Diabetes Susceptibility Alleles Research Articles

HDL levels modulate the impact of type 2 diabetes susceptibility alleles in older adults

BackgroundType 2 Diabetes (T2D) is influenced by genetic, environmental, and ageing factors. Ageing pathways exacerbate metabolic diseases. This study aimed to examine both clinical and genetic factors of T2D in older adults.MethodsA total of 2,909 genotyped patients were enrolled in this study. Genome Wide Association Study was conducted, comparing T2D patients to non-diabetic older adults aged ≥ 60, ≥ 65, or ≥ 70 years, respectively. Binomial logistic regressions were applied to examine the association between T2D and various risk factors. Stepwise logistic regression was conducted to explore the impact of low HDL (HDL < 40 mg/dl) on the relationship between the genetic variants and T2D. A further validation step using data from the UK Biobank with 53,779 subjects was performed.ResultsThe association of T2D with both low HDL and family history of T2D increased with the age of control groups. T2D susceptibility variants (rs7756992, rs4712523 and rs10946403) were associated with T2D, more significantly with increased age of the control group. These variants had stronger effects on T2D risk when combined with low HDL cholesterol levels, especially in older control groups.ConclusionsThe findings highlight a critical role of age, genetic predisposition, and HDL levels in T2D risk. The findings suggest that individuals over 70 years who have high HDL levels without the T2D susceptibility alleles may be at the lowest risk of developing T2D. These insights can inform tailored preventive strategies for older adults, enhancing personalized T2D risk assessments and interventions.

Associations between parental type 2 diabetes risk and offspring birthweight and placental weight: a survival analysis using the Walker cohort

Aims/hypothesisLow birthweight (BW) is associated with the development of type 2 diabetes. Genome-wide analyses have identified a strong genetic component to this association, with many BW-associated loci also involved in glucose metabolism. We hypothesised that offspring BW and placental weight (PW) are correlated with parental type 2 diabetes risk, reflecting the inheritance of diabetes risk alleles that also influence fetal growth.MethodsThe Walker cohort, a collection of birth records from Dundee, Scotland, from the 1950s and the 1960s was used to test this hypothesis by linking BW and PW measurements to parental health outcomes. Using data from SCI-Diabetes and the national death registry, we obtained health records for over 20,000 Walker parents. We performed Fine–Gray survival analyses of parental type 2 diabetes risk with competing risk of death, and Cox regression analyses of risk of death, independently in the maternal and paternal datasets, modelled by offspring BW and PW.ResultsWe found significant associations between increased paternal type 2 diabetes risk and reduced offspring BW (subdistribution hazard ratio [SHR] 0.92 [95% CI 0.87, 0.98]) and PW (SHR 0.87 [95% CI 0.81, 0.94]). The association of maternal type 2 diabetes risk with offspring BW or PW was not significant. Lower offspring BW was also associated with increased risk of death in both mothers (HR 0.91 [95% CI 0.89, 0.94]) and fathers (HR 0.95 [95% CI 0.92, 0.98]), and higher offspring PW was associated with increased maternal mortality risk (HR 1.08 [95% CI 1.04, 1.13]) when adjusted for BW.Conclusions/interpretationWe identified associations between offspring BW and reduced paternal type 2 diabetes risk, most likely resulting from the independent effects of common type 2 diabetes susceptibility alleles on fetal growth, as described by the fetal insulin hypothesis. Moreover, we identified novel associations between offspring PW and reduced paternal type 2 diabetes risk, a relationship that might also be caused by the inheritance of diabetes predisposition variants. We found differing associations between offspring BW and PW and parental risk of death. These results provide novel epidemiological support for the use of offspring BW and PW as predictors for future risk of type 2 diabetes and death in mothers and fathers.Graphical abstract

2071-P: C2CD4A, Pancreatic Beta-Cell Function, and Type 2 Diabetes Susceptibility

To this day, intergenic single nucleotide polymorphisms (SNPs) identified from genome-wide association studies (GWAS) are still a geneticist’s nightmare, because these SNPs are steps away from revealing the disease causative gene, relevant tissue(s), and mechanism of action. For instance, fine mapping and validation of genes causing β cell failure from susceptibility loci identified in type 2 diabetes GWAS poses a significant challenge. The VPS13C-C2CD4A-C2CD4B locus on chromosome 15 confers diabetes susceptibility in every ethnic group studied to date. However, the causative gene is unknown. FoxO1, a transcription factor, is involved in the pathogenesis of β cell dysfunction, but its link to human diabetes GWAS has not been explored. To this end, we generated a genome-wide map of FoxO1 super-enhancers in chemically identified β cells using 2-photon live-cell imaging to monitor FoxO1 localization. Super-enhancers mark genes underpinning β cell identity, and comparing super-enhancers in mouse and human bridge the mouse data to human relevance. When parsed against human super-enhancers and GWAS-derived diabetes susceptibility alleles, this map revealed a conserved super-enhancer in C2CD4A, a gene encoding a β cell/stomach-enriched nuclear protein of unknown function. Genetic ablation of C2cd4a in β cells of mice phenocopied the metabolic abnormalities of human carriers of C2CD4A-linked polymorphisms, resulting in impaired insulin secretion during glucose tolerance tests as well as hyperglycemic clamps. C2cd4a regulates glycolytic genes, and notably represses key β cell “disallowed” genes, such as lactate dehydrogenase A, Aldolase B, and monocarboxylate transporter. We propose that C2CD4A is a transcriptional coregulator of the glycolytic pathway whose dysfunction accounts for the diabetes susceptibility associated with the chromosome 15 GWAS locus. Disclosure T. Kuo: None. D. Accili: Board Member; Self; Lilly Diabetes. Other Relationship; Self; Forkhead BioTherapeutics Inc. Funding National Institutes of Health (K01DK114372)

Identification of C2CD4A as a human diabetes susceptibility gene with a role in β cell insulin secretion

Fine mapping and validation of genes causing β cell failure from susceptibility loci identified in type 2 diabetes genome-wide association studies (GWAS) poses a significant challenge. The VPS13C-C2CD4A-C2CD4B locus on chromosome 15 confers diabetes susceptibility in every ethnic group studied to date. However, the causative gene is unknown. FoxO1 is involved in the pathogenesis of β cell dysfunction, but its link to human diabetes GWAS has not been explored. Here we generated a genome-wide map of FoxO1 superenhancers in chemically identified β cells using 2-photon live-cell imaging to monitor FoxO1 localization. When parsed against human superenhancers and GWAS-derived diabetes susceptibility alleles, this map revealed a conserved superenhancer in C2CD4A, a gene encoding a β cell/stomach-enriched nuclear protein of unknown function. Genetic ablation of C2cd4a in β cells of mice phenocopied the metabolic abnormalities of human carriers of C2CD4A-linked polymorphisms, resulting in impaired insulin secretion during glucose tolerance tests as well as hyperglycemic clamps. C2CD4A regulates glycolytic genes, and notably represses key β cell "disallowed" genes, such as lactate dehydrogenase A We propose that C2CD4A is a transcriptional coregulator of the glycolytic pathway whose dysfunction accounts for the diabetes susceptibility associated with the chromosome 15 GWAS locus.

Type 1 diabetes susceptibility alleles are associated with distinct alterations in the gut microbiota

BackgroundDysbiosis of the gut microbiota has been implicated in the pathogenesis of many autoimmune conditions including type 1 diabetes (T1D). It is unknown whether changes in the gut microbiota observed in T1D are due to environmental drivers, genetic risk factors, or both. Here, we have performed an analysis of associations between the gut microbiota and T1D genetic risk using the non-obese diabetic (NOD) mouse model of T1D and the TwinsUK cohort.ResultsThrough the analysis of five separate colonies of T1D susceptible NOD mice, we identified similarities in NOD microbiome that were independent of animal facility. Introduction of disease protective alleles at the Idd3 and Idd5 loci (IL2, Ctla4, Slc11a1, and Acadl) resulted in significant alterations in the NOD microbiome. Disease-protected strains exhibited a restoration of immune regulatory pathways within the gut which could also be reestablished using IL-2 therapy. Increased T1D disease risk from IL-2 pathway loci in the TwinsUK cohort of human subjects resulted in some similar microbiota changes to those observed in the NOD mouse.ConclusionsThese findings demonstrate for the first time that type 1 diabetes-associated genetic variants that restore immune tolerance to islet antigens also result in functional changes in the gut immune system and resultant changes in the microbiota.

Association of HLA class II markers with autoantibody-negative ketosis-prone atypical diabetes compared to type 2 diabetes in a population of sub-Saharan African patients

AimWe investigated the association of HLA DRB1 and DQB1 alleles, haplotypes and genotypes with unprovoked antibody-negative ketosis-prone atypical diabetes (A− KPD) in comparison to type 2 diabetes (T2D). MethodsA− KPD and T2D sub-Saharan African patients aged 19–63 years were consecutively recruited. Patients positive for cytoplasmic islet cell, insulin, glutamic acid decarboxylase or islet antigen-2 autoantibodies were excluded. Odds ratios were obtained via logistic regression after considering alleles with a minimum frequency of 5% in the study population. Bonferroni correction was used in the case of multiple comparisons. ResultsAmong the 130 participants, 35 (27%) were women and 57 (44%) were A− KPD. DRB1 and DQB1 allele frequencies were similar for both A− KPD and T2D patients; they did not confer any substantial risk even after considering type 1 diabetes susceptibility and resistance alleles. We found no association between A− KPD and the derived DRB1*07-DQB1*02:02 (OR: 0.55 [95%CI: 0.17–1.85], P=0.336); DRB1*11-DQB1*03:01 (OR: 2.42 [95%CI: 0.79–7.42], P=0.123); DRB1*15-DQB1*06:02 (OR: 0.87 [95%CI: 0.39–1.95], P=0.731) and DRB1*03:01-DQB1*02:01 (OR: 1.48 [95%CI: 0.55–3.96], P=0.437) haplotypes. Overall, we did not find any evidence of susceptibility to ketosis associated with DRB1 and DQB1 genotypes (all P>0.05) in A− KPD compared to T2D. Similar results were obtained after adjusting the analysis for age and sex. ConclusionFactors other than DRB1 and DQB1 genotype could explain the propensity to ketosis in A− KPD. These results need to be confirmed in a larger population with the perspective of improving the classification and understanding of the pathophysiology of A− KPD.

Shared and distinct immunogenetic pathways in myocarditis and type 1 diabetes (P4108)

Abstract The transgenic expression of the human type 1 diabetes (T1D) susceptibility allele, HLA-DQ8, in I-Aβ-/- NOD - but not in C57BL/6 - mice results in fatal autoimmune myocarditis. We have found that mortality from myocarditis in each of three lines of DQ8+NOD mice paralleled the incidence of T1D in the corresponding DQ8+/-I-Ag7+/-NOD lines, indicating that these two disease processes, although clinically distinct, share common DQ8-mediated pathways. To study the impact of non-MHC T1D susceptibility genes on myocarditis development, we crossed our highest-incidence myocarditis line with congenic NOD.B6 Idd3/B10 Idd5 mice that are protected from insulitis and T1D, and NOD.B10 Idd9 mice that develop insulitis but no T1D. The DQ8+NOD.Idd3/5 mice harbored the expected B10-derived splice variant of CTLA-4 (Idd5.1) and were strongly protected from myocarditis with a mortality of 9% (3 of 35 mice) compared to 80% in control mice (33 of 41 mice; P &amp;lt; 0.0001), and the majority of DQ8+NOD.Idd3/5 mice showed normal heart histology. In contrast, the Idd9 locus had minimal impact on myocarditis, with similar mortality in DQ8+NOD.Idd9 and control mice. These results show that susceptibility to myocarditis arises from the combined effects of MHC and non-MHC genes, some of which are shared with T1D. Since the human homologue of the Idd5.1 locus confers increased risk for human T1D and other autoimmune diseases, these findings have implications for the pathogenesis of human myocarditis.

Characteristics of rapid vs slow progression to type 1 diabetes in multiple islet autoantibody-positive children

Islet autoantibody-positive children progress to type 1 diabetes at variable rates. In our study, we asked whether characteristic autoantibody and/or gene profiles could be defined for phenotypes showing extreme progression. Autoantibodies to insulin (IAA), GAD (GADA), insulinoma-associated antigen-2 (IA-2A) and zinc transporter 8 (ZnT8A) were measured in follow-up sera, and genotyping for type 1 diabetes susceptibility genes (HLA-DR/HLA-DQ, INS variable number of tandem repeats [VNTR] and single nucleotide polymorphisms at PTPN22, PTPN2, ERBB3, IL2, SH2B3, CTLA4, IFIH1, KIAA0350 [also known as CLEC16A], CD25, IL18RAP, IL10, COBL) was performed on the DNA samples of children born to a parent with type 1 diabetes and prospectively followed from birth for up to 22years. Of the 1,650 children followed, 23 developed multiple autoantibodies and progressed to diabetes within 3years (rapid progressors), while 24 children developed multiple autoantibodies and remained non-diabetic for more than 10years from seroconversion (slow progressors). Rapid and slow progressors were similar with respect to HLA-DR/HLA-DQ genotypes, development of IAA, GADA and ZnT8A, and progression to multiple autoantibodies. In contrast, IA-2A development was considerably delayed in the slow progressors. Furthermore, both groups were effectively distinguished by the combined presence or absence of type 1 diabetes susceptibility alleles of non-HLA genes, most notably IL2, CD25, INS VNTR, IL18RAP, IL10, IFIH1 and PTPN22, and discrimination was improved among children carrying high-risk HLA-DR/HLA-DQ genotypes. Our data suggest that genotypes of non-HLA type 1 diabetes susceptibility genes influence the likelihood or rate of diabetes progression among children with multiple islet autoantibodies.

Higher Maternal Body Mass Index Is Associated with an Increased Risk for Later Type 2 Diabetes in Offspring

To investigate whether the body mass index (BMI) of a child's mother is associated with an increased future risk of type 2 diabetes, independent of genetic risk or childhood metabolic, behavioral, and environmental factors. The analyses were based on the Cardiovascular Risk in Young Finns Study including 1835 individuals aged 3-18 years at baseline with data on maternal BMI, childhood metabolic factors, as well as 34 newly identified type 2 diabetes susceptibility alleles. These subjects were then followed-up over 21-27 years. Maternal BMI (OR for 1-SD increase 1.54 [95% CI 1.12-2.11], P = .008) and child's systolic blood pressure (1.54 [1.01-2.35], P = .04) were significantly associated with increased odds for later type 2 diabetes, in a multivariable analysis adjusted for age, sex, type 2 diabetes genetic risk score, childhood BMI, insulin, lipids, dietary factors, socioeconomic status, and mother's age, and history of type 2 diabetes. A risk prediction model, which included maternal BMI status outperformed one which utilized only child's BMI data (area under the receiver operating characteristic curve 0.720 vs 0.623, P = .02). The inclusion of genetic risk score and other baseline risk variables did not additionally improve prediction (area under the receiver operating characteristic curve 0.720 vs 0.745, P = .40). Maternal BMI is a useful variable in determining offspring risk of developing type 2 diabetes.

BMI at Age 8 Years Is Influenced by the Type 2 Diabetes Susceptibility Genes HHEX-IDE and CDKAL1

OBJECTIVETo determine whether HHEX-IDE and CDKAL1 genes, which are associated with birth weight and susceptibility to type 2 diabetes, continue to influence growth during childhood.RESEARCH DESIGN AND METHODSBMI, weight, and height at age 8 years expressed as age- and sex-corrected standard deviation scores (SDS) against national reference data and single-nucleotide polymorphism genotyping of HHEX-IDE and CDKAL1 loci were analyzed in 646 prospectively followed children in the German BABYDIAB cohort. All children were singleton full-term births; 386 had mothers with type 1 diabetes, and 260 had fathers with type 1 diabetes and a nondiabetic mother.RESULTSType 2 diabetes risk alleles at the HHEX-IDE locus were associated with reduced BMI-SDS at age 8 years (0.17 SDS per allele; P = 0.004). After stratification for birth weight, both HHEX-IDE and CDKAL1 risk alleles were associated with reduced BMI-SDS (0.45 SDS, P = 0.0002; 0.52 SDS, P = 0.0001) and weight-SDS (0.22 SDS, P = 0.04; 0.56 SDS, P = 0.0002) in children born large for gestational age (>90th percentile) but not children born small or appropriate for gestational age. Within children born large for gestational age, BMI and weight decreased with each additional type 2 diabetes risk allele (∼ −2 kg per allele; >8 kg overall). Findings were consistent in children of mothers with type 1 diabetes (P < 0.0001) and children of nondiabetic mothers (P = 0.008).CONCLUSIONSThe type 2 diabetes susceptibility alleles at HHEX-IDE and CDKAL1 loci are associated with low BMI at age 8 years in children who were born large for gestational age.

Identification of genetic loci involved in diabetes using a rat model of depression.

While diabetic patients often present with comorbid depression, the underlying mechanisms linking diabetes and depression are unknown. The Wistar Kyoto (WKY) rat is a well-known animal model of depression and stress hyperreactivity. In addition, the WKY rat is glucose intolerant and likely harbors diabetes susceptibility alleles. We conducted a quantitative trait loci (QTL) analysis in the segregating F(2) population of a WKY x Fischer 344 (F344) intercross. We previously published QTL analyses for depressive behavior and hypothalamic-pituitary-adrenal (HPA) activity in this cross. In this study we report results from the QTL analysis for multiple metabolic phenotypes, including fasting glucose, post-restraint stress glucose, postprandial glucose and insulin, and body weight. We identified multiple QTLs for each trait and many of the QTLs overlap with those previously identified using inbred models of type 2 diabetes (T2D). Significant correlations were found between metabolic traits and HPA axis measures, as well as forced swim test behavior. Several metabolic loci overlap with loci previously identified for HPA activity and forced swim behavior in this F(2) intercross, suggesting that the genetic mechanisms underlying these traits may be similar. These results indicate that WKY rats harbor diabetes susceptibility alleles and suggest that this strain may be useful for dissecting the underlying genetic mechanisms linking diabetes, HPA activity, and depression.

The influence of genetic variations in HHEX gene on insulin metabolism in the German MESYBEPO cohort

In the present study, we aimed to validate the type 2 diabetes (T2DM) susceptibility alleles identified in the first genome-wide association study in the hematopoietically expressed homeobox protein (HHEX) gene region (rs1111875 and rs7923837). Furthermore, we investigated quantitative metabolic risk phenotypes of these two variants for association with three key components of the insulin metabolism: insulin secretion, insulin sensitivity and insulin degradation. Two HHEX polymorphisms were genotyped in 1026 subjects from the German MESYBEPO cohort. Complete OGTT data were available for a subset of 420 with normal glucose tolerance (NGT), 282 with impaired glucose tolerance/impaired fasting glucose (IGT/IFG) and 146 diabetic subjects. We validated association of both HHEX polymorphisms with T2DM. In the non-diabetic subcohort including NGT and IFG/IGT subjects, the risk alleles of rs7923837 and rs1111875 were significantly associated with decreased first and second phases of insulin secretion and lower insulinogenic index after oral glucose loading. In healthy, normal glucose-tolerant subjects, the same association of HHEX SNP rs1111875 with OGTT-derived phases of insulin secretion were detectable, however, rs7923837 was only weakly associated with reduced insulinogenic index. For both polymorphisms, no significant correlations with insulin sensitivity were obtained. Reduced insulin clearance was also observed in heterozygous carriers of rs1111875. We validated the association of polymorphisms of the HHEX gene with T2DM in the MESYBEPO cohort. Importantly, variations within the HHEX gene conferred the impaired insulin secretion and changes of insulin degradation but no alteration in insulin sensitivity in carriers of risk alleles.

Single Nucleotide Transcription Factor 7-Like 2 (TCF7L2) Gene Polymorphisms in Antiislet Autoantibody-Negative Patients at Onset of Diabetes

There is controversy as to whether type 2 diabetes genetic susceptibility contributes to type 1 diabetes, and it is not known what proportion of islet autoantibody-negative new onset subjects have type 2 diabetes risk alleles. We designed this study to evaluate whether two type 2 diabetes-associated single nucleotide polymorphisms (SNPs) of transcription factor 7-like 2 (TCF7L2) gene are associated with the development of islet autoantibody-negative diabetes vs. islet autoantibody-positive diabetes in young patients and whether these SNPs are associated with specific clinical phenotypes. Autoantibody against glutamic acid decarboxylase 65, islet cell antibody 512bdc (form of IA-2), insulin, ZnT8 transporter, and cytoplasmic islet cell antibody were assayed in patients with new onset diabetes seen at the Barbara Davis Center using sera obtained within 2 wk of diagnosis. We genotyped two noncoding variants in the TCF7L2 gene, rs12255372 and rs7903146, in diabetic subjects and normal controls. A total of 140 patients (15.7%) were negative for all islet autoantibodies among 893 subjects less than age 25 at the onset of diabetes. The allele and genotype frequencies of two SNPs showed that these are associated (odds ratio up to 4) with the development of diabetes in the autoantibody-negative diabetic cohort, but not in the autoantibody-positive diabetic cohort. TCF7L2 type 2 diabetes susceptibility alleles are associated with islet autoantibody-negative but not autoantibody-positive new onset diabetes in young patients.

A new model defines the minimal set of polymorphism in HLA-DQ and -DR that determines susceptibility and resistance to autoimmune diabetes

BackgroundThe mechanism underlying autoimmune diabetes has been difficult to define. There is a strong genetic contribution and numerous studies associate the major histocompatibility complex, especially the class II region, with predisposition or resistance. However, how these molecules are implicated remains obscure.Presentation of the hypothesisWe have supplemented structural analysis with computational biophysical and sequence analyses and propose an heuristic for distinguishing between human leukocyte antigen molecules that predispose to insulin dependent diabetes mellitus and those that are protective. Polar residues at both β37 and β9 suffice to distinguish accurately between class II alleles that predispose to type 1 diabetes and those that do not. The electrostatic potential within the peptide binding pocket exerts a strong influence on diabetogenic epitopes with basic residues. Diabetes susceptibility alleles are predicted to bind autoantigens strongly with tight affinity, prolonged association and altered cytokine expression profile. Protective alleles bind moderately, and neutral alleles poorly or not at all. Non-Asp β57 is a modifier that supplements disease risk but only in the presence of the polymorphic, polar pair at β9 and β37. The nature of β37 determines resistance on one hand, and susceptibility or dominant protection on the other.ConclusionThe proposed ideas are illustrated with structural, functional and population studies from the literature. The hypothesis, in turn, rationalizes their results. A plausible mechanism of immune mediated diabetes based on binding affinity and peptide kinetics is discussed. The number of the polymorphic markers present correlates with onset of disease and severity. The molecular elucidation of disease susceptibility and resistance paves the way for risk prediction, treatment and prevention of disease based on analogue peptides.ReviewersThis article was reviewed by Eugene V. Koonin, Michael Lenardo, Hossam Ashour, and Bhagirath Singh. For the full reviews, please go to the Reviewers' comments section.

Studies of Association of Variants Near the HHEX, CDKN2A/B, and IGF2BP2 Genes With Type 2 Diabetes and Impaired Insulin Release in 10,705 Danish Subjects

In the present study, we aimed to validate the type 2 diabetes susceptibility alleles identified in six recent genome-wide association studies in the HHEX/KIF11/IDE (rs1111875), CDKN2A/B (rs10811661), and IGF2BP2 (rs4402960) loci, as well as the intergenic rs9300039 variant. Furthermore, we aimed to characterize quantitative metabolic risk phenotypes of the four variants. The variants were genotyped in the population-based Inter99 cohort (n = 5,970), the ADDITION Study (n = 1,626), a population-based sample of young healthy subjects (n = 377), and in additional type 2 diabetic case (n = 2,111) and glucose-tolerant (n = 521) subjects. The case-control studies involved a total of 4,089 type 2 diabetic patients and 5,043 glucose-tolerant control subjects. We validated association of variants near HHEX/KIF11/IDE, CDKN2A/B, and IGF2BP2 with type 2 diabetes. Interestingly, in middle-aged people, the rs1111875 C-allele of HHEX/KIF11/IDE strongly associated with lower acute insulin response during an oral glucose tolerance test (P = 6 x 10(-7)). In addition, decreased insulin release following intravenous tolbutamide injection was observed in young healthy subjects (P = 0.02). Also, a reduced insulin release was observed for the CDKN2A/B rs10811661 T-allele after both oral and intravenous glucose challenges (P = 0.001 and P = 0.009, respectively). We validate that variants in the proximity of the HHEX/KIF11/IDE, CDKN2A/B, and IFG2BP2 loci associate with type 2 diabetes. Importantly, variations within the HHEX/KIF11/IDE and CDKN2A/B loci confer impaired glucose- and tolbutamide-induced insulin release in middle-aged and young healthy subjects, suggesting a role for these variants in the pathogenesis of pancreatic beta-cell dysfunction.

Common Variants of the Novel Type 2 Diabetes GenesCDKAL1andHHEX/IDEAre Associated With Decreased Pancreatic β-Cell Function

Type 2 diabetes is characterized by impaired pancreatic beta-cell function and decreased insulin sensitivity. Genome-wide association studies have identified common, novel type 2 diabetes susceptibility loci within the FTO, CDKAL1, CDKN2A/CDKN2B, IGF2BP2, HHEX/IDE, and SLC30A8 gene regions. Our objective was to explore the relationships between the diabetes-associated alleles and measures of beta-cell function and whole-body insulin sensitivity. A total of 1,276 healthy subjects of European ancestry were studied at 19 centers. Indexes of beta-cell function (including 30-min insulin response and glucose sensitivity) were derived from a 75-g oral glucose tolerance test, and whole-body insulin sensitivity (M/I) was assessed by hyperinsulinemic-euglycemic clamp. Genotype/phenotype relationships were studied by linear trend analysis correcting for age, sex, and recruitment center. CDKAL1 and HHEX/IDE diabetes-associated alleles were both associated with decreased 30-min insulin response (both P = 0.0002) and decreased pancreatic beta-cell glucose sensitivity (P = 9.86 x 10(-5) and 0.009, respectively), and these relationships remained after correction for M/I. The FTO susceptibility allele showed a weak but consistent association with increased adiposity, which in turn was linked to a decrease in M/I. However, none of the other novel diabetes susceptibility alleles were associated with insulin sensitivity. CDKAL1 and HHEX/IDE diabetes-associated alleles are associated with decreased pancreatic beta-cell function, including decreased beta-cell glucose sensitivity that relates insulin secretion to plasma glucose concentration. We confirmed the association between the FTO allele and increased adiposity, but none of the other novel susceptibility alleles were associated with whole-body insulin sensitivity.

HNF‐1α G574S is a functional variant with decreased transactivation activity

To assess the functional consequence of the hepatocyte nuclear factor 1alpha gene (HNF-1alpha) G574S variant previously proposed as a diabetes susceptibility allele, in a group of Mexican Type 2 diabetic patients with end-stage renal disease (ESRD). The transcriptional activity of the HNF-1alpha G574S recombinant protein on the human insulin promoter was assessed by transfection assays in RINm5f and HepG2 cell lines. Two unrelated Mexican diabetic patients with no known African ancestry were found to carry the G574S variant. This substitution was not found among unrelated healthy control subjects. Whereas the G574S HNF-1alpha transcription activation of the human insulin promoter was 40% lower than that of the wild-type protein in RINm5f beta cells, no difference was found in a hepatic cell line (HepG2). G574S affects the transactivation potential of HNF-1alpha on the insulin promoter in pancreatic beta-cells. Although it has been difficult to prove its role in the development of diabetes in case-control association studies, this variant exhibits functional effects consistent with it being a potential diabetes susceptibility allele.

Overexpression of HLA class I molecules on T cells among type 1 diabetes Brazilian patients

To evaluate the membrane expression of histocompatibility (HLA) class I (A–C) molecules on lymphomononuclear cells involved in the pathogenesis of type 1 diabetes, we studied 20 newly diagnosed Brazilian patients and 20 matched controls. The coexpression of HLA and cluster of differentiation (CD) molecules was evaluated by flow cytometry. Compared to controls, patients presented increased fluorescence intensity of HLA class I molecules on CD3 +, CD4 + and CD8 + cells. Patients exhibiting the HLA-DQB1 ∗0201 and/or DQB1 ∗0302 alleles presented increased expression of class I molecules in relation to HLA-matched healthy controls. The increased HLA class I expression in subsets of T cells may be due to the proinflammatory profile of the disease as well as to the presence of diabetes susceptibility alleles.

Large-scale association studies of variants in genes encoding the pancreatic beta-cell KATP channel subunits Kir6.2 (KCNJ11) and SUR1 (ABCC8) confirm that the KCNJ11 E23K variant is associated with type 2 diabetes.

The genes ABCC8 and KCNJ11, which encode the subunits sulfonylurea receptor 1 (SUR1) and inwardly rectifying potassium channel (Kir6.2) of the beta-cell ATP-sensitive potassium (K(ATP)) channel, control insulin secretion. Common polymorphisms in these genes (ABCC8 exon 16-3t/c, exon 18 T/C, KCNJ11 E23K) have been variably associated with type 2 diabetes, but no large ( approximately 2,000 subjects) case-control studies have been performed. We evaluated the role of these three variants by studying 2,486 U.K. subjects: 854 with type 2 diabetes, 1,182 population control subjects, and 150 parent-offspring type 2 diabetic trios. The E23K allele was associated with diabetes in the case-control study (odds ratio [OR] 1.18 [95% CI 1.04-1.34], P = 0.01) but did not show familial association with diabetes. Neither the exon 16 nor the exon 18 ABCC8 variants were associated with diabetes (1.04 [0.91-1.18], P = 0.57; 0.93 [0.71-1.23], P = 0.63, respectively). Meta-analysis of all case-control data showed that the E23K allele was associated with type 2 diabetes (K allele OR 1.23 [1.12-1.36], P = 0.000015; KK genotype 1.65 [1.34-2.02], P = 0.000002); but the ABCC8 variants were not associated. Our results confirm that E23K increases risk of type 2 diabetes and show that large-scale association studies are important for the identification of diabetes susceptibility alleles.

Genes and environment in type 2 diabetes and atherosclerosis in aboriginal Canadians.

The incidence of coronary heart disease (CHD) among aboriginal people in northern Ontario has tripled over the past 20 years. This is inextricably linked to the remarkably high prevalence of type 2 diabetes in these native communities. Approximately 40% of the Oji-Cree of northern Ontario have typical obesity-related type 2 diabetes, which represents a drastic increase from virtually unreportable levels 50 years ago. The Oji-Cree have a private mutation in the HNF1A gene, namely G319S, which is absent from other ethnic groups and aboriginal populations. The most compelling reasons that HNF1A S319 is a diabetes-susceptibility allele are its consistent statistical association with the presence and severity of diabetes. Also, HNF1A S319 has specificity and positive predictive values of 97% and 95%, respectively, for the development of diabetes in the Oji-Cree by 50 years of age. This makes the HNF1A G319S genotype the most specific predictive genetic test for diabetes in any human population. HNF1A S319 has all the attributes of a thrifty allele in the Oji-Cree. It is possible that the recent increase in CHD in the aboriginal people of northern Ontario is the result of the expression of diabetes susceptibility due to HNF1A S319 as a consequence of rapid changes in environment and lifestyle.