Joint analysis of individual participants' data from 17 studies on the association of the IL6 variant -174G>C with circulating glucose levels, interleukin-6 levels, and body mass index.

BACKGROUND: Several studies have investigated associations between the -174G>C single nucleotide polymorphism (rs1800795) of the IL6 gene and phenotypes related to type 2 diabetes mellitus (T2DM) but presented inconsistent results. AIMS: This joint analysis aimed to clarify whether IL6 -174G>C was associated with glucose and circulating interleukin-6 concentrations as well as body mass index (BMI). METHODS: Individual-level data from all studies of the IL6-T2DM consortium on Caucasian subjects with available BMI were collected. As study-specific estimates did not show heterogeneity (P>0.1), they were combined by using the inverse-variance fixed-effect model. RESULTS: The main analysis included 9440, 7398, 24,117, or 5659 non-diabetic and manifest T2DM subjects for fasting glucose, 2-hour glucose, BMI, or circulating interleukin-6 levels, respectively. IL6 -174 C-allele carriers had significantly lower fasting glucose (-0.091 mmol/L, P=0.014). There was no evidence for association between IL6 -174G>C and BMI or interleukin-6 levels, except in some subgroups. CONCLUSIONS: Our data suggest that C-allele carriers of the IL6 -174G>C polymorphism have lower fasting glucose levels on average, which substantiates previous findings of decreased T2DM risk of these subjects.

Genetic analysis of Kruppel-like zinc finger 11 variants in 5864 Danish individuals: potential effect on insulin resistance and modified signal transducer and activator of transcription-3 binding by promoter variant -1659G>C.

CONTEXT: The transcription factor Krüppel-like zinc finger 11 (KLF11) has been suggested to contribute to genetic risk of type 2 diabetes (T2D). Our previous results showed that four KLF11 variants, in strong linkage disequilibrium (LD block including +185 A>G/Gln62Arg and -1659 G>C) were associated with T2D in a north European case-control study. Here we further analyzed these variants for T2D association in a general Danish population and assess their possible effect on gene function. METHODS: We genotyped Gln62Arg variant, representative for the LD block, in 5864 subjects of the INTER99 study to assess association to T2D and glucose metabolism-related quantitative traits. We studied effects of LD-block variants on KLF11 function and in particular, the effect of -1659G>C on transcriptional regulation of KLF11 using EMSA, chromatin immunoprecipitation, gene reporter assays, and small interfering RNA transfection. RESULTS: We could not confirm T2D association of the KLF11 LD block, however, in glucose-tolerant subjects; it was significantly associated with higher fasting serum insulin and C-peptide levels and increased homeostasis model assessment insulin resistance indexes (P = 0.00004, P = 0.006, and P = 0.00002, respectively). In addition, binding of signal transducer and activator of transcription (STAT)-3 to the wild-type (-1659G>C) allele stimulated gene transcription, whereas STAT3 did not bind onto the mutant allele. CONCLUSIONS: We showed that KLF11 may interfere with glucose homeostasis in a Danish general population and that STAT3-mediated up-regulation of KLF11 transcription was impaired by the -1659G>C variant. Overall, KLF11 variants may have a deleterious effect on insulin sensitivity, although that may not be sufficient to lead to T2D.

The HADHSC gene encoding short-chain L-3-hydroxyacyl-CoA dehydrogenase (SCHAD) and type 2 diabetes susceptibility: the DAMAGE study.

The short-chain l-3-hydroxyacyl-CoA dehydrogenase (SCHAD) protein is involved in the penultimate step of mitochondrial fatty acid oxidation. Previously, it has been shown that mutations in the corresponding gene (HADHSC) are associated with hyperinsulinism in infancy. The presumed function of the SCHAD enzyme in glucose-stimulated insulin secretion led us to the hypothesis that common variants in HADHSC on chromosome 4q22-26 might be associated with development of type 2 diabetes. In this study, we have performed a large-scale association study in four different cohorts from the Netherlands and Denmark (n = 7,365). Direct sequencing of HADHSC cDNA and databank analysis identified four tagging single nucleotide polymorphisms (SNPs) including one missense variant (P86L). Neither the SNPs nor haplotypes investigated were associated with the disease, enzyme function, or any relevant quantitative measure (all P > 0.1). The present study provides no evidence that the specific HADHSC variants or haplotypes examined do influence susceptibility to develop type 2 diabetes. We conclude that it is unlikely that variation in HADHSC plays a major role in the pathogenesis of type 2 diabetes in the examined cohorts.

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

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

Mutation analysis of the preproghrelin gene: no association with obesity and type 2 diabetes.

OBJECTIVE: To investigate the preproghrelin gene for variants and their association with obesity and type 2 diabetes. DESIGN AND METHOD: 82 obese probands were analyzed for mutations using single-strand conformational polymorphism, heteroduplex analyses and sequencing. Association studies were performed in 234 juvenile-onset obese and 323 lean men and in 557 type 2 diabetic and 233 glucose tolerant subjects. RESULTS: We identified two novel variants, 36C > T and IVS3 + 715delC, and 4 known variants, Arg51Gln, Leu72Met, Gln90Leu, and IVS1 + 169G > A. None of the variants showed any significant association with obesity or type 2 diabetes or estimates of glucose and lipid metabolism in glucose tolerant subjects. CONCLUSION: Variation in the preproghrelin gene is not associated with juvenile-onset obesity, type 2 diabetes or related phenotypes among the examined Danish Caucasian subjects.

Role of transcription factor KLF11 and its diabetes-associated gene variants in pancreatic beta cell function.

KLF11 (TIEG2) is a pancreas-enriched transcription factor that has elicited significant attention because of its role as negative regulator of exocrine cell growth in vitro and in vivo. However, its functional role in the endocrine pancreas remains to be established. Here, we report, for the first time, to our knowledge, the characterization of KLF11 as a glucose-inducible regulator of the insulin gene. A combination of random oligonucleotide binding, EMSA, luciferase reporter, and chromatin immunoprecipitation assays shows that KLF11 binds to the insulin promoter and regulates its activity in beta cells. Genetic analysis of the KLF11 gene revealed two rare variants (Ala347Ser and Thr220Met) that segregate with diabetes in families with early-onset type 2 diabetes, and significantly impair its transcriptional activity. In addition, analysis of 1,696 type 2 diabetes mellitus and 1,776 normoglycemic subjects show a frequent polymorphic Gln62Arg variant that significantly associates with type 2 diabetes mellitus in North European populations (OR = 1.29, P = 0.00033). Moreover, this variant alters the corepressor mSin3A-binding activity of KLF11, impairs the activation of the insulin promoter and shows lower levels of insulin expression in pancreatic beta cells. In addition, subjects carrying the Gln62Arg allele show decreased plasma insulin after an oral glucose challenge. Interestingly, all three nonsynonymous KLF11 variants show increased repression of the catalase 1 promoter, suggesting a role in free radical clearance that may render beta cells more sensitive to oxidative stress. Thus, both functional and genetic analyses reveal that KLF11 plays a role in the regulation of pancreatic beta cell physiology, and its variants may contribute to the development of diabetes.

Variation of the McKusick-Kaufman gene and studies of relationships with common forms of obesity.

Obesity is a prominent feature of the Bardet-Biedl syndrome (BBS), one subset of which, BBS6, is due to mutations in the chaperonin-like gene termed the McKusick-Kaufman syndrome (MKKS) gene. We tested whether variation in MKKS contributes to common and probably polygenic forms of obesity by performing mutation analysis of the coding region in 60 Danish white men with juvenile-onset obesity. Five variants were identified, including two synonymous mutations (Pro(39)Pro and Ile(178)Ile) and three nonsynonymous variants (Ala(242)Ser, Arg(517)Cys, and Gly(532)Val). Furthermore, the rare Ala(242)Ser was identified in two families and showed partial cosegregation with obesity. The Pro(39)Pro, Ile(178)Ile, and Arg(517)Cys variants are in complete linkage disequilibrium and defined a prevalent haplotype. In a case-control study, the Arg(517)Cys polymorphism allele prevalence was 11.4% [95% confidence interval (CI), 9.7-13.0] among 744 men with juvenile-onset obesity and 9.3% (CI, 7.9-10.7) among 867 control subjects (P = 0.048). However, among middle-aged men the allelic prevalence was 9.7% (CI, 7.9-11.4) among 523 obese men and 12.2% (CI, 10.8-13.6) among 1051 lean men (P = 0.037). In conclusion, it is unlikely that MKKS variants play a major role in the pathogenesis of nonsyndromic obesity, although in rare cases the A242S allele may contribute to obesity.

Variation in the interleukin-6 receptor gene associates with type 2 diabetes in Danish whites.

Interleukin-6 (IL-6) is a pleiotropic cytokine involved in the pathophysiology of various human diseases such as type 2 diabetes and obesity. IL-6 signals via a heterodimeric receptor complex consisting of a soluble IL-6 alpha-subunit (IL-6 receptor [IL6R]) and a signal transducing subunit (gp130). The IL6R gene maps to an important candidate locus for type 2 diabetes on chromosome 1q21. An Asp358Ala polymorphism of the IL6R has been reported to associate with obesity in Pima Indians. We investigated the Asp358Ala polymorphism in relation to type 2 diabetes, obesity, and other pre-diabetic quantitative traits among Danish whites. By applying a recessive genetic model in a case-control study of 1,349 type 2 diabetic patients and 4,596 glucose-tolerant control subjects, we found a significant difference in genotype distribution (P = 0.008) and in allele frequency (Ala-allele 38.3% [95% CI 36.5-40.1] in diabetic subjects vs. 41.2% [40.2-42.2] in control subjects; P = 0.007). The odds ratio for the Asp/Asp carriers versus Ala/Ala carriers was 1.38 (1.09-1.71). Among 4,251 middle-aged glucose-tolerant subjects, the Asp358Ala polymorphism was not associated with estimates of obesity, post-oral glucose tolerance test serum insulin release, or the homeostasis model assessment of insulin resistance index. In conclusion, the Asp358Ala polymorphism of the IL6R associates with type 2 diabetes in Danish whites.