Polymorphisms in <Emphasis Type="Italic">AHI1</Emphasis> are not associated with type 2 diabetes or related phenotypes in Danes: non-replication of a genome-wide association result

Aims/hypothesis A genome-wide association study recently identified an association between common variants, rs1535435 and rs9494266, in the AHI1 gene and type 2 diabetes. The aim of the present study was to investigate the putative association between these polymorphisms and type 2 diabetes or type 2 diabetes-related metabolic traits in Danish individuals. Methods The previously associated polymorphisms were genotyped in the population-based Inter99 cohort (n = 6162), the Danish ADDITION study (n = 8428), a population-based sample of young healthy participants (n = 377) and in additional type 2 diabetes (n = 2107) and glucose-tolerant participants (n = 483) using Taqman allelic discrimination. The case–control study involved 4,104 type 2 diabetic patients and 5,050 glucose-tolerant control participants. Type 2 diabetes-related traits were investigated in 17,521 individuals. Results rs1535435 and rs9494266 were not associated with type 2 diabetes. Odds ratios (OR) were OR_add 1.0 (95% C.I. 0.9–1.2; p _add = 0.7) and OR_add 1.1 (0.9–1.2; p _add = 0.4), respectively, a finding supported by meta-analyses: OR_add 1.0 (0.9–1.1; p _add = 0.6) and OR_add 1.0 (0.9–1.1; p _add = 0.6), respectively. Neither rs1535435 nor rs9494266 were consistently associated with any of the tested type 2 diabetes-related metabolic traits. Conclusions/interpretation Data from large samples of Danish individuals do not support a role for AHI1 rs1535435 nor rs9494266 as major type 2 diabetes variants. This study highlights the importance of independent and well-powered replication studies of the recent genome-wide association scans before a locus is robustly validated as being associated with type 2 diabetes. Electronic supplementary material The online version of this article (doi:) contains supplementary material, which is available to authorised users.     

Strong association of common variants in the <Emphasis Type="Italic">CDKN2A/CDKN2B</Emphasis> region with type 2 diabetes in French Europids

Aims/hypothesis Genome-wide association studies (GWASs) recently identified common variants in the CDKN2A/CDKN2B region on chromosome 9p as being strongly associated with type 2 diabetes. Since these association signals were not picked up by the French-Canadian GWAS, we sought to replicate these findings in the French Europid population and to further characterise the susceptibility variants at this novel locus. Methods We genotyped 20 single nucleotide polymorphisms (SNPs) spanning the CDKN2A/CDKN2B locus in our type 2 diabetes case-control cohort. The association between CDKN2A/CDKN2B SNPs and quantitative metabolic traits was also examined in the normoglycaemic participants comprising the control cohort. Results We report replication of the strong association of rs10811661 with type 2 diabetes found in the GWASs (; OR 1.43 [95% CI 1.24–1.64]). The other CDKN2A/CDKN2B susceptibility variant, rs564398, did not attain statistical significance (p = 0.053; OR 1.11 [95% CI 1.00–1.24]) in the present study. We also obtained several additional nominal association signals (p < 0.05) at the CDKN2A/CDKN2B locus; however, only the rs3218018 result (p = 0.002) survived Bonferroni correction for multiple testing (adjusted p = 0.04). Conclusions/interpretation Our comprehensive association study of common variation spanning the CDKN2A/CDKN2B locus confirms the strong association between the distal susceptibility variant rs10811661 and type 2 diabetes in the French population. Further genetic and functional studies are required to identify the aetiological variants at this locus and determine the cellular and physiological mechanisms by which they act to modulate type 2 diabetes susceptibility. Electronic supplementary material The online version of this article (doi:) contains supplementary material, which is available to authorised users. K. Duesing and G. Fatemifar contributed equally to this work.     

No association between <Emphasis Type="Italic">MDR1</Emphasis> (<Emphasis Type="Italic">ABCB1</Emphasis>) 2677G>T and 3435C>T polymorphism and sporadic colorectal cancer among Bulgarian patients

Purpose Variation in genetic factors together with xenobiotic exposure may result in increased risk of colorectal cancer. The P-glycoprotein (P-gp) is highly expressed in the apical membrane of enterocytes, where it pumps xenobiotics from the enterocytes back into the intestinal lumen. Thus, polymorphisms that reduce the activity of the MDR1 (ABCB1) efflux pump are potential risk factors for colorectal carcinogenesis. The aim of the present study is to genotype the MDR1 2677G>T (rs2032582) and 3435C>T (rs1045642) polymorphism in patients with colorectal cancer and controls and to identify a possible association between individual genetic variation and susceptibility to colorectal cancer. Methods In the present study, 146 Bulgarian patients with sporadic colorectal cancer and 160 healthy Bulgarian volunteers were evaluated for the two polymorphisms in MDR1. Polymorphisms were identified using rapid-cycle real-time amplification with allele-specific probes and subsequent melting curve analyses on a LightCycler™ (Roche Diagnostics, Mannheim, Germany). Results No differences were found between the frequencies of the two mutant alleles in the tumor tissue from the cases and lymphocytes from the controls [frequencies of 2677T: 43.5% in patients and 44.1% in controls; frequencies of 3435T: 48.3% in patients and 50.9% in controls (both P > 0.05)]. The MDR1 polymorphic sequence of the tumor tissue always matched that of normal intestinal tissue from the same patient. Consequently, genotyping of DNA from archived tumor tissues is a valid alternative to the use of leukocyte DNA. Conclusions The present study suggests that MDR1 2677G>T and 3435C>T polymorphism is not a risk factor for sporadic colon cancer among Bulgarians and that somatic mutation at these sites is not involved in the genesis of colon tumors. Further examination using larger number of samples must be necessary to reach to more reliable conclusions.     

An <Emphasis Type="Italic">RBP4</Emphasis> promoter polymorphism increases risk of type 2 diabetes

AIMS/HYPOTHESIS: Retinol-binding protein 4 (RBP4), originally known for retinol transport, was recently identified as an adipokine affecting insulin resistance. The RBP4 -803GA promoter polymorphism influences binding of hepatic nuclear factor 1alpha and is associated with type 2 diabetes in case-control studies. We hypothesised that the RBP4 -803GA polymorphism increases type 2 diabetes risk at a population-based level. In addition, information on retinol intake and plasma vitamin A levels enabled us to explore the possible underlying mechanism. METHODS: In the Rotterdam Study, a prospective, population-based, follow-up study, the -803GA polymorphism was genotyped. In Cox proportional hazards models, associations of the -803GA polymorphism and retinol intake with type 2 diabetes risk were examined. Moreover, the interaction of the polymorphism with retinol intake on type 2 diabetes risk was assessed. In a subgroup of participants the association of the polymorphism and vitamin A plasma levels was investigated. RESULTS: Homozygous carriers of the -803A allele had increased risk of type 2 diabetes (HR 1.83; 95% CI 1.26-2.66). Retinol intake was not associated with type 2 diabetes risk and showed no interaction with the RBP4 -803GA polymorphism. Furthermore, there was no significant association of the polymorphism with plasma vitamin A levels. CONCLUSIONS/INTERPRETATION: Our results provide evidence that homozygosity for the RBP4 -803A allele is associated with increased risk of type 2 diabetes in the Rotterdam population. This relationship was not clearly explained by retinol intake and vitamin A plasma levels. Therefore, we cannot differentiate between a retinol-dependent or -independent mechanism of this RBP4 variant.     

Polymorphisms in the <Emphasis Type="Italic">TCF7L2</Emphasis>, <Emphasis Type="Italic">CDKAL1</Emphasis> and <Emphasis Type="Italic">SLC30A8</Emphasis> genes are associated with impaired proinsulin conversion

Aims/hypothesis Variation within six novel genetic loci has been reported to confer risk of type 2 diabetes and may be associated with beta cell dysfunction. We investigated whether these polymorphisms are also associated with impaired proinsulin to insulin conversion. Methods We genotyped 1,065 German participants for single nucleotide polymorphisms rs7903146 in TCF7L2, rs7754840 in CDKAL1, rs7923837 and rs1111875 in HHEX, rs13266634 in SLC30A8, rs10811661 in CDKN2A/B and rs4402960 in IGF2BP2. All participants underwent an OGTT. Insulin, proinsulin and C-peptide concentrations were measured at 0, 30, 60, 90 and 120 min during the OGTT. Insulin secretion was estimated from C-peptide or insulin levels during the OGTT using validated indices. We used the ratio proinsulin/insulin during the OGTT as indicator of proinsulin conversion. Results In our cohort, we confirmed the significant association of variants in TCF7L2, CDKAL1 and HHEX with reduced insulin secretion during the OGTT (p < 0.05 for all). Variation in SLC30A8, CDKN2A/B and IGF2BP2 was not associated with insulin secretion. The risk alleles of the variants in TCF7L2, CDKAL1 and SLC30A8 reduced proinsulin to insulin conversion (p < 0.05 for all), whereas the risk alleles in HHEX, CDKN2A/B and IGF2BP2 were not associated with reduced proinsulin to insulin conversion (p > 0.6). Conclusions/interpretation Diabetes-associated variants in TCF7L2 and CDKAL1 impair insulin secretion and conversion of proinsulin to insulin. However, both aspects of beta cell function are not necessarily linked, as impaired insulin secretion is specifically present in variants of HHEX and impaired proinsulin conversion is specifically present in a variant of SLC30A8. Electronic supplementary material The online version of this article (doi:) contains supplementary material, which is available to authorised users.     

Variations in KCNQ1 are associated with type 2 diabetes and beta cell function in a Chinese population

Aims/hypothesis  Recent genome-wide association studies in East Asian populations reported that single nucleotide polymorphisms (SNPs) in KCNQ1 are associated with type 2 diabetes. The aim of this study was to validate this finding in a Chinese population. Methods  We genotyped four SNPs, rs2074196, rs2237892, rs2237895 and rs2237897, in a group of 3,503 Shanghai Chinese individuals, comprising 1,769 type 2 diabetic patients and 1,734 normoglycaemic controls. Both the cases and the controls were extensively phenotyped for anthropometric and biochemical traits related to glucose metabolism. Arginine stimulation tests under fasting conditions were performed in a subgroup of 466 cases. Results  All four of the SNPs were associated with type 2 diabetes, with rs2237892 showing strongest evidence for association (OR 1.532, 95% CI 1.381–1.698, p = 5.0 × 10⁻¹⁶). The SNP rs2237897 was associated with both acute insulin and C-peptide response after arginine stimulation in a subgroup of cases (p = 0.0471 and p = 0.0156, respectively). The SNP rs2237895 was associated with both first- and second-phase insulin secretion in the controls (p = 0.0334 and p = 0.0002, respectively). Conclusions/interpretation  In this study we found that KCNQ1 was associated with type 2 diabetes susceptibility in a Chinese population, possibly through its effect on beta cell function. Electronic supplementary material  The online version of this article (doi:) contains supplementary material, which is available to authorised users.     

Joint effects of HLA, <Emphasis Type="Italic">INS</Emphasis>, <Emphasis Type="Italic">PTPN22</Emphasis> and <Emphasis Type="Italic">CTLA4</Emphasis> genes on the risk of type 1 diabetes

Background/hypothesis HLA, INS, PTPN22 and CTLA4 are considered to be confirmed type 1 diabetes susceptibility genes. HLA, PTPN22 and CTLA4 are known to be involved in immune regulation. Few studies have systematically investigated the joint effect of multiple genetic variants. We evaluated joint effects of the four established genes on the risk of childhood-onset type 1 diabetes. Methods We genotyped 421 nuclear families, 1,331 patients and 1,625 controls for polymorphisms of HLA-DRB1, −DQA1 and −DQB1, the insulin gene (INS, −23 HphI), CTLA4 (JO27_1) and PTPN22 (Arg620Trp). Results The joint effect of HLA and PTPN22 on type 1 diabetes risk was significantly less than multiplicative in the case-control data, but a multiplicative model could not be rejected in the trio data. All other two-way gene–gene interactions fitted multiplicative models. The high-risk HLA genotype conferred a very high risk of type 1 diabetes (OR 20.6, using the neutral-risk HLA genotype as reference). When including also intermediate-risk HLA genotypes together with risk genotypes at the three non-HLA loci, the joint odds ratio was 61 (using non-risk genotypes at all loci as reference). Conclusion Most established susceptibility genes seem to act approximately multiplicatively with other loci on the risk of disease except for the joint effect of HLA and PTPN22. The joint effect of multiple susceptibility loci conferred a very high risk of type 1 diabetes, but applies to a very small proportion of the general population. Using multiple susceptibility genotypes compared with HLA genotype alone seemed to influence the prediction of disease only marginally. Electronic supplementary material The online version of this article (doi:) contains supplementary material, which is available to authorised users.     

Association of<Emphasis Type="Italic"> TAP2</Emphasis> gene polymorphisms in Chinese patients with rheumatoid arthritis

The aim of this study was to investigate the association between the polymorphism of transporters associated with antigen processing (TAP1/TAP2) genes and rheumatoid arthritis in Chinese patients. A total of 100 RA patients and 99 healthy control subjects were enrolled. Analyses with polymerase chain reaction (PCR) based restrictions were used to identify the polymorphisms of the TAP1 and TAP2 genes, which were mapped on chromosome 6. There was a significant difference in the distribution of the TAP2 gene codon 565 polymorphism frequency between the RA patients and healthy control subjects (p<0.001). The odds ratio for the risk of the A allele in RA patients was 1.60 (95% CI: 0.82–2.92). No statistical associations in the distribution of the TAP1 gene polymorphism frequency were found between RA patients and controls. There were some physical links found between TAP1/TAP2 gene polymorphism loci. However, there was no linkage observed from TAP1/TAP2 gene polymorphisms and HLA-DRB1*04 between RA patients and healthy controls. We concluded that the TAP2 gene codon 565 A allele was associated with RA in Chinese patients in Taiwan. Individuals possessing the A allele had a higher incidence of RA. A lack of association of TAP1 gene polymorphisms between RA patients and healthy individuals was noted. The results of this study provide genetic evidence that TAP2 gene codon 565 polymorphism may play a role in RA.Abbreviations MHC Major histocompatibility - MS Multiple sclerosis - PCR Polymerase chain reaction - RA Rheumatoid arthritis - SNP Single nucleotide polymorphism     

<Emphasis Type="Italic">ENPP1</Emphasis> K121Q polymorphism and obesity,hyperglycaemia and type 2 diabetes in the prospective DESIR Study

AIMS/HYPOTHESIS: We assessed the predictive value of ectonucleotide pyrophosphatase/phosphodiesterase 1 gene (ENPP1) SNPs with regard to the risk of developing obesity and/or type 2 diabetes in a large French general population. METHODS: We genotyped the ENPP1 SNPs K121Q (rs1044498), IVS20delT-11 (rs1799774) and A/G+1044TGA (rs7754561) in 5,153 middle-aged participants of the Data from an Epidemiological Study on the Insulin Resistance Syndrome (DESIR) cohort. RESULTS: At baseline, the K121Q polymorphism was not associated either with BMI (p = 0.98) or with class I obesity (odds ratio [OR] 0.99, p = 0.81), but showed a borderline association with class II obesity (OR 1.65, p = 0.02). The K121Q variant was not associated with any trait during the 9-year follow-up. Pooled analyses both at baseline and at follow-up failed to show any association with hyperglycaemia (OR 1.08, p = 0.28) or type 2 diabetes (OR 1.15, p = 0.38). However, we did show an association of the Q121 allele with the risk of hyperglycaemia (OR 1.45, p = 0.001; n = 265) and type 2 diabetes (OR 1.65, p = 0.01; n = 103) in participants reporting a family history of type 2 diabetes. These results did not remain significant after a Bonferroni correction. The IVS20delT-11 and A/G+1044TGA polymorphisms and the three-allele risk haplotype (K121Q, IVS20delT-11 and A-->G+1044TGA [QdelTG]) were not associated with any trait, either at baseline or at follow-up. CONCLUSIONS/INTERPRETATION: In a general French population we did not find an association of the QdelTG risk haplotype with adult obesity and type 2 diabetes. We detected nominal evidence of association between the K121Q polymorphism and both severe adult obesity at baseline and the risk of hyperglycaemia or type 2 diabetes in participants with a family history of type 2 diabetes in pooled analyses both at baseline and follow-up.