ENPP1 K121Q polymorphism and obesity, hyperglycaemia and type 2 diabetes in the prospective DESIR Study

Levels of serum ecto-nucleotide pyrophosphatase/phosphodiesterase 1 (ENPP1) predicts severity of abdominal aortic calcification in end-stage renal disease patients receiving regular dialysis

OBJECTIVE

To investigate the correlation between serum ectonucleotide pyrophosphatase/phosphodiesterase-1 (ENPP1) level and severity of abdominal vascular calcification in end-stage renal disease (ESRD) patients receiving dialysis.

METHODS

A total of 124 patients were consecutively enrolled into the study in our local institution. Based on the Kidney Disease Improving Global Outcomes (KDIGO) guidelines and recommendations, abdomen lateral X-ray was used to determine abdominal aortic calcification score (AACS) for each patient at enrollment. Patients were divided into three groups based on AACS: no or mild calcification group, moderate calcification group, and severe calcification group. The relationships between ENPP1 levels and AACS were assessed by Spearman analysis and the value of ENPP1 in predicting severity of abdominal aortic calcification was evaluated by receiver operating characteristic (ROC).

RESULTS

The level of ENPP1 in dialysis patients was (7.68 ± 1.67) ng/ml. There was no significant difference in serum ENPP1 level between peritoneal dialysis patients and hemodialysis patients (p > 0.05). The AACS of dialysis patients was negatively correlated with ENPP1 value (r = -0.70). Compared to no/mild calcification patients, the levels of serum ENPP1 in patients with moderate/severe calcification were decreased significantly (p < 0.01). The severity of vascular calcification was correlated with serum ENPP1 value, the severer the vascular calcification, the lower the serum ENPP1 level, and the difference was statistically significant (all p < 0.05). The area under ROC curve of ENPP1 was 0.90, the corresponding sensitivity was 0.86, and the specificity was 0.87.

CONCLUSION

Levels of serum ENPP1 in non-diabetic ESRD patients are negatively related to the severity of abdominal aortic vascular calcification.

Influence of Single Nucleotide Polymorphism of ENPP1 and ADIPOQ on Insulin Resistance and Obesity: A Case-Control Study in a Javanese Population

Single nucleotide polymorphisms (SNPs) in obesity-related genes, such as ectonucleotide pyrophosphatase phosphodiesterase 1 (ENPP1) and adiponectin (ADIPOQ), potentially increase the risk of insulin resistance, the most common metabolic dysregulation related to obesity. We investigated the association of ENPP1 SNP K121Q (rs1044498) with insulin resistance and ADIPOQ SNP + 267G > T (rs1501299) with circulating adiponectin levels in a case–control study involving 55 obese and 55 lean Javanese people residing in Yogyakarta, Indonesia. Allele frequency was determined by a chi squared test or Fisher’s exact test with an expected value less than 0.05. Odds ratios and 95% confidence intervals were estimated by regression logistic analysis. The presence of the Q121 allele of ENPP1 resulted in significantly higher fasting glucose, fasting insulin levels, and HOMA-IR, as compared to homozygous K121 carriers. The risk of insulin resistance was elevated in obese individuals carrying Q121 instead of homozygous K121. Adiponectin level was significantly lower in the obese group as compared to the lean group. Obese individuals carrying homozygous protective alleles (TT) of ADIPOQ tended to have lower adiponectin levels as compared to GT and GG carriers, however, we did not find statistically significant effects of the +276G > T SNP of the ADIPOQ gene on the plasma adiponectin levels or on the development of obesity.

Established and emerging strategies to crack the genetic code of obesity

Tremendous progress has been made in the genetic elucidation of obesity over the past two decades, driven largely by technological, methodological and organizational innovations. Current strategies for identifying obesity-predisposing loci/genes, including cytogenetics, linkage analysis, homozygosity mapping, admixture mapping, candidate gene studies, genome-wide association studies, custom genotyping arrays, whole-exome sequencing and targeted exome sequencing, have achieved differing levels of success, and the identified loci in aggregate explain only a modest fraction of the estimated heritability of obesity. This review outlines the successes and limitations of these approaches and proposes novel strategies, including the use of exceptionally large sample sizes, the study of diverse ethnic groups and deep phenotypes and the application of innovative methods and study designs, to identify the remaining obesity-predisposing genes. The use of both established and emerging strategies has the potential to crack the genetic code of obesity in the not-too-distant future. The resulting knowledge is likely to yield improvements in obesity prediction, prevention and care.

Evaluation of NPP1 as a Novel Biomarker of Coronary Artery Disease: A Pilot Study in Human Beings

Purpose: Coronary artery calcification (CAC) is utilized as an important tool for global risk assessment of cardiovascular events in individuals with intermediate risk. Ecto phosphodiesterase/nucleotide phosphohydrolase-1(ENPP1) converts extracellular nucleotides into inorganic pyrophosphate and it is a key regulator of tissue calcification that adjusts calcification in tissues like vascular smooth muscle cells. The main purpose of this clinical study was to find out the correlation between ENPP1 serum concentration and CAC in human for the first time.

Methods: In this study 83 patients (16 diabetic patients and 67 non-diabetic patients) with coronary artery disease who fulfilled inclusion and exclusion criteria, entered the study. For all patients a questionnaire consisting demographic data and traditional cardiovascular risk factors were completed. Computed tomography (CT)-Angiography was carried out to determine coronary artery calcium score and enzyme-linked immunosorbent assay (ELISA) method was used for measuring ENPP1 serum concentrations.

Results: There was a reverse significant correlation between ENPP1 serum concentration and total CAC score and also CAC of right coronary artery (RCA) (P<0.05) in non-diabetic patients.

Conclusion: On the basis of our results, ENPP1 serum concentration may be a suitable biomarker for coronary artery disease at least in non-diabetic patients. However, more studies with higher sample size are necessary for its confirmation.

Association and in silico studies of ENPP1 gene variants with type 2 diabetes mellitus in a Northern Iranian population

In the current study, a sample population of Northern Iranians was selected to investigate the association of K121Q, rs1799774, rs7754561, and rs997509 ENPP1 gene variants and their haplotypes with T2DM. Genomic DNAs of 978 samples were extracted by Salting Out standard technique and then genotyped by the TaqMan assay. The results show significant differences between study groups for K121Q (p = 0.0004) under a Dominant and rs7754561 (p = 0.002) under a co-dominant hereditary model. Based on allele frequency, there was a significant difference between two study groups at K121Q and rs7754561 variants (p = 0.010 and p = 0.01, respectively). There was no evidence for an association between ENPP1 haplotypes and overall risk of T2DM. Genotype-phenotype sub-analyses showed no significant relationship of four studied polymorphisms with age, gender, FBS, and systolic and diastolic blood pressures. Homology modeling and molecular docking of ENPP1 in K173 and Q173 models with ATP, AMP, and 2'3'-cGAMP as ligands revealed that all ligands had a more binding affinity to Lys173 protein model, and 2'3'-cGAMP had a higher affinity to both ENPP1 protein models compared to ATP and AMP. These findings suggest that ENPP1 gene variants may have a potential impact on the occurrence of T2DM in Northern Iranians.

The ENPP1 K121Q polymorphism is associated with type 2 diabetes and related metabolic phenotypes in a Taiwanese population

Increased risk of developing type 2 diabetes (T2D) has been associated with a single nucleotide polymorphism (SNP), rs1044498 (K121Q), in the ectonucleotide pyrophosphatase/phosphodiesterase 1 (ENPP1) gene, but this association is unclear among Asians. In this replication study, we reassessed whether the ENPP1 rs1044498 SNP is associated with T2D, obesity, and T2D/obesity-related metabolic traits in a Taiwanese population. A total of 1513 Taiwanese subjects were assessed in this study. The ENPP1 rs1044498 SNP was genotyped by the Taqman assay. T2D/Obesity-related quantitative traits, such as waist circumference and fasting glucose, were measured. Our data showed a significant association of the ENPP1 rs1044498 SNP with T2D (P < 0.001) among the subjects. Moreover, the ENPP1 rs1044498 SNP was significantly associated with T2D/obesity-related metabolic traits, such as waist circumference (P = 0.002) and fasting glucose (P < 0.001), among the subjects. However, we found no association of ENPP1 rs1044498 with obesity (BMI ≧ 27 kg/m(2)). Our study indicates that the ENPP1 rs1044498 SNP is associated with T2D, waist circumference, and fasting glucose in Taiwanese subjects.

Association of the ENPP1 K121Q polymorphism with susceptibility to type 2 diabetes in different populations: evidence based on 40 studies

The K121Q gene polymorphism of ectoenzyme nucleotide pyrophosphate phosphodiesterase 1(ENPP1) has been widely investigated, however, results have been somewhat conflicting. The aim of this meta-analysis was to establish a precise estimation of the association between ENPP1 gene polymorphisms and type 2 diabetes (T2D). A literature search in PubMed, Embase, Cochrane Library and China Biology Medicine (CBM) databases was conducted on publications published prior to November 21(st), 2013. The combined odds ratio (OR) with 95% confidence intervals (95% CI) was calculated to estimate the strength of the association using a random-effects/fixed-effects model. Statistical analyses were performed using the STATA 11.0 software. For the overall population, there was a significant association between ENPP1 gene polymorphisms and T2D when comparing the Q allele versus K allele (OR = 1.29, 95% CI 1.16-1.44, p = 0.000). Considering diverse ethnic groups, effect sizes were consistent for patients of Caucasian and Asian descent (OR = 1.20, 95% CI = 1.08-1.33 and OR = 1.47, 95% CI = 1.15-1.89, respectively); however, effect size was not consistent for those of African descent. Under other models of inheritance, significant associations were also observed. Sensitivity analyses did not leading to differing he results. In summary, the Q allele of the ENPP1 K121Q gene may contribute to the susceptibility for T2D in Caucasians and Asians.

Reassessment of the putative role of BLK-p.A71T loss-of-function mutation in MODY and type 2 diabetes

AIMS/HYPOTHESIS

MODY is believed to be caused by at least 13 different genes. Five rare mutations at the BLK locus, including only one non-synonymous p.A71T variant, were reported to segregate with diabetes in three MODY families. The p.A71T mutation was shown to abolish the enhancing effect of BLK on insulin content and secretion from pancreatic beta cell lines. Here, we reassessed the contribution of BLK to MODY and tested the effect of BLK-p.A71T on type 2 diabetes risk and variations in related traits.

METHODS

BLK was sequenced in 64 unelucidated MODY samples. The BLK-p.A71T variant was genotyped in a French type 2 diabetes case-control study including 4,901 cases and 4,280 controls, and in the DESIR (Data from an Epidemiological Study on the Insulin Resistance Syndrome) and SUVIMAX (Supplementation en Vitamines et Mineraux Antioxydants) population-based cohorts (n = 6,905). The variant effects were assessed by logistic and linear regression models.

RESULTS

No rare non-synonymous BLK mutations were found in the MODY patients. The BLK p.A71T mutation was present in 52 normoglycaemic individuals, making it very unlikely that this loss-of-function mutation causes highly penetrant MODY. We found a nominal association between this variant and increased type 2 diabetes risk, with an enrichment of the mutation in the obese diabetic patients, although no significant association with BMI was identified.

CONCLUSIONS/INTERPRETATION

No mutation in BLK was found in our MODY cohort. From our findings, the BLK-p.A71T mutation may weakly influence type 2 diabetes risk in the context of obesity; however, this will require further validation.

Identification of shared genetic susceptibility locus for coronary artery disease, type 2 diabetes and obesity: a meta-analysis of genome-wide studies

Type 2 diabetes (2DM), obesity, and coronary artery disease (CAD) are frequently coexisted being as key components of metabolic syndrome. Whether there is shared genetic background underlying these diseases remained unclear. We performed a meta-analysis of 35 genome screens for 2DM, 36 for obesity or body mass index (BMI)-defined obesity, and 21 for CAD using genome search meta-analysis (GSMA), which combines linkage results to identify regions with only weak evidence and provide genetic interactions among different diseases. For each study, 120 genomic bins of approximately 30 cM were defined and ranked according to the best linkage evidence within each bin. For each disease, bin 6.2 achieved genomic significanct evidence, and bin 9.3, 10.5, 16.3 reached suggestive level for 2DM. Bin 11.2 and 16.3, and bin 10.5 and 9.3, reached suggestive evidence for obesity and CAD respectively. In pooled all three diseases, bin 9.3 and 6.5 reached genomic significant and suggestive evidence respectively, being relatively much weaker for 2DM/CAD or 2DM/obesity or CAD/obesity. Further, genomewide significant evidence was observed of bin 16.3 and 4.5 for 2DM/obesity, which is decreased when CAD was added. These findings indicated that bin 9.3 and 6.5 are most likely to be shared by 2DM, obesity and CAD. And bin 16.3 and 4.5 are potentially common regions to 2DM and obesity only. The observed shared susceptibility regions imply a partly overlapping genetic aspects of disease development. Fine scanning of these regions will definitely identify more susceptibility genes and causal variants.

ENPP1 K121Q polymorphism and type 2 diabetes mellitus in the Chinese population: a meta-analysis including 11,855 subjects

Ectoenzyme nucleotide pyrophosphate phosphodiesterase 1 (ENPP1) K121Q gene polymorphism has been suggested to be associated with the increased risk of developing type 2 diabetes mellitus (T2D), but relevant research results are still contradictory. To explore the relationship between ENPP1 K121Q gene polymorphism and T2D in the Chinese population, a meta-analysis was performed. Fourteen independent studies involving 11 855 subjects were retrieved from electronic databases. The pooled odds ratio (ORs) for the distribution of Q allele frequency of the ENPP1 K121Q gene and its corresponding 95% confidence interval (95% CI) were assessed using a random-effects model. Under an allelic model of inheritance, the distribution of Q allele frequency was 0.107 for the T2D group and 0.093 for the control group. The pooled OR for the distribution of Q allele frequency of ENPP1 K121Q gene was 1.29 (95% CI, 1.09-1.53; P(heterogeneity) = .006; I(2) = 55.6%). There was a significant association between ENPP1 K121Q gene polymorphism and T2D in the Chinese population (P = .003). Under a dominant model of inheritance, the KQ + QQ/KK value was 0.259 for the T2D group and 0.220 for the control group. The pooled OR for the KQ + QQ/KK value was 1.51 (95% CI, 1.20-1.91; P(heterogeneity) < .0001; I(2) = 71.8%). The association between ENPP1 K121Q gene polymorphism and T2D in the Chinese population followed a dominant model of inheritance (P = .0005). In the Chinese population, the ENPP1 K121Q gene polymorphism was implied to be involved with T2D susceptibility. People with the Q allele of the ENPP1 K121Q gene might be predisposed to T2D.

The ENPP1 K121Q polymorphism is not associated with type 2 diabetes in northern Chinese

The K121Q polymorphism of the ectoenzyme nucleotide pyrophosphate phosphodiesterase 1 (ENPP1) gene has been studied in relation to insulin resistance, type 2 diabetes, and obesity, and conflicting results were observed in various populations. The purpose of the present study was to investigate the prevalence of K121Q polymorphism of ENPP1 gene and to clarify whether this polymorphism is associated with type 2 diabetes susceptibility in northern Chinese population. We studied the association of the ENPP1 K121Q polymorphism with type 2 diabetes (T2D) in 639 unrelated patients and 885 control subjects with normal glucose tolerance of northern China. The patients were diagnosed in accordance with the guidelines of the American Diabetes Association (ADA). Genotypes were determined by the polymerase chain reaction-restriction fragment length polymorphism (PCR-RFLP) method. The distribution of KK, KQ, and QQ genotypes among patients was 79.5, 19.2, and 1.3%, similar to that of the control group (79.2, 20.1, and 0.7%). After readjusting for the confounding effects of age, gender, and BMI, no significant effect of genotypes on T2D was found for any of the genetic models tested (recessive model, dominant model, or additive model). All clinical characteristics tested were similar among the different genotypes, and no significant associations were observed both in T2D patients and in controls. When subgroup analyses of T2D patients and non-diabetic controls were stratified according to BMI and waist circumference, the variant was still not associated with T2D. The results showed that the ENPP1 K121Q polymorphism is not associated with genetic susceptibility of type 2 diabetes in the northern Chinese population.

Recent progress in the genetics of common obesity

The genetic contribution to interindividual variation in common obesity has been estimated at 40-70%. Yet, despite a relatively high heritability, the search for obesity susceptibility genes has been an arduous task. This paper reviews recent progress made in the obesity genetics field with an emphasis on established obesity susceptibility loci identified through candidate gene as well as genome-wide studies. For the last 15 years, candidate gene and genome-wide linkage studies have been the two main genetic epidemiological approaches to identify genetic loci for common traits, yet progress has been slow and success limited. Only recently have candidate gene studies started to succeed; by means of large-scale studies and meta-analyses at least five variants in four candidate genes have been found to be robustly associated with obesity-related traits. Genome-wide linkage studies, however, have so far not been able to pinpoint genetic loci for common obesity. The genome-wide association approach, which has become available in recent years, has dramatically changed the pace of gene discoveries for common disease, including obesity. Three waves of large-scale high-density genome-wide association studies have already discovered at least 15 previously unanticipated genetic loci incontrovertibly associated with body mass index and extreme obesity risk. Although the combined contribution of these loci to the variation in obesity risk at the population level is small and their predictive value is typically low, these recently discovered loci are set to improve fundamentally our insights into the pathophysiology of obesity.

Candidate gene association study conditioning on individual ancestry in patients with type 2 diabetes and metabolic syndrome from Mexico City

BACKGROUND

Type 2 diabetes (T2D) is influenced by diverse environmental and genetic risk factors. Metabolic syndrome (MS) increases the risk of cardiovascular disease and diabetes. We analysed 14 cases of polymorphisms located in 10 candidate loci, in a sample of patients with T2D and controls from Mexico City.

METHODS

We analysed the association of 14 polymorphisms located within 10 genes (TCF7L2, ENPP1, ADRB3, KCNJ11, LEPR, PPARgamma, FTO, CDKAL1, SIRT1 and HHEX) with T2D and MS. The analysis included 519 subjects with T2D defined according to the ADA criteria, 389 with MS defined according to the AHA/NHLBI criteria and 547 controls. Association was tested with the program ADMIXMAP including individual ancestry, age, sex, education and in some cases body mass index (BMI), in a logistic regression model.

RESULTS

The two markers located within the TCF7L2 gene showed strong associations with T2D (rs7903146, T allele, odd ratio (OR) = 1.76, p = 0.001 and rs12255372, T allele, OR = 1.78, p = 0.002), but did not show significant association with MS. The non-synonymous rs4994 polymorphism of the ADRB3 gene was associated with T2D (Trp allele, OR = 0.62, p = 0.001) and MS (Trp allele, OR = 0.74, p = 0.018). Nominally significant associations were also observed between T2D and the SIRT1 rs3758391 SNP and MS and the HHEX rs5015480 polymorphism.

CONCLUSIONS

Variants located within the gene TCF7L2 are strongly associated with T2D but not with MS, providing support to previous evidence indicating that polymorphisms at the TCF7L2 gene increase T2D risk. In contrast, the non-synonymous ADRB3 rs4994 polymorphism is associated with T2D and MS.

Impact of ENPP1 and MMP3 gene polymorphisms on aortic calcification in patients with type 2 diabetes in a Korean population

AIMS

We investigated whether gene polymorphisms of Ecto-nucleotide pyrophosphatase/phosphodiesterase 1 (ENPP1) and matrix metalloproteinase 3 (MMP3) are associated with increased vascular calcification in patients with type 2 diabetes (T2D) and evaluated whether serum MMP3 and osteoprotegerin (OPG) levels are related to calcification.

METHODS

This study included 464 subjects: 269 patients with T2D and 195 healthy controls in South Korea. We genotyped subjects for four single nucleotide polymorphisms (SNPs): ENPP1 K121Q, ENPP1 A/G+1044TGA, MMP3 -709A>G and MMP3 -1475G>A. The presence or absence of calcifications in the aortic arch was assessed by plain chest radiography.

RESULTS

The SNPs ENPP1 K121Q and MMP3 -709A>G showed significant associations with T2D (P=0.001 and P=0.004). The SNP ENPP1 K121Q showed a significant association with aortic arch calcification in T2D (P=0.036). Serum OPG levels were significantly higher in T2D patients than in the control group (P<0.001). However, serum MMP3 levels were significantly lower in T2D patients than in the control group (P<0.001).

CONCLUSIONS

Our study demonstrates that the ENPP1 K121Q and MMP3 -709A>G polymorphisms are associated with T2D, and that the ENPP1 Q allele is associated with increased aortic arch calcification in a Korean population.

Morphological and biochemical features of obesity are associated with mineralization genes' polymorphisms

BACKGROUND

Ectonucleotide pyrophosphatase/phosphodiesterase 1 (ENPP1) was recently extensively studied as a candidate gene for obesity phenotypes. As the human homologue of the mouse progressive ankylosis (ANKH) and alkaline phosphatase (ALPL) are known functional partners of ENPP1 in bone mineralization, we hypothesized that these genes may also be jointly involved in determining obesity features.

AIM

To examine the effects of the three genes, possible gene-sex and gene-gene interactions on variability of four obesity phenotypes: the body mass index (BMI), the waist-hip ratio (WHR), the epidermal growth factor receptor (EGFR), and leptin.

SUBJECTS AND METHODS

In all, 962 healthy individuals from 230 families were genotyped for 45 single nucleotide polymorphisms (SNPs). The association analysis was performed using two family based association tests (family based association test and pedigree disequilibrium test). The combined P-values of the two tests were estimated by Monte-Carlo simulations. Relative magnitude of the genetic and familial effects, gene-sex and gene-gene interactions were assessed using variance component models.

RESULTS

Associations were observed between ENPP1 polymorphisms and BMI (P=0.0037) and leptin (P=0.0068). ALPL markers were associated with WHR (P=0.0026) and EGFR (P=0.0001). The ANKH gene was associated with all four studied obesity-related traits (P<0.0184), and its effects were modulated by sex. Gene-gene interactions were not detected.

CONCLUSION

The observed pattern of association signals indicates that ANKH may have a generalized effect on adipose tissue physiology, whereas ENPP1 and ALPL affect distinct obesity features. The joint analysis of related genes and integration of the results obtained by different methods used in this research should benefit other studies of similar design.

Genetic variants of the ENPP1/PC-1 gene are associated with hypertriglyceridemia in male subjects

BACKGROUND

Hypertriglyceridemia is associated with insulin resistance, type 2 diabetes, and the metabolic syndrome. Membrane glycoprotein PC-1 (also termed ENPP1) is a direct insulin receptor inhibitor, and certain polymorphisms of the ENPP1/PC-1 gene have been associated with insulin resistance, type 2 diabetes, obesity, and diabetic complications.

METHODS

We examined the effect of 3 ENPP1/PC-1 variants (K121Q, rs1044498, and IVS20delT-11, rs1799774, and A-->G+1044TGA, rs7754561) on plasma triglyceride levels in 1112 subjects of non-Hispanic American white European ancestry.

RESULTS

Two of the ENPP1/PC-1 variants--A-->G+1044TGA (odds ratio [OR] 1.48, 95% confidence interval [CI], 1.54-1.82, P = 0.002) and IVS20delT-11 (OR 1.41, 95% CI, 1.08-1.84, P = 0.012)--were significantly associated with hypertriglyceridemia. Haplotype analyses also revealed an association with hypertriglyceridemia. In the variant analyses and in the haplotype analysis, the associations with hypertriglyceridemia were observed in male but not female subjects. Interestingly, the more widely studied K121Q ENPP1/PC-1 variant was not associated with hypertriglyceridemia in any group or subgroup analysis.

CONCLUSION

In the present study, we find that genetic variants of the ENPP1/PC-1 gene are associated with hypertriglyceridemia in male subjects, and may contribute to the development of the insulin resistance/metabolic syndrome in this population.

Progress in the genetics of common obesity and type 2 diabetes

The prevalence of obesity and diabetes, which are heritable traits that arise from the interactions of multiple genes and lifestyle factors, continues to rise worldwide, causing serious health problems and imposing a substantial economic burden on societies. For the past 15 years, candidate gene and genome-wide linkage studies have been the main genetic epidemiological approaches to identify genetic loci for obesity and diabetes, yet progress has been slow and success limited. The genome-wide association approach, which has become available in recent years, has dramatically changed the pace of gene discoveries. Genome-wide association is a hypothesis-generating approach that aims to identify new loci associated with the disease or trait of interest. So far, three waves of large-scale genome-wide association studies have identified 19 loci for common obesity and 18 for common type 2 diabetes. Although the combined contribution of these loci to the variation in obesity and diabetes risk is small and their predictive value is typically low, these recently identified loci are set to substantially improve our insights into the pathophysiology of obesity and diabetes. This will require integration of genetic epidemiological methods with functional genomics and proteomics. However, the use of these novel insights for genetic screening and personalised treatment lies some way off in the future.

Genetic heterogeneity in latent autoimmune diabetes is linked to various degrees of autoimmune activity: results from the Nord-Trøndelag Health Study

OBJECTIVE

Previous studies have indicated that the latent autoimmune diabetes in adults (LADA) phenotype is heterogeneous and that LADA patients share features of type 1 and type 2 diabetes in various proportions. We tested for association of known type 1 and type 2 diabetes susceptibility genes in LADA subjects and analyzed relationships to a marker of autoimmune activity (titers of anti-GAD) and a phenotypic risk factor of type 2 diabetes (BMI).

RESEARCH DESIGN AND METHODS

Data were assembled from the Nord-Trøndelag Health Study (HUNT) study, which comprises the adult population of an entire county in Norway. We genotyped 60 single nucleotide polymorphisms (SNPs) known to be associated with type 1 or type 2 diabetes, including 14 tag SNPs used for HLA haplotyping in 120 type 1 diabetic, 126 LADA, and 1,090 type 2 diabetic patients and 1,503 age- and sex-matched nondiabetic subjects.

RESULTS

The majority of the strongly associated HLA haplotypes for type 1 diabetes were significantly associated with LADA in general, but mainly with high anti-GAD LADA patients. Two distinct HLA haplotypes were associated only with LADA and mainly in low anti-GAD LADA patients. There were no associations of non-HLA type 1 diabetes loci with LADA. Of type 2 diabetes-associated genes, the CC/CT genotypes of rs7961581 (TSPAN8) and the obesity-linked AA/AC genotypes of rs8050136 (FTO) were associated with LADA in general, but mainly in low anti-GAD LADA patients (P = 0.004 and P = 0.004, respectively).

CONCLUSIONS

Genetic heterogeneity in LADA is linked to various degrees of autoimmune activity and may be partly distinct from both type 1 and type 2 diabetes.

Insulin signaling regulating genes: effect on T2DM and cardiovascular risk

Type 2 diabetes mellitus (T2DM) is a complex disorder that has a heterogeneous genetic and environmental background. In this Review, we discuss the role of relatively infrequent polymorphisms of genes that regulate insulin signaling (including the K121Q polymorphism of ENPP1, the G972R polymorphism of IRS1 and the Q84R polymorphism of TRIB3) in T2DM and other conditions related to insulin resistance. The biological relevance of these three polymorphisms has been very thoroughly characterized both in vitro and in vivo and the available data indicate that they all affect insulin signaling and action as well as insulin secretion. They also affect insulin-mediated regulation of endothelial cell function. In addition, several reports indicate that the effects of all three polymorphisms on the risk of T2DM and cardiovascular diseases related to insulin resistance depend on the clinical features of the individual, including their body weight and age at disease onset. Thus, these polymorphisms might be used to demonstrate how difficult it is to ascertain the contribution of relatively infrequent genetic variants with heterogeneous effects on disease susceptibility. Unraveling the role of such variants might be facilitated by improving disease definition and focusing on specific subsets of patients.

Pathomechanisms of type 2 diabetes genes

Type 2 diabetes mellitus is a complex metabolic disease that is caused by insulin resistance and beta-cell dysfunction. Furthermore, type 2 diabetes has an evident genetic component and represents a polygenic disease. During the last decade, considerable progress was made in the identification of type 2 diabetes risk genes. This was crucially influenced by the development of affordable high-density single nucleotide polymorphism (SNP) arrays that prompted several successful genome-wide association scans in large case-control cohorts. Subsequent to the identification of type 2 diabetes risk SNPs, cohorts thoroughly phenotyped for prediabetic traits with elaborate in vivo methods allowed an initial characterization of the pathomechanisms of these SNPs. Although the underlying molecular mechanisms are still incompletely understood, a surprising result of these pathomechanistic investigations was that most of the risk SNPs affect beta-cell function. This favors a beta-cell-centric view on the genetics of type 2 diabetes. The aim of this review is to summarize the current knowledge about the type 2 diabetes risk genes and their variants' pathomechanisms.

Possible role for ENPP1 polymorphism in obesity but not for INSIG2 and PLIN variants

Previous studies have suggested that ENPP1, INSIG2, and PLIN may be linked with a higher risk for obesity or with increased phenotypic measures of obesity. We selected polymorphisms in these candidate genes based on their prior associations with obesity risk or obesity parameters. K121Q (rs1044498) in ENPP1, rs7566605 in INSIG2, and rs894160 in PLIN were genotyped by Taqman assays in a Belgian sample of 1,078 obese subjects (body mass index (BMI) > 30 kg/m(2)) and 323 lean controls (18.5 < BMI < 25 kg/m(2)). BMI, waist circumference, and waist-to-hip ratio (WHR) were assessed by standard methods while a computerized tomography-scan was used to measure visceral (VFA), subcutaneous (SFA), and total (TFA) abdominal fat areas. Presence of the rare allele was not significantly different between cases and controls for the three variants that were tested, while only WHR was associated with ENPP1 in obese subjects. Our data thus indicate that K121Q, rs7566605, and rs894160 are not major contributing factors for obesity.

The T-381C SNP in BNP gene may be modestly associated with type 2 diabetes: an updated meta-analysis in 49 279 subjects

A recent study reported an association between the brain natriuretic peptide (BNP) promoter T-381C polymorphism (rs198389) and protection against type 2 diabetes (T2D). As replication in several studies is mandatory to confirm genetic results, we analyzed the T-381C polymorphism in seven independent case-control cohorts and in 291 T2D-enriched pedigrees totalling 39 557 subjects of European origin. A meta-analysis of the seven case-control studies (n = 39 040) showed a nominal protective effect [odds ratio (OR) = 0.86 (0.79-0.94), P = 0.0006] of the CC genotype on T2D risk, consistent with the previous study. By combining all available data (n = 49 279), we further confirmed a modest contribution of the BNP T-381C polymorphism for protection against T2D [OR = 0.86 (0.80-0.92), P = 1.4 x 10(-5)]. Potential confounders such as gender, age, obesity status or family history were tested in 4335 T2D and 4179 normoglycemic subjects and they had no influence on T2D risk. This study provides further evidence of a modest contribution of the BNP T-381C polymorphism in protection against T2D and illustrates the difficulty of unambiguously proving modest-sized associations even with large sample sizes.

Common genetic variation near MC4R is associated with eating behaviour patterns in European populations

Both rs17782313 (near MC4R) and rs1421085 (FTO) polymorphisms have been consistently associated with increased risk of obesity and with body mass index (BMI) variation. An effect of both polymorphisms on satiety has recently been suggested. We genotyped rs17782313 and rs1421085 in 5764 relatives from 1109 French pedigrees with familial obesity, 1274 Swiss class III obese adults as well as in 4877 French adults and 5612 Finnish teenagers from two randomly selected population cohorts. In all subjects, eating behaviour traits were documented through questionnaires. We first assessed the association of both single nucleotide polymorphisms with BMI and then studied eating behaviour. Under an additive model, the rs17782313-C MC4R allele showed a trend towards higher percentages of snacking in both French obese children (P=0.01) and Swiss obese adults (P=0.04) as well as in adolescents from the Finnish general population (P=0.04). In French adults with familial obesity, this allele tended to be also associated with a higher Stunkard hunger score (P=0.02) and in obese children with a higher prevalence of eating large amounts of food (P=0.04). However, no consistent association of the FTO rs1421085-C allele and available eating behaviour trait was found in our studied populations. The rs17782313-C allele nearby MC4R may modulate eating behaviour-related phenotypes in European obese and randomly selected populations, in both children and adults, supporting a regulatory role of this genetic variant on eating behaviour, as previously shown for MC4R non-synonymous loss-of-function mutations. The potential effect of the obesity-associated FTO gene on eating behaviour deserves additional investigation.

The Q121 variant of ENPP1 may protect from childhood overweight/obesity in the Italian population

Ectonucleotide Pyrophosphatase Phosphodiesterase 1 (ENPP1) downregulates insulin signaling by inhibiting the insulin receptor's tyrosine-kinase. K121Q and other ENPP1 single-nucleotide polymorphisms (SNPs), IVS20delT-11 and A/G+1044TGA, have been previously associated with obesity in French children, and the risk haplotype QdelTG has also been associated with this condition in both French and German children. Our aim was to perform a case-control replication study in order to assess the possible association of childhood obesity and overweight with the above-mentioned ENPP1 SNPs, and with the QdelTG haplotype, in the Italian population. A total of 865 healthy Italian children were studied: 453 normal-weight, 243 overweight and 169 obese subjects. Genotyping was performed by Taq-Man or Light-Cycler Technology. The Q variant of K121Q showed a negative association with overweight-obesity under both additive (odds ratio (OR) = 0.74, 95% confidence interval (CI) = 0.57-0.97, P = 0.030) and recessive (OR = 0.32, 95% CI = 0.10-0.97, P = 0.035) modes of inheritance. The Z-score of BMI showed a significant decreasing trend from children K/K homozygous to K/Q heterozygous, and to Q/Q homozygous (0.45 vs. 0.28 vs. -0.19; P = 0.009), according to the additive model. The two other SNPs and the QdelTG haplotype did not exhibit any association with overweight/obesity. This is the first child-based study showing a protective role of the 121Q variant of ENPP1 against overweight/obesity.

Association of the Q121 variant of ENPP1 gene with decreased kidney function among patients with type 2 diabetes

BACKGROUND

Insulin resistance has a role in diabetic kidney complications. The K121Q (lysine to glutamine substitution at amino acid 121, encoded by single-nucleotide polymorphism rs1044498) variant of the ectonucleotide pyrophosphatase/phosphodiesterase gene (ENPP1) has been associated with insulin resistance and related vascular complications in patients with type 2 diabetes (T2D) in many, although not all, studies. This study investigated whether the ENPP1 Q121 variant modulates the risk of decreased glomerular filtration rate (GFR) in patients with T2D.

STUDY DESIGN

Cross-sectional study.

SETTING & PARTICIPANTS

2 diabetes units from Italy (in Gargano and Padua) and 1 from the United States (Boston, MA) recruited a total of 1,392 patients with T2D.

PREDICTOR

The ENPP1 Q121 variant.

MEASUREMENTS

Estimated GFR from serum creatinine, urinary albumin excretion, blood pressure, hemoglobin A(1c), triglycerides, total cholesterol, and high-density lipoprotein cholesterol.

OUTCOMES

Decreased GFRs (ie, estimated GFR <60 mL/min/1.73 m(2)).

RESULTS

In the Gargano and Boston populations, according to the dominant model of inheritance, Q121 carriers (ie, individual with either KQ or QQ alleles) had an increased risk of decreased GFR: odds ratios (ORs) of 1.69 (95% confidence interval [CI], 1.1 to 2.6) and 1.50 (95% CI, 1.0 to 2.2), respectively. In the Padua set, the association was in the same direction, but did not reach formal statistical significance (OR, 1.77; 95% CI, 0.7 to 4.5). When the 3 studies were pooled, Q121 carriers showed an increased risk of decreased GFR (OR, 1.58; 95% CI, 1.2 to 2.1; P = 0.002). Also, pooled mean differences in absolute GFRs were different across genotype groups, with Q121 carriers showing lower GFRs compared with KK individuals (P = 0.04).

LIMITATIONS

P values not approaching a genome-wide level of significance.

CONCLUSIONS

Our data suggest that patients with T2D carrying the ENPP1 Q121 variant are at increased risk of decreased GFR.

Further evidence for the role of ENPP1 in obesity: association with morbid obesity in Finns

The aim of this study was to investigate a series of single-nucleotide polymorphisms (SNPs) in the genes MC2R, MC3R, MC4R, MC5R, POMC, and ENPP1 for association with obesity. Twenty-five SNPs (2-7 SNPs/gene) were genotyped in 246 Finns with extreme obesity (BMI > or = 40 kg/m2) and in 481 lean subjects (BMI 20-25 kg/m2). Of the obese subjects, 23% had concomitant type 2 diabetes. SNPs and SNP haplotypes were tested for association with obesity and type 2 diabetes. Allele frequencies differed between obese and lean subjects for two SNPs in the ENPP1 gene, rs1800949 (P = 0.006) and rs943003 (P = 0.0009). These SNPs are part of a haplotype (rs1800949 C-rs943003 A), which was observed more frequently in lean subjects compared to obese subjects (P = 0.0007). Weaker associations were detected between the SNPs rs1541276 in the MC5R, rs1926065 in the MC3R genes and obesity (P = 0.04 and P = 0.03, respectively), and between SNPs rs2236700 in the MC5R, rs2118404 in the POMC, rs943003 in the ENPP1 genes and type 2 diabetes (P = 0.03, P = 0.02 and P = 0.02, respectively); these associations did not, however, remain significant after correction for multiple testing. In conclusion, a previously unexplored ENPP1 haplotype composed of SNPs rs1800949 and rs943003 showed suggestive evidence for association with adult-onset morbid obesity in Finns. In this study, we did not find association between the frequently studied ENPP1 K121Q variant, nor SNPs in the MCR or POMC genes and obesity or type 2 diabetes.

New insights into the genetics of body weight

PURPOSE OF REVIEW

These last months, the wave of genome-wide association scans finally reached the shores of body weight and obesity complex trait. In parallel, thanks to the increasing sequencing and genotyping capacities, large studies on rare mutations can now be carried out.

RECENT FINDINGS

In this review, I tried to cover the most recent findings in genome-wide association analyses, the outcome of conclusions subsequently not replicated, and the weight of rare mutations with strong effects on common obesity. The strongest predictor of obesity, FTO, is responsible for 1% of the total heritability, and results from other genome-wide scans do not provide, so far, any clue of other variants of this effect size. Thus, monogenic obesity studies might well reinstall the importance of rare nonsynonymous mutations of already known genes, especially melanocortin-4 receptor gene, in the general population. Nevertheless, additional genome-wide association analyses and replication are expected to confirm these first intuitions.

SUMMARY

Initial results both support the common variant-common disease hypothesis because at least one such variant exists in FTO, and also tone down its importance because such variants may be fewer than expected. Moreover, having a polymorphism associated with body weight is clearly not the end but rather the beginning of a long search for the gene function and pathway.

Haplotype structure of the ENPP1 Gene and Nominal Association of the K121Q missense single nucleotide polymorphism with glycemic traits in the Framingham Heart Study

OBJECTIVE

A recent meta-analysis demonstrated a nominal association of the ectonucleotide pyrophosphatase phosphodiesterase 1 (ENPP1) K-->Q missense single nucleotide polymorphism (SNP) at position 121 with type 2 diabetes. We set out to confirm the association of ENPP1 K121Q with hyperglycemia, expand this association to insulin resistance traits, and determine whether the association stems from K121Q or another variant in linkage disequilibrium with it.

RESEARCH DESIGN AND METHODS

We characterized the haplotype structure of ENPP1 and selected 39 tag SNPs that captured 96% of common variation in the region (minor allele frequency > or =5%) with an r(2) value > or =0.80. We genotyped the SNPs in 2,511 Framingham Heart Study participants and used age- and sex-adjusted linear mixed effects (LME) models to test for association with quantitative metabolic traits. We also examined whether interaction between K121Q and BMI affected glycemic trait levels.

RESULTS

The Q allele of K121Q (rs1044498) was associated with increased fasting plasma glucose (FPG), A1C, fasting insulin, and insulin resistance by homeostasis model assessment (HOMA-IR; all P = 0.01-0.006). Two noncoding SNPs (rs7775386 and rs7773477) demonstrated similar associations, but LME models indicated that their effects were not independent from K121Q. We found no association of K121Q with obesity, but interaction models suggested that the effect of the Q allele on FPG and HOMA-IR was stronger in those with a higher BMI (P = 0.008 and 0.01 for interaction, respectively).

CONCLUSIONS

The Q allele of ENPP1 K121Q is associated with hyperglycemia and insulin resistance in whites. We found an adiposity-SNP interaction, with a stronger association of K121Q with diabetes-related quantitative traits in people with a higher BMI.

The ENPP1 K121Q polymorphism is associated with type 2 diabetes in European populations: evidence from an updated meta-analysis in 42,042 subjects

OBJECTIVE

Functional studies suggest that the nonsynonymous K121Q polymorphism in the ectoenzyme nucleotide pyrophosphate phosphodiesterase 1 (ENPP1) may confer susceptibility to insulin resistance; genetic evidence on its effect on type 2 diabetes, however, has been conflicting. We therefore conducted a new meta-analysis that includes novel unpublished data from the ENPP1 Consortium and recent negative findings from large association studies to address the contribution of K121Q to type 2 diabetes.

RESEARCH DESIGN AND METHODS

After a systematic review of the literature, we evaluated the effect of ENPP1 K121Q on diabetes risk under three genetic models using a random-effects approach. Our primary analysis consisted of 30 studies comprising 15,801 case and 26,241 control subjects. Due to considerable heterogeneity and large differences in allele frequencies across populations, we limited our meta-analysis to those of self-reported European descent and, when available, included BMI as a covariate.

RESULTS

We found a modest increase in risk of type 2 diabetes for QQ homozygotes in white populations (combined odds ratio [OR] 1.38 [95% CI 1.10-1.74], P = 0.005). There was no evidence of publication bias, but we noted significant residual heterogeneity among studies (P = 0.02). On meta-regression, 16% of the effect was accounted for by the mean BMI of control subjects. This association was stronger in studies in which control subjects were leaner but disappeared after adjustment for mean control BMI (combined OR 0.93 [95% CI 0.75-1.15], P = 0.50).

CONCLUSIONS

The ENPP1 Q121 variant increases risk of type 2 diabetes under a recessive model of inheritance in whites, an effect that appears to be modulated by BMI.

Progress in the genetics of common obesity: size matters

PURPOSE OF REVIEW

Over the past two decades serious efforts has been invested in the search for genes that predispose to common obesity, but progress has been slow and success limited. Genome-wide association, however, has revived optimism. Here we review recent advances in the field of obesity genetics and discuss the most important findings of candidate gene, genome-wide linkage studies and genome-wide association studies. We conclude by speculating about the way forward in the near future.

RECENT FINDINGS

Although large-scale candidate gene studies have placed MC4R more firmly on the human obesity map, the major breakthrough in obesity genetics was the discovery of FTO through genome-wide association. Variants located in the first intron of FTO were unequivocally associated with a 1.67-fold increased risk for obesity and a 0.40-0.66 kg/m2 increase in body mass index.

SUMMARY

Genome-wide association promises to enhance greatly our understanding of the genetic basis of common obesity, although candidate gene studies will remain a valuable approach because they allow more detailed analyses of biologically relevant candidates. A key factor contributing to continued success lies in large-scale data integration through international collaboration, which will provide the sample sizes required to identify genetic association with conclusive evidence.

Analysis of novel risk loci for type 2 diabetes in a general French population: the D.E.S.I.R. study

Recently, Genome Wide Association (GWA) studies identified novel single nucleotide polymorphisms (SNPs), highly associated with type 2 diabetes (T2D) in several case-control studies of European descent. However, the impact of these markers on glucose homeostasis in a population-based study remains to be clarified. The French prospective D.E.S.I.R. study (N = 4,707) was genotyped for 22 polymorphisms within 14 loci showing nominal to strong association with T2D in recently published GWA analyses (CDKAL1, IGFBP2, CDKN2A/2B, EXT2, HHEX, LOC646279, SLC30A8, MMP26, KCTD12, LDLR, CAMTA1, LOC38776, NGN3 and CXCR4). We assessed their effects on quantitative traits related to glucose homeostasis in 4,283 normoglycemic middle-aged participants at baseline and their contribution to T2D incidence during 9 years of follow-up. Individuals carrying T2D risk alleles of CDKAL1 or SLC30A8 had lower fasting plasma insulin level (rs7756992 P = 0.003) or lower basal insulin secretion (rs13266634 P = 0.0005), respectively, than non-carriers. Furthermore, NGN3 and MMP26 risk alleles associated with higher fasting plasma glucose levels (rs10823406 P = 0.01 and rs2499953 P = 0.04, respectively). However, for these SNPs, only modest associations were found with a higher incidence of T2D: hazard ratios of 2.03 [1.00-4.11] for MMP26 (rs2499953 P = 0.05) and 1.33 [1.02-1.73] for NGN3 (rs10823406 P = 0.03). We confirmed deleterious effects of SLC30A8, CDKAL1, NGN3 and MMP26 risk alleles on glucose homeostasis in the D.E.S.I.R. prospective cohort. However, in contrast to TCF7L2, the contribution of novel loci to T2D incidence seems only modest in the general middle-aged French population and should be replicated in larger cohorts.