A major locus for fasting insulin concentrations and insulin resistance on chromosome 6q with strong pleiotropic effects on obesity-related phenotypes in nondiabetic Mexican Americans

Further evidence supporting a potential role for ADH1B in obesity

Insulin is an essential hormone that regulates glucose homeostasis and metabolism. Insulin resistance (IR) arises when tissues fail to respond to insulin, and it leads to serious health problems including Type 2 Diabetes (T2D). Obesity is a major contributor to the development of IR and T2D. We previously showed that gene expression of alcohol dehydrogenase 1B (ADH1B) was inversely correlated with obesity and IR in subcutaneous adipose tissue of Mexican Americans. In the current study, a meta-analysis of the relationship between ADH1B expression and BMI in Mexican Americans, African Americans, Europeans, and Pima Indians verified that BMI was increased with decreased ADH1B expression. Using established human subcutaneous pre-adipocyte cell lines derived from lean (BMI < 30 kg m-2) or obese (BMI ≥ 30 kg m-2) donors, we found that ADH1B protein expression increased substantially during differentiation, and overexpression of ADH1B inhibited fatty acid binding protein expression. Mature adipocytes from lean donors expressed ADH1B at higher levels than obese donors. Insulin further induced ADH1B protein expression as well as enzyme activity. Knockdown of ADH1B expression decreased insulin-stimulated glucose uptake. Our findings suggest that ADH1B is involved in the proper development and metabolic activity of adipose tissues and this function is suppressed by obesity.

The E3 ubiquitin ligase parkin is dispensable for metabolic homeostasis in murine pancreatic β cells and adipocytes

The E3 ubiquitin ligase parkin is a critical regulator of mitophagy and has been identified as a susceptibility gene for type 2 diabetes (T2D). However, its role in metabolically active tissues that precipitate T2D development is unknown. Specifically, pancreatic β cells and adipocytes both rely heavily on mitochondrial function in the regulation of optimal glycemic control to prevent T2D, but parkin's role in preserving quality control of β cell or adipocyte mitochondria is unclear. Although parkin has been reported previously to control mitophagy, here we show that, surprisingly, parkin is dispensable for glucose homeostasis in both β cells and adipocytes during diet-induced insulin resistance in mice. We observed that insulin secretion, β cell formation, and islet architecture were preserved in parkin-deficient β cells and islets, suggesting that parkin is not necessary for control of β cell function and islet compensation for diet-induced obesity. Although transient parkin deficiency mildly impaired mitochondrial turnover in β cell lines, parkin deletion in primary β cells yielded no deficits in mitochondrial clearance. In adipocyte-specific deletion models, lipid uptake and β-oxidation were increased in cultured cells, whereas adipose tissue morphology, glucose homeostasis, and beige-to-white adipocyte transition were unaffected in vivo In key metabolic tissues where mitochondrial dysfunction has been implicated in T2D development, our experiments unexpectedly revealed that parkin is not an essential regulator of glucose tolerance, whole-body energy metabolism, or mitochondrial quality control. These findings highlight that parkin-independent processes maintain β cell and adipocyte mitochondrial quality control in diet-induced obesity.

Association of donor small ubiquitin-like modifier 4 rs237025 genetic variant with tacrolimus elimination in the early period after liver transplantation

BACKGROUNDS & AIMS

Individualized tacrolimus treatment can improve drug safety and efficacy. In this study, we aimed to investigate the association of donor and recipient small ubiquitin-like modifier 4 (SUMO4) rs237025 polymorphisms with tacrolimus elimination and the potential mechanism.

METHODS

A total of 297 liver transplant patients were enrolled in the study. CYP3A5 rs776746 and SUMO4 rs237025 were genotyped using TaqMan SNPs assays. The activity of nuclear factor-kB (NF-kB) was evaluated by luciferase assay. The expressions of CYP3A5 were detected by qRT-PCR and western blotting.

RESULTS

Tacrolimus C/D ratios was significantly lower for donor SUMO4 rs237025 AA carriers than AG/GG carriers at weeks 1, 2, 3. In multivariate analysis, donor and recipient CYP3A5 rs776747, donor SUMO4 rs237025 and total bilirubin were independent predictors of tacrolimus C/D ratios in the early post-transplantation period both in Cohort A and Cohort B. When combined donor CYP3A5 rs776746 and donor SUMO4 rs237025 genotypes, tacrolimus C/D ratios was highly significant at all investigated time points within the four groups. CYP3A5 mRNA expression in liver tissues was significantly higher for AA carriers than AG/GG patients under inflammatory stimuli after liver transplantation (LT). Furthermore, we demonstrated that SUMO4 rs237025 G allele could increase NF-κB transcriptional activity under inflammatory condition. And activation of NF-kB suppressed the expression of pregnane X receptor (PXR)-mediated CYP3A5 gene.

CONCLUSIONS

Donor SUMO4 rs237025 genetic variant was associated with higher Tac C/D ratios in the early period after LT, which might be related to the down-regulation of CYP3A5 enzyme through the NF-kB signalling pathway.

Association between promoter polymorphism (-108C>T) of paraoxonase1 gene and it's paraoxonase activity in patients with Type2 diabetes in northern Iran

Type 2 diabetes mellitus (T2DM) is one of the diseases which depend on the obesity associated with insulin resistance. Various factors, such as a reduction in the activity of paraoxonase-1 enzyme (PON1), could affect T2DM. PON1 is a multifunctional enzyme with paraoxonase and arylesterase activities. The Activity of PON1 is influenced by various SNPs. The aim of presence study is to investigate the association between promoter polymorphism (-108C>T) of PON1 gene and its paraoxonase activity in patients suffering from Type 2 diabetes in Golestan Province, north of Iran. To this end, genomic DNA was extracted from whole blood then genotyping was carried out using PCR-RFLP and enzymatic activity of paraoxonase was measured in the serum of 90 healthy subjects and 90 diabetic patients. Data was analyzed using SPSS version 16. The relationship between the level of paraoxonase activity with polymorphisms of CC, CT, and TT was statistically significant in patients with T2DM. There was a significant association between polymorphism C-108>T of PON1 and type2 diabetes mellitus, with 24.4% of control group subjects and 15.5% of patients having CC genotype; p<0.05. The ratio for CT genotype in target and control groups was 51.1% and 61.1% respectively; p<0.05. TT genotype was 33.3% in patients and 14.4% in the control group; p<0.05. In the present study, the highest frequency belonged to CT genotype in both the control and the target groups, followed by CC genotype in control group and TT genotype in target group. Our findings revealed that paraoxonase activity of PON1 in the control group was significantly higher in comparison with diabetic patients.

Association of donor and recipient SUMO4 rs237025 genetic variant with new-onset diabetes mellitus after liver transplantation in a Chinese population

BACKGROUNDS & AIMS

New-onset diabetes mellitus (NODM) is a common complication after liver transplantation (LT). The small ubiquitin-like modifier 4 (SUMO4) rs237025 polymorphism has been reported to be associated with type 2 diabetes mellitus (T2DM). In this study, we aimed to evaluate the association of donor and recipient SUMO4 rs237025 polymorphisms with NODM and the long-term consequences of NODM after LT.

METHODS

A total of 126 liver transplant patients were enrolled in the study. One single nucleotide polymorphism, SUMO4 rs237025, was genotyped in both donors and recipients.

RESULTS

Both donor and recipient SUMO4 rs237025 polymorphisms were found to be significantly associated with NODM after LT. In multivariate analysis, recipient age>50 years, tacrolimus trough concentrations>10ng/mL at 1month after LT, donor and recipient rs237025 genetic variant, and the combined donor and recipient rs237025 genetic variant were independent predictive factors of NODM. Area under the receiver operating characteristic curve (AUROC) analysis indicated the higher predictive ability of the model containing combined donor and recipient rs237025 polymorphisms than the clinical model (p=0.046). Furthermore, Kaplan-Meier survival analysis demonstrated that NODM was related to significantly poorer patient survival in comparison with non-NODM patients (p=0.041).

CONCLUSIONS

Both donor and recipient SUMO4 rs237025 polymorphisms contribute to the development of NODM after LT and NODM is a frequent complication that negatively affects patient survival.

Small Ubiquitin-Like Modifier 4 (SUMO4) Gene M55V Polymorphism and Type 2 Diabetes Mellitus: A Meta-analysis Including 6,823 Subjects

BACKGROUND

Many studies suggest that the small ubiquitin-like modifier 4 (SUMO4) M55V gene polymorphism (rs237025) may be associated with an increased risk of type 2 diabetes mellitus (T2DM). However, due to other conflicting results, a clear consensus is lacking in the matter.

OBJECTIVE AND METHODS

A meta-analysis consisting of 6,823 subjects from 10 studies was conducted to elucidate relationship between the SUMO4 M55V gene polymorphism and T2DM. Depending on the heterogeneity of the data, either a fixed or random-effects model would be used to assess the combined odds ratio (ORs) and their corresponding 95% confidence interval (CI).

RESULTS

SUMO4 gene M55V polymorphism was significantly associated with T2DM in the whole population under allelic (OR: 1.18, 95% CI: 1.10-1.28, P = 1.63 × 10^-5), recessive (OR: 1.59, 95% CI: 1.14-2.23, P = 0.006), dominant (OR: 0.815, 95% CI: 0.737-0.901, P = 6.89 × 10^-5), homozygous (OR: 1.415, 95% CI: 1.170-1.710, P = 0.0003), heterozygous (OR: 1.191, 95% CI: 1.072-1.323, P = 0.001), and additive genetic models (OR: 1.184, 95% CI: 1.097-1.279, P = 1.63 × 10^-5). In our subgroup analysis, a significant association was found again in the Chinese population, but not in Japanese or Iranian population.

CONCLUSION

SUMO4 gene M55V polymorphism may correlate with increased T2DM risk. Chinese carriers of the V allele of the SUMO4 gene M55V polymorphism may be predisposed to developing T2DM.

The Relevance of Genomic Signatures at Adhesion GPCR Loci in Humans

Adhesion G protein-coupled receptors (aGPCRs) have a long evolutionary history dating back to very basal unicellular eukaryotes. Almost every vertebrate is equipped with a set of different aGPCRs. Genomic sequence data of several hundred extinct and extant species allows for reconstruction of aGPCR phylogeny in vertebrates and non-vertebrates in general but also provides a detailed view into the recent evolutionary history of human aGPCRs. Mining these sequence sources with bioinformatic tools can unveil many facets of formerly unappreciated aGPCR functions. In this review, we extracted such information from the literature and open public sources and provide insights into the history of aGPCR in humans. This includes comprehensive analyses of signatures of selection, variability of human aGPCR genes, and quantitative traits at human aGPCR loci. As indicated by a large number of genome-wide genotype-phenotype association studies, variations in aGPCR contribute to specific human phenotypes. Our survey demonstrates that aGPCRs are significantly involved in adaptation processes, phenotype variations, and diseases in humans.

Obesity genetics in mouse and human: back and forth, and back again

Obesity is a major public health concern. This condition results from a constant and complex interplay between predisposing genes and environmental stimuli. Current attempts to manage obesity have been moderately effective and a better understanding of the etiology of obesity is required for the development of more successful and personalized prevention and treatment options. To that effect, mouse models have been an essential tool in expanding our understanding of obesity, due to the availability of their complete genome sequence, genetically identified and defined strains, various tools for genetic manipulation and the accessibility of target tissues for obesity that are not easily attainable from humans. Our knowledge of monogenic obesity in humans greatly benefited from the mouse obesity genetics field. Genes underlying highly penetrant forms of monogenic obesity are part of the leptin-melanocortin pathway in the hypothalamus. Recently, hypothesis-generating genome-wide association studies for polygenic obesity traits in humans have led to the identification of 119 common gene variants with modest effect, most of them having an unknown function. These discoveries have led to novel animal models and have illuminated new biologic pathways. Integrated mouse-human genetic approaches have firmly established new obesity candidate genes. Innovative strategies recently developed by scientists are described in this review to accelerate the identification of causal genes and deepen our understanding of obesity etiology. An exhaustive dissection of the molecular roots of obesity may ultimately help to tackle the growing obesity epidemic worldwide.

Type 2 diabetes mellitus-related genetic polymorphisms in microRNAs and microRNA target sites

MicroRNAs (miRNAs) are important endogenous regulators in eukaryotic gene expression and a broad range of biological processes. MiRNA-related genetic variations have been proved to be associated with human diseases, such as type 2 diabetes mellitus (T2DM). Polymorphisms in miRNA genes (primary miRNAs, precursor miRNAs, mature miRNAs, and miRNA regulatory regions) may be involved in the development of T2DM by changing the expression and structure of miRNAs and target gene expression. Genetic polymorphisms of the 3'-untranslated region (UTR) in miRNA target genes may destroy putative miRNA binding sites or create new miRNA binding sites, which affects the binding of UTRs with miRNAs, finally resulting in susceptibility to and development of T2DM. Therefore, focusing on studies into genetic polymorphisms in miRNAs or miRNA binding sites will help our understanding of the pathophysiology of T2DM development and lead to better health management. Herein, we review the association of genetic polymorphisms in miRNA and miRNA targets genes with T2DM development.

The PARK2 gene is involved in the maintenance of pancreatic β-cell functions related to insulin production and secretion

Several association studies have implicated the PARK2 gene that encodes parkin--the key molecule orchestrating the mitochondrial quality control system--as a candidate susceptibility gene for diabetes. A total of 7551 unrelated Korean KARE cohort subjects were analyzed to investigate the association between the PARK2 single nucleotide polymorphism (SNP) and quantitative glycemic traits. Two SNPs, rs10455889 and rs9365294, were significantly associated with fasting plasma glucose level (p=∼1.2×10(-4)) and insulin secretion indices (p=∼7.4×10(-5)) in male KARE subjects. Parkin was expressed predominantly in the rat pancreatic islets. Downregulation of the Park2 gene in rat INS-1 β-cells resulted in a significant decrease in the glucose-stimulated insulin secretion, intracellular insulin gene expression, and intracellular ATP level. The Park2-depleted β-cells also exhibited increased mitochondrial fragmentation and ROS production and decreased mitochondrial membrane potential. Both population-based statistical evaluation and experimental evidence demonstrated a fundamental role of the PARK2 gene in the maintenance of β-cell function.

Cited2, a transcriptional modulator protein, regulates metabolism in murine embryonic stem cells

CREB-binding protein (CBP)/p300 interacting transactivator with glutamic acid (Glu) and aspartic acid (Asp)-tail 2 (Cited2) was recently shown to be essential for gluconeogenesis in the adult mouse. The metabolic function of Cited2 in mouse embryonic stem cells (mESCs) remains elusive. In the current study, the metabolism of glucose was investigated in mESCs, which contained a deletion in the gene for Cited2 (Cited2(Δ/-)). Compared with its parental wild type counterpart, Cited2(Δ/-) ESCs have enhanced glycolysis, alternations in mitochondria morphology, reduced glucose oxidation, and decreased ATP content. Cited2 is recruited to the hexokinase 1 (HK1) gene promoter to regulate transcription of HK1, which coordinates glucose metabolism in wild type ESCs. Reduced glucose oxidation and enhanced glycolytic activity in Cited2(Δ/-) ESCs correlates with defective differentiation during hypoxia, which is reflected in an increased expression of pluripotency marker (Oct4) and epiblast marker (Fgf5) and decreased expression of lineage specification markers (T, Gata-6, and Cdx2). Knockdown of hypoxia inducible factor-1α in Cited2(Δ/-) ESCs re-initiates the expression of differentiation markers T and Gata-6. Taken together, a deletion of Cited2 in mESCs results in abnormal mitochondrial morphology and impaired glucose metabolism, which correlates with a defective cell fate decision.

Genetic epidemiology of cardiometabolic risk factors and their clustering patterns in Mexican American children and adolescents: the SAFARI Study

Pediatric metabolic syndrome (MS) and its cardiometabolic components (MSCs) have become increasingly prevalent, yet little is known about the genetics underlying MS risk in children. We examined the prevalence and genetics of MS-related traits among 670 non-diabetic Mexican American (MA) children and adolescents, aged 6-17 years (49 % female), who were participants in the San Antonio Family Assessment of Metabolic Risk Indicators in Youth study. These children are offspring or biological relatives of adult participants from three well-established Mexican American family studies in San Antonio, TX, at increased risk of type 2 diabetes. MS was defined as ≥3 abnormalities among 6 MSC measures: waist circumference, systolic and/or diastolic blood pressure, fasting insulin, triglycerides, HDL-cholesterol, and fasting and/or 2-h OGTT glucose. Genetic analyses of MS, number of MSCs (MSC-N), MS factors, and bivariate MS traits were performed. Overweight/obesity (53 %), pre-diabetes (13 %), acanthosis nigricans (33 %), and MS (19 %) were strikingly prevalent, as were MS components, including abdominal adiposity (32 %) and low HDL-cholesterol (32 %). Factor analysis of MS traits yielded three constructs: adipo-insulin-lipid, blood pressure, and glucose factors, and their factor scores were highly heritable. MS itself exhibited 68 % heritability. MSC-N showed strong positive genetic correlations with obesity, insulin resistance, inflammation, and acanthosis nigricans, and negative genetic correlation with physical fitness. MS trait pairs exhibited strong genetic and/or environmental correlations. These findings highlight the complex genetic architecture of MS/MSCs in MA children, and underscore the need for early screening and intervention to prevent chronic sequelae in this vulnerable pediatric population.

Genome-wide linkage scan of antisocial behavior, depression, and impulsive substance use in the UCSF family alcoholism study

OBJECTIVE

Epidemiological and clinical studies suggest that the rates of antisocial behavior, depression, and impulsive substance use are increased among individuals diagnosed with alcohol dependence relative to those who are not. Thus, the present study conducted genome-wide linkage scans of antisocial behavior, depression, and impulsive substance use in the University of California at San Francisco Family Alcoholism Study.

METHODS

Antisocial behavior, depressive symptoms, and impulsive substance use were assessed using three scales from the Minnesota Multiphasic Personality Inventory - 2nd ed.: the Antisocial Practices content scale, the Depression content scale, and the revised MacAndrew Alcoholism scale. Linkage analyses were carried out using a variance components approach.

RESULTS

Suggestive evidence of linkage to three genomic regions independent of alcohol and cannabis dependence diagnostic status was observed: the Antisocial Practices content scale showed evidence of linkage to chromosome 13 at 11 cM, the MacAndrew Alcoholism scale showed evidence of linkage to chromosome 15 at 47 cM, and all three scales showed evidence of linkage to chromosome 17 at 57-58 cM.

CONCLUSION

Each of these regions has shown previous evidence of linkage and association to substance dependence as well as other psychiatric disorders such as mood and anxiety disorders, attention-deficit hyperactivity disorder, and schizophrenia, thus suggesting potentially broad relations between these regions and psychopathology.

Metabolic syndrome is linked to chromosome 7q21 and associated with genetic variants in CD36 and GNAT3 in Mexican Americans

The prevalence of metabolic syndrome (MS) has been rising alarmingly worldwide, including in the United States, but knowledge on specific genetic determinants of MS is very limited. Therefore, we planned to identify the genetic determinants of MS as defined by National Cholesterol Education Program/Adult Treatment Panel III (NCEP/ATPIII) criteria. We performed linkage screen for MS using data from 692 Mexican Americans, who participated in the San Antonio Family Diabetes/Gallbladder Study (SAFDGS). We found strong evidence for linkage of MS on chromosome 7q (LOD = 3.6, empirical P = 6.0 × 10(-5)), between markers D7S2212 and D7S821. In addition, six chromosomal regions exhibited potential evidence for linkage (LOD ≥1.2) with MS. Furthermore, we examined 29 single-nucleotide polymorphisms (SNPs) from the fatty acid translocase (FAT or CD36, 18 SNPs) gene and guanine nucleotide binding protein, α transducing 3 (GNAT3, 11 SNPs) gene, located within the 1-LOD support interval region for their association with MS and its related traits. Several SNPs were associated with MS and its related traits. Remarkably, rs11760281 in GNAT3 and rs1194197 near CD36 exhibited the strongest associations with MS (P = 0.0003, relative risk (RR) = 1.6 and P = 0.004, RR = 1.7, respectively) and several other related traits. These two variants explained ~18% of the MS linkage evidence on chromosome 7q21, and together conferred approximately threefold increase in MS risk (RR = 2.7). In conclusion, our linkage and subsequent association studies implicate a region on chromosome 7q21 to influence MS in Mexican Americans.

Pleiotropic Effects of Genes for Insulin Resistance on Adiposity in Baboons

OBJECTIVE

Previous research has suggested a genetic contribution to the development of insulin resistance and obesity. We hypothesized that the same genes influencing insulin resistance might also contribute to the variation in adiposity.

RESEARCH METHODS AND PROCEDURES

A total of 601 (200 male, 401 female) adult baboons (Papio hamadryas) from nine families with pedigrees ranging in size from 43 to 121 were used in this study. Plasma insulin, glucose, C-peptide, and adiponectin were analyzed, and homeostasis model assessment of insulin resistance (HOMA IR) was calculated. Fat biopsies were collected from omental fat tissue, and triglyceride concentration per gram of fat tissue was determined. Body weight and length were measured, and BMI was derived. Univariate and bivariate quantitative genetic analyses were performed using SOLAR.

RESULTS

Insulin, glucose, C-peptide, and adiponectin levels, HOMA IR, triglyceride concentration of fat tissue, body weight, and BMI were all found to be significantly heritable, with heritabilities ranging from 0.15 to 0.80. Positive genetic correlations (r(G)s) were observed for HOMA IR with C-peptide (r(G) = 0.88 +/- 0.10, p = 0.01), triglyceride concentration in fat tissue (r(G) = 0.86 +/- 0.33, p = 0.02), weight (r(G) = 0.50 +/- 0.20, p = 0.03), and BMI (r(G) = 0.64 +/- 0.22, p = 0.02).

DISCUSSION

These results suggest that a set of genes contributing to insulin resistance also influence general and central adiposity phenotypes. Further genetic research in a larger sample size is needed to identify the common genes that constitute the genetic basis for the development of insulin resistance and obesity.

Integrating genomic analysis with the genetic basis of gene expression: preliminary evidence of the identification of causal genes for cardiovascular and metabolic traits related to nutrition in Mexicans

Whole-transcriptome expression profiling provides novel phenotypes for analysis of complex traits. Gene expression measurements reflect quantitative variation in transcript-specific messenger RNA levels and represent phenotypes lying close to the action of genes. Understanding the genetic basis of gene expression will provide insight into the processes that connect genotype to clinically significant traits representing a central tenet of system biology. Synchronous in vivo expression profiles of lymphocytes, muscle, and subcutaneous fat were obtained from healthy Mexican men. Most genes were expressed at detectable levels in multiple tissues, and RNA levels were correlated between tissue types. A subset of transcripts with high reliability of expression across tissues (estimated by intraclass correlation coefficients) was enriched for cis-regulated genes, suggesting that proximal sequence variants may influence expression similarly in different cellular environments. This integrative global gene expression profiling approach is proving extremely useful for identifying genes and pathways that contribute to complex clinical traits. Clearly, the coincidence of clinical trait quantitative trait loci and expression quantitative trait loci can help in the prioritization of positional candidate genes. Such data will be crucial for the formal integration of positional and transcriptomic information characterized as genetical genomics.

Genomic copy number of a carcinogenic single nucleotide polymorphism at 8q24 in non-risk allele colorectal cancer associated with insulin growth factor 2 receptor expression

BACKGROUND AND AIM

The incidence of both diabetes mellitus and hyperlipidemia is increasing and they are risk factors for colorectal cancer (CRC). On the other hand, the carcinogenic significance of the single nucleotide polymorphism (SNP), rs6983267 at 8q24, in CRC has been reported. The association between the SNP genotype and genes associated with diabetes or hyperlipidemia was investigated in cases of CRC.

METHODS

In 107 cases of CRC diagnosed in eight institutes from 2003 to 2008, array-CGH and cDNA microarray was performed and the data analyzed from two groups subdivided according to SNP genotype.

RESULTS

In the array-CGH data, we selected 38 genes related to diabetes or fat metabolism, and of these 10 had a correlation coefficient between the genome copy number at 8q24 locus and that of each gene. Of the 10 genes, insulin growth factor 2 receptor (IGF2R) was the only one with an expression level significantly associated with the 8q24 genotype. IGF2R expression was significantly lower in non-risk allele than in risk allele cases (P = 0.012). There was neither a diabetes- nor a fat metabolism-related gene that was significantly associated with CRC cases with the risk allele at 8q24.

CONCLUSIONS

SNP at 8q24 makes diabetes a risk factor of CRC via IGF2R, especially in genetically non-risk allele cases. We speculate that the risk allele of 8q24 might be risky enough that diabetes is not necessary to worsen the risk for CRC.

Linkage scan of nicotine dependence in the University of California, San Francisco (UCSF) Family Alcoholism Study

BACKGROUND

Nicotine dependence has been shown to represent a heritable condition, and several research groups have performed linkage analysis to identify genomic regions influencing this disorder though only a limited number of the findings have been replicated.

METHOD

In the present study, a genome-wide linkage scan for nicotine dependence was conducted in a community sample of 950 probands and 1204 relatives recruited through the University of California, San Francisco (UCSF) Family Alcoholism Study. A modified version of the Semi-Structured Assessment for the Genetics of Alcoholism (SSAGA) with additional questions that probe nicotine use was used to derive DSM-IV nicotine dependence diagnoses.

RESULTS

A locus on chromosome 2q31.1 at 184 centiMorgans nearest to marker D2S2188 yielded a logarithm (base 10) of odds (LOD) score of 3.54 (point-wise empirical p=0.000012). Additional peaks of interest were identified on chromosomes 2q13, 4p15.33-31, 11q25 and 12p11.23-21. Follow-up analyses were conducted examining the contributions of individual nicotine dependence symptoms to the chromosome 2q31.1 linkage peak as well as examining the relationship of this chromosomal region to alcohol dependence.

CONCLUSIONS

The present report suggests that chromosome 2q31.1 confers risk to the development of nicotine dependence and that this region influences a broad range of nicotine dependence symptoms rather than a specific facet of the disorder. Further, the results show that this region is not linked to alcohol dependence in this population, and thus may influence nicotine dependence specifically.

Insulin resistance at the crossroads of metabolic syndrome: systemic analysis using microarrays

Recently, it has been suggested that insulin resistance is a better predictor of metabolic syndrome than obesity. Numerous studies have been conducted to identify insulin resistance susceptibility genes in various model systems. This review focuses on recent findings in microarray analyses, which have indicated that (i) in the liver, genes involved in lipid synthesis and gluconeogenesis are increased in an animal model of insulin resistance that leads into liver steatosis and hyperglycemia; (ii) in adipose tissues, genes involved in fatty acid synthesis and adipogenesis are down-regulated both in insulin-resistant humans and in animals; and (iii) in muscle, overall gene expression, including genes involved in fatty acid oxidation and biosynthesis, is either decreased or unresponsive compared to that of insulin-sensitive control human subjects or animals. Considering the multifaceted effects of insulin resistance in various tissues, aiming at multi-targets rather than a single target will be a more promising strategy for the prevention or treatment of insulin resistance.

No association of the SUMO4 polymorphism M55V variant in type 2 diabetes in Iranian subjects

INTRODUCTION

Diabetes mellitus incidence has an increasing rate and it's genetic aspect is an important approach as a risk factor and predictive value in this disorder. In some population, SUMO4, a regulator of NF-κB, gene polymorphism is associated with diabetes. A single-nucleotide polymorphism was detected in SUMO4; substituting a highly conserved methionine with a valine residue (M55V). We studied the association between M55V polymorphism in the SUMO4 gene insusceptibility of type 2 diabetes in patients with type 2 diabetes.

MATERIALS AND METHODS

Participants were 50 patients with type 2 diabetes and 50 control Iranian subjects. Genotyping was done using polymorphism chain reaction (PCR) technique and subsequent cleavage by restriction endonuclease (RFLP) for the M55V SUMO4 gene variant.

RESULTS

The frequency of SUMO4 AA, AG and GG were 13%, 25% and 12% in control group and 20%, 22%, 18% in the type 2 diabetes patients respectively. The SUMO4 M55V variant was not associated with the susceptibility of type 2 diabetes.

CONCLUSION

The study indicates that the SUMO4 gene M55V variant was not associated with the susceptibility of the type 2 diabetes polymorphism.

The characterization of Abelson helper integration site-1 in skeletal muscle and its links to the metabolic syndrome

The human Abelson helper integration site-1 (AHI1) gene is associated with both neurologic and hematologic disorders; however, it is also located in a chromosomal region linked to metabolic syndrome phenotypes and was identified as a type 2 diabetes mellitus susceptibility gene from a genomewide association study. To further define a possible role in type 2 diabetes mellitus development, AHI1 messenger RNA expression levels were investigated in a range of tissues and found to be highly expressed in skeletal muscle as well as displaying elevated levels in brain regions and gonad tissues. Further analysis in a rodent polygenic animal model of obesity and type 2 diabetes mellitus identified increased Ahi-1 messenger RNA levels in red gastrocnemius muscle from fasted impaired glucose-tolerant and diabetic rodents compared with healthy animals (P < .002). Moreover, elevated gene expression levels were confirmed in skeletal muscle from fasted obese and type 2 diabetes mellitus human subjects (P < .02). RNAi-mediated suppression of Ahi-1 resulted in increased glucose transport in rat L6 myotubes in both the basal and insulin-stimulated states (P < .01). Finally, single nucleotide polymorphism association studies identified 2 novel AHI1 genetic variants linked with fasting blood glucose levels in Mexican American subjects (P < .037). These findings indicate a novel role for AHI1 in skeletal muscle and identify additional genetic links with metabolic syndrome phenotypes suggesting an involvement of AHI1 in the maintenance of glucose homeostasis and type 2 diabetes mellitus progression.

Agreement among type 2 diabetes linkage studies but a poor correlation with results from genome-wide association studies

AIMS/HYPOTHESIS

Little of the genetic basis for type 2 diabetes has been explained, despite numerous genetic linkage studies and the discovery of multiple genes in genome-wide association (GWA) studies. To begin to resolve the genetic component of this disease, we searched for sites at which genetic results had been corroborated in different studies, in the expectation that replication among studies should direct us to the genomic locations of causative genes with more confidence than the results of individual studies.

METHODS

We have mapped the physical location of results from 83 linkage reports (for type 2 diabetes and diabetes precursor quantitative traits [QTs, e.g. plasma insulin levels]) and recent large GWA reports (for type 2 diabetes) onto the same human genome sequence to identify replicated results in diabetes genetic 'hot spots'.

RESULTS

Genetic linkage has been found at least ten times at 18 different locations, and at least five times in 56 locations. All replication clusters contained study populations from more than one ethnic background and most contained results for both diabetes and QTs. There is no close relationship between the GWA results and linkage clusters, and the nine best replication clusters have no nearby GWA result.

CONCLUSIONS/INTERPRETATION

Many of the genes for type 2 diabetes remain unidentified. This analysis identifies the broad location of yet to be identified genes on 6q, 1q, 18p, 2q, 20q, 17pq, 8p, 19q and 9q. The discrepancy between the linkage and GWA studies may be explained by the presence of multiple, uncommon, mildly deleterious polymorphisms scattered throughout the regulatory and coding regions of genes for type 2 diabetes.

Beta amyloid and hyperphosphorylated tau deposits in the pancreas in type 2 diabetes

Strong epidemiologic evidence suggests an association between Alzheimer disease (AD) and type 2 diabetes. To determine if amyloid beta (Abeta) and hyperphosphorylated tau occurs in type 2 diabetes, pancreas tissues from 21 autopsy cases (10 type 2 diabetes and 11 controls) were analyzed. APP and tau mRNAs were identified in human pancreas and in cultured insulinoma beta cells (INS-1) by RT-PCR. Prominent APP and tau bands were detected by Western blotting in pancreatic extracts. Aggregated Abeta, hyperphosphorylated tau, ubiquitin, apolipoprotein E, apolipoprotein(a), IB1/JIP-1 and JNK1 were detected in Langerhans islets in type 2 diabetic patients. Abeta was co-localized with amylin in islet amyloid deposits. In situ beta sheet formation of islet amyloid deposits was shown by infrared microspectroscopy (SIRMS). LPS increased APP in non-neuronal cells as well. We conclude that Abeta deposits and hyperphosphorylated tau are also associated with type 2 diabetes, highlighting common pathogenetic features in neurodegenerative disorders, including AD and type 2 diabetes and suggesting that Abeta deposits and hyperphosphorylated tau may also occur in other organs than the brain.

Ordered stratification to reduce heterogeneity in linkage to diabetes-related quantitative traits

Phenotypic heterogeneity complicates detection of genomic loci predisposing to type 2 diabetes, potentially obscuring or unmasking specific loci. We conducted ordered-subsets linkage analyses (OSAs) for diabetes-related quantitative traits (fasting insulin and glucose, hemoglobin A1c (HbA1c), and 28-year-time-averaged fasting plasma glucose (FPG)) from 330 families of the Framingham Offspring Study. We calculated mean BMI, waist circumference (WC), and a diabetes "age-of-onset score" for each family. We constructed subsets by adding one family at a time in increasing (lean family to obese) or decreasing (obese to lean) adiposity order, or increasing or decreasing propensity to develop diabetes at a younger age, with the OSA LOD reported as the maximum LOD observed in any subset. Permutation P values tested the hypothesis that phenotypic ordering showed stronger linkage than random ordering. On chromosome 1, ordering by increasing family mean WC increased linkage to time-averaged FPG at 256 cM from LOD = 2.4 to 3.5 (permuted P = 0.02) and to HbA1c at 180 cM from LOD = 2.0 to 3.3 (P = 0.01). On chromosome 19, ordering by decreasing WC increased linkage to fasting insulin at 68 cM from LOD = 2.7 to 4.6 (P = 0.002), and ordering by decreasing propensity to develop diabetes at a young age increased linkage to fasting insulin at 73 cM from LOD = 2.7 to 4.0 (P = 0.046). We conclude that chromosomes 1 and 19 could harbor adiposity-interacting diabetes susceptibility genes. Such interactions might also influence trait-locus associations and may be useful to consider in diabetes genome-wide association studies.

Functional genetic variation of human miRNAs and phenotypic consequences

A large number of human protein-coding genes are finely regulated by one or more microRNAs. Members of this small noncoding RNA family have emerged as important post-transcriptional regulators of gene expression and are involved in a number of disease phenotypes. Variability in the human genome is extensive and includes the common and rare single nucleotide polymorphisms (SNPs) and copy number variations (CNVs). The functional significance of the genome's variability is under intense investigation. In this article we review the emerging literature on how human genomic variation influences the outcome of microRNA targeting and the associated phenotypic effects. Illustrative examples are discussed that demonstrate the biological importance of functional polymorphisms affecting miRNA-mediated gene regulation.

Association of genetic variation in ENPP1 with obesity-related phenotypes

Ectonucleotide pyrophosphatase phosphodiesterase (ENPP1) is a positional candidate gene at chromosome 6q23 where we previously detected strong linkage with fasting-specific plasma insulin and obesity in Mexican Americans from the San Antonio Family Diabetes Study (SAFDS). We genotyped 106 single-nucleotide polymorphisms (SNPs) within ENPP1 in all 439 subjects from the linkage study, and measured association with obesity and metabolic syndrome (MS)-related traits. Of 72 polymorphic SNPs, 24 were associated, using an additive model, with at least one of eight key metabolic traits. Three traits were associated with at least four SNPs. They were high-density lipoprotein cholesterol (HDL-C), leptin, and fasting plasma glucose (FPG). HDL-C was associated with seven SNPs, of which the two most significant P values were 0.0068 and 0.0096. All SNPs and SNP combinations were analyzed for functional contribution to the traits using the Bayesian quantitative-trait nucleotide (BQTN) approach. With this SNP-prioritization analysis, HDL-C was the most strongly associated trait in a four-SNP model (P=0.00008). After accounting for multiple testing, we conclude that ENPP1 is not a major contributor to our previous linkage peak with MS-related traits in Mexican Americans. However, these results indicate that ENPP1 is a genetic determinant of these traits in this population, and are consistent with multiple positive association findings in independent studies in diverse human populations.

Evaluation of a SNP map of 6q24-27 confirms diabetic nephropathy loci and identifies novel associations in type 2 diabetes patients with nephropathy from an African-American population

Previously, we performed a genome scan for type 2 diabetes (T2DM) using 638 African-American (AA) affected sibling pairs from 247 families; non-parametric linkage analysis suggested evidence of linkage at 6q24-27 (LOD 2.26). To comprehensively evaluate this region, we performed a two-stage association study by first constructing a SNP map of 754 SNPs selected from HapMap on the basis of linkage disequilibrium (LD) in 300 AAT2DM end-stage renal disease (ESRD) subjects, 311 AA controls, 43 European American controls and 45 Yoruba Nigerian samples (Set 1). Replication analyses were conducted in an independent population of 283 AA T2DM-ESRD subjects and 282 AA controls (Set 2). In addition, we adjusted for the impact of admixture on association results by using ancestry informative markers (AIMs). In Stage 1, 137 (18.2%) SNPs showed nominal evidence of association (P < 0.05) in one or more of tests of association: allelic (n = 33), dominant (n = 36), additive (n = 29), or recessive (n = 34) genotypic models, and 2- (n = 47) and 3-SNP (n = 43) haplotypic analyses. These SNPs were selected for follow-up genotyping. Stage 2 analyses confirmed association with a predicted 2-SNP "risk" haplotype in the PARK2 gene. Also, two intergenic SNPs showed consistent genotypic association with T2DM-ESRD: rs12197043 and rs4897081. Combined analysis of all subjects from both stages revealed nominal associations with 17 SNPs within genes, including suggestive associations in ESR1 and PARK2. This study confirms known diabetic nephropathy loci and identifies potentially novel susceptibility variants located within 6q24-27 in AA.

Association of ENPP1 (PC-1) K121Q polymorphism with obesity-related parameters in subjects with metabolic syndrome

BACKGROUND

The metabolic syndrome (MS), a cluster of several metabolic disorders, is increasingly being recognized as a risk factor for cardiovascular disease. Ectonucleotide pyrophosphatase/phosphodiesterase 1 (ENPP1), originally described as a plasma cell allo-antigen and named plasma cell membrane glycoprotein (PC-1), is an inhibitor of insulin-induced activation of the insulin receptor. The single nucleotide polymorphism (SNP) K121Q in the ENPP1 gene has been studied in relation to obesity, insulin resistance and other features of MS in several populations with conflicting results. We therefore investigate the role of the K121Q SNP in the ENPP1 gene in MS in Caucasians from the province of Segovia in Central Spain (Castille).

DESIGN AND METHODS

We recruited 794 unrelated persons (46.5% males and 53.5% females), ages 35-74 years from a cross-sectional population-based epidemiological survey in the province of Segovia in Central Spain (Castille). Obesity-related anthropometric measurements included BMI, waist circumference, blood pressure and lipid profile. MS was defined by International Diabetes Federation (IDF) guidelines. K121Q PC-1 genotypes were determined by polymerase chain reaction-restriction fragment length polymorphism (PCR-RFLP).

RESULTS

The 121Q allele was associated with an increased BMI and waist circumference among subjects fulfilling the criteria for MS. These differences remained statistically significant even after the adjustment for sex, age and degree of glucose tolerance (beta = 1.347, P = 0.017 and beta = 2.824, P = 0.046; for BMI and waist circumference, respectively). Moreover, among type 2 diabetic patients those carrying the 121Q allele had higher BMI and higher leptin levels than subjects carrying the K121K genotype.

CONCLUSIONS

Our results suggest that the ENPP1121Q allele might contribute to the genetic susceptibility to abdominal obesity among subjects with MS.

Effect of acute physiological hyperinsulinemia on gene expression in human skeletal muscle in vivo

This study was undertaken to test the hypothesis that short-term exposure (4 h) to physiological hyperinsulinemia in normal, healthy subjects without a family history of diabetes would induce a low grade inflammatory response independently of glycemic status. Twelve normal glucose tolerant subjects received a 4-h euglycemic hyperinsulinemic clamp with biopsies of the vastus lateralis muscle. Microarray analysis identified 121 probe sets that were significantly altered in response to physiological hyperinsulinemia while maintaining euglycemia. In normal, healthy human subjects insulin increased the mRNAs of a number of inflammatory genes (CCL2, CXCL2 and THBD) and transcription factors (ATF3, BHLHB2, HES1, KLF10, JUNB, FOS, and FOSB). A number of other genes were upregulated in response to insulin, including RRAD, MT, and SGK. CITED2, a known coactivator of PPARalpha, was significantly downregulated. SGK and CITED2 are located at chromosome 6q23, where we previously detected strong linkage to fasting plasma insulin concentrations. We independently validated the mRNA expression changes in an additional five subjects and closely paralleled the results observed in the original 12 subjects. A saline infusion in healthy, normal glucose-tolerant subjects without family history of diabetes demonstrated that the genes altered during the euglycemic hyperinsulinemic clamp were due to hyperinsulinemia and were unrelated to the biopsy procedure per se. The results of the present study demonstrate that insulin acutely regulates the levels of mRNAs involved in inflammation and transcription and identifies several candidate genes, including HES1 and BHLHB2, for further investigation.

OLETF allele of hyperglycemic QTL Nidd3/of is dominant

The OLETF rat is a well-established model for the study of type 2 diabetes associated with obesity and has been shown to possess multiple hyperglycemic alleles in its genome. Here we focused on and carefully characterized one of the previously reported congenic strains, F.O-Nidd3/of that carries the OLETF allele of the Nidd3/of locus (also known as Niddm21 in the Rat Genome Database) in the normoglycemic F344 genetic background. A prominent finding was that the F1 progeny between the congenic and the F344 stain, whose genotype is heterozygote at the Nidd3/of locus, showed mild hyperglycemia equal to the parental congenic rat, suggesting that the OLETF allele is dominant. To our knowledge, this is the first study in which a diabetic QTL has been directly demonstrated to be dominant by using congenic strains.

Polymorphisms in AHI1 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.

The role of membrane glycoprotein plasma cell antigen 1/ectonucleotide pyrophosphatase phosphodiesterase 1 in the pathogenesis of insulin resistance and related abnormalities

Insulin resistance is a major feature of most patients with type 2 diabetes mellitus (T2D). A number of laboratories have observed that PC-1 (membrane [corrected] glycoprotein plasma cell antigen 1; also termed [corrected] ectonucleotide pyrophosphatase phosphodiesterase 1 or ENPP1) [corrected] is either overexpressed or overactive in muscle, adipose tissue, fibroblasts, and other tissues of insulin-resistant individuals, both nondiabetic and diabetic. Moreover, PC-1 (ENPP1) overexpression [corrected] in cultured cells in vitro and in transgenic mice in vivo, [corrected] impairs insulin stimulation of insulin receptor (IR) activation and downstream signaling. PC-1 binds to the connecting domain of the IR alpha-subunit that is located in residues 485-599. The connecting domain transmits insulin binding in the alpha-subunit to activation of tyrosine kinase activation in the beta-subunit. When PC-1 is overexpressed, it inhibits insulin [corrected]induced IR beta-subunit tyrosine kinase activity. In addition, a polymorphism of PC-1 (K121Q) in various ethnic populations is closely associated with insulin resistance, T2D, and cardio [corrected] and nephrovascular diseases. The product of this polymorphism has a 2- to 3-fold increased binding affinity for the IR and is more potent than the wild-type PC-1 protein (K121K) in inhibiting the IR. These data suggest therefore that PC-1 is a candidate protein that may play a role in human insulin resistance and T2D by its overexpression, its overactivity, or both.

Pediatric obesity: the unique issues in Latino-American male youth

Pediatric obesity in the United States has been steadily rising over the past few decades, and it is a clear risk factor for adult obesity and obesity-related morbidity and mortality. A review of the literature from three major national databases reveals that the prevalence rates of obesity within Latino male children and adolescents is, in general, higher than other major gender-ethnic groups. Additionally, obese Latino male youth seem to be especially prone to a variety of obesity-related morbidities. Given the rising percentage of Latinos among our nation's youth, there is an urgency to develop and implement clinical and community research strategies to prevent and treat obesity within this high-risk gender-ethnic group. This article reviews the prevalence of pediatric obesity within the three largest databases in the U.S. with Latino representation. The paper then discusses unique issues in the etiology and ramifications of obesity within young Latino-American boys, reviews the few intervention studies that focus on Latino youth, and discusses potential strategies for further research.

Genetics of variation in HOMA-IR and cardiovascular risk factors in Mexican-Americans

Insulin resistance is a major biochemical defect underlying the pathogenesis of cardiovascular disease (CVD). Mexican-Americans are known to have an unfavorable cardiovascular profile. Thus, the aim of this study was to investigate the genetic effect on variation in HOMA-IR and to evaluate its genetic correlations with other phenotypes related to risk of CVD in Mexican-Americans. The homeostatic model assessment method (HOMA-IR) is one of several approaches that are used to measure insulin resistance and was used here to generate a quantitative phenotype for genetic analysis. For 644 adults who had participated in the San Antonio Family Heart Study (SAFHS), estimates of genetic contribution were computed using a variance components method implemented in SOLAR. Traits that exhibited significant heritabilities were body mass index (BMI) (h (2) = 0.43), waist circumference (h (2) = 0.48), systolic blood pressure (h (2) = 0.30), diastolic blood pressure (h (2) = 0.21), pulse pressure (h (2) = 0.32), triglycerides (h (2) = 0.51), LDL cholesterol (h (2) = 0.31), HDL cholesterol (h (2) = 0.24), C-reactive protein (h (2) = 0.17), and HOMA-IR (h (2) = 0.33). A genome-wide scan for HOMA-IR revealed significant evidence of linkage on chromosome 12q24 (close to PAH (phenylalanine hydroxylase), LOD = 3.01, p < 0.001). Bivariate analyses demonstrated significant genetic correlations (p < 0.05) of HOMA-IR with BMI (rho (G) = 0.36), waist circumference (rho (G) = 0.47), pulse pressure (rho (G) = 0.39), and HDL cholesterol (rho (G) = -0.18). Identification of significant linkage for HOMA-IR on chromosome 12q replicates previous family-based studies reporting linkage of phenotypes associated with type 2 diabetes in the same chromosomal region. Significant genetic correlations between HOMA-IR and phenotypes related to CVD risk factors suggest that a common set of gene(s) influence the regulation of these phenotypes.

A quantitative trait locus on chromosome 13q affects fasting glucose levels in Hispanic children

OBJECTIVE

The prevalence of childhood obesity has increased dramatically in the United States. Early presentation of type 2 diabetes has been observed in children and adolescents, especially in the Hispanic population. The genetic contribution of glucose homeostasis related to childhood obesity is poorly understood. The objective of this study was to localize quantitative trait loci influencing fasting serum glucose levels in Hispanic children participating in the Viva La Familia Study.

DESIGN

Subjects were 1030 children ascertained through an overweight child from 319 Hispanic families. Fasting serum glucose levels were measured enzymatically, and genetic linkage analyses were conducted using SOLAR software.

RESULTS

Fasting glucose was heritable, with a heritability of 0.62 +/- 0.08 (P < 0.01). Genome-wide scan mapped fasting serum glucose to markers D13S158-D13S173 on chromosome 13q (LOD score of 4.6). A strong positional candidate gene is insulin receptor substrate 2, regulator of glucose homeostasis and a candidate gene for obesity. This region was reported previously to be linked to obesity- and diabetes-related phenotypes.

CONCLUSIONS

A quantitative trait locus on chromosome 13q contributes to the variation in fasting serum glucose levels in Hispanic children at high risk for obesity.

ENPP1 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.

Bivariate genome-wide scan for metabolic phenotypes in non-diabetic Chinese individuals from the Stanford, Asia and Pacific Program of Hypertension and Insulin Resistance Family Study

AIMS/HYPOTHESIS

Hypertension, obesity, impaired glucose tolerance and dyslipidaemia are metabolic abnormalities that often cluster together more often than expected by chance alone. Since these metabolic variables are highly heritable and are at least partially genetically determined, the clustering of defects in these traits implies that pleiotropic effects, where a common set of genes influences more than one trait simultaneously, are likely.

METHODS

We conducted bivariate linkage analyses for highly correlated traits, aiming to dissect the genetic architecture affecting these traits, in 411 Chinese families participating in the Stanford Asia-Pacific Program of Hypertension and Insulin Resistance Study.

RESULTS

We confirmed the pleiotropic effects of the locus at 37 cM on chromosome 20 on the following pairs: (1) fasting insulin and insulin AUC (empirical p = 0.0006); (2) fasting insulin and homeostasis model assessment of beta cell function (HOMA-beta) (empirical p = 0.0051); and (3) HOMA of insulin resistance (IR) and HOMA-beta (empirical p = 0.0044). In addition, the peak logarithm of the odds (LOD) scores of linkage between a chromosomal locus and a trait for the pair fasting insulin and HOMA-IR rose to 5.10 (equivalent LOD score in univariate analysis, LOD([1]) = 4.01, empirical p = 8.0 x 10(-5)) from 3.67 and 3.42 respectively for these two traits in univariate analysis. Additional significant linkage evidence, not shown in single-trait analysis, was identified at 45 cM on chromosome 16 for the pair 1 h insulin and the AUC for insulin, with a LOD score of 4.29 (or LOD([1]) = 3.27, empirical p = 2.0 x 10(-4)). This new locus is also likely to harbour the common genes regulating these two traits (p = 1.73 x 10(-6)).

CONCLUSIONS/INTERPRETATION

These data help provide a better understanding of the genomic structure underlying the metabolic syndrome.

Genome-wide scan for adiposity-related phenotypes in adults from American Samoa

OBJECTIVE

To detect quantitative trait loci influencing adiposity-related phenotypes assessed by body mass index (BMI), abdominal circumference (ABDCIR), percent body fat (%BFAT) and fasting serum leptin and adiponectin using a whole genome linkage scan of families from American Samoa.

DESIGN

Family-based linkage analysis, the probands and family members were unselected for obesity.

SUBJECTS

A total of 583 phenotyped American Samoan adults, of which 578 were genotyped in 34 pedigrees.

MEASUREMENTS

A total of 377 autosomal and 18 X chromosome microsatellite markers were typed at an approximate average spacing of 10 cM spanning the genome. Multipoint LOD (logarithm of the odds) scores were calculated using variance-components approaches and SOLAR/LOKI software. The covariates simultaneously evaluated were age, sex, education, farm work and cigarette smoking, with a significance level of 0.1. Due to the stochastic nature of LOKI, we report the average of maximum LOD scores from 10 runs.

RESULTS

Significant linkage to leptin was found at 6q32.2 with LOD of 3.83. Suggestive linkage to leptin was found at 16q21:LOD=2.98, 1q42.2:LOD=1.97, 5q11.2:LOD=2.08, 12q24.23:LOD=2.00, 19p13.3:LOD=2.05; adiponectin was linked to 13q33.1-q22.1:LOD=2.41; %BFAT was linked to 16q12.2-q21, LOD=2.24; ABDCIR was linked to 16q23.1:LOD=1.95; %BFAT-adjusted leptin to 14q12, LOD=2.01; %BFAT-adjusted ABDCIR to 1q31.1, LOD=2.36, to 3q27.3-q28, LOD=2.10 and to 12p12.3, LOD=2.04.

CONCLUSION

We found strong evidence for a major locus on 6q23.2 influencing serum leptin levels in American Samoans. The 16q21 region appears to harbor a susceptibility locus that has significant pleiotrophic effects on phenotypes BMI, %BFAT, leptin and ABDCIR as shown by bivariate linkage analyses. Several other loci of varying significance were detected across the genome.

ENPP1 gene, insulin resistance and related clinical outcomes

PURPOSE OF REVIEW

Insulin resistance plays a significant role in both morbidity and mortality of the general population. Understanding the molecular mechanisms of insulin resistance would help the identification of at-risk individuals in the presymptomatic stage, and the discovery of novel and more effective treatments. The transmembrane glycoprotein ectonucleotide pyrophosphatase phosphodiesterase 1 (ENPP1) inhibits insulin receptor signalling and has recently emerged as a key player in the development of insulin resistance. This review will summarize data available on the relationship between ENPP1 and insulin resistance.

RECENT FINDINGS

Overexpression of ENPP1 in insulin target tissues is an early, intrinsic defect observed in human insulin resistance. A missense ENPP1 single nucleotide polymorphism, K121Q, has been recently described with the Q121 variant being a stronger inhibitor than K121 of insulin receptor function. In addition, the Q121 variant has been repeatedly associated with insulin resistance and related abnormalities including body weight changes, type 2 diabetes and macrovascular complications, thus suggesting a pleiotropic role of the ENPP1 gene on several metabolic abnormalities.

SUMMARY

A deep understanding of ENPP1 mode of action and the mechanisms regulating its expression and function are likely to provide new tools for early identification and treatments of patients at risk for the devastating clinical outcomes related to insulin resistance.

Association of small ubiquitin-like modifier 4 (SUMO4) variant, located in IDDM5 locus, with type 2 diabetes in the Japanese population

CONTEXT

Despite distinct differences in the pathogenesis, epidemiological data have indicated familial clustering of type 1 and type 2 diabetes, suggesting a common genetic basis between these two types of diabetes. Few shared susceptibility genes, however, have been reported to date.

OBJECTIVE

Small ubiquitin-like modifier 4 (SUMO4) has been identified as a candidate gene for the IDDM5 locus and suggested to have possible involvement in immune responses, such as autoimmunity and inflammation. Recent reports demonstrated that a polymorphism with an amino acid substitution (Met55Val) in SUMO4 was associated with type 1 diabetes in Asian populations, although no association was reproduced in subjects of Caucasian descent. The present study aimed to clarify the contribution of SUMO4 to type 2 diabetes susceptibility in the Japanese population.

SUBJECTS

The 753 subjects included 355 cases and 398 control subjects.

METHODS

The SUMO4 Met55Val (rs237025) and 001Msp (rs577001) polymorphisms were genotyped.

RESULTS

Strong linkage disequilibrium (D': 1.0 in each pair of single-nucleotide polymorphisms) across the MAP3K7IP2/SUMO4 region was shown in the Japanese population. The frequency of genotypes with the G allele of the SUMO4 Met55Val polymorphism was significantly higher in patients with type 2 diabetes [odds ratio, 1.46; 95% confidence interval (CI), 1.08-1.93; P = 0.01, chi(2) test]. The association was concentrated in patients without insulin therapy (odds ratio, 1.56; 95% CI, 1.13-2.15; P = 0.0072), but not in those with insulin (odds ratio, 1.24; 95% CI, 0.81-1.89; not significant).

CONCLUSIONS

These data, together with previous reports, suggest the contribution of the SUMO4 Met55Val polymorphism to both type 1 and type 2 diabetes susceptibility in the Japanese population.

Genetics of the metabolic syndrome

The concept of a metabolic syndrome (MetS), a cluster of pre-clinical metabolic alterations commonly associated with obesity, is the object of much debate. Genetic studies have the potential to contribute to some of the key questions, including the true nature of the cluster of pre-clinical features and whether it is associated with human genetic variation. This review summarizes the evidence for the presence of familial aggregation for the individual components of MetS and their heritability levels. It also provides an overview of the studies that have dealt with candidate genes for MetS. Potential leads from genome-wide linkage scans are also discussed. The assumption is made that obesity, ectopic fat deposition and abnormal adipose tissue metabolism are responsible for alterations in lipid metabolism, which in turn generates the commonly observed pre-clinical shifts in glucose tolerance, lipids and lipoprotein profile, blood pressure, inflammatory markers, endothelial function, and a prothrombotic state. Progress in the understanding of the genetic basis of MetS should occur as soon as a consensus is reached on the true nature of MetS, its components and diagnostic criteria.

Association of neuropeptide Y receptor Y5 polymorphisms with dyslipidemia in Mexican Americans

We examined the genetic association of neuropeptide Y receptor Y5 (NPY5R) single nucleotide polymorphisms (SNPs) with measures of the insulin resistance (metabolic) syndrome. We genotyped 10 NPY5R SNPs in 439 Mexican American individuals (age=43.3+/-17.3 years and BMI=30.0+/-6.7 kg/m2) distributed across 27 pedigrees from the San Antonio Family Diabetes Study and performed association analyses using the measured genotype approach as implemented in Sequential Oligogenic Linkage Analysis Routines (SOLAR). Minor alleles for five (rs11100493, rs12501691, P1, rs11100494, rs12512687) of the NPY5R SNPs were found to be significantly (p<0.05) associated with fasting plasma triglyceride concentrations and decreased high-density lipoprotein concentrations. In addition, the minor allele for SNP P2 was significantly associated (p=0.031) with a decreased homeostasis model assessment of beta-cell function (HOMA-%beta). Linkage disequilibrium between SNP pairs indicated one haplotype block of five SNPs (rs11100493, rs12501691, P1, rs11100494, rs12512687) that were highly correlated (r2>0.98). These preliminary results provide evidence for association of SNPs in the NPY5R gene with dyslipidemia (elevated triglyceride concentrations and reduced high-density lipoprotein levels) in our Mexican American population.

The genetic landscape of type 2 diabetes in mice

Inbred mouse strains provide genetic diversity comparable to that of the human population. Like humans, mice have a wide range of diabetes-related phenotypes. The inbred mouse strains differ in the response of their critical physiological functions, such as insulin sensitivity, insulin secretion, beta-cell proliferation and survival, and fuel partitioning, to diet and obesity. Most of the critical genes underlying these differences have not been identified, although many loci have been mapped. The dramatic improvements in genomic and bioinformatics resources are accelerating the pace of gene discovery. This review describes how mouse genetics can be used to discover diabetes-related genes, summarizes how the mouse strains differ in their diabetes-related phenotypes, and describes several examples of how loci identified in the mouse may directly relate to human diabetes.

Diabetes and hypertension increases in a society with abdominal obesity: results of the Mexican National Health Survey 2000

Objectives:

To determine the prevalences of overweight, obesity, type 2 diabetes mellitus (DM) and hypertension (HT) in the Mexican population and compare them with those of a previous Mexican urban survey and an American survey.

Design:

A structured, randomised, nationally representative Mexican sample was compared with a 1993 Mexican urban survey and the US Third National Health and Nutrition Examination Survey (NHANES III) of non-Hispanic Whites.

Setting:

The Mexican National Health Survey 2000.

Subjects:

Subjects were 12856 men and 28332 women, aged 20–69 years, who had their body weight, height, waist circumference (WC), blood pressure and fasting capillary blood glucose measured.

Results:

Mexican adult men and women had a high prevalence of overweight (41.3 and 36.3%, respectively) and obesity (19.4 and 29.0%, respectively), similar to those in the USA in 1988–1992 and exceeding those of the 1993 Mexican survey. The prevalence of HT was 33.3% in men and 25.6% in women, with inferred DM rates of 5.6 and 9.7%, respectively. Abdominal obesity affected 46.3% of men (WC ≥ 94 cm) and 81.4% of women (WC ≥ 80 cm). There was a high prevalence of abdominal obesity in normal-weight women, with co-morbidities relating better to WC than to body mass index (BMI) in both sexes. Rates of DM and HT exceeded US rates on a comparable BMI or WC basis in adults aged <50 years.

Conclusion:

The high prevalence of obesity and abdominal obesity in Mexicans is associated with markedly increased prevalences of DM and HT to levels comparable with, or even higher than, those in NHANES III of non-Hispanic Whites.