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Examines the prevalence, clinical characteristics, and suitability for defining type 2 susceptibility genes of European type 2 diabetes trios. Role of trios in defining genes in a number of polygenic conditions; Existence of polymorphisms that have been reported as showing association with type 2 diabetes; Clinical characteristics of type 2 trio probands.

Differences in glucose metabolism among categories of prediabetes have not been systematically investigated. In this longitudinal study, participants (N = 2,111) underwent a 2-h 75-g oral glucose tolerance test (OGTT) at baseline and 48 months. HbA1c was also measured. We classified participants as having isolated prediabetes defect (impaired fasting glucose [IFG], impaired glucose tolerance [IGT], or HbA1c indicative of prediabetes [IA1c]), two defects (IFG+IGT, IFG+IA1c, or IGT+IA1c), or all defects (IFG+IGT+IA1c). β-Cell function (BCF) and insulin sensitivity were assessed from OGTT. At baseline, in pooling of participants with isolated defects, they showed impairment in both BCF and insulin sensitivity compared with healthy control subjects. Pooled groups with two or three defects showed progressive further deterioration. Among groups with isolated defect, those with IGT showed lower insulin sensitivity, insulin secretion at reference glucose (ISRr), and insulin secretion potentiation (P < 0.002). Conversely, those with IA1c showed higher insulin sensitivity and ISRr (P < 0.0001). Among groups with two defects, we similarly found differences in both BCF and insulin sensitivity. At 48 months, we found higher type 2 diabetes incidence for progressively increasing number of prediabetes defects (odds ratio >2, P < 0.008). In conclusion, the prediabetes groups showed differences in type/degree of glucometabolic impairment. Compared with the pooled group with isolated defects, those with double or triple defect showed progressive differences in diabetes incidence. [ABSTRACT FROM AUTHOR]

Obesity is a major health problem, and many family-based studies have suggested that it has a strong genetic basis. We performed a genome-wide quantitative trait linkage scan for loci influencing BMI in 573 pedigrees from the U.K. We identified genome-wide significant linkage (logarithm of odds = 3.74, between D10S208 and D10S196, genomewide P = 0.0186) on chromosome 10p. The size of our study population and the statistical significance of our findings provide substantial contributions to the body of evidence for a locus on chromosome 10p. We examined eight single nucleotide polymorphisms (SNPs) in GAD2, which maps to this linkage region, tagging the majority of variation in the gene, and observed marginally significant (0.01 < P < 0.05) associations between four common variants and BMI. However, these SNPs did not account for our evidence of linkage to BMI, and they did not replicate (in direction of effect) the previous associations. We therefore conclude that these SNPs are not the etiological variants underlying this locus. We cannot rule out the possibility that other untagged variations in GAD2 may, in part, be involved, but it is most likely that alternative gene(s) within the broad gene-rich region of linkage on 10p are responsible for variation in body mass and susceptibility to obesity. [ABSTRACT FROM AUTHOR]

The mechanisms that predispose to hypertension, coronary artery disease (CAD), and type 2 diabetes (T2D) in individuals of normal weight are poorly understood. In contrast, in monogenic primary lipodystrophy--a reduction in subcutaneous adipose tissue--it is clear that it is adipose dysfunction that causes severe insulin resistance (IR), hypertension, CAD, and T2D. We aimed to test the hypothesis that common alleles associated with IR also influence the wider clinical and biochemical profile of monogenic IR. We selected 19 common genetic variants associated with fasting insulin-based measures of IR. We used hierarchical clustering and results from genome-wide association studies of eight nondisease outcomes of monogenic IR to group these variants. We analyzed genetic risk scores against disease outcomes, including 12,171 T2D cases, 40,365 CAD cases, and 69,828 individuals with blood pressure measurements. Hierarchical clustering identified 11 variants associated with a metabolic profile consistent with a common, subtle form of lipodystrophy. A genetic risk score consisting of these 11 IR risk alleles was associated with higher triglycerides (β = 0.018; P = 4 x 10-29), lower HDL cholesterol (β = -0.020; P = 7 x 10-37), greater hepatic steatosis (β = 0.021; P = 3 x 10-4), higher alanine transaminase (β = 0.002; P = 3 x 10-5), lower sex-hormone-binding globulin (β = -0.010; P = 9 x 10-13), and lower adiponectin (β = -0.015; P = 2 x 10-26). The same risk alleles were associated with lower BMI (per-allele β = -0.008; P = 7 x 10-8) and increased visceral-to-subcutaneous adipose tissue ratio (β = -0.015; P = 6 x 10-7). Individuals carrying ≥17 fasting insulin-raising alleles (5.5% population) were slimmer (0.30 kg/m²) but at increased risk of T2D (odds ratio [OR] 1.46; per-allele P = 5 x 10-13), CAD (OR 1.12; per-allele P = 1 x 10-5), and increased blood pressure (systolic and diastolic blood pressure of 1.21 mmHg [per-allele P = 2 x 10-5] and 0.67 mmHg [per-allele P = 2 x 10-4], respectively) compared with individuals carrying ≤9 risk alleles (5.5% population). Our results provide genetic evidence for a link between the three diseases of the "metabolic syndrome" and point to reduced subcutaneous adiposity as a central mechanism. [ABSTRACT FROM AUTHOR]

Objective: Recent work has shown that insulin stimulates its own secretion in insulin-sensitive humans, suggesting that insulin resistance in the β-cell could cause β-cell dysfunction. We have tested whether insulin exposure and insulin sensitivity modulate β-cell function in subjects with normal glucose tolerance (NGT) and whether they contribute to dysglycemia in impaired glucose regulation (IGR).Research Design and Methods: Insulin sensitivity (by euglycemic clamp), insulin-induced secretory response at isoglycemia (IISR) (as C-peptide percent change from basal during the clamp), glucose-induced secretory response (GISR) to an intravenous glucose bolus, and β-cell glucose sensitivity (β-GS) (by oral glucose tolerance test [OGTT] modeling) were measured in 1,151 NGT and 163 IGR subjects from the RISC (Relationship between Insulin Sensitivity and Cardiovascular Disease) study.Results: In NGT, IISR was related to both insulin sensitivity and antecedent insulin exposure; GISR was related to insulin exposure. IISR was positively, if weakly, related to β-GS (r= 0.16, P < 0.0001). Both IISR (-23 [39] vs. -9 [2]%, median [interquartile range], P < 0.03) and β-GS (69 [47] vs. 118 [83] pmol ⋅ min(-1) ⋅ m(-2) ⋅ mmol(-1) ⋅ L, P < 0.0001) were decreased in IGR compared with NGT. Insulin sensitivity and β-GS were the major determinants of mean OGTT glucose in both NGT and IGR, with a minor role for IISR. In a multivariate logistic model, IGR was predicted by β-GS (odds ratio 4.84 [95% CI 2.89-8.09]) and insulin sensitivity (3.06 [2.19-4.27]) but not by IISR (1.11 [0.77-1.61]).Conclusions: Pre-exposure to physiological hyperinsulinemia stimulates insulin secretion to a degree that depends on insulin sensitivity. However, this phenomenon has limited impact on β-cell dysfunction and dysglycemia. [ABSTRACT FROM AUTHOR]

OBJECTIVE--Recent work has shown that insulin stimulates its own secretion in insulin-sensitive humans, suggesting that insulin resistance in the β-cell could cause β-cell dysfunction. We have tested whether insulin exposure and insulin sensitivity modulate β-cell function in subjects with normal glucose tolerance (NGT) and whether they contribute to dysglycemia in impaired glucose regulation (IGR). RESEARCH DESIGN AND METHODS--Insulin sensitivity (by euglycemic clamp), insulin-induced secretory response at isoglycemia (IISR) (as C-peptide percent change from basal during the clamp), glucose-induced secretory response (GISR) to an intravenous glucose bolus, and β-cell glucose sensitivity (β-GS) (by oral glucose tolerance test [OGTT] modeling) were measured in 1,151 NGT and 163 IGR subjects from the RISC (Relationship between Insulin Sensitivity and Cardiovascular Disease) study. RESULTS--In NGT, IISR was related to both insulin sensitivity and antecedent insulin exposure; GISR was related to insulin exposure. IISR was positively, if weakly, related to β-GS (r = 0.16, P < 0.0001). Both IISR (-23 [39] vs. 29 [2]%, median [interquartile range], P < 0.03) and β-GS (69 [47] vs. 118 [83] pmol x min--1 x m--2 x mmol--1 x L, P < 0.0001) were decreased in IGR compared with NGT. Insulin sensitivity and β-GS were the major determinants of mean OGTT glucose in both NGT and IGR, with a minor role for IISR. In a multivariate logistic model, IGR was predicted by β-GS (odds ratio 4.84 [95% CI 2.89--8.09]) and insulin sensitivity (3.06 [2.19--4.27]) but not by IISR (1.11 [0.77--1.61]). CONCLUSIONS--Pre-exposure to physiological hyperinsulinemia stimulates insulin secretion to a degree that depends on insulin sensitivity. However, this phenomenon has limited impact on β-cell dysfunction and dysglycemia. [ABSTRACT FROM AUTHOR]

OBJECTIVE--This study examined how differences in the BMI distribution of type 2 diabetic case subjects affected genomewide patterns of type 2 diabetes association and considered the implications for the etiological heterogeneity of type 2 diabetes. RESEARCH DESIGN AND METHODS--We reanalyzed data from the Wellcome Trust Case Control Consortium genome-wide association scan (1,924 case subjects, 2,938 control subjects: 393,453 single-nucleotide polymorphisms [SNPs]) after stratifying case subjects (into "obese" and "nonobese") according to median BMI (30.2 kg/m²). Replication of signals in which alternative case-ascertainment strategies generated marked effect size heterogeneity in type 2 diabetes association signal was sought in additional samples. RESULTS--In the "obese-type 2 diabetes" scan, FTO variants had the strongest type 2 diabetes effect (rs8050136: relative risk [RR] 1.49 [95% CI 1.34-1.66], P = 1.3 x 10--13), with only weak evidence for TCF7L2 (rs7901695 RR 1.21 [1.09-1.35], P = 0.001). This situation was reversed in the "nonobese" scan, with FTO association undetectable (RR 1.07 [0.97-1.19], P = 0.19) and TCF7L2 predominant (RR 1.53 [1.37-1.71], P = 1.3 x 10-14). These patterns, continued by replication, generated strong combined evidence for between-stratum effect size heterogeneity (FTO: PDIFF = 1.4 x 10-7; TCFTL2: PDIFF = 4.0 x 10-6). Other signals displaying evidence of effect size heterogeneity in the genome-wide analyses (on chromosomes 3, 12, 15, and 18) did not replicate. Analysis of the current list of type 2 diabetes susceptibility variants revealed nominal evidence for effect size heterogeneity for the SLC3OA8 locus alone (RR[sub obese] 1.08 [1.011.15]; RR[sub nonobese] 1.18 [1.10-1.27]: PDIFF = 0.04). CONCLUSIONS--This study demonstrates the impact of differences in case ascertainment on the power to detect and replicate genetic associations in genome-wide association studies. These data reinforce the notion that there is substantial etiological heterogeneity within type 2 diabetes. Diabetes 58:505-510, 2009 [ABSTRACT FROM AUTHOR]

OBJECTIVE--Single nucleotide polymorphisms (SNPs) in the P2 promoter region of HNF4A were originally shown to be associated with predisposition for type 2 diabetes in Finnish, Ashkenazi, and, more recently, Scandinavian populations, but they generated conflicting results in additional populations. We aimed to investigate whether data from a large-scale mapping approach would replicate this association in novel Ashkenazi samples and in U.K. populations and whether these data would allow us to refine the association signal. RESEARCH DESIGN AND METHODS--Using a dense linkage disequilibrium map of 20q, we selected SNPs from a 10-Mb interval centered on HNF4A. In a staged approach, we first typed 4,608 SNPs in case-control populations from four U.K. populations and an Ashkenazi population (n = 2,516). In phase 2, a subset of 763 SNPs was genotyped in 2,513 additional samples from the same populations. RESULTS--Combined analysis of both phases demonstrated association between HNF4A P2 SNPs (rs1884613 and rs2144908) and type 2 diabetes in the Ashkenazim (n = 991; P < 1.6 x 10[sup -6]). Importantly, these associations are significant in a subset of Ashkenazi samples (n = 531) not previously tested for association with P2 SNPs (odds ratio [OR] ∼1.7; P < 0.002), thus providing replication within the Ashkenazim. In the U.K. populations, this association was not significant (n = 4,022; P > 0.5), and the estimate for the OR was much smaller (OR 1.04; [95%CI 0.91-1.19]). CONCLUSIONS--These data indicate that the risk conferred by HNF4A P2 is significantly different between U.K. and Ashkenazi populations (P < 0.00007), suggesting that the underlying causal variant remains unidentified. Interactions with other genetic or environmental factors may also contribute to this difference in risk between populations. Diabetes 57:3161-3165, 2008 [ABSTRACT FROM AUTHOR]

OBJECTIVE-- Type 2 diabetes is characterized by impaired pancreatic β-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 β-cell function and whole-body insulin sensitivity. RESEARCH DESIGN AND METHODS-- A total of 1,276 healthy subjects of European ancestry were studied at 19 centers. Indexes of β-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. RESULTS-- CDKAL1 and HHEX/IDE diabetes-associated alleles were both associated with decreased 30-min insulin response (both P = 0.0002) and decreased pancreatic β-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. CONCLUSIONS-- CDKAL1 and HHEX/IDE diabetes-associated alleles are associated with decreased pancreatic β-cell function, including decreased β-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. Diabetes 56: 3101-3104, 2007 [ABSTRACT FROM AUTHOR]

Mutations in the LMNA gene (encoding lamin A/C) underlie familial partial lipodystrophy, a syndrome of monogenic insulin resistance and diabetes. LMNA maps to the well-replicated diabetes-linkage region on chromosome 1q, and there are reported associations between LMNA single nucleotide polymorphisms (SNPs) (particularly rs4641; H566H) and metabolic syndrome components. We examined the relationship between LMNA variation and type 2 diabetes (using six tag SNPs capturing >90% of common variation) in several large datasets. Analysis of 2,490 U.K. diabetic case and 2,556 control subjects revealed no significant associations at either genotype or haplotype level: the minor allele at rs4641 was no more frequent in case subjects (allelic odds ratio [OR] 1.07 [95% CI 0.98-1.17], P = 0.15). In 390 U.K. trios, family-based association analyses revealed nominally significant overtransmission of the major allele at rs12063564 (P = 0.01), which was not corroborated in other samples. Finally, genotypes for 2,817 additional subjects from the International 1q Consortium revealed no consistent case-control or family-based associations with LMNA variants. Across all our data, the OR for the rs4641 minor allele approached but did not attain significance (1.07 [0.99-1.15], P = 0.08). Our data do not therefore support a major effect of LMNA variation on diabetes risk. However, in a meta-analysis including other available data, there is evidence that rs4641 has a modest effect on diabetes susceptibility (1.10 [1.04-1.16], P = 0.001). Diabetes 56:879-883, 2007 [ABSTRACT FROM AUTHOR]

An important question in human genetics is the extent to which genes causing monogenic forms of disease harbor common variants that may contribute to the more typical form of that disease. We aimed to comprehensively evaluate the extent to which common variation in the six known maturity-onset diabetes of the young (MODY) genes, which cause a monogenic form of type 2 diabetes, is associated with type 2 diabetes. Specifically, we determined patterns of common sequence variation in the genes encoding Gck, Ipf1, Tcf2, and NeuroD1 (MODY2 and MODY4-MODY6, respectively), selected a comprehensive set of 107 tag single nucleotide polymorphisms (SNPs) that captured common variation, and genotyped each in 4,206 patients and control subjects from Sweden, Finland, and Canada (including family-based studies and unrelated case-control subjects). All SNPs with a nominal P value <0.1 for association to type 2 diabetes in this initial screen were then genotyped in an additional 4,470 subjects from North America and Poland. Of 30 nominally significant SNPs from the initial sample, 8 achieved consistent results in the replication sample. We found the strongest effect at rs757210 in intron 2 of TCF2, with corrected P values <0.01 for an odds ratio (OR) of 1.13. This association was observed again in an independent sample of 5,891 unrelated case and control subjects and 500 families from the U.K., for an overall OR of 1.12 and a P value <10[sup -e] in >15,000 samples. We combined these results with our previous studies on HNF4α and TCF1 and explicitly tested for gene-gene interactions among these variants and with several known type 2 diabetes susceptibility loci, and we found no genetic interactions between these six genes. We conclude that although rare variants in these six genes explain most cases of MODY, common variants in these same genes contribute very modestly, if at all, to the common form of type 2 diabetes. Diabetes 56:685-693, 2007 [ABSTRACT FROM AUTHOR]

Ectoenzyme nucleotide pyrophosphate phosphodiesterase 1 (ENPP1) is an inhibitor of insulin-induced activation of the insulin receptor. There is strong evidence from several previous studies that a common coding variant of ENPP1 (K121Q) and a three-marker haplotype (Q121, IVS20delT-11, and G+1044TGA) are associated with type 2 diabetes and obesity. We examined the impact of ENPP1 variation on type 2 diabetes and obesity in a large U.K. genetic association study. We genotyped the three previously associated polymorphisms in 2,363 type 2 diabetic case and 4,045 control subjects, as well as 1,681 subjects from 529 type 2 diabetic families. We used the same subjects for morbid and moderate obesity association studies. For type 2 diabetes, moderate and morbid obesity, and for both the Q121 and three-marker haplotype, our results exclude with >95% confidence the effect sizes from previous studies (Q121 allele: odds ratio 1.02 [95% CI 0.93-1.12], P = 0.61; 1.00 [0.85-1.18], P = 0.99; and 0.92 [0.70-1.20], P = 0.41; three-marker haplotype: 1.10 [0.96-1.26], P = 0.17; 0.97 [0.77-1.23], P = 0.81; and 0.86 [0.57-1.30], P = 0.46 for type 2 diabetes, moderate, and morbid obesity, respectively). A K121Q type 2 diabetes meta-analysis of all previously published studies remained significant after the inclusion of this study (1.25 [1.10-1.43], P = 0.0007), although there was some evidence of publication bias. In conclusion, we find no evidence that previously associated variants of ENPP1 are associated with type 2 diabetes or obesity in the U.K. population. Diabetes 55:3175-3179, 2006 [ABSTRACT FROM AUTHOR]

Recent data suggest that common variation in the transcription factor 7-like 2 (TCF7L2) gene is associated with type 2 diabetes. Evaluation of such associations in independent samples provides necessary replication and a robust assessment of effect size. Using four TCF7L2 single nucleotide polymorphisms (SNPs; including the two most associated in the previous study), we conducted a case-control study in 2,158 type 2 diabetic subjects and 2,574 control subjects and a family-based association analysis in 388 parent-offspring trios all from the U.K. All SNPs showed powerful associations with diabetes in the case-control analysis, with strongest effects at rs7903146 (allele-wise relative risk 1.36 [95% CI 1.24-1.48], P = 1.3 x 10-11). Data were consistent with a multiplicative model. The family-based analyses provided independent evidence for association at all loci (e.g., rs4506565, 62% transmission, P = 7 x 10-5) with no parent-of-origin effects. The frequency of diabetes-associated TCF7L2 genotypes was greater in cases ascertained for positive family history and early onset (rs4606565, P = 0.02); the population-attributable risk, estimated from the least-selected cases, is ∼16%. The overall evidence for association for these variants (P = 4.4 x 10-14 combining case-control and family-based analyses for rs4506565) exceeds genome-wide significance criteria and clearly establishes TCF7L2 as a type 2 diabetes susceptibility gene of substantial importance. Diabetes 55:2640-2644, 2006 [ABSTRACT FROM AUTHOR]

The gene encoding the transcription factor upstream stimulatory factor (USF)1 influences susceptibility to familial combined hyperlipidemia (FCHL) and triglyceride levels. Phenotypic overlap between FCHL and type 2 diabetes makes USF1 a compelling positional candidate for the widely replicated type 2 diabetes linkage signal on chromosome 1q. We typed 22 variants in the F11R/USF1 region (1 per 3 kb), including those previously implicated in FCHL-susceptibility (or proxies thereof) in 3,726 samples preferentially enriched for 1q linkage. We also examined glucose- and lipid-related continuous traits in an overlapping set of 1,215 subjects of European descent. There was no convincing evidence for association with type 2 diabetes in any of seven case-control comparisons, individually or combined. Family-based association analyses in 832 Pima subjects were similarly negative. At rs3737787 (the variant most strongly associated with FCHL), the combined odds ratio, per copy of the rarer A-allele, was 1.10 (95% CI 0.97-1.24, P = 0.13). In 124 Utah subjects, rs3737787 was significantly associated (P = 0.002) with triglyceride levels, but direction of this association was opposite to previous reports, and there was no corroboration in three other samples. These data exclude USF1 as a major contributor to type 2 diabetes susceptibility and the basis for the chromosome 1q linkage. They reveal only limited evidence for replication of USF1 effects on continuous metabolic traits. Diabetes 55:2541-2548, 2006 [ABSTRACT FROM AUTHOR]

Recent evidence supports the strong overlap between genes implicated in monogenic diabetes and susceptibility to type 2 diabetes. Transient neonatal diabetes mellitus (TNDM) is a rare disorder associated with overexpression of genes at a paternally expressed imprinted locus on chromosome 6q24. There are two overlapping genes in this region: the transcription factor zinc finger protein associated with cell cycle control and apoptosis (ZAC also known as PLAGL1) and HYMA1, which encodes an untranslated mRNA. Several type 2 diabetes linkage studies have reported linkage to chromosome 6q22-25. We hypothesized that common genetic variation at this TNDM region influences type 2 diabetes susceptibility. In addition to the coding regions, we used comparative genomic analysis to identify conserved noncoding regions, which were resequenced for single nucleotide polymorphism (SNP) discovery in 47 individuals. Twenty-six SNPs were identified. Fifteen tag SNPs (tSNPs) were successfully genotyped in a large case-control (n = 3,594) and family-based (n = 1,654) study. We did not find any evidence of association or overtransmission of any tSNP to affected offspring or of a parent-of-origin effect. Using a study sufficiently powered to detect odds ratios of <1.2, we conclude that common variation in the TNDM region does not play an important role in the genetic susceptibility to type 2 diabetes. Diabetes 55:2272-2276, 2006 [ABSTRACT FROM AUTHOR]

The etiopathological relationship between latent autoimmune diabetes in adults (LADA) and classical type 1 (insulin dependent) diabetes remains unclear. Variation at the insulin gene variable number of tandem repeats (VNTR) minisatellite influences susceptibility to type 1 diabetes, but studies in LADA have been small and inconsistent. We examined the role of insulin gene variation (using flanking variants as surrogates for VNTR subtypes) in the largest case-control study of LADA to date (400 case and 332 control subjects). Highly significant associations were identified with disease, with dominant protective effects of the T allele at -23HphI (odds ratio [OR] 0.42 [95% CI 0.31-0.58], P = 2.4 X 10-8), A allele at +1,404Fnu4HI (0.50 [0.36-0.70], P = 3.2 x 10-5), and C allele at +3,580MspI (0.55 [0.35-0.85], P = 0.0046). As with type 1 diabetes, the -23HphI variant (a surrogate for the subdivision of VNTR into class I and III alleles) most clearly defined susceptibility in LADA. However, there was no association with age at diagnosis or requirement for insulin therapy 6 years postdiagnosis. This study establishes that variation within the insulin gene region does influence susceptibility to LADA, with the direction and magnitude of effect indistinguishable from that previously reported for type 1 diabetes. In conclusion, differences in VNTR-encoded susceptibility do not explain the differences in clinical presentation that distinguish classical type 1 diabetes and LADA. [ABSTRACT FROM AUTHOR]

HNF1alpha (TCF1) is a key transcription factor that is essential for pancreatic beta-cell development and function. Rare mutations of HNF1alpha cause maturity-onset diabetes of the young. A common variant, G319S, private to the Oji-Cree population, predisposes to type 2 diabetes, but the role of common HNF1alpha variation in European populations has not been comprehensively assessed. We determined the linkage disequilibrium and haplotype structure across the HNF1alpha gene region using 29 single nucleotide polymorphisms (SNPs). Eight tagging SNPs (tSNPs) that efficiently capture common haplotypes and the amino acid-changing variant, A98V, were genotyped in 5,307 subjects (2,010 type 2 diabetic case subjects, 1,643 control subjects, and 1,654 members of 521 families). We did not find any evidence of association between the tSNPs or haplotypes and type 2 diabetes. We could exclude odds ratios (ORs) >1.25 for all tSNPs. The rare V98 allele (approximately 3% frequency) showed possible evidence of association with type 2 diabetes (OR 1.23 [95% CI 0.99-1.54], P = 0.07), a result that was supported by meta-analysis of this and published studies (OR 1.31 [1.08-1.59], P = 0.007). Further studies are required to investigate this association, demonstrating the difficulty of defining the role of rare (<5%) alleles in type 2 diabetes risk. [ABSTRACT FROM AUTHOR]

HNF1α (TCF1) is a key transcription factor that is essential for pancreatic β-cell development and function. Rare mutations of HNF1α cause maturity-onset diabetes of the young. A common variant, G319S, private to the Oji-Cree population, predisposes to type 2 diabetes, but the role of common HNF1α variation in European populations has not been comprehensively assessed. We determined the linkage disequilibrium and haplotype structure across the HNF1α gene region using 29 single nucleotide polymorphisms (SNPs). Eight tagging SNPs (tSNPs) that efficiently capture common haplotypes and the amino acid-changing variant, A98V, were genotyped in 5,307 subjects (2,010 type 2 diabetic case subjects, 1,643 control subjects, and 1,654 members of 521 families). We did not find any evidence of association between the tSNPs or haplotypes and type 2 diabetes. We could exclude odds ratios (ORs) > 1.25 for all tSNPs. The rare V98 allele (∼3% frequency) showed possible evidence of association with type 2 diabetes (OR 1.23 [95% CI 0.99-1.54], P = 0.07), a result that was supported by meta-analysis of this and published studies (OR 1.31 [1.08-1.59], P = 0.007). Further studies are required to investigate this association, demonstrating the difficulty of defining the role of rare (<5%) alleles in type 2 diabetes risk. Diabetes 54:2487-2491, 2005 [ABSTRACT FROM AUTHOR]

The gene encoding insulin receptor substrate-1 (IRS1) represents a strong biological candidate for a contributory role in type 2 diabetes susceptibility. Indeed, functional studies have implicated the G971R variant, and a recent meta-analysis of 27 association studies suggested that carriage of 971R was associated with a 25% increase in disease risk. However, this association has not been evaluated in large samples. The present study genotyped the P512A and G971R IRS1 variants in 971 U.K. type 2 diabetic subjects ascertained for strong family history and/or early onset, as well as 1,257 control subjects matched by ethnicity. There was no evidence for association with type 2 diabetes for either variant. (For example, the odds ratio [OR] for carriage of 971R was 1.11 [95% CI 0.86-1.44, P = 0.44]) An updated meta-analysis (31 studies: 5,104 case and 7,418 control subjects) remained significant for the G971R association (P = 0.025), albeit with a diminished OR (1.15 [95% CI 1.02-1.31]). Additional studies of IRS1 variation will be required to obtain a robust estimate of the overall contribution of IRS1 variation to type 2 diabetes susceptibility, but the current study suggests that previous studies have overestimated the magnitude of this effect. [ABSTRACT FROM AUTHOR]

Hepatocyte nuclear factor (HNF)-4alpha is part of a transcription factor network that is key for the development and function of the beta-cell. Rare mutations in the HNF4alpha gene cause maturity-onset diabetes of the young. A number of type 2 diabetes linkage studies have found evidence of linkage to 20q12-13.1 where the HNF4alpha gene is located. Two recent studies have found an association between four common variants of the alternative P2 promoter region and type 2 diabetes. These variants are in strong linkage disequilibrium, and the minor alleles define one common risk haplotype. In both studies, the risk haplotype explained a large proportion of the evidence of linkage to 20q12-13.1. We aimed to assess this haplotype in a U.K. Caucasian study of 5,256 subjects. We typed two single nucleotide polymorphisms tagging the risk haplotype (rs4810424 and rs2144908) and found evidence of association in both case-control and family-based studies; rs4810424 marginally demonstrated the stronger association with an overall estimated odds ratio of 1.15 (95% CI 1.02-1.33) (P = 0.02). The effect of the P2 haplotype on type 2 diabetes risk is less than in the initial studies, probably reflecting that these studies used 20q12-13.1-linked cases. In conclusion, we have replicated the association of the HNF4alpha P2 promoter haplotype with type 2 diabetes in a U.K. Caucasian population where there is no evidence of linkage to 20q. [ABSTRACT FROM AUTHOR]

Additional information on genetic susceptibility effects relevant to type 2 diabetes pathogenesis can be extracted from existing genome scans by extending examination to related phenotypes such as age at disease onset. In this study, we report the reanalysis of data from 573 U.K. sibships ascertained for multiplex type 2 diabetes, using age at onset (assessed by the proxy measure of age at diagnosis) as the phenotype of interest. Genome-wide evidence for linkage to age at diagnosis was evaluated using both variance components and Haseman-Elston (HECOM) regression approaches, with extensive simulations to derive empirical significance values. There was broad agreement across analyses with six regions of interest (logarithm of odds [LOD] >/==" BORDER="0">1.18) identified on chromosomes 1qter, 4p15-4q12, 5p15, 12p13-12q13, 12q24, and 14q12-14q21. The strongest empirically "suggestive" evidence for linkage comes from regions on chromosome 12. The first region (12p13-12q13), peaking at D12S310 (variance components LOD [LOD(VC)] = 2.08, empirical pointwise P = 0.0007; HECOM LOD [LOD(HECOM)] = 2.58, P = 0.0010) seems to be novel. The second (12q24) peaking between D12S324 and D12S1659 (LOD(VC) = 1.87, P = 0.0016; LOD(HECOM) = 1.93, P = 0.0027) overlaps a region showing substantial prior evidence for diabetes linkage. These data provide additional evidence that genes mapping to these chromosomal regions are involved in the susceptibility to, and/or development of, type 2 diabetes. [ABSTRACT FROM AUTHOR]

A young onset of type 2 diabetes is likely to result, in part, from greater genetic susceptibility. Young-onset families may therefore represent a group in which genes are more easily detectable by linkage. To test this hypothesis, we conducted age at diagnosis (AAD) stratified linkage analyses in the Diabetes UK Warren 2 sibpairs. In the previously published unstratified analysis, evidence for linkage (logarithm of odds [LOD] >1.18) was found at seven loci. The LOD scores at these seven loci were higher in the 245 families with AAD <55 years (L55) compared with the 328 families with AAD >55 years (G55). Five of these seven loci (1q24-25, 5q13, 8p21-22, 8q24.2, and 10q23.2) had LOD scores >1.18 in the L55 subset but only one (8p21-22) did in the G55 subset. Two additional loci (8q21.13 and 21q22.2) showed evidence for linkage in the L55 subset alone. Another locus (22q11) showed evidence for linkage in a subset of families with AAD <45 years. Using a locus-counting approach, the L55 subset had significantly more loci (P approximately 0.01) than expected under the null hypothesis of no linkage across the LOD score range 0.59-3.0. In contrast, the G55 subset contained no more susceptibility loci than that expected by chance. In conclusion, young-onset families provide both disproportionate evidence for linkage to known loci and evidence for additional novel loci. Our data confirm our hypothesis that families segregating young-onset type 2 diabetes represent a more powerful resource for defining susceptibility genes by linkage. [ABSTRACT FROM AUTHOR]

The gene for insulin-degrading enzyme (IDE) represents a strong positional and biological candidate for type 2 diabetes susceptibility. IDE maps to chromosome 10q23.3, a region linked to diabetes in several populations; the rat homolog has been directly implicated in diabetes susceptibility; and known functions of IDE support an important role in glucose homeostasis. We sought evidence for association between IDE variation and diabetes by mutation screening, defining local haplotype structure, and genotyping variants delineating common haplotypic diversity. An initial case-control analysis (628 diabetic probands from multiplex sibships and 604 control subjects) found no haplotypic associations, although one variant (IDE2, -179T-->C) showed modest association with diabetes (odds ratio [OR]1.25, P = 0.03). Linkage partitioning analyses failed to support this association, but provided borderline evidence for a different variant (IDE10, IVS20-405A-->G) (P = 0.06). Neither variant was associated with diabetes when replication was sought in 377 early onset diabetic subjects and 825 control subjects, though combined analysis of all typed cohorts indicated a nominally significant effect at IDE2 (OR 1.21 [1.04-1.40], P = 0.013). In the absence of convincing support for this association from linkage partitioning or analyses of continuous measures of glycemia, we conclude that analysis of over 2,400 samples provides no compelling evidence that variation in IDE contributes to diabetes susceptibility in humans. [ABSTRACT FROM AUTHOR]

The orphan receptor small heterodimer partner (SHP, NR0B2) modulates the transcription activity of the MODY1 gene HNF4a. Mutations in SHP were found in 7% of Japanese obese young-onset type 2 diabetic patients and were associated with moderate obesity and increased birth weight. We investigated SHP in 1927 U.K. subjects, examining relationships with type 2 diabetes, obesity, and birth weight. Sequencing of the coding region of SHP in 122 obese, young-onset type 2 diabetic patients detected the polymorphism G171A. The polymorphism was not associated with diabetes in case control or familial association studies. The A allele (frequency 0.07) was not associated with obesity in type 2 diabetic subjects (n = 348), their parents (n = 272), or young nondiabetic adults (n = 925). However, the rare (<1%) AA homozygotes had a raised BMI in each cohort; this was significant when all cohorts were combined (Z score = 0.67 AA vs. -0.05 G/x, P = 0.02). There was no association with corrected birth weight in 382 normal babies, but the only AA baby was 4,069 g. Our study suggests that genetic variation in SHP is unlikely to be common in the predisposition to diabetes, obesity, or increased birth weight in U.K. Caucasians. [ABSTRACT FROM AUTHOR]

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. [ABSTRACT FROM AUTHOR]

For any mitochondrial DNA (mtDNA) mutation, the ratio of mutant to wild-type mtDNA (% heteroplasmy) varies across tissues, with low levels in leukocytes and high levels in postmitotic tissues (e.g., skeletal muscle). Direct sequencing is the gold-standard method used to detect novel mutations, but can only reliably detect % heteroplasmy >25%, which is rare in leukocytes. Therefore, we investigated the role of mtDNA defects in maternally inherited diabetes by first screening for the A3243G tRNA(Leu(UUR)) mutation by restriction assay, followed by sequencing of the entire mitochondrial genome using skeletal muscle derived mtDNA. A total of 28 patients had maternally inherited diabetes either alone (group 1, n = 17) or with one or more additional features of mitochondrial disease, including bilateral sensori-neural deafness and neuromuscular disease (group 2, n = 11). Three patients (all from group 2) carried the A3243G mutation. Skeletal muscle mtDNA from eight group 1 patients and six more group 2 patients was sequenced. No pathogenic mutations were found in the group 1 patients, while two patients from group 2 had mutations at positions 12258 and 14709 in the tRNA serine and glutamic acid genes, respectively. We conclude, therefore, that screening for mtDNA mutations should be considered in patients with maternally inherited diabetes, but only when additional features of mitochondrial disease are present. [ABSTRACT FROM AUTHOR]

Mutations in the WFS1 gene cause beta-cell death, resulting in a monogenic form of diabetes known as Wolfram syndrome. The role of variation in WFS1 in type 2 diabetes susceptibility is not known. We sequenced the WFS1 gene in 29 type 2 diabetic probands and identified 12 coding variants. We used 152 parent-offspring trios to look for familial association; the R allele at residue 456 (P = 0.04) and the H allele at residue 611 (P = 0.05) as well as the R456-H611 haplotype (P = 0.032) were overtransmitted to affected offspring from heterozygous parents. In a further cohort of 327 type 2 diabetic subjects and 357 normoglycemic control subjects, the H611 allele and the R456-H611 haplotype were present in more type 2 diabetic subjects than control subjects (one-tailed P = 0.06 and P = 0.023, respectively). In a combined analysis, the H611 allele was present in 60% of all diabetes chromosomes and 55% of all control chromosomes (odds ratio [OR] 1.24 [95% CI 1.03-1.48], P = 0.02), and the R456-H611 haplotype was significantly more frequent in type 2 diabetic subjects than in control subjects (60 vs. 54%, OR 1.29 [95% CI 1.08-1.54], P = 0.0053). Our results provide the first evidence that variation in the WFS1 gene may influence susceptibility to type 2 diabetes. [ABSTRACT FROM AUTHOR]

Variation in the calpain-10 gene (CAPN10) has been shown to be associated with type 2 diabetes in Mexican-Americans and in at least three Northern European populations. Studies in nondiabetic Pima Indians showed that one of the at-risk DNA polymorphisms, single-nucleotide polymorphism (SNP)-43, in CAPN10 was associated with insulin resistance, and individuals with the G/G-genotype had significantly higher fasting plasma glucose and 2-h insulin concentrations after a 75-g oral glucose tolerance test (OGTT). We have examined the effect of variation in CAPN10 on plasma glucose and insulin levels in a group of 285 nondiabetic British subjects after a 75-g OGTT. The results showed that subjects with G/G genotype at SNP-43 had higher 2-h plasma glucose levels than the combined G/A + A/A group (P = 0.05). We also examined the SNP-43, -19, and -63 haplotype combination 112/121, which is associated with an approximately threefold increased risk of diabetes. Subjects with the 112/121 haplotype combination (n = 29) had increased fasting (P = 0.004) and 2-h plasma glucose levels (P = 0.003) compared with the rest of the study population after correction for age, sex, and BMI. The 112/121 haplotype combination was also associated with a marked decrease in the insulin secretory response, adjusted for the level of insulin resistance (P = 0.002). We conclude that genetic variation in the CAPN10 gene influences blood glucose levels in nondiabetic British subjects and that this is due, at least in part, to the effects of calpain-10 on the early insulin secretory response. [ABSTRACT FROM AUTHOR]

To investigate the contribution of inherited biochemical defects to the peripheral insulin resistance of type 2 diabetes, we studied cultured skeletal muscle from 10 insulin-resistant nondiabetic first-degree relatives of type 2 diabetic families and 6 control subjects. Insulin stimulation of glucose uptake and glycogen synthesis was maximal in myoblasts. Insulin-stimulated glucose uptake (fold-stimulation over basal uptake) was decreased in relative compared with control myoblasts at 0.001 micromol/l (0.93 +/- 0.05 [mean +/- SE] vs. 1.15 +/- 0.06, P < 0.05) and 0.1 micromol/l (1.38 +/- 0.10 vs. 1.69 +/- 0.08, P = 0.025) insulin. Insulin responsiveness was markedly impaired in 5 of the relative myoblast cultures, and in 4 of these, there was an associated increase in basal glucose uptake (76.7 +/- 7.0 vs. 47.4 +/- 5.5 pmol x min(-1) x mg(-1) protein, relative vs. control; P < 0.02). Expression of insulin receptor substrate 1, phosphatidylinositol 3-kinase, protein kinase B, and glycogen synthase was normal in the relative cultures with impaired insulin responsiveness. Glycogen synthesis was also normal in the relative cultures. We conclude that the persistence of impaired insulin responsiveness in some of the relative cultures supports the role of inherited factors in the insulin resistance of type 2 diabetes and that the association with increased basal glucose uptake suggests that the 2 abnormalities may be linked. [ABSTRACT FROM AUTHOR]

Variation at the variable number tandem repeat (VNTR) minisatellite 5' of the insulin gene (INS) is associated with several phenotypes, including type 1 diabetes, polycystic ovary syndrome, and birth weight. Case-control studies have suggested that class III VNTR alleles are also associated with type 2 diabetes, but results have been inconsistent and may reflect population stratification. To explore further the role of the INS-VNTR in type 2 diabetes susceptibility, we used family-based association methods in 155 parent-offspring trios from the British Diabetic Association-Warren Trios repository, each ascertained via a Europid proband with type 2 diabetes. Overall, there was no significant association between diabetes and the INS-VNTR genotype, with 65 of 119 heterozygous parents (55%) transmitting class III and 54 class I (P = 0.16, one-sided). However, whereas maternal transmissions followed Mendelian expectation, there was a marked excess of class III transmission from the 49 heterozygous fathers (34 [69%] vs. 15, P = 0.003 vs. 50% expectation, P = 0.003 vs. maternal transmission). These results confirm that variation within the TH-INS-IGF2 locus, most plausibly at the VNTR itself, influences type 2 diabetes susceptibility. By demonstrating that this effect is mediated exclusively by the paternally derived allele, these findings implicate imprinted genes in the pathogenesis of type 2 diabetes. [ABSTRACT FROM AUTHOR]

Background: The consumption of large (∼50g) doses of whey protein [WP] before meals (i.e., preload) has been shown to improve postprandial glycemic [PPG] excursions in people with type 2 diabetes [T2D]. Yet, studies to date have not accounted for treatment palatability, the energy associated with large WP doses, or the burden allied with preload preparation, limiting its ecological translation. Herein, we examined the PPG responses to a mixed-meal tolerance test [MMTT] following prior consumption of a low dose of WP from a novel, pre-made shot in people with T2D. Methods: Nine adults with T2D (8M/1F; HbA1c 57.6±10.1 mmol∙mol) attended the laboratory on two occasions, ∼14d apart. After an overnight fast, subjects randomly consumed a bespoke, ready-to-drink WP (15g) or placebo [PLA] shot (100ml) 10min prior to a 4hr MMTT (387kcal; 58% CHO). At 4hr, a further shot was consumed 10min before an ad libitum lunch. Subjective appetite and preload palatability were assessed by visual analog scales. Interstitial glucose was measured throughout. Data (mean±SD) were analyzed by a two-way repeated measures ANOVA. Results: Compared to PLA, WP attenuated early [0-60min] (-48.9±35.9%; p=0.01) and total [0-240min] PPG area under the curve (-22.7±17.5%; p<0.001). During both trials, peak PPG occurred ∼80min post-MMTT and was reduced following WP (-13.8±7.8% [range: -23.0 to +2.1%]; p<0.01). The peak incremental change in PPG was 1.36±1.08 mmol∙L less following WP vs. PLA (p<0.01). Subjective appetite (p>0.05) and ad libitum energy intake were similar between trials (p=0.48). Both preloads were rated highly palatable. Conclusion: Consuming a small, bespoke WP shot lowers post-meal hyperglycemia in people with T2D without affecting satiety and satiation. We highlight the potential for small, contemporary WP beverages that encompass both glycemic benefit but also patient taste and convenience, which may have lasting clinical value beyond formal research studies. Disclosure: K. Smith: None. G.S. Taylor: None. K.A. Bowden Davies: None. L.H. Brunsgaard: None. E. Jensen: Employee; Self; Arla Foods Ingredients. M. Walker: None. E.J. Stevenson: None. D.J. West: None. Funding: Arla Foods Ingredients Group P/S [ABSTRACT FROM AUTHOR]

Examines the genetic defects in mitochondrial diabetes. Structure of mitochondrial genome; Identification of mitochondrial DNA point mutations and rearrangements in families with diabetes; Major factor limiting the identification of the DNA defects in diabetes.

Studies the primary molecular events underlying non-insulin dependent diabetes (NIDDM) and obesity. Individual susceptibility to interrelated conditions under genetic influence; Processing of proinsulin to mature insulin; Evidence for linkage between the gene region and NIDDM.

Women with a history of adverse outcomes in pregnancy (including pre-term birth, delivery of a small-for-gestational-age (SGA) infant, preeclampsia, and gestational diabetes (GDM)) have a higher prevalence of metabolic syndrome (MetS) and cardiovascular disease, as compared to their peers. However, it is not known if MetS precedes the index pregnancy in women who develop these outcomes. Thus, we sought to evaluate the impact of pre-gravid MetS on the risk of adverse outcomes in pregnancy. In this prospective pre-conception cohort study, 1183 newly-married women underwent systematic assessment of cardiovascular risk factors (anthropometry, blood pressure, lipids, glucose) and then were followed across a subsequent pregnancy for the outcomes of interest. The women were stratified into two groups based on the presence (n=49) or absence (n=1134) of pre-gravid MetS (harmonized definition). The groups did not differ in length of gestation (p=0.31) or infant birthweight (p=0.21). Of note, women with pre-gravid MetS were more likely to have a Caesarean delivery (61.4% vs. 38.6%, p=0.003). However, there were no differences between the groups in the incidence of pre-term delivery, SGA, LGA, preeclampsia or GDM (Table). In conclusion, the increased lifetime risk of MetS observed in women with a history of these adverse pregnancy outcomes does not necessarily manifest prior to their pregnancy. Disclosure: R. Retnakaran: Consultant; Self; Eli Lilly and Company, Novo Nordisk Inc., Sanofi. Research Support; Self; Boehringer Ingelheim International GmbH, Novo Nordisk Inc. S. Wen: None. H. Tan: None. C. Ye: None. M. Shen: None. G.N. Smith: None. M.C. Walker: None. Funding: Canadian Institutes of Health Research [ABSTRACT FROM AUTHOR]

Introduction: Age-related cumulative mitochondrial mutations can cause mitochondrial dysfunction. The mitochondrial DNA mutator mouse (PolgAmut/mut) is a model of premature ageing and has been previously shown to develop impaired insulin secretion with age. Methods: Immunofluorescence was used to study mitochondrial respiratory chain protein expression (complex I and IV) and the cell composition in islets. Experiments were conducted on pancreas tissue from PolgAmut/mut mice and age-matched wild type (WT) mice at two ages: 12 weeks (young) and 44 weeks (old). Results: (1) Comparing young WT mice versus old WT mice, there was no difference in islet complex I expression, while islet size and beta cell number increased with age (both P<0.01). (2) Comparing young PolgA mut/mut mice versus young WT mice, complex I expression was significantly lower (P<0.01) in islets from young PolgA mut/mut mice. However, there were no significant differences in islet size and cell composition between young PolgA mut/mut and young WT mice. (3) Comparing old PolgA mut/mut mice versus old WT mice, complex I expression was significantly lower (P<0.01) and complex IV expression was significantly higher (P<0.01) in islets from the old PolgA mut/mut mice. Old PolgA mut/mut islets had a lower beta cell percentage (mean ± SEM; 71.8 ± 4 % vs. 89.3 ± 4% P<0.01) but a higher alpha cell percentage (mean ± SEM; 29.6 ± 4 % vs. 12.5 ± 5%; P<0.01) versus old WT mice (both P<0.01). Conclusions: In PolgA mut/mut mice, complex I deficiency was already present in the islets of young mice and persisted with age. This was associated with a proportional increase in alpha cells and decrease in beta cells in islets from old PolgA mut/mut versus the old WT mice. We conclude that complex I deficiency in PolgA mut/mut mice is linked to altered islet cell composition with increasing age. Disclosure: X. Yu: None. C. Arden: None. C. Chen: None. C. Bradshaw: None. J. Whitehall: None. M.G. White: None. S.J. Anderson: None. J.A. Shaw: Advisory Panel; Self; Sanofi. Other Relationship; Self; Novo Nordisk A/S. D. Turnbull: None. L. Greaves: None. M. Walker: None. [ABSTRACT FROM AUTHOR]

The BAIR consortium has been formed to provide insight into the biological processes underlying insulin resistance through multidisciplinary research combining various genomic/proteomic/metabolomic approaches in animal models, followed by haman genetic analysis. Based on previously described associations, function and on BAIR biological data, we selected 11 candidate genes (ARNT; RBP4; HIF1a; EIF2S1; AKT1; ONECUT1; RPS6KB1; TRB3; FOXA2; PCK1; FOXO3A) for investigation. Pairwise tags (r²>0.8) spanning these genes were selected based on HapMap phase II CEU data to exhaustively capture common variation (MAF>0.05). 103 SNPs were genotyped in 5,602 samples (935 UKT2D, 1927 UK-controls, 926 French T2D, 934 French obese and 880 French controls) by iPLEX & SNPlex methods. Single-point analyses on 92 SNPs were carried out after stringent quality control. Coverage of common variation remained high (74%-100% per gene). There was no significant association with T2D or obesity (at the p=0.01 level) in 9 of the strong candidate genes examined. In the UK population, rs11908628 of PCK1 (encoding phosphoenolpyruvate carboxykinase 1, the main control point for the regulation of gluconeogenesis) was found to be protective against diabetes (MAFs 2.7% v 4.3%, OR(95%CIs): 0.62 (0.44-0.86); p=0.003 additive). Mantel-Haenszel meta-analysis of rs11908628 across the UK and French T2D samples provided additional support for this finding (p=0.002), although further investigation, given low MAFs, is warranted. When comparing genotypes between T2D cases and controls in the French population, 2 independent associations were seen in RPS6KB1: rs180535 (MAFs 18% v 15%; OR 1.29 (1.07 -1.55); p=0.006) and rs180531 (24% v 28%; OR 0.81 (0.69-0.95) p=0.008) (r²=0.06 in controls). RPS6KB1 codes for ribosomal protein S6 kinase 70KD 1, which negatively regulates insulin signalling. Interestingly, rs180531 (23% v 28%; OR 0.80 (0.69-0.94) p=0.005) was also associated with protection against obesity in the French. In conclusion, our genetic data suggest modest effects of the BAIR insulin resistance candidates PEPCK and S6K1 gene variation in UK (T2D) and French (T2D and obese) samples, results that require replication in additional populations. [ABSTRACT FROM AUTHOR]

The capacity to undertake systematic surveys of common variation through genome-wide association analysis has the potential to deliver substantial insights into type 2 diabetes (T2D) pathogenesis. We recently completed genotyping of 1954 T2D cases (enriched for positive family history/early onset) and 2922 population-based controls (all UK origin) on the Affymetrix 500k chip as part of the Wellcome Trust Case-Control Consortium. The preliminary analyses reported here are based on ∼309,000 SNPs with exemplary quality control and minor allele frequency (MAF)>5% [estimated to provide ∼60% coverage of CEU HapMap (MAF>5%, pairwise, r²>0.8)]. Variants within TCF7L2 emerge as the strongest cluster of susceptibility variants (12 SNPs, best = rs7901695, p=9.9x 10[sup -13]), but we find an additional 5 signals achieving nominal genome-wide significance with additive model p<6x10[sup -6] (controlling the false discovery rate at 0.05). These signals (located on chromosomes 1, 2, 6, 12 and 16) include a cluster of 5 SNPs with p< 10[sup -4] at ∼20.8Mbp on chr6, in a region including the CDK5 regulatory subunit associated protein 1-like 1 gene (CDKAL1) [for example, rs9465871, OR(95%CIs) for allele T (MAF∼80%) dominance: 0.51(0.37-0.70), exact p=1x10[sup -5]]. Extensive replication studies in 3073 T2D cases and 3879 controls (0.70(0.53-0.92), exact p=0.005) and meta-analysis across all ∼11800 subjects (0.61 (0.49-0.75), exact p=5.7x 10[sup -7]) provide supporting evidence for this finding. Haplotype-based analyses across a 2Mb region surrounding rs9465871 show no additional signal. Based on HapMap CEU data, rs9465871 is in perfect LD with several other intronic variants within CDKAL1; we have thus far covered ∼60% of common variation in the region (r²>0.8). Whilst further replication studies and fine-mapping will be required to refine the allelic architecture of this locus, these findings provide strong preliminary evidence that the CDKAL1 region harbours a novel locus affecting T2D risk. [ABSTRACT FROM AUTHOR]

The insulin gene is a strong candidate for a role in type 2 diabetes susceptibility. Both the VNTR minisatellite 5′ to the gene, and the -23HphI variant, with which it is in strong LD in non-African populations, are thought to have direct functional effects on insulin expression and splicing; and the relationship between class I VNTR alleles and T1D susceptibility is established. However, small-scale case-control and family-based studies associating possession of the longer class III VNTR alleles (and/or the T at -23HphI) with T2D have not been substantiated in recent larger studies. We typed 3 SNPs which tag major haplotype groups across INS, [rs689 (-23HphI), rs3842755 (+1404Fnu4HI) and rs2000993 (+3580MspI)] in a total of 2022 UK T2D cases (enriched for family history and early onset) and 2480 UK population controls, plus 387 UK parent-offspring triads. Single-point analyses revealed a significant association between the -23T (tagging the VNTR class III) allele and T2D risk (allele frequencies in cases and controls: 31.5% v. 28.9%; OR 1.13 (1.03-1.24); p=0.007 additive). There was a weaker association with the + 1404T allele (denoting the IIIA subclass) (23.9% v. 22.0%; OR 1.11 (1.00-1.23); p=0.04), but this was not independent of the -23T finding. There was marginal evidence for excess transmission of the -23T (class III allele) from heterozygous parents to T2D offspring (125 v.99, p=2.04 one-sided) extending an earlier report which featured ∼37% of this trio sample. A marginally significant parent of origin effect was observed for paternal overtransmission of the associated allele (52 v.32, p=0.03) Haplotype analyses did not contribute additional information. In summary, these findings are consistent with the hypothesis that individuals carrying the class III VNTR and -23T alleles are at modestly-increased risk (OR∼1.10) of developing T2D. The magnitude and direction of effect are consistent with the estimates from previous association studies and the known functional consequences of these alleles. [ABSTRACT FROM AUTHOR]

Deterioration in pancreatic β-cell function is central to the pathophysiology of Type 2 diabetes (T2D). Indeed, genes with important roles in β-cells have been shown to influence susceptibility to this disease. We performed a candidate gene association study examining 1,367 SNPs in 84 β-cell genes in three UK case-control studies. In a log-additive model, 18 SNPs were associated with T2D risk with P<0.01. Further typing in Ashkenazim revealed two SNPs that remained associated with T2D risk (P<0.05) in this population. Both SNPs mapped within the WFS1 gene, and the associations replicated in three further UK case control studies. Pooled analysis of all studies, comprising 9,533 cases and 11,389 controls, showed strong statistical evidence for the association of WFSI SNPs with T2D risk (P≦3.4x10[sup -7]). WFS1 mutations cause Wolfram Syndrome, a rare autosomal recessive syndrome partly characterised by severe juvenile type 2 diabetes. Our data indicate that the WFS1 gene also contributes to risk of common type 2 diabetes (PAT = 9%). [ABSTRACT FROM AUTHOR]