinically manifest. The mechanisms of insulin resistance involve conditions leading to an increased supply of fatty acids (e.g., high energy intake, obesity) and conditions in which the degradation/oxidation of muscular fatty acids is impaired. Several large-scale studies have documented the fact that increased physical activity can reduce or at least postpone the development of type 2 diabetes, and low physical fitness is a clear independent risk factor for the development of type 2 diabetes. The mechanisms responsible for the improvement in insulin sensitivity after exercise training have been studied extensively, but are not fully understood. This review focuses on insulin resistance in skeletal muscle and, in particular, its relation to changes in aerobic fitness in type 2 diabetics and their first-degree relatives.

Reduced plasma adiponectin concentrations may contribute to impaired insulin activation of glycogen synthase in skeletal muscle of patients with type 2 diabetes

AIMS/HYPOTHESIS

Circulating levels of adiponectin are negatively associated with multiple indices of insulin resistance, and the concentration is reduced in humans with insulin resistance and type 2 diabetes. However, the mechanisms by which adiponectin improves insulin sensitivity remain unclear.

SUBJECTS AND METHODS

Combining euglycaemic-hyperinsulinaemic clamp studies with indirect calorimetry and skeletal muscle biopsies, we examined the relationship between plasma adiponectin and parameters of whole-body glucose and lipid metabolism, and muscle glycogen synthase (GS) activity in 51 Caucasians (ten lean, 21 obese and 20 with type 2 diabetes).

RESULTS

Plasma adiponectin was significantly reduced in type 2 diabetic compared with obese and lean subjects. In lean and obese subjects, insulin significantly reduced plasma adiponectin, but this response was blunted in patients with type 2 diabetes. Plasma adiponectin was positively associated with insulin-stimulated glucose disposal (r = 0.48), glucose oxidation (r = 0.54), respiratory quotient (r = 0.58) and non-oxidative glucose metabolism (r = 0.38), and negatively associated with lipid oxidation during insulin stimulation (r = -0.60) after adjustment for body fat (all p < 0.01). Most notably, we found a positive association between plasma adiponectin and insulin stimulation of GS activity in skeletal muscle (r = 0.44, p < 0.01).

CONCLUSIONS/INTERPRETATION

Our results indicate that plasma adiponectin may enhance insulin sensitivity by improving the capacity to switch from lipid to glucose oxidation and to store glucose as glycogen in response to insulin, and that low adiponectin may contribute to impaired insulin activation of GS in skeletal muscle of patients with type 2 diabetes.

The Genetic Basis of Type 2 Diabetes

Type 2 Diabetes results from a complex physiologic process that includes the pancreatic beta cells, peripheral glucose uptake in muscle, the secretion of multiple cytokines and hormone-like molecules from adipocytes, hepatic glucose production, and likely the central nervous system. Consistent with the complex web of physiologic defects, the emerging picture of the genetics will involve a large number of risk susceptibility genes, each individually with relatively small effect (odds ratios below 1.2 in most cases). The challenge for the future will include cataloging and confirming the genetic risk factors, and understanding how these risk factors interact with each other and with the known environmental and lifestyle risk factors that increase the propensity to type 2 diabetes.

Genetic epidemiology of diabetes

Conventional genetic analysis focuses on the genes that account for specific phenotypes, while traditional epidemiology is more concerned with the environmental causes and risk factors related to traits. Genetic epidemiology is an alliance of the 2 fields that focuses on both genetics, including allelic variants in different populations, and environment, in order to explain exactly how genes convey effects in different environmental contexts and to arrive at a more complete comprehension of the etiology of complex traits. In this review, we discuss the epidemiology of diabetes and the current understanding of the genetic bases of obesity and diabetes and provide suggestions for accelerated accumulation of clinically useful genetic information.

[Genetics of type 2 diabetes]

In the last years type 2 diabetes has reached almost epidemic proportions. More than 170 million individuals are affected worldwide, about 6 million in Germany. Manifestation of type 2 diabetes is determined by both environmental factors such as lack of physical exercise and overeating and a genetic predisposition. Despite enormous efforts in medical research to identify susceptibility loci and high risk alleles, the genetics of common type 2 diabetes (non-MODY) remain unknown. To date, only a few susceptibility genes have been identified (such as PPARG, KCNJ11, CAPN10). However, replication of initial studies is often difficult. This can be explained by both locus and allelic heterogeneity as well as ethnic differences between different populations. Studies in genetically isolated populations such as the Pima Indians are advantageous to identify susceptibility alleles. Despite some recent advances, it is not possible to predict an individual's risk of type 2 diabetes based on the presence of a certain disease-risk allele.

Type 2 diabetes: principles of pathogenesis and therapy

Type 2 diabetes mellitus has become an epidemic, and virtually no physician is without patients who have the disease. Whereas insulin insensitivity is an early phenomenon partly related to obesity, pancreas beta-cell function declines gradually over time already before the onset of clinical hyperglycaemia. Several mechanisms have been proposed, including increased non-esterified fatty acids, inflammatory cytokines, adipokines, and mitochondrial dysfunction for insulin resistance, and glucotoxicity, lipotoxicity, and amyloid formation for beta-cell dysfunction. Moreover, the disease has a strong genetic component, but only a handful of genes have been identified so far: genes for calpain 10, potassium inward-rectifier 6.2, peroxisome proliferator-activated receptor gamma, insulin receptor substrate-1, and others. Management includes not only diet and exercise, but also combinations of anti-hyperglycaemic drug treatment with lipid-lowering, antihypertensive, and anti platelet therapy.

An insulin-response element-binding protein that ameliorates hyperglycemia in diabetes

Insulin modulates glucose homeostasis, but the role of insulin-responsive transcription factors in such actions is not well understood. Recently, we have identified the insulin-response element-binding protein-1 (IRE-BP1) as a transcription factor that appears to mediate insulin action on multiple target genes. To examine the possibility that IRE-BP1 is an insulin-responsive glucoregulatory factor involved in the metabolic actions of insulin, we investigated the effect of adenoviral overexpression of hepatic IRE-BP1 on the glycemic control of insulin-resistant diabetic rats. Adenoviral IRE-BP1 lowered both fasting and postprandial glucose levels, and microarray of hepatic RNA revealed modulation of the expression of genes involved in gluconeogenesis, lipogenesis, and fatty acid oxidation. The insulin mimetic effects of IRE-BP1 were also confirmed in L6 myocytes; stable constitutive expressions of IRE-BP1 enhanced glucose transporter expression, glucose uptake, and glycogen accumulation in these cells. These findings showed physiologic sufficiency of IRE-BP1 as the transcriptional mediator of the metabolic action of insulin. Understanding IRE-BP1 action should constitute a useful probe into the mechanisms of metabolic regulation and an important target to develop therapeutic agents that mimic or enhance insulin action.

Genetic Factors in Type 2 Diabetes: The End of the Beginning?

The intensive search for genetic variants that predispose to type 2 diabetes was launched with optimism, but progress has been slower than was hoped. Even so, major advances have been made in the understanding of monogenic forms of the disease which together represent a substantial health burden, and a few common gene variants that influence susceptibility have now been unequivocally identified. Armed with a better understanding of the tools needed to detect such genes, it seems inevitable that the rate of progress will increase and the relevance of genetic information to the diagnosis, treatment, and prevention of diabetes will become increasingly tangible.

Fetal programming: the perspective of single and twin pregnancies

Multiple pregnancy is associated with increased risk of adverse consequences for both mother and fetus(es), including increased rates of maternal hypertension and pre-eclampsia, spontaneous abortion, Caesarean delivery, low birthweight, birth prematurity, perinatal mortality, admission to neonatal intensive care and extended length of care, respiratory distress, cerebral palsy, developmental delay, contact with disability services and mortality to age 5 years. Premature birth, which affects 97% of triplets and 53.3% of twins in Australia, is not the sole factor involved. The rate of multiple pregnancy in Australia is 1.7%. This compares to 22.1% for pregnancies resulting from assisted reproduction technology (ART). As a result, 21.8% of babies born from ART are from a multiple pregnancy, in comparison to the USA where the majority of babies born from ART are from a multiple pregnancy. Additionally, the population rate of multiple births is rising due to the more frequent use of ART and continued multi-embryo transfers, which is operating against a background of rising implantation rates within ART clinics. Twins have been of interest from a programming perspective. However, analysis of associations between crude birthweight and subsequent metabolic risk factors or mortality in adulthood from chronic disease indicate that adaptations in pregnancy to support multi-fetal growth are not identical to fetal growth restriction in singleton pregnancies. Indeed, the process of ‘maternal constraint’ is incompletely understood and confounds such comparisons. From a programming perspective, it is a challenge to identify in twin pregnancies the transition from physiological adaptation to pathological growth restriction. Growth disparity between twins has been more illuminating of subtle adverse effects for the smaller of twin pairs in both blood pressure and insulin resistance in adulthood. Interestingly, these effects can be observed in both dizygotic and to a lesser degree in monozygotic twins, which indicates a role for both genetic and environmental factors in these measures. This suggests that, consistent with experimental studies in other species, the relationship between impaired growth in utero and chronic disease in later life is not simply mediated by a common genetic pathway.

Current status of the E23K Kir6.2 polymorphism: implications for type-2 diabetes

The ATP-sensitive potassium (KATP) channel couples membrane excitability to cellular metabolism and is a critical mediator in the process of glucose-stimulated insulin secretion. Increasing numbers of KATP channel polymorphisms are being described and linked to altered insulin secretion indicating that genes encoding this ion channel could be susceptibility markers for type-2 diabetes. Genetic variation of KATP channels may result in altered beta-cell electrical activity, glucose homeostasis, and increased susceptibility to type-2 diabetes. Of particular interest is the Kir6.2 E23K polymorphism, which is linked to increased susceptibility to type-2 diabetes in Caucasian populations and may also be associated with weight gain and obesity, both of which are major diabetes risk factors. This association highlights the potential contribution of both genetic and environmental factors to the development and progression of type-2 diabetes. In addition, the common occurrence of the E23K polymorphism in Caucasian populations may have conferred an evolutionary advantage to our ancestors. This review will summarize the current status of the association of KATP channel polymorphisms with type-2 diabetes, focusing on the possible mechanisms by which these polymorphisms alter glucose homeostasis and offering insights into possible evolutionary pressures that may have contributed to the high prevalence of KATP channel polymorphisms in the Caucasian population.