Genome-wide linkage of plasma adiponectin reveals a major locus on chromosome 3q distinct from the adiponectin structural gene: the IRAS family study

Association of adiponectin gene single nucleotide polymorphisms with environmental risk factors in type 2 diabetes mellitus: An updated evidence of haplotype-based analysis study

BACKGROUND AND AIM

Adiponectin (ADIPOQ) gene is considered to be one of the promising players in deciphering the genetic bases of type 2 diabetes. This study investigated the associations between haplotype combinations of three single nucleotide polymorphisms (SNPs) of the ADIPOQ gene and two SNPs of the adiponectin receptor 1 (AdipoR1) and 2 (AdipoR2) genes with environmental risk factors for the prediction of T2DM disorder susceptibility in the Iranian population.

METHODS

This case-control and cross-sectional study was conducted on 182 patients with T2DM and 155 healthy controls. Genotyping was performed using amplification refractory mutation system-PCR (ARMS-PCR) for rs17300539G/A, rs2241766T/G, and rs1501299G/T of the ADIPOQ gene, rs1342387C/T of the AdipoR1 gene, and rs10773989T/C of the AdipoR2 gene.

RESULTS

All polymorphisms met the Hardy-Weinberg equilibrium (p> 0.05). The studied SNPs; rs17300539, rs2241766 of the ADIPOQ gene and rs10773989 of the AdipoR2 gene, were significantly associated with an increased risk of T2DM. Two-way ANOVA analysis indicated that GG carriers of rs2241766T/G had a significantly lower waist-to-hip ratio (P= 0.049) and body mass index (P= 0.011) and higher HbA1c (P= 0.048) compared to TT carriers, while TT genotype carriers of rs2241766T/G showed the higher plasma adiponectin concentration compared to TG and GG carriers (P= 0.009 and P= 0.013, respectively). CC carriers of rs10773989T/C displayed a significantly higher LDL level compared to the TT genotype carries (P= 0.036). Also plasma adiponectin concentrations were significantly lower in AA genotype carriers of rs17300539G/A compared to GG and GA genotypes carriers in the control group only (P= 0.005 and P= 0.016, respectively). According to Combined Haplotype ([rs17300539, rs2241766, rs1501299]/[rs17300539, rs2241766, rs1501299]) analysis, GTT-homozygote carriers displayed the highest plasma adiponectin concentration and in contrast, GGG/GTG, ATG/GTG, and GGG/GGG showed the lowest plasma adiponectin concentration in the controls (p> 0.05).

CONCLUSION

The adiponectin gene haplotype combinations were associated with plasma adiponectin concentration in healthy individuals. In T2DM, adiponectin genetic variants displayed less effect on adiponectin plasma concentration.

Novel Loci (EIF4A2, ADIPOQ, TPRG1) for Triglyceride / High-density Lipoprotein Cholesterol Ratio Longitudinal Change (ΔTHR) among Subjects without Type 2 Diabetes: Evidence from the Long Life Family Study (LLFS) and the Framingham Heart Study (FHS) Offspring Cohort (OS)

Aims/hypothesis

Triglyceride (TG) /High density lipoprotein cholesterol (HDL-C) ratio (THR) represents a single surrogate predictor of hyperinsulinemia or insulin resistance that is associated with premature aging processes, risk of diabetes and increased mortality. To identify novel genetic loci for THR change over time (ΔTHR), we conducted genome-wide association study (GWAS) and genome-wide linkage scan (GWLS) among subjects of European ancestry who had complete data from two exams collected about seven years apart from the Long Life Family Study (LLFS, n=1384), a study with familial clustering of exceptional longevity in the US and Denmark.

Methods

Subjects with diabetes or using medications for dyslipidemia were excluded from this analysis. ΔTHR was derived using growth curve modeling, and adjusted for age, sex, field centers, and principal components (PCs). GWAS was conducted using a linear mixed model accounted for familial relatedness. Our linkage scan was built on haplotype-based IBD estimation with 0.5 cM average spacing.

Results

Heritability of ΔTHR was moderate (46%). Our GWAS identified a significant locus at the LPL (p=1.58e-9) for ΔTHR; this gene locus has been reported before influencing baseline THR levels. Our GWLS found evidence for a significant linkage with a logarithm of the odds (LODs) exceeding 3 on 3q28 (LODs=4.1). Using a subset of 25 linkage enriched families (pedigree-specific LODs>0.1), we assessed sequence elements under 3q28 and identified two novel variants (EIF4A2/ADIPOQ-rs114108468, p=5e-6, MAF=1.8%; TPRG1-rs16864075, p=3e-6, MAF=8%; accounted for ~28% and ~29% of the linkage, respectively, and 57% jointly). While the former variant was associated with EIF4A2 (p=7e-5) / ADIPOQ (p=3.49e-2) RNA transcriptional levels, the latter variant was not associated with TPRG1 (p=0.23) RNA transcriptional levels. Replication in FHS OS observed modest effect of these loci on ΔTHR. Of 188 metabolites from 13 compound classes assayed in LLFS, we observed multiple metabolites (e.g., DG.38.5, PE.36.4, TG.58.3) that were significantly associated with the variants (p<3e-4).

Conclusions

our linkage-guided sequence analysis approach permitted our discovery of two novel gene variants EIF4A2/ADIPOQ-rs114108468 and TPRG1-rs16864075 on 3q28 for ΔTHR among subjects without diabetes selected for exceptional survival and healthy aging.

Adiponectin protects skeletal muscle from ischaemia–reperfusion injury in mice through miR ‐21/ PI3K /Akt signalling pathway

Previous studies have confirmed that adiponectin (APN) plays a protective role in myocardial ischaemia-reperfusion (IR) injury, and the aim of this study was to investigate its effect on skeletal muscle. ELISA was used to detect the levels of Creatinine Kinase (CK), LDH, SOD and MDA in the plasma of the lower limbs of mice, and the levels of IL-6, IL-1β and TNF-α in the gastrocnemius. Quantitative PCR was used to detect the expression level of miR-21. TUNEL staining was used to detect the apoptosis of the gastrocnemius. The expression levels of apoptosis proteins, autophagy marker proteins and downstream target genes of miR-21 in gastrocnemius were detected by Western Blot. The results of this study revealed that APN levels were significantly reduced in gastrocnemius of IR mice. The oxidative stress, inflammatory response, apoptosis and autophagy induced by IR were significantly ameliorated by APN injection. The above effects of APN may be achieved through miR-21/PI3K signalling pathway, as found by interfering gene expression levels with miRNA antagomir and lentiviral injection. Taken together, our study revealed that APN protects skeletal muscle from IR injury through miR-21 /PI3K/Akt signalling pathway through inhibiting inflammatory response, apoptosis and autophagy.

Quantile-dependent expressivity of plasma adiponectin concentrations may explain its sex-specific heritability, gene-environment interactions, and genotype-specific response to postprandial lipemia

Background

"Quantile-dependent expressivity" occurs when the effect size of a genetic variant depends upon whether the phenotype (e.g. adiponectin) is high or low relative to its distribution. We have previously shown that the heritability (h² ) of adiposity, lipoproteins, postprandial lipemia, pulmonary function, and coffee and alcohol consumption are quantile-specific. Whether adiponectin heritability is quantile specific remains to be determined.

Methods

Plasma adiponectin concentrations from 4,182 offspring-parent pairs and 1,662 sibships from the Framingham Heart Study were analyzed. Quantile-specific heritability from offspring-parent (β _OP,h² = 2β _OP/(1 + r_spouse)) and full-sib regression slopes (β _FS, h² = {(1 + 8r_spouse β _FS)^0.05-1}/(2r_spouse)) were robustly estimated by quantile regression with nonparametric significance assigned from 1,000 bootstrap samples.

Results

Quantile-specific h² (± SE) increased with increasing percentiles of the offspring's age- and sex-adjusted adiponectin distribution when estimated from β _OP (P _trend = 2.2 × 10^-6): 0.30 ± 0.03 at the 10th, 0.33 ± 0.04 at the 25th, 0.43 ± 0.04 at the 50th, 0.55 ± 0.05 at the 75th, and 0.57 ± 0.08 at the 90th percentile, and when estimated from β _FS (P _trend = 7.6 × 10^-7): 0.42 ± 0.03 at the 10th, 0.44 ± 0.04 at the 25th, 0.56 ± 0.05 at the 50th, 0.73 ± 0.08 at the 75th, and 0.79 ± 0.11 at the 90th percentile. Consistent with quantile-dependent expressivity, adiponectin's: (1) heritability was greater in women in accordance with their higher adiponection concentrations; (2) relationships to ADIPOQ polymorphisms were modified by adiposity in accordance with its adiponectin-lowering effect; (3) response to rosiglitazone was predicted by the 45T> G ADIPOQ polymorphism; (4) difference by ADIPOQ haplotypes increased linearly with increasing postprandial adiponectin concentrations.

Conclusion

Adiponectin heritability is quantile dependent, which may explain sex-specific heritability, gene-environment and gene-drug interactions, and postprandial response by haplotypes.

Adiponectin is associated with cardio-metabolic traits in Mexican children

The adipocyte-derived adiponectin hormone bridges obesity and its cardio-metabolic complications. Genetic variants at the ADIPOQ locus, in ADIPOR1, and ADIPOR2 have been associated with adiponectin concentrations and cardio-metabolic complications in diverse ethnicities. However, no studies have examined these associations in Mexican children. We recruited 1 457 Mexican children from Mexico City. Six genetic variants in or near ADIPOQ (rs182052, rs2241766, rs266729, rs822393), ADIPOR1 (rs10920533), and ADIPOR2 (rs11061971) were genotyped. Associations between serum adiponectin, genetic variants, and cardio-metabolic traits were assessed using linear and logistic regressions adjusted for age, sex, and recruitment center. Serum adiponectin concentration was negatively associated with body mass index, waist to hip ratio, low-density lipoprotein cholesterol, total cholesterol, triglycerides, fasting glucose, fasting insulin, homeostatic model assessment of insulin resistance, dyslipidemia and overweight/obesity status (7.76 × 10⁻⁴⁰ ≤ p ≤ 3.00 × 10⁻³). No significant associations between genetic variants in ADIPOQ, ADIPOR1, and ADIPOR2 and serum adiponectin concentration were identified (all p ≥ 0.30). No significant associations between the six genetic variants and cardio-metabolic traits were observed after Bonferroni correction (all p < 6.9 × 10⁻⁴). Our study suggests strong associations between circulating adiponectin concentration and cardio-metabolic traits in Mexican children.

Adipokines and Aging: Findings From Centenarians and the Very Old

Adipose tissue, which was once considered as a simple energy storage depot, is now recognized as an active endocrine organ that regulates the whole-body energy homeostasis by secreting hundreds of bioactive substances termed adipokines. Dysregulation of adipokines is a key feature of insulin resistance and a metabolic syndrome associated with obesity. Adipokine dysregulation and insulin resistance are also associated with energy-deprivation conditions, such as frailty in old age. Previous studies have demonstrated that preserved insulin sensitivity and low prevalence of diabetes are the metabolic peculiarities of centenarians, suggesting the possible role of adipokine homeostasis in healthy longevity. Among the numerous adipokines, adiponectin is regarded as unique and salutary, showing negative correlations with several age- and obesity-related metabolic disturbances and a positive correlation with longevity and insulin sensitivity among centenarians. However, large-scale epidemiological studies have implied the opposite aspect of this adipokine as a prognostic factor for all-cause and cardiovascular mortality in patients with heart failure or kidney disease. In this review, the clinical significance of adiponectin was comparatively addressed in centenarians and the very old, in terms of frailty, cardiovascular risk, and mortality.

Leptin gene variants and colorectal cancer risk: Sex-specific associations

BACKGROUND

High levels of serum leptin and low levels of serum adiponectin are strongly correlated with obesity, a well-established risk factor for colorectal cancer (CRC). Growing evidence suggests that dysregulation of leptin and adiponectin levels may play an etiological role in colorectal carcinogenesis. We evaluated 20 candidate variants in 4 genes previously shown to alter serum leptin and adiponectin levels for associations with obesity (BMI>30 kg/m2) and CRC risk.

METHODS

We analyzed 6,246 CRC cases and 7,714 population-based controls from 11 studies within the Genetics and Epidemiology of Colorectal Cancer Consortium (GECCO). Associations of each variant with obesity or CRC were evaluated using multivariate logistic regression models stratified by sex and adjusted for age, a study variable, and the first three principal components of genetic ancestry. Gene-specific False Discovery Rate (FDR)-adjusted p-values <0.05 denoted statistical significance.

RESULTS

Two variants in the leptin gene showed statistically significant associations with CRC among women: LEP rs2167270 (OR = 1.13, 95% CI: 1.06-1.21) and LEP rs4731426 (OR = 1.09, 95% CI: 1.02-1.17). These associations remained significant after adjustment for obesity, suggesting that leptin SNPs may influence CRC risk independent of obesity. We observed statistically significant interactions of the leptin variants with hormone replacement therapy (HRT) for CRC risk; these variant associations were strengthened when analyses were restricted to post-menopausal women with low estrogen exposure, as estimated by 'never use' of HRT and/or non-obese BMI. No variants were associated with CRC among men.

CONCLUSIONS

Leptin gene variants may exhibit sex-specific associations with CRC risk. Endogenous and exogenous estrogen exposure may modify the association between these variants, leptin levels, and CRC risk.

The association of two polymorphisms in adiponectin-encoding gene with hypertension risk and the changes of circulating adiponectin and blood pressure: A meta-analysis

Objectives

This meta-analysis was prepared to synthesize published data on the association of two polymorphisms (T45G and G276T) in adiponectin-encoding gene (ADIPOQ) with hypertension risk and the changes of circulating adiponectin and blood pressure.

Methodology and Major Findings

Data were collected and corrected by two authors, and were managed with Stata software. In total, 12 articles were synthesized, including 12 studies (3358 cases and 5121 controls) for the association of two study polymorphisms with hypertension risk and 11 studies (3053 subjects) for the between-genotype changes of adiponectin and/or blood pressure. Based on all qualified studies, the risk prediction for hypertension was nonsignificant for both polymorphisms, with significant heterogeneity for G276T polymorphism (I² = 53.8%). Overall changes in adiponectin and blood pressure were also nonsignificant for T45G, while contrastingly 276GT genotype was associated with significantly higher levels of adiponectin (weighted mean difference [WMD] = 0.72 μg/mL, 95% confidence interval [CI]: 0.04 to 1.41, P = 0.038), systolic (WMD = 5.15 mm Hg, 95% CI: 0.98 to 9.32, P = 0.016) and diastolic (WMD = 3.45 mm Hg, 95% CI: 0.37 to 6.53, P = 0.028) blood pressure with evident heterogeneity (I² = 72.0%, 78.3% and 80.0%, respectively), and these associations were more obvious in hypertensive patients. Publication bias was a low probability event for overall comparisons.

Conclusions

Our findings suggested that in spite of the nonsignificant association between ADIPOQ T45G or G276T polymorphism and hypertension, the heterozygous mutation of G276T was observed to account for increased levels of circulating adiponectin and blood pressure, especially in hypertensive patients.

Adiponectin Isoform Patterns in Ethnic-Specific ADIPOQ Mutation Carriers: The IRAS Family Study

OBJECTIVE

Adiponectin is found in human serum in three groups of multimers (high molecular weight [HMW], medium molecular weight [MMW], and low molecular weight [LMW]). Two ethnic-specific variants in ADIPOQ, G45R (Hispanic-Americans) and R55C (African-Americans), were previously reported. Although carriers of both variants had mean adiponectin levels ≤ 20% of those of noncarriers, they were not clinically different from noncarriers. To compare carriers of both variants and noncarriers, relative quantification of adiponectin isoforms to total adiponectin was performed on serum samples.

METHODS

The multimeric patterns of serum adiponectin in G45R carriers (n = 23), R55C carriers (n = 3), and Hispanic- and African-American noncarriers (n = 84 and 44, respectively) from the Insulin Resistance Atherosclerosis Family Study were explored using native Western blotting and densitometry.

RESULTS

Serum samples from carriers showed an absence of the HMW isoform and a marked reduction in the MMW isoform but an approximate twofold increase in the amount of the LMW isoform. Thus, individuals making only LMW adiponectin are metabolically normal.

CONCLUSIONS

The results contrast with the proposed biological importance of the HMW multimer. This suggests that the LMW isoform may functionally compensate for some of the loss or reduction of the higher-order multimers in carriers of the G45R and R55C mutations.

Analysis of Whole Exome Sequencing with Cardiometabolic Traits Using Family-Based Linkage and Association in the IRAS Family Study

Family-based methods are a potentially powerful tool to identify trait-defining genetic variants in extended families, particularly when used to complement conventional association analysis. We utilized two-point linkage analysis and single variant association analysis to evaluate whole exome sequencing (WES) data from 1205 Hispanic Americans (78 families) from the Insulin Resistance Atherosclerosis Family Study. WES identified 211,612 variants above the minor allele frequency threshold of ≥0.005. These variants were tested for linkage and/or association with 50 cardiometabolic traits after quality control checks. Two-point linkage analysis yielded 10,580,600 logarithm of the odds (LOD) scores with 1148 LOD scores ≥3, 183 LOD scores ≥4, and 29 LOD scores ≥5. The maximal novel LOD score was 5.50 for rs2289043:T>C, in UNC5C with subcutaneous adipose tissue volume. Association analysis identified 13 variants attaining genome-wide significance (P < 5 × 10^-08 ), with the strongest association between rs651821:C>T in APOA5 and triglyceride levels (P  =  3.67 × 10^-10 ). Overall, there was a 5.2-fold increase in the number of informative variants detected by WES compared to exome chip analysis in this population, nearly 30% of which were novel variants relative to the Database of Single Nucleotide Polymorphisms (dbSNP) build 138. Thus, integration of results from two-point linkage and single-variant association analysis from WES data enabled identification of novel signals potentially contributing to cardiometabolic traits.

Impact of dipeptidyl peptidase-4 inhibitors on serum adiponectin: a meta-analysis

BACKGROUND

Adiponectin, an adipose-specific protein, is negatively correlated with pro-atherogenic low-density lipoprotein cholesterol (LDL-C) and other cardiovascular risk factors such as insulin resistance. Therefore, low levels of adiponectin are associated with a higher risk for diabetes and cardiovascular disease. Dipeptidyl peptidase-4 inhibitors (DPP4i) have been used for the treatment of type 2 diabetes mellitus (T2DM) as reversible inhibitors through interacting with DPP4 substrate and increase serum incretins such as glucagon-like peptide-1 (GLP-1). The present study aimed to evaluate the effect of DPP4i on serum adiponectin in T2DM patients.

METHODS

The PubMed, Embase, and Cochrane library databases were searched from inception to February 2016. Randomized controlled trials, evaluating the DPP4i (sitagliptin and vildagliptin) versus comparator (placebo or active-comparison), in T2DM patients with duration of ≥ 12 weeks, were identified. Weighted differences in means of adiponectin levels were calculated by using a fixed or random-effects model.

RESULTS

Ten randomized controlled trials, including 1,495 subjects, were identified. Compared with placebo, DPP4i (sitagliptin and vildagliptin) treatment significantly elevated adiponectin levels by 0.74 μg/mL (95% confidence interval [CI], 0.45 to 1.03) relative to that using an active-comparison by 0.00 μg/mL (95% CI, -0.57 to 0.56). Compared with active-comparison, vildagliptin treatment increased adiponectin levels by 0.32 μg/mL (95% CI, -0.01 to 0.65), whereas sitagliptin treatment decreased adiponectin levels by -0.24 μg/mL (95% CI, -1.07 to 0.58). Trials examining effects of other DPP4i were not found.

CONCLUSIONS

Sitagliptin and vildagliptin increased serum adiponectin levels and had no stronger effect than traditional oral antidiabetic drugs. Further trials with larger sample size are needed to confirm the results and investigate the association between serum adiponectin levels and treatment of other DPP-4 inhibitors.

TRIAL REGISTRATION

Registration No in PROSPERO: CRD42016037399 .

Effects of adiponectin polymorphisms on the risk of advanced age-related macular degeneration

OBJECTIVE

To determine the relationships between variants in adiponectin gene (ADIPOQ) with advanced forms of age-related macular degeneration (AMD) susceptibility.

METHODS

A total of 189 advanced AMD patients and 168 controls were recruited. Seven tagging single-nucleotide polymorphisms in ADIPOQ were genotyped by the SNaPshot method.

RESULTS

Alleles or genotypes of rs822396 distributed significantly differently in advanced AMD patients and controls. The minor allele G at rs822396 was associated with an increased risk of advanced AMD in a dominant model. Furthermore, haplotype analysis revealed that haplotypes AGGACCT and TGACCCC were significantly increased the advanced AMD susceptibility, whereas haplotypes AGAACGC, TGAACGT and TGACAGC had protective effects.

CONCLUSION

ADIPOQ genetic variant rs822396 might affect an individual's susceptibility to AMD, making it efficient genetic biomarkers for early detection of AMD.

Genetic variants of CDH13 determine the susceptibility to chronic obstructive pulmonary disease in a Chinese population

AIM

Adiponectin has been implicated in the development of chronic obstructive pulmonary disease (COPD). The CDH13 gene encodes T-cadherin that is an adiponectin receptor, and genetic variants of CDH13 determine blood adiponectin levels. The aim of this study was to investigate the effects of CDH13 variants on COPD susceptibility in a Chinese population.

METHODS

Ten single-nucleotide polymorphisms (SNP) in CDH13 were screened using the SNaPshot method in 279 COPD patients and 367 control subjects. Association of genotypes or haplotypes constructed from these loci with COPD was analyzed in different genetic models.

RESULTS

Among the 10 SNPs tested, rs4783244 and rs12922394 exhibited significant differences in allele or genotype frequencies between COPD patients and control subjects, whereas 8 other SNPs did not. The minor allele T was associated with decreased risk of COPD in the recessive model at rs4783244 (OR=0.42, P=0.023) and in the dominant model at rs12922394 (OR=0.70, P=0.022). The genotype TT at either rs4783244 or rs12922394 was associated with a significantly low level of plasma adiponectin when compared to genotypes GG and CC (P<0.05). Haplotypes GC in block 1 (rs4783244-rs12922394) as well as GTAC and ATGT in block 3 (rs4783266-rs11640522-rs11646849-rs11860282) significantly increased the risk of COPD, whereas haplotypes TT in block 1, TG in block 2 (rs11646011- rs11640875) and ATGC in block 3 were protective against COPD.

CONCLUSION

CDH13 genetic variants determine Chinese individuals' susceptibility to COPD and thus are efficient genetic biomarkers for early detection of COPD.

Empirical characteristics of family-based linkage to a complex trait: the ADIPOQ region and adiponectin levels

We previously identified a low-frequency (1.1 %) coding variant (G45R; rs200573126) in the adiponectin gene (ADIPOQ) which was the basis for a multipoint microsatellite linkage signal (LOD = 8.2) for plasma adiponectin levels in Hispanic families. We have empirically evaluated the ability of data from targeted common variants, exome chip genotyping, and genome-wide association study data to detect linkage and association to adiponectin protein levels at this locus. Simple two-point linkage and association analyses were performed in 88 Hispanic families (1,150 individuals) using 10,958 SNPs on chromosome 3. Approaches were compared for their ability to map the functional variant, G45R, which was strongly linked (two-point LOD = 20.98) and powerfully associated (p value = 8.1 × 10(-50)). Over 450 SNPs within a broad 61 Mb interval around rs200573126 showed nominal evidence of linkage (LOD > 3) but only four other SNPs in this region were associated with p values < 1.0 × 10(-4). When G45R was accounted for, the maximum LOD score across the interval dropped to 4.39 and the best p value was 1.1 × 10(-5). Linked and/or associated variants ranged in frequency (0.0018-0.50) and type (coding, non-coding) and had little detectable linkage disequilibrium with rs200573126 (r (2) < 0.20). In addition, the two-point linkage approach empirically outperformed multipoint microsatellite and multipoint SNP analysis. In the absence of data for rs200573126, family-based linkage analysis using a moderately dense SNP dataset, including both common and low-frequency variants, resulted in stronger evidence for an adiponectin locus than association data alone. Thus, linkage analysis can be a useful tool to facilitate identification of high-impact genetic variants.

Influence of serum adiponectin level and SNP +45 polymorphism of adiponectin gene on myocardial fibrosis

Adiponectin plays an important role in the development of hypertension, atherosclerosis, and cardiomyocyte hypertrophy, but very little was known about the influence of serum adiponectin or the adiponectin gene polymorphism on myocardial fibrosis. Our study investigates the influence of the SNP +45 polymorphism of the adiponectin gene and serum levels of adiponectin on myocardial fibrosis in patients with essential hypertension. A case-control study was conducted on 165 hypertensive patients and 126 normotensive healthy controls. The genotypes of adiponectin gene polymorphisms were detected by the polymerase chain reaction (PCR) method. Serum concentrations of procollagen were measured by a double antibody sandwich enzyme-linked immunosorbent assay (ELISA) in all subjects. The integrated backscatter score (IBS) was measured in the left ventricular myocardium using echocardiography. The serum levels of adiponectin in hypertensive patients were significantly lower than those in the normal control group ((2.69±1.0) μg/ml vs. (4.21±2.89) μg/ml, respectively, P<0.001). The serum levels of type-I procollagen carboxyl end peptide (PICP) and type-III procollagen ammonia cardinal extremity peptide (PIIINP) in the hypertension group were significantly higher than those in the control group. In the hypertension group, serum levels of adiponectin were significantly and negatively related to the average acoustic intensity and corrected acoustic intensity of the myocardium (r=0.46 and 0.61, respectively, P<0.05 for both). The serum levels of PICP and PIIINP were significantly different among the three genotypes of SNP +45 (P<0.01). Logistic regression analyses showed that sex and genotype (GG+GT) were the major risk factors of myocardial fibrosis in hypertensive patients (OR=5.343 and 3.278, respectively, P<0.05). These data suggest that lower levels of adiponectin and SNP +45 polymorphism of the adiponectin gene are likely to play an important role in myocardial fibrosis in hypertensive patients.

Genetic analysis of adiponectin variation and its association with type 2 diabetes in African Americans

OBJECTIVE

Adiponectin is an adipocytokine that has been implicated in a variety of metabolic disorders, including T2D and cardiovascular disease. Studies evaluating genetic variants in ADIPOQ have been contradictory when testing association with T2D in different ethnic groups.

DESIGN AND METHODS

In this study, 18 SNPs in ADIPOQ were tested for association with plasma adiponectin levels and diabetes status. SNPs were examined in two independent African-American cohorts (nmax = 1,116) from the Insulin Resistance Atherosclerosis Family Study (IRASFS) and the African American-Diabetes Heart Study (AA-DHS).

RESULTS

Five polymorphisms were nominally associated with plasma adiponectin levels in the meta-analysis (P = 0.035-1.02 × 10(-6) ) including a low frequency arginine to cysteine mutation (R55C) which reduced plasma adiponectin levels to <15% of the mean. Variants were then tested for association with T2D in a meta-analysis of these and the Wake Forest T2D case-control study (n = 3,233 T2D, 2645 non-T2D). Association with T2D was not observed (P ≥ 0.08), suggesting limited influence of ADIPOQ variants on T2D risk.

CONCLUSIONS

Despite identification of variants associated with adiponectin levels, a detailed genetic analysis of ADIPOQ revealed no association with T2D risk. This puts into question the role of adiponectin in T2D pathogenesis: whether low adiponectin levels are truly causal for or rather a consequence.

Association of adiponectin promoter variants with traits and clusters of metabolic syndrome in Arabs: family-based study

Plasma levels of adiponectin are decreased in type 2 diabetes, obesity and hypertension. Our aim was to use a family-based analysis to identify the genetic variants of the adiponectin (ADIPOQ) gene that are associated with obesity, insulin resistance, dyslipidemia and hypertension, among Arabs. We screened 328 Arabs in one large extended family for single nucleotide polymorphisms (SNPs) in the promoter region of the ADIPOQ gene. Two common SNPs were detected: rs17300539 and rs266729. Evidences of association between traits related to the metabolic syndrome and the SNPs were studied by implementing quantitative genetic association analysis. Results showed that SNP rs266729 was significantly associated with body weight (p-value=0.001), waist circumference (p-value=0.037), BMI (p-value=0.015) and percentage of total body fat (p-value=0.003). Up to 4.1% of heritability of obesity traits was explained by the rs266729 locus. Further cross-sectional analysis showed that carriers of the G allele had significantly higher values of waist circumference, BMI and percentage of total body fat (p-values 0.014, 0.004 and 0.032, respectively). No association was detected between SNP rs266729 and other clusters of metabolic syndrome or their traits except for HOMA-IR and fasting plasma insulin levels, p-values 0.035 and 0.004, respectively. In contrast, both measured genotype and cross-sectional analysis failed to detect an association between the SNP rs17300539 with traits and clusters of metabolic syndrome. In conclusion, we showed family-based evidence of association of SNP rs266729 at ADIPOQ gene with traits defining obesity in Arab population. This is important for future prediction and prevention of obesity in population where obesity is in an increasing trend.

Genetic polymorphisms of the main transcription factors for adiponectin gene promoter in regulation of adiponectin levels: association analysis in three European cohorts

Adiponectin serum concentrations are an important biomarker in cardiovascular epidemiology with heritability etimates of 30–70%. However, known genetic variants in the adiponectin gene locus (ADIPOQ) account for only 2%–8% of its variance. As transcription factors are thought to play an under-acknowledged role in carrying functional variants, we hypothesized that genetic polymorphisms in genes coding for the main transcription factors for the ADIPOQ promoter influence adiponectin levels. Single nucleotide polymorphisms (SNPs) at these genes were selected based on the haplotype block structure and previously published evidence to be associated with adiponectin levels. We performed association analyses of the 24 selected SNPs at forkhead box O1 (FOXO1), sterol-regulatory-element-binding transcription factor 1 (SREBF1), sirtuin 1 (SIRT1), peroxisome-proliferator-activated receptor gamma (PPARG) and transcription factor activating enhancer binding protein 2 beta (TFAP2B) gene loci with adiponectin levels in three different European cohorts: SAPHIR (n = 1742), KORA F3 (n = 1636) and CoLaus (n = 5355). In each study population, the association of SNPs with adiponectin levels on log-scale was tested using linear regression adjusted for age, sex and body mass index, applying both an additive and a recessive genetic model. A pooled effect size was obtained by meta-analysis assuming a fixed effects model. We applied a significance threshold of 0.0033 accounting for the multiple testing situation. A significant association was only found for variants within SREBF1 applying an additive genetic model (smallest p-value for rs1889018 on log(adiponectin) = 0.002, β on original scale = −0.217 µg/ml), explaining ∼0.4% of variation of adiponectin levels. Recessive genetic models or haplotype analyses of the FOXO1, SREBF1, SIRT1, TFAPB2B genes or sex-stratified analyses did not reveal additional information on the regulation of adiponectin levels. The role of genetic variations at the SREBF1 gene in regulating adiponectin needs further investigation by functional studies.

Association between ADIPOQ SNPs with plasma adiponectin and glucose homeostasis and adiposity phenotypes in the IRAS Family Study

CONTEXT

Adiponectin is an adipocytokine associated with a variety of metabolic traits. These associations in human studies, in conjunction with functional studies in model systems, have implicated adiponectin in multiple metabolic processes.

OBJECTIVE

We hypothesize that genetic variants associated with plasma adiponectin would also be associated with glucose homeostasis and adiposity phenotypes.

DESIGN AND SETTING

The Insulin Resistance Atherosclerosis Family Study was designed to identify the genetic and environmental basis of insulin resistance and adiposity in the Hispanic- (n=1,424) and African-American (n=604) population.

MAIN OUTCOME MEASURES

High quality metabolic phenotypes, e.g. insulin sensitivity (S(I)), acute insulin response (AIR), disposition index (DI), fasting glucose, body mass index (BMI), visceral adipose tissue (VAT), subcutaneous adipose tissue (SAT), and waist circumference, were explored.

RESULTS

Based on association analysis of more than 40 genetic polymorphisms in the adiponectin gene (ADIPOQ), we found no consistent association of ADIPOQ variants with plasma adiponectin levels and adiposity phenotypes. However, there were two promoter variants, rs17300539 and rs822387, associated with plasma adiponectin levels (P=0.0079 and 0.021, respectively) in the Hispanic-American cohort that were also associated with S(I) (P=0.0067 and 0.013, respectively). In contrast, there was only a single promoter SNP, rs17300539, associated with plasma adiponectin levels (P=0.0018) and fasting glucose (P=0.042) in the African-American cohort. Strikingly, high impact coding variants did not show evidence of association.

CONCLUSIONS

The lack of consistent patterns of association between variants, adiponectin levels, glucose homeostasis, and adiposity phenotypes suggests a reassessment of the influence of adiponectin in these pathways.

Genetic variations in ADIPOQ gene are associated with chronic obstructive pulmonary disease

BACKGROUND

Adiponectin is reported to be related to the development of chronic obstructive pulmonary disease (COPD). Genetic variants in the gene encoding adiponectin (ADIPOQ) have been reported to be associated with adiponectin level in several genome-wide linkage and association studies. However, relatively little is known about the effects of ADIPOQ gene variants on COPD susceptibility. We determined the frequencies of single-nucleotide polymorphisms (SNPs) in ADIPOQ in a Chinese Han population and their possible association with COPD susceptibility.

METHODS

We conducted a case-control study of 279 COPD patients and 367 age- and gender-distribution-matched control subjects. Seven tagging SNPs in ADIPOQ, including rs710445, rs16861205, rs822396, rs7627128, rs1501299, rs3821799 and rs1063537 were genotyped by SNaPshot. Association analysis of genotypes/alleles and haplotypes constructed from these loci with COPD was conducted under different genetic models.

RESULTS

The alleles or genotypes of rs1501299 distributed significantly differently in COPD patients and controls (allele: P = 0.002, OR = 1.43 and 95%CI = 1.14-1.79; genotype: P = 0.008). The allele A at rs1501299 was potentially associated with an increased risk of COPD in all dominant model analysis (P = 0.009; OR: 1.54; 95%CI: 1.11-2.13), recessive model analyses (P = 0.015; OR: 1.75; 95% CI: 1.11-2.75) and additive model analyses (P = 0.003; OR: 2.11; 95% CI: 1.29-3.47). In haplotype analysis, we observed haplotypes AAAAACT and GGACCTC had protective effects, while haplotypes AGAACTC, AGGCCTC, GGAACTC, GGACACT and GGGCCTC were significantly associated with the increased risk of COPD.

CONCLUSIONS

We conducted the first investigation of the association between the SNPs in ADIPOQ and COPD risk. Our current findings suggest that ADIPOQ may be a potential risk gene for COPD. Further studies in larger groups are warranted to confirm our results.

Estimating the contributions of rare and common genetic variations and clinical measures to a model trait: adiponectin

Common genetic variation frequently accounts for only a modest amount of interindividual variation in quantitative traits and complex disease susceptibility. Circulating adiponectin, an adipocytokine implicated in metabolic disease, is a model for assessing the contribution of genetic and clinical factors to quantitative trait variation. The adiponectin locus, ADIPOQ, is the primary source of genetically mediated variation in plasma adiponectin levels. This study sought to define the genetic architecture of ADIPOQ in the comprehensively phenotyped Hispanic (n = 1,151) and African American (n = 574) participants from the Insulin Resistance Atherosclerosis Family Study (IRASFS). Through resequencing and bioinformatic analysis, rare/low frequency (<5% MAF) and common variants (>5% MAF) in ADIPOQ were identified. Genetic variants and clinical variables were assessed for association with adiponectin levels and contribution to adiponectin variance in the Hispanic and African American cohorts. Clinical traits accounted for the greatest proportion of variance (POV) at 31% (P = 1.16 × 10-(47)) and 47% (P = 5.82 × 10-(20)), respectively. Rare/low frequency variants contributed more than common variants to variance in Hispanics: POV = 18% (P = 6.40 × 10-(15)) and POV = 5% (P = 0.19), respectively. In African Americans, rare/low frequency and common variants both contributed approximately equally to variance: POV = 6% (P = 5.44 × 10-(12)) and POV = 9% (P = 1.44 × 10-(10)), respectively. Importantly, single low frequency alleles in each ethnic group were as important as, or more important than, common variants in explaining variation in adiponectin. Cumulatively, these clinical and ethnicity-specific genetic contributors explained half or more of the variance in Hispanic and African Americans and provide new insight into the sources of variation for this important adipocytokine.

Linkage analysis in the next-generation sequencing era

Linkage analysis was developed to detect excess co-segregation of the putative alleles underlying a phenotype with the alleles at a marker locus in family data. Many different variations of this analysis and corresponding study design have been developed to detect this co-segregation. Linkage studies have been shown to have high power to detect loci that have alleles (or variants) with a large effect size, i.e. alleles that make large contributions to the risk of a disease or to the variation of a quantitative trait. However, alleles with a large effect size tend to be rare in the population. In contrast, association studies are designed to have high power to detect common alleles which tend to have a small effect size for most diseases or traits. Although genome-wide association studies have been successful in detecting many new loci with common alleles of small effect for many complex traits, these common variants often do not explain a large proportion of disease risk or variation of the trait. In the past, linkage studies were successful in detecting regions of the genome that were likely to harbor rare variants with large effect for many simple Mendelian diseases and for many complex traits. However, identifying the actual sequence variant(s) responsible for these linkage signals was challenging because of difficulties in sequencing the large regions implicated by each linkage peak. Current 'next-generation' DNA sequencing techniques have made it economically feasible to sequence all exons or the whole genomes of a reasonably large number of individuals. Studies have shown that rare variants are quite common in the general population, and it is now possible to combine these new DNA sequencing methods with linkage studies to identify rare causal variants with a large effect size. A brief review of linkage methods is presented here with examples of their relevance and usefulness for the interpretation of whole-exome and whole-genome sequence data.

ADIPOQ, ADIPOR1, and ADIPOR2 polymorphisms in relation to serum adiponectin levels and BMI in black and white women

Adiponectin is an adipose-secreted protein with influence on several physiologic pathways including those related to insulin sensitivity, inflammation, and atherogenesis. Adiponectin levels are highly heritable and several single-nucleotide polymorphisms (SNPs) in adiponectin-related genes (ADIPOQ, ADIPOR1, ADIPOR2) have been examined in relation to circulating adiponectin levels and obesity phenotypes, but despite differences in adiponectin levels and obesity prevalence by race, few studies have included black participants. Using cross-sectional interview data and blood samples collected from 990 black and 977 white women enrolled in the Southern Community Cohort Study (SCCS) from 2002 to 2006, we examined 25 SNPs in ADIPOQ, 19 in ADIPOR1, and 27 in ADIPOR2 in relation to serum adiponectin levels and BMI using race-stratified linear regression models adjusted for age and percentage African ancestry. SNP rs17366568 in ADIPOQ was significantly associated with serum adiponectin levels in white women only (adjusted mean adiponectin levels = 15.9 for G/G genotype, 13.7 for A/G, and 9.3 for A/A, P = 0.00036). No other SNPs were associated with adiponectin or BMI among blacks or whites. Because adiponectin levels as well as obesity are highly heritable and vary by race but associations with polymorphisms in the ADIPOQ, ADIPOR1, and ADIPOR2 genes have been few in this and other studies, future work including large populations from diverse racial groups is needed to detect additional genetic variants that influence adiponectin and BMI.

Variations in Adipokine Genes AdipoQ, Lep, and LepR are Associated with Risk for Obesity-Related Metabolic Disease: The Modulatory Role of Gene-Nutrient Interactions

Obesity rates are rapidly increasing worldwide and facilitate the development of many related disease states, such as cardiovascular disease, the metabolic syndrome, type 2 diabetes mellitus, and various types of cancer. Variation in metabolically important genes can have a great impact on a population's susceptibility to becoming obese and/or developing related complications. The adipokines adiponectin and leptin, as well as the leptin receptor, are major players in the regulation of body energy homeostasis and fat storage. This paper summarizes the findings of single nucleotide polymorphisms in these three genes and their effect on obesity and metabolic disease risk. Additionally, studies of gene-nutrient interactions involving adiponectin, leptin, and the leptin receptor are highlighted to emphasize the critical role of diet in susceptible populations.

Molecular basis of a linkage peak: exome sequencing and family-based analysis identify a rare genetic variant in the ADIPOQ gene in the IRAS Family Study

Family-based linkage analysis has been a powerful tool for identification of genes contributing to traits with monogenic patterns of inheritance. These approaches have been of limited utility in identification of genes underlying complex traits. In contrast, searches for common genetic variants associated with complex traits have been highly successful. It is now widely recognized that common variations frequently explain only part of the inter-individual variation in populations. 'Rare' genetic variants have been hypothesized to contribute significantly to phenotypic variation in the population. We have developed a combination of family-based linkage, whole-exome sequencing, direct sequencing and association methods to efficiently identify rare variants of large effect. Key to the successful application of the method was the recognition that only a few families in a sample contribute significantly to a linkage signal. Thus, a search for mutations can be targeted to a small number of families in a chromosome interval restricted to the linkage peak. This approach has been used to identify a rare (1.1%) G45R mutation in the gene encoding adiponectin, ADIPOQ. This variant explains a strong linkage signal (LOD > 8.0) and accounts for ∼17% of the variance in plasma adiponectin levels in a sample of 1240 Hispanic Americans and 63% of the variance in families carrying the mutation. Individuals carrying the G45R mutation have mean adiponectin levels that are 19% of non-carriers. We propose that rare variants may be a common explanation for linkage peaks observed in complex trait genetics. This approach is applicable to a wide range of family studies and has potential to be a discovery tool for identification of novel genes influencing complex traits.

Suggestion for linkage of chromosome 1p35.2 and 3q28 to plasma adiponectin concentrations in the GOLDN Study

BACKGROUND

Adiponectin is inversely associated with obesity, insulin resistance, and atherosclerosis, but little is known about the genetic pathways that regulate the plasma level of this protein. To find novel genes that influence circulating levels of adiponectin, a genome-wide linkage scan was performed on plasma adiponectin concentrations before and after 3 weeks of treatment with fenofibrate (160 mg daily) in the Genetics of Lipid Lowering Drugs and Diet Network (GOLDN) Study. We studied Caucasian individuals (n = 1121) from 190 families in Utah and Minnesota. Of these, 859 individuals from 175 families had both baseline and post-fenofibrate treatment measurements for adiponectin. Plasma adiponectin concentrations were measured with an ELISA assay. All participants were typed for microsatellite markers included in the Marshfield Mammalian Genotyping Service marker set 12, which includes 407 markers spaced at approximately 10 cM regions across the genome. Variance components analysis was used to estimate heritability and to perform genome-wide scans. Adiponectin was adjusted for age, sex, and field center. Additional models also included BMI adjustment.

RESULTS

Baseline and post-fenofibrate adiponectin measurements were highly correlated (r = 0.95). Suggestive (LOD > 2) peaks were found on chromosomes 1p35.2 and 3q28 (near the location of the adiponectin gene).

CONCLUSION

Two candidate genes, IL22RA1 and IL28RA, lie under the chromosome 1 peak; further analyses are needed to identify the specific genetic variants in this region that influence circulating adiponectin concentrations.

Adiponectin and its association with insulin resistance and type 2 diabetes

Adiponectin is an adipokine, which is expressed in adipose tissue and is thought to play an important role in glucose metabolism. Hypoadiponectinemia can cause reduction of fatty acid oxidation, decreased glucose uptake in skeletal muscle cells, and increased gluconeogenesis in hepatic cells. The level of plasma glucose can be increased. On the other hand, the decrease of fatty acid oxidation increases the level of free fatty acid (FFA), which increases the insulin resistance, and then decreases the glucose uptake, which ultimately causes increased plasma glucose and type 2 diabetes (T2D). This review describes the process from hypoadiponectinemia to T2D and the genesis of hypoadiponectinemia at a molecular level.

Genome-wide linkage and association analyses to identify genes influencing adiponectin levels: the GEMS Study

Adiponectin has a variety of metabolic effects on obesity, insulin sensitivity, and atherosclerosis. To identify genes influencing variation in plasma adiponectin levels, we performed genome-wide linkage and association scans of adiponectin in two cohorts of subjects recruited in the Genetic Epidemiology of Metabolic Syndrome Study. The genome-wide linkage scan was conducted in families of Turkish and southern European (TSE, n = 789) and Northern and Western European (NWE, N = 2,280) origin. A whole genome association (WGA) analysis (500K Affymetrix platform) was carried out in a set of unrelated NWE subjects consisting of approximately 1,000 subjects with dyslipidemia and 1,000 overweight subjects with normal lipids. Peak evidence for linkage occurred at chromosome 8p23 in NWE subjects (lod = 3.10) and at chromosome 3q28 near ADIPOQ, the adiponectin structural gene, in TSE subjects (lod = 1.70). In the WGA analysis, the single-nucleotide polymorphisms (SNPs) most strongly associated with adiponectin were rs3774261 and rs6773957 (P < 10(-7)). These two SNPs were in high linkage disequilibrium (r(2) = 0.98) and located within ADIPOQ. Interestingly, our fourth strongest region of association (P < 2 x 10(-5)) was to an SNP within CDH13, whose protein product is a newly identified receptor for high-molecular-weight species of adiponectin. Through WGA analysis, we confirmed previous studies showing SNPs within ADIPOQ to be strongly associated with variation in adiponectin levels and further observed these to have the strongest effects on adiponectin levels throughout the genome. We additionally identified a second gene (CDH13) possibly influencing variation in adiponectin levels. The impact of these SNPs on health and disease has yet to be determined.

Genome-wide linkage analysis for circulating levels of adipokines and C-reactive protein in the Quebec family study (QFS)

Adipose tissue synthesizes and secretes a wide range of biologically active molecules considered as inflammatory markers whose dysregulation in obesity plays a role in the development of insulin resistance and vascular disorders. Thus, finding genes that influence circulating levels of inflammatory biomarkers may provide insights into the genetic determinants of obesity-related metabolic diseases. We performed linkage analyses for fasting plasma levels of adiponectin, C-reactive protein (CRP), interleukin-6 (IL-6) and tumor-necrosis factor-alpha (TNF-alpha) in 764 subjects enrolled in the Quebec family study (QFS). A maximum of 393 pairs of siblings from 211 nuclear families were available for analyses. A total of 443 markers spanning the 22 autosomal chromosomes with an average inter-marker distance of 6.24 Mb were genotyped. Linkage was tested using both allele-sharing (SIBPAL) and variance component linkage methods (MERLIN). We showed suggestive evidence of linkage for plasma adiponectin levels on chromosome 15q21.1 [D15S659; logarithm of the odds (LOD) score = 2.23], 3q13.33 (D3S3023; LOD = 2.09), 20q13.2 (D20S197; LOD = 1.96) and 14q32.2 (D14S1426; LOD = 1.79). Evidence of linkage (SIBPAL) was also found for CRP on 12p11.23 (P = 0.001) and 12q15 (P = 0.0005) and for IL-6 on 14q12 (P = 0.002). None of these linkages remained significant after adjustment for body mass index. No evidence of linkage was found for TNF-alpha plasma levels. These results suggest that several QTLs can influence plasma levels of adiponectin and CRP, partly via their effects on adiposity.

Associations of adiponectin with body fat distribution and insulin sensitivity in nondiabetic Hispanics and African-Americans

CONTEXT

Hypoadiponectinemia has emerged as an independent risk factor for type 2 diabetes and cardiovascular disease. Although associations of adiponectin with central obesity and insulin resistance have been reported, very little data are available from studies using detailed measures of insulin sensitivity (S(I)) and/or body fat distribution in ethnic groups at high risk for metabolic disease.

OBJECTIVE

The aim of the study was to identify the correlates of adiponectin in 1636 nondiabetic Hispanics and African-Americans.

DESIGN

A cross-sectional analysis of participants in the Insulin Resistance Atherosclerosis Family Study was conducted. S(I) was determined from frequently sampled iv glucose tolerance tests with minimal model analysis. Subcutaneous and visceral adipose tissues (SAT, VAT, respectively) were determined with computed tomography. Triglyceride, high-density lipoprotein, C-reactive protein, and adiponectin were measured in fasting samples. Generalized estimating equation (GEE) models were used to identify factors associated with adiponectin concentration.

SETTING

A multicenter study using a family-based design was conducted.

PARTICIPANTS

A total of 1636 nondiabetic Hispanic and African-American subjects participated.

MAIN OUTCOME MEASURES

Circulating adiponectin concentration was measured.

RESULTS

Age, female gender, high-density lipoprotein, SAT, and S(I) were positive independent correlates of adiponectin, whereas glucose, CRP, and VAT were negative independent correlates (all P < 0.05). Ethnicity was not an independent correlate of adiponectin in this model (P = 0.27); however, an ethnicity by VAT interaction term was retained, indicating a stronger negative association of VAT with adiponectin in African-Americans compared with Hispanics.

CONCLUSION

Directly measured S(I), VAT, and SAT were independently correlated with adiponectin in Hispanic and African-American subjects. The inverse association of VAT with adiponectin was stronger in African-Americans compared with Hispanics, a finding that suggests possible ethnic differences in the effects of visceral obesity.

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.

Genetic influences of adiponectin on insulin resistance, type 2 diabetes, and cardiovascular disease

Recent evidence points to molecules secreted by the adipose tissue, or adipokines, as possible links between increased adipose mass and metabolic abnormalities. Among these molecules, adiponectin has drawn much attention because of its insulin-sensitizing and antiatherogenic actions, suggesting that genetic deficits in its production or action may contribute to insulin resistance and coronary artery disease (CAD). A meta-analysis of the data published to date supports this hypothesis. Two independent effects, corresponding to the two linkage disequilibrium blocks that can be identified at the adiponectin locus, appear to be present. In the 5' block, the g.-11391G-->A variant has a modest but significant effect on adiponectinemia, with a mean difference between genotypes of 1.64 ng/ml (95% CI 0.88-2.41). In the 3' block, the g.+276G-->T variant is a strong determinant of insulin resistance and CAD, with minor allele homozygotes having a lower homeostasis model assessment of insulin resistance (HOMA(IR)) index (-0.36 units, 95% CI 0.24-0.47) and a lower cardiovascular risk (odds ratio 0.55, 95% CI 0.38-0.80) than carriers of other genotypes. No consistent effect on BMI or risk of type 2 diabetes is evident. Polymorphisms in the genes coding for the adiponectin receptors may also influence the risk of insulin resistance and CAD, but data on these genes are still too sparse to draw firm conclusions. In summary, the studies published to date indicate that polymorphisms at the adiponectin locus are indeed predictors of circulating adiponectin levels, insulin sensitivity, and atherosclerosis, highlighting the pivotal role of this adipokine in the modulation of metabolism and atherogenesis.

Metabolic syndrome pathophysiology: the role of adipose tissue

Several pathophysiological explanations for the metabolic syndrome have been proposed involving insulin resistance, chronic inflammation and ectopic fat accumulation following adipose tissue saturation. However, current concepts create several paradoxes, including limited cardiovascular risk reduction with intensive glucose control in diabetics, therapies that result in weight gain (PPAR agonists), and presence of some of the metabolic traits among some lipodystrophies. We propose the functional failure of an organ, in this case, the adipose tissue as a model to interpret its manifestations and to reconcile some of the apparent paradox. A cornerstone of this model is the failure of the adipose tissue to buffer postprandial lipids. In addition, homeostatic feedback loops guide physiological and pathological adipose tissue activities. Fat turnover is determined by a complex equilibrium in which insulin is a main factor but not the only one. Chronically inadequate energy balance may be a key factor, stressing the system. In this situation, an adipose tissue functional failure occurs resulting in changes in systemic energy delivery, impaired glucose consumption and activation of self-regulatory mechanisms that extend their influence to whole body homeostasis system. These include changes in adipokines secretion and vascular effects. The functional capacity of the adipose tissue varies among subjects explaining the incomplete overlapping among the metabolic syndrome and obesity. Variations at multiple gene loci will be partially responsible for these interindividual differences. Two of those candidate genes, the adiponectin (APM1) and the perilipin (PLIN) genes, are discussed in more detail.

Common adiponectin gene variants show different effects on risk of cardiovascular disease and type 2 diabetes in European subjects

Alterations in the secretion of adipokines may explain the link between obesity, type 2 diabetes (T2DM) and coronary artery disease (CAD). These conditions have been associated with variation in the adiponectin gene, although evidence for this relationship has been variable, with differences found even in similar samples. This study aims to clarify these inconsistencies by determining the impact of identified adiponectin gene (ADIPOQ) variants (-11391G>A,-1377C>G[promoter] and +45T>G[exon 2] and +276G>T[intron 2]) on the prospective risk of CAD and T2DM in healthy men, and on adverse metabolic markers, in myocardial infarct survivors and controls from different parts of Europe. The hazard ratio for cardiovascular disease varied across the -11391GG/GA/AA(p = 0.03) and -11371CC/CG/GG(p = 0.05) genotypes only. In contrast, only the +45T>G variant (3.80[1.76-8.24]) was associated with T2DM, while two haplotypes GCTT/GCGG (p < 0.05) and +276G>T(p = 0.01) increased risk in interaction with obesity. The variants were associated with a number of biomarkers in Southern but not Northern Europe (p = 0.01), despite no significant differences in allele or haplotype frequencies (p > 0.44). A risk haplotype could not be identified in either sample. Adiponectin gene variants are hence currently poor markers for the development of T2DM and CAD. Their influence on risk depends significantly on interactions that are not currently understood with either genetic variation elsewhere or the environment of the sample studied.

Genetic analysis of adiponectin and obesity in Hispanic families: the IRAS Family Study

Adiponectin, coded for by the APM1 gene, is a novel adipocyte-derived hormone implicated in energy homeostasis and obesity. Several genetic studies have observed evidence of association between APM1 gene polymorphisms and features of the metabolic syndrome, such as insulin resistance and obesity. As part of a comprehensive genetic analysis of the APM1 gene, we have screened 96 unrelated individuals for polymorphisms in the promoter, coding regions, and 3'untranslated region (UTR). Three promoter single-nucleotide polymorphisms (SNPs), two rare coding SNPs (G113A and T1233C), and 13 SNPs in the 3'UTR were identified. Eighteen SNPs were genotyped in 811 Hispanic individuals from 45 families in the IRAS Family Study (IRASFS). SNPs were tested for association with six obesity quantitative traits (body mass index, waist, waist:hip ratio, subcutaneous adipose tissue, visceral adipose tissue, and visceral:subcutaneous ratio). Significant evidence of association to at least one of the obesity traits was identified in seven of the 18 SNPs (<0.001-0.05). The promoter SNP INS CA-11156 was the most consistently associated SNP and was associated significantly with all measures of obesity, except the visceral:subcutaneous ratio (P-values 0.009-0.03). Haplotype analysis supported this evidence of association, with haplotypes containing an insertion of one CA repeat at position -11156 consistently being associated with lower obesity values (P-value <0.001-0.05). The adiponectin polymorphisms, in particular those in the promoter region, thus show significant association with obesity measures in the Hispanic population. Additional studies are needed to confirm our findings and determine which polymorphism causes the functional effect.