Genetics of type 2 diabetes and potential clinical implications

Type 2 diabetes in children and adolescents: distinct characteristics and evidence-based management

PURPOSE

Since the dramatic rise of obesity prevalence in childhood and adolescence has contributed to increased rates of type 2 diabetes (T2D) in youth, we sought to explore current evidence-based management options for pediatric T2D patients.

METHODS

A comprehensive literature search was performed for studies of T2D in childhood and adolescence until September 2021.

RESULTS

Special pathophysiological and diagnostic characteristics of T2D in this age are presented, while the main focus of the article is on management. Lifestyle interventions with healthy diet and exercise are of great importance for the treatment of T2D in children and adolescents. Metformin and insulin remain the traditional therapeutical means, while liraglutide recently gained indication for children older than 10 years both in USA and Europe. Data on the use, efficacy, safety and therapeutic considerations of other pharmacological treatments in children and adolescents with T2D are critically discussed.

CONCLUSION

Although many new and promising therapeutic strategies have been introduced during recent years for the management of T2D in adults, available therapeutic options for the management of pediatric T2D remain limited.

Chemical characterization and DPP-IV inhibitory activity evaluation of tripeptides from Gynura divaricata (L.) DC

ETHNOPHARMACOLOGICAL RELEVANCE

Gynura divaricata (L.) DC. (GD), a herbal medicine, has been used for the prevention and treatment of hyperglycemia in China. However, hypoglycemic ingredients within GD have not yet been well studied.

AIM OF THE STUDY

The aim of this study was to explore undiscovered compounds with dipeptidyl peptidase IV (DPP-IV) inhibitory activity within GD.

MATERIALS AND METHODS

A four-step strategy was developed to explore undiscovered DPP-IV inhibitors within GD. First, the components were preliminarily characterized using UHPLC-HRMS combined with a library search. Second, preliminarily characterized compounds were searched for potential bioactivity. Third, a mixture of these preliminarily characterized compounds was isolated and thoroughly characterized based on fragmentation patterns associated with molecular networking. Fourth, the activities of these compounds were verified using DPP-IV inhibitory assay and molecular docking.

RESULTS

Diprotin A, a tripeptide inhibitor against DPP-IV, was identified. Thereafter, a mixture of twenty-five diprotin A analogs was isolated and characterized, which exhibited IC₅₀ of 0.40 mg/mL for DPP-IV. Molecular docking results also confirmed the interactions between the tripeptide analogs and DPP-IV mainly via H-bonds and hydrophobic interactions.

CONCLUSIONS

This is the first report of DPP-IV inhibitors within GD. These findings demonstrate that the extract of GD might be beneficial for the treatment of type 2 diabetes mellitus, and is expected to promote further development and utilization of GD in herbal medicine.

Ten SNPs May Affect Type 2 Diabetes Risk in Interaction with Prenatal Exposure to Chinese Famine

Increasing studies have demonstrated that gene and famine may interact on type 2 diabetes risk. The data derived from the cross-sectional 2010-2012 China National Nutrition and Health Survey (CNNHS) was examined to explore whether gene and famine interacted to influence type 2 diabetes risk. In total, 2216 subjects were involved. The subjects born in 1960 and 1961 were selected as the famine-exposed group, whereas subjects born in 1963 were selected as the unexposed group. A Mass Array system was used to detect the genotypes of 50 related single-nucleotide polymorphisms (SNPs). Interactions were found between prenatal exposure to famine and ten SNPs (rs10401969, rs10886471, rs10946398, rs1470579, rs2796441, rs340874, rs3794991, rs5015480, rs7961581, and rs9470794) on type 2 diabetes risk after adjustments. The stratified results showed that famine exposure exacerbated the effect of CILP2-rs10401969 to fasting serum insulin (FINS), GRK5-rs10886471 to fasting plasma glucose (FPG) and FINS, IGF2BP2-rs1470579 to FINS, TLE1-rs2796441 to impaired fasting glucose (IFG), PROX1-rs340874 to impaired glucose tolerance (IGT), GATAD2A-rs3794991 to FINS, TSPAN8/LGR5-rs7961581 to FPG, and ZFAND3-rs9470794 to IGT and FINS. Famine exposure weakened the effect of CDKAL1-rs10946398 to type 2 diabetes. Famine exposure weakened the effect of HHEX-rs5015480 to IFG, but exacerbated the effect of HHEX-rs5015480 to FINS. The present study suggests that ten SNPs may affect type 2 diabetes risk in interaction with prenatal exposure to Chinese famine.

Metabolic outcomes of surgery in youth with type 2 diabetes

Youth-onset type 2 diabetes (T2D) is a formidable threat to the health of obese adolescents because of its potential for early-onset and aggressive co-morbidities and complications. The physiology of youth-onset T2D differs from T2D in adults and is associated with a greater degree of insulin resistance, a more rapid decline in pancreatic β-cell function, and a poorer response to medications. Medical management in youth is focused on combining lifestyle intervention and pharmacological treatment, but these therapies have yet to demonstrate improvements in disease progression. Metabolic bariatric surgery (MBS) is now recommended for the treatment of T2D in adults largely because of the beneficial effects on weight, ability to improve glycemic control, and, in a large proportion of people, induce diabetes remission. MBS is now being performed in adolescents with severe obesity and T2D, with initial results also showing high rates of T2D remission. Here, we review the state of medical management of youth-onset T2D and the outcomes of MBS studies in youth with T2D published to date.

Effects of variants of 50 genes on diabetes risk among the Chinese population born in the early 1960s

BACKGROUND

Genome-wide association studies have identified loci that significantly increase diabetes risk. This study explored the genetic susceptibility in relation to diabetes risk in adulthood among a Chinese population born in the early 1960s.

METHODS

In all, 2129 subjects (833 males, 1296 females) were selected from the cross-sectional 2010 to 2012 China National Nutrition and Health Survey. Fifty diabetes-related single nucleotide polymorphisms (SNPs) were detected. Two diabetes genetic risk scores (GRSs) based on the 50 diabetes-predisposing variants were developed to examine the association of these SNPs with diabetes risk.

RESULTS

Associations were found between diabetes risk and SNPs in the MTNR1B (rs10830963), KLHDC5 (rs10842994), GRK5 (rs10886471), cyclindependentkinase 5 regulatory subunit associated protein 1 (rs10946398), adaptorrelated protein complex 3 subunit sigma 2 (rs2028299), diacylglycerol kinase beta/transmembrane protein 195 (rs2191349), SREBF chaperone (rs4858889), ankyrin1 (rs516946), RAS guanyl releasing protein 1 (rs7403531), and zinc finger AN1-type containing 3 (rs9470794) genes. As a continuous variable, with a 1-point increase in the GRS or weighted (w) GRS, fasting plasma glucose (FPG) increased 0.045 and 0.044 mM, respectively (P < 0.001 for both), after adjusting for confounders. Both GRS and wGRS showed an association with diabetes, with a multivariable-adjusted odds ratio (95% confidence interval) of 1.09 (1.00-1.19) and 1.12 (1.03-1.22), respectively, among all subjects. No significant associations were found between the GRS or wGRS and impaired fasting glucose or impaired glucose tolerance.

CONCLUSIONS

The data suggest the association of 10 SNPs and the GRS or wGRS with diabetes risk. Genetic susceptibility to diabetes may synergistically affect the risk of diabetes in adulthood.

Spousal diabetes status as a risk factor for incident type 2 diabetes: a prospective cohort study and meta-analysis

AIMS

It is unclear if the presence of type-2 diabetes in one spouse is associated with the development of diabetes in the other spouse. We studied the concordance of diabetes among black and white participants in the Atherosclerosis Risk in Communities (ARIC) study and summarized existing studies in a meta-analysis.

METHODS

We conducted a prospective cohort analysis of ARIC data from 8077 married men and women (mean age 54 years) without diabetes at baseline (1987-1989). Complementary log-log models that accounted for interval censoring was used to model the hazard ratio (HR) for the association of spousal diabetes status with the incidence of diabetes. For the meta-analysis, we searched MEDLINE and EMBASE for observational studies published through December 2018 that evaluated spousal concordance for diabetes.

RESULTS

During a median follow-up of 22 years, 2512 incident cases of diabetes were recorded. In models with adjustment for general adiposity, spousal cardiometabolic factors and other diabetes risk factors, adults who had a spouse with diabetes had elevated risk for incident diabetes compared to those without a spouse diagnosed with diabetes (HR 1.20, 95% confidence interval 1.02-1.41). This association did not differ by sex or race. Summarized estimates from the 17 studies (489,798 participants from 9 countries) included in the meta-analysis showed a positive association between spousal diabetes status and the development of diabetes (Pooled odds ratio 1.88, 95% CI 1.52-2.33).

CONCLUSIONS

Results from this large prospective biracial cohort and meta-analysis provides evidence that spouses of persons with diabetes are a high-risk group for diabetes.

Pathophysiology of Type 2 Diabetes in Koreans

The pathophysiology of type 2 diabetes is characterized by variable degrees of insulin resistance and impaired insulin secretion. Both genetic and environmental factors serve as etiologic factors. Recent genetic studies have identified at least 83 variants associated with diabetes. A significant number of these loci are thought to be involved in insulin secretion, either through β-cell development or β-cell dysfunction. Environmental factors have changed rapidly during the past half century, and the increased prevalence of obesity and diabetes can be attributed to these changes. Environmental factors may affect epigenetic changes and alter susceptibility to diabetes. A recent epidemiologic study revealed that Korean patients with type 2 diabetes already had impaired insulin secretion and insulin resistance 10 years before the onset of diabetes. Those who developed diabetes showed impaired β-cell compensation with an abrupt decrease in insulin secretion during the last 2 years before diabetes developed. The retrograde trajectory of the disposition index differed according to the baseline subgroups of insulin secretion and insulin sensitivity. We hope that obtaining a more detailed understanding of the perturbations in the major pathophysiologic process of diabetes on the individual level will eventually lead to the implementation of precision medicine and improved patient outcomes.

Genetic Epidemiology of Type 2 Diabetes in Mexican Mestizos

There are currently about 415 million people with diabetes worldwide, a figure likely to increase to 642 million by 2040. In 2015, Mexico was the second Latin American country and sixth in the world in prevalence of this disorder with nearly 11.5 million of patients. Type 2 diabetes (T2D) is the main kind of diabetes and its etiology is complex with environmental and genetic factors involved. Indeed, polymorphisms in several genes have been associated with this disease worldwide. To estimate the genetic epidemiology of T2D in Mexican mestizos a systematic bibliographic search of published articles through PubMed, Scopus, Google Scholar, and Web of Science was conducted. Just case-control studies of candidate genes about T2D in Mexican mestizo inhabitants were included. Nineteen studies that met the inclusion criteria were found. In total, 68 polymorphisms of 41 genes were assessed; 26 of them were associated with T2D risk, which were located in ABCA1, ADRB3, CAPN10, CDC123/CAMK1D, CDKAL1, CDKN2A/2B, CRP, ELMO1, FTO, HHEX, IGF2BP2, IRS1, JAZF1, KCNQ1, LOC387761, LTA, NXPH1, SIRT1, SLC30A8, TCF7L2, and TNF-α genes. Overall, 21 of the 41 analyzed genes were associated with T2D in Mexican mestizos. Such a genetic heterogeneity compares with findings in other ethnic groups.

Lack of association between rs1800795 (-174 G/C) polymorphism in the promoter region of interleukin-6 gene and susceptibility to type 2 diabetes in Isfahan population

BACKGROUND

Type 2 diabetes mellitus (T2DM) is an inflammatory autoimmune disease that mostly affects older adults. The etiology of T2DM includes both genetic and environmental factors. rs1800795 (-174 G/C) single nucleotide polymorphism (SNP) linked with autoimmune disorders predispositions, identified by Genome-Wide Association Study among genes, which immunologically related is considerably over signified. The goal of this study was to evaluate the association between rs1800795 (-174 G/C) polymorphisms in the promoter of interleukin-6 (IL-6) gene with susceptibility to T2DM in a subset of the Iranian population.

MATERIALS AND METHODS

In this case-control study, 120 healthy subjects and 120 patients with T2DM were included. Genomic DNA obtained from whole blood samples and the polymerase chain reaction was used to amplify the fragment of interest contain rs1800795 SNP, restriction fragment length polymorphism method was applied for genotyping of the DNA samples with NlaIII as a restriction enzyme. SPSS for Windows software (version 18.0, SPSS, Chicago, IL, USA) was performed for statistical analysis.

RESULTS

No significant differences were found between healthy controls and T2DM patients with respect to the frequency distribution of the cytokine gene polymorphism investigated. Odds ratio, adjusted for sex, age, and smoking status has displayed similar outcomes.

CONCLUSION

These results indicated that the rs1800795 SNP is not a susceptibility gene variant for the development of T2DM in the Isfahan population. Further studies using new data on complex transcriptional interactions between IL-6 polymorphic sites are necessary to determine IL-6 haplotype influence on susceptibility to T2DM.

The changing face of diabetes in youth: lessons learned from studies of type 2 diabetes

The incidence of youth type 2 diabetes (T2D), linked with obesity and declining physical activity in high-risk populations, is increasing. Recent multicenter studies have led to a number of advances in our understanding of the epidemiology, pathophysiology, diagnosis, treatment, and complications of this disease. As in adult T2D, youth T2D is associated with insulin resistance, together with progressive deterioration in β cell function and relative insulin deficiency in the absence of diabetes-related immune markers. In contrast to adult T2D, the decline in β cell function in youth T2D is three- to fourfold faster, and therapeutic failure rates are significantly higher in youth than in adults. Whether the more aggressive nature of youth T2D is driven by genetic heterogeneity or physiology/metabolic maladaptation is yet unknown. Besides metformin, the lack of approved pharmacotherapeutic agents for youth T2D that target the pathophysiological mechanisms is a major barrier to optimal diabetes management. There is a significant need for effective therapeutic options, in addition to increased prevention, to halt the projected fourfold increase in youth T2D by 2050 and the consequences of heightened diabetes-related morbidity and mortality at younger ages.

Association of LEPR Gln223Arg polymorphism with T2DM: A meta-analysis

A meta-analysis was conducted to evaluate the association of LEPR Gln223Arg polymorphism with type 2diabetes (T2DM). Sixteen individual studies with 7827 subjects were included into the meta-analysis. Current studies suggest that LEPR Gln223Arg polymorphism may not affect the susceptibility with type 2diabetes (T2DM).

Utilizing Genetic Predisposition Score in Predicting Risk of Type 2 Diabetes Mellitus Incidence: A Community-based Cohort Study on Middle-aged Koreans

Contribution of genetic predisposition to risk prediction of type 2 diabetes mellitus (T2DM) was investigated using a prospective study in middle-aged adults in Korea. From a community cohort of 6,257 subjects with 8 yr' follow-up, genetic predisposition score with subsets of 3, 18, 36 selected single nucleotide polymorphisms (SNPs) (genetic predisposition score; GPS-3, GPS-18, GPS-36) in association with T2DM were determined, and their effect was evaluated using risk prediction models. Rs5215, rs10811661, and rs2237892 were in significant association with T2DM, and hazard ratios per risk allele score increase were 1.11 (95% confidence intervals: 1.06-1.17), 1.09 (1.01-1.05), 1.04 (1.02-1.07) with GPS-3, GPS-18, GPS-36, respectively. Changes in AUC upon addition of GPS were significant in simple and clinical models, but the significance disappeared in full clinical models with glycated hemoglobin (HbA1c). For net reclassification index (NRI), significant improvement observed in simple (range 5.1%-8.6%) and clinical (3.1%-4.4%) models were no longer significant in the full models. Influence of genetic predisposition in prediction ability of T2DM incidence was no longer significant when HbA1c was added in the models, confirming HbA1c as a strong predictor for T2DM risk. Also, the significant SNPs verified in our subjects warrant further research, e.g. gene-environmental interaction and epigenetic studies.

Novel epigenetic determinants of type 2 diabetes in Mexican-American families

Although DNA methylation is now recognized as an important mediator of complex diseases, the extent to which the genetic basis of such diseases is accounted for by DNA methylation is unknown. In the setting of large, extended families representing a minority, high-risk population of the USA, we aimed to characterize the role of epigenome-wide DNA methylation in type 2 diabetes (T2D). Using Illumina HumanMethylation450 BeadChip arrays, we tested for association of DNA methylation at 446 356 sites with age, sex and phenotypic traits related to T2D in 850 pedigreed Mexican-American individuals. Robust statistical analyses showed that (i) 15% of the methylome is significantly heritable, with a median heritability of 0.14; (ii) DNA methylation at 14% of CpG sites is associated with nearby sequence variants; (iii) 22% and 3% of the autosomal CpG sites are associated with age and sex, respectively; (iv) 53 CpG sites were significantly associated with liability to T2D, fasting blood glucose and insulin resistance; (v) DNA methylation levels at five CpG sites, mapping to three well-characterized genes (TXNIP, ABCG1 and SAMD12) independently explained 7.8% of the heritability of T2D (vi) methylation at these five sites was unlikely to be influenced by neighboring DNA sequence variation. Our study has identified novel epigenetic indicators of T2D risk in Mexican Americans who have increased risk for this disease. These results provide new insights into potential treatment targets of T2D.

Spousal diabetes as a diabetes risk factor: a systematic review and meta-analysis

BACKGROUND

Diabetes history in biologically-related individuals increases diabetes risk. We assessed diabetes concordance in spouses (that is, biologically unrelated family members) to gauge the importance of socioenvironmental factors.

METHODS

We selected cross-sectional, case-control and cohort studies examining spousal association for diabetes and/or prediabetes (impaired fasting glucose or impaired glucose tolerance), indexed in Medline, Embase or Scopus (1 January 1997 to 28 February 2013). Effect estimates (that is, odds ratios, incidence rate ratios, and so on) with body mass index (BMI) adjustment were pooled separately from those without BMI adjustment (random effects models) to distinguish BMI-dependent and independent concordance.

RESULTS

Searches yielded 2,705 articles; six were retained (n = 75,498 couples) for systematic review and five for meta-analysis. Concordance was lowest in a study that relied on women's reports of diabetes in themselves and their spouses (effect estimate 1.1, 95% CI 1.0 to 1.30) and highest in a study with systematic assessment of glucose tolerance (2.11, 95% CI 1.74 to 5.10). The random-effects pooled estimate adjusted for age and other covariates but not BMI was 1.26 (95% CI 1.08 to 1.45). The estimate with BMI adjustment was lower (1.18, 95% CI 0.97 to 1.40). Two studies assessing between-spouse associations of diabetes/prediabetes determined by glucose testing reported high concordance (OR 1.92, 95% CI 1.55 to 2.37 without BMI adjustment; 2.32, 95% CI 1.87 to 3.98 with BMI adjustment). Two studies did not distinguish type 1 and type 2 diabetes. However given that around 95% of adults is type 2, this is unlikely to have influenced the results.

CONCLUSIONS

Our pooled estimate suggests that a spousal history of diabetes is associated with a 26% diabetes risk increase. Recognizing shared risk between spouses may improve diabetes detection and motivate couples to increase collaborative efforts to optimize eating and physical activity habits.

Association between type 2 diabetes mellitus-related SNP variants and obesity traits in a Saudi population

Obesity, commonly measured as body mass index (BMI), has been on a rapid rise around the world and is an underlying cause of several chronic non-communicable diseases, including type 2 diabetes mellitus (T2DM). In addition to the environmental factors, genetic factors may also contribute to the ongoing obesity epidemic in Saudi Arabia. This study investigated the association between variants of 36 previously established T2DM SNPs and obesity phenotypes in a population of Saudi subjects. Study subjects consisted of 975 obese (BMI: ≥30), 825 overweight (25-30) and 423 lean controls (18-25) and of these 927 had a history of T2DM. Subjects were genotyped for 36 SNPs, which have been previously proved to be T2DM linked, using the KASPar method and the means of BMI and waist circumference (WC) corresponding to each of the genotypes were compared by additive, recessive and dominant genetic models. Five and seven of 36 T2DM-related SNPs were significantly associated with the BMI and WC, respectively. Variants of SNPs rs7903146, rs1552224 and rs11642841 in the control group and rs7903146 in T2DM group showed significant association with both BMI and WC. Variant of SNP rs10440833 was significantly associated with BMI in T2DM group of both males [OR = 1.8 (1.0, 3.3); P = 0.04] and females [OR = 2.0 (1.0, 3.9); P = 0.04]. Genetic risk scores explained 19 and 14% of WC and hip size variance in this population. Variants of a number of established T2DM related SNPs were associated with obesity phenotypes and may be significant hereditary factors in the pathogenesis of T2DM.

The architecture of risk for type 2 diabetes: understanding Asia in the context of global findings

The prevalence of Type 2 diabetes is rising rapidly in both developed and developing countries. Asia is developing as the epicentre of the escalating pandemic, reflecting rapid transitions in demography, migration, diet, and lifestyle patterns. The effective management of Type 2 diabetes in Asia may be complicated by differences in prevalence, risk factor profiles, genetic risk allele frequencies, and gene-environment interactions between different Asian countries, and between Asian and other continental populations. To reduce the worldwide burden of T2D, it will be important to understand the architecture of T2D susceptibility both within and between populations. This review will provide an overview of known genetic and nongenetic risk factors for T2D, placing the results from Asian studies in the context of broader global research. Given recent evidence from large-scale genetic studies of T2D, we place special emphasis on emerging knowledge about the genetic architecture of T2D and the potential contribution of genetic effects to population differences in risk.

Prediction of type 2 diabetes in women with a history of gestational diabetes using a genetic risk score

AIMS/HYPOTHESIS

Women with a history of gestational diabetes mellitus (GDM) are at increased risk of future development of type 2 diabetes. Recently, over 65 genetic variants have been confirmed to be associated with diabetes. We investigated whether this genetic information could improve the prediction of future diabetes in women with GDM.

METHODS

This was a prospective cohort study consisting of 395 women with GDM who were followed annually with an OGTT. A weighted genetic risk score (wGRS), consisting of 48 variants, was assessed for improving discrimination (C statistic) and risk reclassification (continuous net reclassification improvement [NRI] index) when added to clinical risk factors.

RESULTS

Among the 395 women with GDM, 116 (29.4%) developed diabetes during a median follow-up period of 45 months. Women with GDM who went on to develop diabetes had a significantly higher wGRS than those who did not (9.36 ± 0.92 vs 8.78 ± 1.07; p < 1.56 × 10(-7)). In a complex clinical model adjusted for age, prepregnancy BMI, family history of diabetes, blood pressure, fasting glucose and fasting insulin concentration, the C statistic marginally improved from 0.741 without the wGRS to 0.775 with the wGRS (p = 0.015). The addition of the wGRS to the clinical model resulted in a modest improvement in reclassification (continuous NRI 0.430 [95% CI 0.218, 0.642]; p = 7.0 × 10(-5)).

CONCLUSIONS/INTERPRETATION

In women with GDM, who are at high risk of diabetes, the wGRS was significantly associated with the future development of diabetes. Furthermore, it improved prediction over clinical risk factors.

A genome-wide search for type 2 diabetes susceptibility genes in an extended Arab family

Twenty percent of people aged 20 to 79 have type 2 diabetes (T2D) in the United Arab Emirates (UAE). Genome-wide association studies (GWAS) to identify genes for T2D have not been reported for Arab countries. We performed a discovery GWAS in an extended UAE family (N=178; 66 diabetic; 112 healthy) genotyped on the Illumina Human 660 Quad Beadchip, with independent replication of top hits in 116 cases and 199 controls. Power to achieve genome-wide significance (commonly P=5×10(-8)) was therefore limited. Nevertheless, transmission disequilibrium testing in FBAT identified top hits at Chromosome 4p12-p13 (KCTD8: rs4407541, P=9.70×10(-6); GABRB1: rs10517178/rs1372491, P=4.19×10(-6)) and 14q13 (PRKD1: rs10144903, 3.92×10(-6)), supported by analysis using a linear mixed model approximation in GenABEL (4p12-p13 GABRG1/GABRA2: rs7662743, Padj-agesex=2.06×10(-5); KCTD8: rs4407541, Padj-agesex=1.42×10(-4); GABRB1: rs10517178/rs1372491, Padj-agesex=0.027; 14q13 PRKD1: rs10144903, Padj-agesex=6.95×10(-5)). SNPs across GABRG1/GABRA2 did not replicate, whereas more proximal SNPs rs7679715 (Padj-agesex=0.030) and rs2055942 (Padj-agesex=0.022) at COX7B2/GABRA4 did, in addition to a trend distally at KCTD8 (rs4695718: Padj-agesex=0.096). Modelling of discovery and replication data support independent signals at GABRA4 (rs2055942: Padj-agesex-combined=3×10(-4)) and at KCTD8 (rs4695718: Padj-agesex-combined=2×10(-4)). Replication was observed for PRKD1 rs1953722 (proxy for rs10144903; Padj-agesex=0.031; Padj-agesex-combined=2×10(-4)). These genes may provide important functional leads in understanding disease pathogenesis in this population.

Variants of insulin-signaling inhibitor genes in type 2 diabetes and related metabolic abnormalities

Insulin resistance has a central role in the pathogenesis of several metabolic diseases, including type 2 diabetes, obesity, glucose intolerance, metabolic syndrome, atherosclerosis, and cardiovascular diseases. Insulin resistance and related traits are likely to be caused by abnormalities in the genes encoding for proteins involved in the composite network of insulin-signaling; in this review we have focused our attention on genetic variants of insulin-signaling inhibitor molecules. These proteins interfere with different steps in insulin-signaling: ENPP1/PC-1 and the phosphatases PTP1B and PTPRF/LAR inhibit the insulin receptor activation; INPPL1/SHIP-2 hydrolyzes PI3-kinase products, hampering the phosphoinositide-mediated downstream signaling; and TRIB3 binds the serine-threonine kinase Akt, reducing its phosphorylation levels. While several variants have been described over the years for all these genes, solid evidence of an association with type 2 diabetes and related diseases seems to exist only for rs1044498 of the ENPP1 gene and for rs2295490 of the TRIB3 gene. However, overall the data recapitulated in this Review article may supply useful elements to interpret the results of novel, more technically advanced genetic studies; indeed it is becoming increasingly evident that genetic information on metabolic diseases should be interpreted taking into account the complex biological pathways underlying their pathogenesis.