Impact of polymorphisms of the human beta2-adrenoceptor gene on obesity in a French population

The influence of six polymorphisms of uncoupling protein 3 (UCP3) gene and childhood obesity: a case-control study

BACKGROUND

Obesity is defined as a multifactorial disease, marked by excessive accumulation of body fat, responsible for compromising the individual's health over the years. The energy balance is essential for the proper functioning of the body, as the individual needs to earn and spend energy in a compensatory way. Mitochondrial Uncoupling Proteins (UCP) help in energy expenditure through heat release and genetic polymorphisms could be responsible for reducing energy consumption to release heat and consequently generate an excessive accumulation of fat in the body. Thus, this study aimed to investigate the potential association between six UCP3 polymorphisms, that have not yet been represented in ClinVar®, and pediatric obesity susceptibility.

METHODS

A case-control study was conducted with 225 children from Central Brazil. The groups were subdivided into obese (123) and eutrophic (102) individuals. The polymorphisms rs15763, rs1685354, rs1800849, rs11235972, rs647126, and rs3781907 were determined by real-time Polymerase Chain Reaction (qPCR).

RESULTS

Biochemical and anthropometric evaluation of obese group showed higher levels of triglycerides, insulin resistance, and LDL-C and low level of HDL-C. Insulin resistance, age, sex, HDL-C, fasting glucose, triglyceride levels, and parents' BMI explained up to 50% of body mass deposition in the studied population. Additionally, obese mothers contribute 2 × more to the Z-BMI of their children than the fathers. The SNP rs647126 contributed to 20% to the risk of obesity in children and the SNP rs3781907 contribute to 10%. Mutant alleles of UCP3 increase the risk for triglycerides, total cholesterol, and HDL-C levels. The polymorphism rs3781907 is the only one that could not be a biomarker for obesity as the risk allele seem to be protective gains the increase in Z-BMI in our pediatric population. Haplotype analysis demonstrated two SNP blocks (rs15763, rs647126, and rs1685534) and (rs11235972 and rs1800849) that showed linkage disequilibrium, with LOD 76.3% and D' = 0.96 and LOD 57.4% and D' = 0.97, respectively.

CONCLUSIONS

The causality between UCP3 polymorphism and obesity were not detected. On the other hand, the studied polymorphism contributes to Z-BMI, HOMA-IR, triglycerides, total cholesterol, and HDL-C levels. Haplotypes are concordant with the obese phenotype and contribute minimally to the risk of obesity.

Multiple microRNA regulation of lipoprotein lipase gene abolished by 3'UTR polymorphisms in a triglyceride-lowering haplotype harboring p.Ser474Ter

BACKGROUND

Lipoprotein lipase (LPL) is a key enzyme in triglyceride (TG) metabolism. LPL gene single nucleotide polymorphisms (SNPs) are associated with TG concentrations however the functionality of many of these SNPs remains poorly understood. MicroRNAs (miR) exert post-transcriptional down-regulation and their target sequence on the 3'UTR may be altered by SNPs. We therefore investigated whether LPL 3'UTR SNPs could modulate plasma TG concentration through the alteration of miR binding-sites.

METHODS AND RESULTS

We performed genetic association studies of LPL 3'UTR SNPs with TG concentrations in 271 type 2 diabetic patients and in general population samples (2997 individuals). A specific LPL haplotype (Hap4) was associated with lower plasma TG concentration (TG-0.18, IC95% [-0.30, -0.07] mmol/L or logTG-0.13, IC95% [-0.18, -0.08], p = 4.77·10(-8)) in the meta-analysis. Hap4 comprises seven 3'UTR SNP minor alleles and p.Ser474Ter (rs328) a well-documented nonsense mutation associated with low TG concentration although by an unknown mechanism so far. Bio-informatic studies identified several putative miRNA binding-sites on the wild-type Hap1 haplotype, lost on Hap4. Functional validation performed in HEK-293T cells using luciferase expression constructs with various LPL 3'UTR allele combinations demonstrated a binding of miR-29, miR-1277 and miR-410 on Hap1, lost on Hap4. This loss of specific miR binding-site in presence of Hap4 was independent of the allelic variation of p.Ser474Ter (rs328).

CONCLUSIONS

We report the regulation of LPL by the miR-29, miR-1277 and miR-410 that is lost in presence of Hap4, a specific LPL TG-lowering haplotype. Consequently p.Ser474Ter association with TG concentration could be at least partially explained by its strong linkage disequilibrium with these functional 3'UTR SNPs.

Adenylyl Cyclase 9 Polymorphisms Reveal Potential Link to HDL Function and Cardiovascular Events in Multiple Pathologies: Potential Implications in Sickle Cell Disease

Adenylyl cyclase 9 (ADCY9) mediates β2-adrenoceptor (β2-AR) signalling. Both proteins are associated with caveolae, specialized cholesterol-rich membrane substructures. Apolipoprotein A1 (ApoA1), the major protein component of high-density lipoprotein (HDL), removes cholesterol from cell membrane and caveolae and may thereby influence β2-AR signalling, shown in vitro to be modulated by cholesterol. Patients with Sickle Cell Disease (SCD) typically have low HDL and ApoA1 levels. In patients, mainly of African origin, with SCD, β2-AR activation may trigger adhesion of red blood cells to endothelial cells, leading to vascular occlusive events. Moreover, ADCY9 polymorphism is associated with risk of stroke in SCD. In recent clinical trials, ADCY9 polymorphism was found to be a discriminant factor associated with the risk of cardiovascular (CV) events in Caucasian patients treated with the HDL-raising compound dalcetrapib. We hypothesize that these seemingly disparate observations share a common mechanism related to interaction of HDL/ApoA1 and ADCY9 on β2-AR signalling. This review also raises the importance of characterizing polymorphisms that determine the response to HDL-raising and -mimicking agents in the non-Caucasian population at high risk of CV diseases and suffering from SCD. This may facilitate personalized CV treatments.

Influence of ADRB2 Gln27Glu and ADRB3 Trp64Arg polymorphisms on body weight and body composition changes after a controlled weight-loss intervention

The β-2 and β-3 adrenergic receptors (ADRB2 and ADRB3) are thought to play a role in energy expenditure and lipolysis. However, the effects of the ADRB2 glutamine (Gln) 27 glutamic acid (glutamate) (Glu) and ADRB3 tryptophan (Trp) 64 arginine (Arg) polymorphisms on weight loss remain controversial. The aim of this study was to investigate the effect of these polymorphisms on changes in weight and body composition during a controlled weight-loss program. One hundred seventy-three healthy overweight and obese participants (91 women, 82 men) aged 18-50 years participated in a 22-week-long intervention based on a hypocaloric diet and exercise. They were randomly assigned to 1 of 4 groups: strength, endurance, strength and endurance combined, and physical activity recommendations only. Body weight, body mass index (BMI), and body composition variables were assessed before and after the intervention. Genetic analysis was carried out according to standard protocols. No effect of the ADRB2 gene was shown on final weight, BMI, or body composition, although in the supervised male group, Glu27 carriers tended to have greater weight (p = 0.019, 2.5 kg) and BMI (p = 0.019, 0.88 kg/m(2)) reductions than did noncarriers. There seems to be an individual effect of the ADRB3 polymorphism on fat mass (p = 0.004) and fat percentage (p = 0.036), in addition to an interaction with exercise for fat mass (p = 0.038). After the intervention, carriers of the Arg64 allele had a greater fat mass and fat percentage than did noncarriers (p = 0.004, 2.8 kg). In conclusion, the ADRB2 Gln27Glu and ADRB3 Trp64Arg polymorphisms may influence weight loss and body composition, although the current evidence is weak; however, further studies are necessary to clarify their roles.

Association of Gln27Glu and Arg16Gly polymorphisms in Beta2-adrenergic receptor gene with obesity susceptibility: a meta-analysis

BACKGROUND

The beta2-adrenergic receptor (ADRB2) gene polymorphism has been implicated in susceptibility to obesity, but study results are still controversial.

OBJECTIVE

The present meta-analysis is performed to determine whether there are any associations between the Gln27Glu (rs1042714) or the Arg16Gly (rs1042713) polymorphisms in ADRB2 and obesity susceptibility.

METHODS

The PubMed (1950-2014), Embase (1974-2014), and China National Knowledge Infrastructure (CNKI, 1994-2014) databases were searched using the search terms ("Beta2-adrenergic receptor", "β2-adrenergic receptor" or "ADRB2"), "polymorphism," and "obesity". Fixed- or random-effects pooled measures were determined on the bias of heterogeneity tests across studies. Publication bias was examined by Egger's test and the modified Begg's test.

RESULTS

Eighteen published articles were selected for meta-analysis. Overall analyses showed that rs1042714 (Gln27Glu) was associated with significantly increased obesity risk in the heterozygote model (Gln/Glu vs. Gln/Gln: OR: 1.16, 95% CI: 1.04-1.30, I2 = 49%, P = 0.009) and the dominant model (Gln/Glu + Glu/Glu vs. Gln/Gln: OR: 1.2, 95% CI: 1.00-1.44, I2 = 55%, P = 0.04), whereas no significant association was found in the other models for rs1042714. Also, no significant association was found between the rs1042713 (Arg16Gly) gene polymorphism and the risk of obesity in all genetic models. In addition, neither rs1042713 (Arg16Gly) nor rs1042714 (Gln27Glu) showed any significant association with obesity susceptibility when the population were stratified based on gender.

CONCLUSION

Our meta-analysis revealed that the rs1042714 (Gln27Glu) polymorphism is associated with obesity susceptibility. However, our results do not support an association between rs1042713 (Arg16Gly) polymorphisms and obesity in the populations investigated. This conclusion warrants confirmation by more case-control and cohort studies.

Effect of β2-adrenergic receptor polymorphisms on epinephrine and exercise-stimulated lipolysis in humans

The β₂‐adrenergic system is an important regulator of human adipose tissue lipolysis. Polymorphisms that result in amino acid substitutions in the β₂‐adrenergic receptor have been reported to alter lipolysis. We hypothesized that variations in the amino acid at position 16 of the β₂‐adrenergic receptor would result in different lipolytic responses to intravenous epinephrine and exercise. 17 volunteers homozygous for glycine at position 16 (Gly/Gly, nine female) and 16 volunteers homozygous for arginine at position 16 (Arg/Arg, eight female) of the β₂‐adrenergic receptor participated in this study. On one study day participants received infusions of epinephrine at submaximal (5 ng kg⁻¹ min⁻¹) and maximal (40 ng kg⁻¹ min⁻¹) lipolytic doses. The other study day volunteers bicycled for 90 min at 50–60% of maximum oxygen consumption (VO₂max). [9,10‐³H] Palmitate was infused both days to measure free fatty acid – palmitate kinetics. Oxygen consumption was measured using indirect calorimetry. Palmitate release rates in response to epinephrine and exercise were not different in the Gly/Gly and Arg/Arg participants. The only statistically significant difference we observed was a lesser ΔVO₂ in Arg/Arg volunteers in response to the submaximal epinephrine infusion. The polymorphisms resulting in Arg/Arg and Gly/Gly at position 16 of the β₂‐adrenergic receptor do not result in clinically meaningful differences in lipolysis responses to epinephrine or submaximal exercise.

e12017

Some studies suggest the polymorphism in the β₂‐adrenergic receptor have effects on fatty acid mobilization from adipose tissue. We measure lipolysis using tracer kinetics in volunteers selected for different genotypes at position 16 of the β₂‐adrenergic receptor. We found that polymorphisms resulting in Arg/Arg and Gly/Gly at position 16 of the β₂‐adrenergic receptor do not result in clinically meaningful differences in lipolysis responses to epinephrine or submaximal exercise.

Understanding the links among neuromedin U gene, beta2-adrenoceptor gene and bone health: an observational study in European children

Neuromedin U, encoded by the NMU gene, is a hypothalamic neuropeptide that regulates both energy metabolism and bone mass. The beta-2 adrenergic receptor, encoded by the ADRB2 gene, mediates several effects of catecholamine hormones and neurotransmitters in bone. We investigated whether NMU single nucleotide polymorphisms (SNPs) and haplotypes, as well as functional ADRB2 SNPs, are associated with bone stiffness in children from the IDEFICS cohort, also evaluating whether NMU and ADRB2 interact to affect this trait. A sample of 2,274 subjects (52.5% boys, age 6.2±1.8 years) from eight European countries, having data on calcaneus bone stiffness index (SI, mean of both feet) and genotyping (NMU gene: rs6827359, rs12500837, rs9999653; ADRB2 gene: rs1042713, rs1042714), was studied. After false discovery rate adjustment, SI was significantly associated with all NMU SNPs. rs6827359 CC homozygotes showed the strongest association (recessive model, Δ = −1.8, p = 0.006). Among the five retrieved haplotypes with frequencies higher than 1% (range 2.0–43.9%), the CCT haplotype (frequency = 39.7%) was associated with lower SI values (dominant model, Δ = −1.0, p = 0.04) as compared to the most prevalent haplotype. A non-significant decrease in SI was observed in in ADRB2 rs1042713 GG homozygotes, while subjects carrying SI-lowering genotypes at both SNPs (frequency = 8.4%) showed much lower SI than non-carriers (Δ = −3.9, p<0.0001; p for interaction = 0.025). The association was more evident in preschool girls, in whom SI showed a curvilinear trend across ages. In subgroup analyses, rs9999653 CC NMU or both GG ADRB2 genotypes were associated with either lower serum calcium or β-CrossLaps levels (p = 0.01). This study in European children shows, for the first time in humans, a role for NMU gene through interaction with ADRB2 gene in bone strength regulation, more evident in preschool girls.

The Human Obesity Gene Map: The 2004 Update

This paper presents the eleventh update of the human obesity gene map, which incorporates published results up to the end of October 2004. Evidence from single-gene mutation obesity cases, Mendelian disorders exhibiting obesity as a clinical feature, transgenic and knockout murine models relevant to obesity, quantitative trait loci (QTLs) from animal cross-breeding experiments, association studies with candidate genes, and linkages from genome scans is reviewed. As of October 2004, 173 human obesity cases due to single-gene mutations in 10 different genes have been reported, and 49 loci related to Mendelian syndromes relevant to human obesity have been mapped to a genomic region, and causal genes or strong candidates have been identified for most of these syndromes. There are 166 genes which, when mutated or expressed as transgenes in the mouse, result in phenotypes that affect body weight and adiposity. The number of QTLs reported from animal models currently reaches 221. The number of human obesity QTLs derived from genome scans continues to grow, and we have now 204 QTLs for obesity-related phenotypes from 50 genome-wide scans. A total of 38 genomic regions harbor QTLs replicated among two to four studies. The number of studies reporting associations between DNA sequence variation in specific genes and obesity phenotypes has also increased considerably with 358 findings of positive associations with 113 candidate genes. Among them, 18 genes are supported by at least five positive studies. The obesity gene map shows putative loci on all chromosomes except Y. Overall, >600 genes, markers, and chromosomal regions have been associated or linked with human obesity phenotypes. The electronic version of the map with links to useful publications and genomic and other relevant sites can be found at http://obesitygene.pbrc.edu.

The Human Obesity Gene Map: The 2003 Update

This is the tenth update of the human obesity gene map, incorporating published results up to the end of October 2003 and continuing the previous format. Evidence from single-gene mutation obesity cases, Mendelian disorders exhibiting obesity as a clinical feature, quantitative trait loci (QTLs) from human genome-wide scans and animal crossbreeding experiments, and association and linkage studies with candidate genes and other markers is reviewed. Transgenic and knockout murine models relevant to obesity are also incorporated (N = 55). As of October 2003, 41 Mendelian syndromes relevant to human obesity have been mapped to a genomic region, and causal genes or strong candidates have been identified for most of these syndromes. QTLs reported from animal models currently number 183. There are 208 human QTLs for obesity phenotypes from genome-wide scans and candidate regions in targeted studies. A total of 35 genomic regions harbor QTLs replicated among two to five studies. Attempts to relate DNA sequence variation in specific genes to obesity phenotypes continue to grow, with 272 studies reporting positive associations with 90 candidate genes. Fifteen such candidate genes are supported by at least five positive studies. The obesity gene map shows putative loci on all chromosomes except Y. Overall, more than 430 genes, markers, and chromosomal regions have been associated or linked with human obesity phenotypes. The electronic version of the map with links to useful sites can be found at http://obesitygene.pbrc.edu.

β-AR polymorphisms and glycemic and lipid parameters in hypertensive individuals receiving carvedilol or metoprolol

BACKGROUND

β-Blocker therapy and β-adrenergic receptor (β-AR) polymorphisms are associated with increases in glucose and lipid levels. We investigated associations of common β1 and β2-AR single-nucleotide polymorphisms (SNPs) with metabolic and lipid variables, and examined interactions with β-blocker treatment assignment to affect these parameters.

METHODS

This was a post hoc analysis of a double-blinded clinical trial of nondiabetic, hypertensive individuals that were randomized to receive carvedilol or metoprolol succinate. Fasting glucose, insulin, and lipid levels were measured at baseline, 3 months, and after 6 months. Genotypes for β1-AR SNPs Ser49Gly & Gly389Arg and β2-AR Arg16Gly & Gln27Glu were determined. Multivariable mixed models were used to examine associations between β-AR polymorphisms, metabolic parameters, and SNP interactions with β-blocker therapy (p(interaction)).

RESULTS

The 322 subjects were mean (s.d.) 51.5 (11.2) years old. After 6 months, insulin levels increased by 35.6% on metoprolol and 9.9% on carvedilol (P = 0.015). In univariate models, the Gln27Gln genotype had higher overall insulin levels with β-blockade compared to the Glu27Glu genotype (P = 0.006). Both Arg16Gly (P = 0.012) and Gln27Glu (P = 0.037) SNPs were associated with higher triglycerides levels. An interaction between the Arg16Gly SNP and treatment was identified (p(int) = 0.048).

CONCLUSIONS

These data suggest that insulin and triglycerides may be influenced by β2-AR polymorphisms in patients taking β blockers.

Gender-dependent association of a β(2)-adrenergic gene variant with obesity parameters in Malaysian Malays

Recent findings have shown that the rs1042714 (Gln27Glu) single-nucleotide polymorphism (SNP) on the β2-adrenoceptor gene may predispose to obesity. The findings from other studies carried on different populations, however, have been inconsistent. The authors investigated the association between the rs1042714 SNP with obesity-related parameters. DNA of 672 Malaysian Malays was analyzed using real-time polymerase chain reaction. Univariate and multivariate linear regression analyses revealed significant associations between rs1042714 and diastolic blood pressure in the pooled Malaysian Malay subjects under additive and recessive models. After gender stratification, however, a significant association was found between the rs1042714 and triglyceride and the rs1042714 and log-transformed high-density lipoprotein cholesterol levels in Malaysian Malay men. No significant association was found between the SNP and log-transformed body mass index. This polymorphism may have an important role in the development of obesity-related traits in Malaysian Malays. Gender is an effect modifier for the effect of the rs1042714 polymorphism on obesity-related traits in Malaysian Malays.

ADRB2 gene variants, dual-energy x-ray absorptiometry body composition, and hypertension in Tobago men of African descent

Classic tissue effects of β(2)-adrenergic receptor activation include skeletal muscle glycogenolysis and vascular smooth muscle relaxation, factors relevant to obesity and hypertension, respectively. In a population-based study, we examined 2 common amino acid substitutions in the β(2)-adrenergic receptor gene (ADRB2) in relation to body composition and blood pressure. A cross-sectional analysis of 1893 African-descent men living in Tobago and participating in a prostate cancer screening study was performed. Body mass index, waist circumference, blood pressure, dual-energy x-ray absorptiometry body composition, and ADRB2 (Arg16Gly; Gln27Glu) genotype were determined. Twenty-six percent were obese (body mass index ≥30 kg/m(2)), and 50% were hypertensive. ADRB2 Arg16Gly and Gln27Glu alleles were in linkage disequilibrium (D' = 0.96, r(2) = 0.15). ADRB2 16Gly-containing and 27Glu-containing genotypes were equally frequent in low, medium, and high tertiles of percentage of body fat mass (16Gly-containing genotypes: 73.4%, 74.4%, and 74.5%, P(trend) = .66; 27Glu-containing genotypes: 27.6%, 23.8%, and 25.4%, P(trend) = .39) and in normal blood pressure, prehypertensive, and hypertensive men (16Gly-containing genotypes: 73.4%, 72.8%, and 74.4%, P(trend) = .61; 27Glu-containing genotypes: 25.6%, 24.1%, and 26.7%, P(trend) = .50). In a high-obesity and high-hypertension risk population with ancestry in common with African Americans, genetic variation defined by 2 common ADRB2 amino acid substitutions was not associated with body composition or hypertension.

Association of common polymorphisms in the fractalkine receptor (CX3CR1) with obesity

The inflammatory component in obesity is now well established. The CX3CR1 gene encodes the fractalkine (CX3CL1) receptor and has two coding single-nucleotide polymorphisms, V249I and T280M, linked to a lower risk of other inflammatory diseases such as coronary artery disease (CAD) and asthma. To determine whether CX3CR1 is associated with obesity, we genotyped the V249I and T280M polymorphisms of the CX3CR1 gene in subjects with a BMI ≥30 kg/m² and nonobese controls with a BMI <30 kg/m². Binary logistic regression analyses revealed that the 280MM genotype was associated with obesity (P = 0.022). A gender-specific one-way ANOVA was also conducted to investigate mean BMI and waist circumference differences between genotypes of each polymorphism. For both polymorphisms independently, women carrying two copies of the minor allele had significant higher mean waist circumference than those carrying only one copy of the minor allele (MM > TM, P = 0.031; II > VI, P = 0.013) or those who were homozygous for the major allele (MM > TT, P = 0.005; II > VV, P = 0.006). We also observed significant higher mean waist circumference in men carrying one copy of the minor allele when compared to those who were homozygous for the major allele for the T280M polymorphism (TM > TT, P = 0.029). This study suggests that CX3CR1, a biomarker of obesity in this sample, constitutes a potential target for further investigation of the role of inflammation in the expression of obesity-related phenotypes.

Relationships of adrenoceptor polymorphisms with obesity

Obesity, hypertension, and type 2 diabetes are rapidly growing public health problems. Heightened sympathetic nerve activity is a well-established observation in obesity, hypertension, and type 2 diabetes. Human obesity, hypertension, and diabetes have strong genetic as well as environmental determinants. Reduced energy expenditure and resting metabolic rate are predictive of weight gain, and the sympathetic nervous system participates in regulating energy balance through thermogenesis. The thermogenic effects of catecholamines in obesity are mainly mediated via the β2, and β3-adrenergic receptors in humans. Further, β2-adrenoceptors importantly influence vascular reactivity and may regulate blood pressure. β-adrenoceptor polymorphisms have also been associated with adrenoceptor desensitization, increased adiposity, insulin resistance, and enhanced sympathetic nervous activity. Many epidemiological studies have shown strong relationships between adrenoceptor polymorphisms and obesity, but the observations have been discordant. This paper will discuss the current topics involving the influence of the sympathetic nervous system and β2- and β3-adrenoceptor polymorphisms in obesity.

PPAR-gamma2 pro12Ala polymorphism is associated with post-challenge abnormalities of glucose homeostasis in children and adolescents with obesity

AIM

The aim of the study was to investigate the association between PPAR-gamma2 Pro12Ala polymorphism and laboratory characteristics of carbohydrate metabolism in children and adolescents with obesity. In addition, serum levels of tumor necrosis factor (TNF)-alpha, and soluble form of its receptors (sTNFR1 and sTNFR2) were assessed.

METHODS

In a cross-sectional study, 79 obese children and adolescents of Caucasian origin were investigated. PPAR-gamma2 Pro12Ala polymorphism was determined using polymerase chain reaction--restriction fragment length polymorphism technique. Serum levels of TNF-alpha, sTNFR1 and sTNFR2 were measured by enzyme amplified sensitivity immunoassay.

RESULTS

The minor Ala allele frequency was found to be 14.56% in our cohort. No significant differences in age, BMI, waist circumference, blood pressure, serum lipid, uric acid, TNF-alpha, sTNFR1 and sTNFR2 values were found between carriers of the Ala allele (Pro/Ala and Ala/Ala; n=21) vs. homozygous carriers of the Pro allele (Pro/Pro; n=58). However, post-challenge (120 min) plasma glucose and insulin values were significantly lower in Ala allele carriers vs. homozygous Pro allele carriers (6.56 +/- 0.26 vs. 7.36 +/- 0.25 mmol/L and 65.9 +/- 13.8 vs. 111.8 +/- 20.7 microU/mL, respectively; p < 0.05); while no significant differences were found at fasting state.

CONCLUSIONS

The association between PPAR-gamma2 Prol2Ala polymorphism and glucose metabolism is already present in children and adolescents with obesity who might be at the very beginning of the natural course of type 2 diabetes. At this stage, higher insulin sensitivity can be detected in Ala allele carriers compared to homozygous Pro subjects at post-challenge but not in fasting state; however, the TNF-system seems not to be involved in the alteration of glucose homeostasis due to PPAR-gamma2 Pro12Ala polymorphism.

Roles of beta2- and beta3-adrenoceptor polymorphisms in hypertension and metabolic syndrome

Hypertension, diabetes mellitus (especially type 2 diabetes mellitus), metabolic syndrome and obesity are rapidly growing public health problems. Sympathetic nerve activation is observed in obesity, hypertension and diabetes mellitus, which have strong genetic as well as environmental determinants. Reduced energy expenditure and resting metabolic rate are predictive of weight gain, and the sympathetic nervous system participates in regulating energy balance through thermogenesis. The thermogenic effects of catecholamines in obesity have been mainly mediated via the β2- and β3-adrenergic receptors in humans. Further, β2-adrenoceptors importantly influence vascular reactivity and may regulate blood pressure. Genetic polymorphistns of the β-adrenoceptor gene have been shown to alter the function of several adrenoceptor subtypes and thus to modify the response to catecholamine. β2-adrenoceptor polymorphisms (Arg16Gly, Gln27Glu, and Thr164Ile) have been studied in relation to hypertension. Genetic variations in the β3-adrenoceptor (i.e. Try64Arg variant) are also associated with both obesity and hypertension. However, the precise relationships of the polymorphisms of β2- and β3-adrenoceptor genes with sympathetic nervous system activity, hypertension, and metabolic syndrome have not been fully clarified. This paper will discuss the current topics involving the influence of the sympathetic nervous system and β2- and β3- adrenoceptor polymorphisms in hypertension and metabolic syndrome.

Gln27Glu variant of Beta2-adrenoceptor gene affects male type fat accumulation in women

Background

The β₂-adrenergic receptor (BAR2) is the main lipolytic receptor in white human adipose tissue. There is a functional glutamine 27 glutamic acid (Gln27Glu, rs 1042714) polymorphism in its gene, which has been variably associated with body mass index. This gene variant may be associated with male-type adiposity in women and thus increased cardiovascular risk. We investigated whether the BAR2 Gln27Glu polymorphism is associated with visceral fat and coronary intima thickness in women.

Methods

The amount of mesenteric and omental fat was directly measured and anthropometric measurements were done from 112 forensic autopsy cases of women aged 15 to 49 years. The thickness of the coronary intima, which reflects the severity of atherosclerosis, was measured by computerized image analysis. The BAR2 Gln27Glu polymorphism was determined by polymerase chain reaction.

Results

We found that the amount of visceral fat was significantly higher in women with the Glu allele (689 ± 555 g) compared to Gln/Gln homozygotes (481 ± 392 g, P = 0.023). The waist-hip ratio also tended to be higher in women with the Glu allele compared to Gln/Gln homozygotes (p = 0.050). There were no statistically significant differences between the genotype groups in BMI or the thickness of coronary intima.

Conclusion

The Glu allele of the BAR2 gene may be a risk factor for visceral fat accumulation in young to middle-aged women. However, this polymorphism was not associated with preclinical atherosclerosis.

Performance of a neuro-fuzzy model in predicting weight changes of chronic schizophrenic patients exposed to antipsychotics

Artificial intelligence has become a possible solution to resolve the problem of loss of information when complexity of a disease increases. Obesity phenotypes are observable clinical features of drug-naive schizophrenic patients. In addition, atypical antipsychotic medications may cause these unwanted effects. Here we examined the performance of neuro-fuzzy modeling (NFM) in predicting weight changes in chronic schizophrenic patients exposed to antipsychotics. Two hundred and twenty inpatients meeting DSMIV diagnosis of schizophrenia, treated with antipsychotics, either typical or atypical, for more than 2 years, were recruited. All subjects were assessed in the same study period between mid-November 2003 and mid-April 2004. The baseline and first visit's physical data including weight, height and circumference were used in this study. Clinical information (Clinical Global Impression and Life Style Survey) and genotype data of five single nucleotide polymorphisms were also included as predictors. The subjects were randomly assigned into the first group (105 subjects) and second group (115 subjects), and NFM was performed by using the FuzzyTECH 5.54 software package, with a network-type structure constructed in the rule block. A complete learned model trained from merged data of the first and second groups demonstrates that, at a prediction error of 5, 93% subjects with weight gain were identified. Our study suggests that NFM is a feasible prediction tool for obesity in schizophrenic patients exposed to antipsychotics, with further improvements required.

Association of codon 16 and codon 27 beta 2-adrenergic receptor gene polymorphisms with obesity: a meta-analysis

OBJECTIVE

To search for an association between the Glu27Gln (rs1042714; B27) and the Arg16Gly (rs1042713; B16) polymorphisms of the beta 2-adrenergic receptor (ADRB2) gene and obesity.

METHODS

Meta-analysis of published studies, included if subjects were genotyped at either codon 27 ("B27") or codon 16 ("B16") of the ADRB2 gene and both obese and nonobese subjects were selected, based on a reported cutoff BMI limit. Initial selection included 14,444 subjects genotyped at B27 (rs1042714) and 6,825 genotyped at B16 (rs1042713). After testing each control group for Hardy-Weinberg equilibrium, the final selection included 10,404 subjects and 4,328 subjects, respectively. Studies were published before 18 August 2006.

RESULTS

The frequency of Glu27 allele carriers, either homozygous or heterozygous, ranged from 6.71% in Aymara American Indians to 78.29% in a Dutch population. The frequency of Arg16 allele carriers varied from 51.4 to 64.6% in Europeans and from 71.1 to 85.6% in East Asians. The summary odds ratio (OR) from overall analyses showed no association between either rs1042714 or rs1042713 and obesity. In race groups with low Glu27 allele frequency (Asians, Pacific Islanders, and American Indians), ORs revealed a significant obesity risk associated with rs1042714. These results were not found in East Asians for rs1042713.

DISCUSSION

The presence of the Glu27 allele in the ADRB2 gene appears to be a significant risk factor for obesity in Asians, Pacific Islanders, and American Indians, but not in Europeans. Obesity does not appear to be associated with the Arg16 allele.

Glutathione peroxidase 1 Pro198Leu variant contributes to the metabolic syndrome in men in a large Japanese cohort

BACKGROUND

There has been much interest in the role of free radicals and oxidative stress in the pathogenesis of metabolic syndrome (MetS). Cellular antioxidant enzymes such as glutathione peroxidase 1 (GPX1) play a central role in the control of reactive oxygen species.

OBJECTIVE

We examined whether GPX1 polymorphism (Pro198Leu) is associated with MetS as well as with each component of MetS.

DESIGN

The study was a cross-sectional analysis of randomly selected, community-dwelling Japanese persons aged 40-70 y (1128 M, 1105 F).

RESULTS

The genotype frequencies for the GPX1 Pro198Leu polymorphism in this cohort were 0.846, 0.151, and 0.003 for CC, CT, and TT, respectively. The CT/TT genotypes had significantly higher waist-hip ratios, triacylglycerol concentrations, homeostasis model assessment for beta-cell function, and systolic and diastolic blood pressures in men (P = 0.045, 0.012, 0.011, 0.004, and 0.003, respectively) than did the CC genotype; the CC/TT genotypes also had higher insulin in both sexes (P = 0.019 for men, P = 0.010 for women) and higher body fat mass (P = 0.027) and homeostasis model assessment for insulin resistance (P = 0.008) in women. The CT/TT genotypes showed significant association with higher prevalence of MetS as defined by 2 commonly used criteria in men [odds ratio (OR): 2.02; 95% CI: 1.30, 3.15 by the International Diabetes Federation criteria; OR: 1.49; 95% CI: 1.02, 2.18 by the modified National Cholesterol Education Program criteria) but not in women. The CT/TT genotypes showed a higher prevalence of central obesity (OR: 1.93; 95% CI: 1.31, 2.85) and hypertriglyceridemia (OR: 1.52; 95% CI: 1.08, 2.15) in men but not in women; there were no differences in other components of MetS between the CC and CT/TT genotypes in either sex.

CONCLUSION

GPX1 Pro198Leu variants are associated with the prevalence of MetS in Japanese men but not in women.

Genetic contributors to obesity

Genetic and environmental factors interact to regulate body weight. Overall, the heritability of obesity is estimated at 40% to 70%. More than 244 genes have been found to strongly affect adiposity when overexpressed or deleted in mice. These genes can be considered in four broad categories: regulation of food intake by molecular signalling in the hypothalamus and hindbrain by signals originating in adipose tissue, gut and other organs; regulation of adipocyte differentiation and fat storage; regulation of spontaneous exercise activity; and effect on basal and postprandial thermogenesis. Rare variants in the coding sequences of major candidate genes account for an obese phenotype in 5% to 10% of individuals.

The impact of beta-adrenoreceptor gene polymorphisms on survival in patients with congestive heart failure*

OBJECTIVE

Discordant results have been published regarding a possible association between beta-adrenoreceptor (betaAR) gene polymorphisms and survival in patients with congestive heart failure (CHF). The aim of the study was to analyze the impact of five functional betaAR gene polymorphisms in patients with stable CHF.

METHODS

We prospectively studied 444 consecutive patients with CHF related to left ventricular systolic dysfunction. The beta1ARSer49Gly, beta1ARGly389Arg, beta2AR Arg16Gly, beta2AR Gln27Glu and beta2AR Thr164Ile polymorphisms were determined. Patients underwent echocardiography, radionuclide angiography and a cardiopulmonary exercise test.

RESULTS

Mean age was 56.6+/-11.9 years old, left ventricular ejection fraction (LVEF) was 32+/-12%, and peak VO2 was 15.5+/-4.9 ml/min/kg or 63+/-18% of maximal predicted VO2. Most of the patients (95%) were receiving angiotensin converting enzyme inhibitors and 91% beta-blockers. There was no statistically significant differences between baseline characteristics among beta1AR and beta2AR genotypes. During a median follow-up period of 1232 days, there were 110 cardiac-related deaths and five urgent transplantations. Independent predictors of survival were percent (%) of maximal predicted VO2 (p<0.0001), age (p<0.0001), LVEF (p=0.004), creatinine (p=0.02) and atrial fibrillation (p=0.04). No betaAR polymorphisms were associated with survival. However, patients with the combined beta2ARGly16Gly/beta2ARGln27Gln genotype, who express receptors highly sensitive to down-regulation, had a significantly lower survival rate than patients with other genotypes but only in univariate analysis.

CONCLUSIONS

In this prospective study, we found no association between five functional betaAR polymorphisms and survival in patients with stable CHF. However, we demonstrated, only in univariate analysis, a possible association between the combined beta2ARGly16Gly/beta2ARGln27Gln genotype and survival.

The genetic polymorphisms of beta3-adrenergic receptor (AR) Trp64Arg and beta2-AR Gln27Glu are associated with obesity in Chinese male hypertensive patients

BACKGROUND

Genetic polymorphisms of beta3-adrenergic receptor (AR) Trp64Arg and beta2-AR Gln27Glu may result in significant change in the functions of these receptors. The aims of the present study were to investigate the association between Trp64Arg, Arg16Gly and Gln27Glu polymorphisms and the susceptibility to obesity and hypertension in a Chinese population.

METHODS

A total of 437 Chinese subjects including 149 obese hypertensive patients, 139 non-obese essential hypertensive patients, and 149 non-obese normotensive healthy controls were enrolled in the study. Polymerase chain reaction-restriction fragment length polymorphism (PCR-RFLP) and allele-specific (AS)-PCR assays were used to identify Trp64Arg, Arg16Gly, and Gln27Glu genotypes.

RESULTS

The allele frequencies of 64Arg and 27Glu in the obese hypertensive group were 0.178 and 0.128, respectively. Both were significantly higher than in the non-obese hypertensive and the control groups (p<0.05). Further analysis showed that this association existed only in male hypertensive patients.

CONCLUSIONS

These data reveal that frequencies of beta3-AR 64Arg and beta2-AR 27Glu were significantly higher in our obese hypertensive patients than in the non-obese hypertensive population and healthy controls. beta3-AR Trp64Arg and beta2-AR Gln27Glu genetic polymorphisms are associated with obesity in Chinese male hypertensive patients.

Studies of the associations between functional beta2-adrenergic receptor variants and obesity, hypertension and type 2 diabetes in 7,808 white subjects

AIMS/HYPOTHESIS

Functional and common Arg16Gly and Gln27Glu polymorphisms have been identified in ADRB2, the gene encoding the beta2-adrenergic receptor. These variants have previously been examined for association with obesity, hypertension and diabetes with inconclusive results.

MATERIALS AND METHODS

We investigated both of these variants in 7,808 unrelated, middle-aged white people for their association with obesity in a case-control study, quantitative trait analysis and meta-analysis. Moreover, both variants were investigated for their potential influence on measures of hypertension and type 2 diabetes by case-control and quantitative trait analyses.

RESULTS

The present study did not find consistent evidence for an association of these beta2-adrenergic receptor variants with obesity or hypertension; neither did the quantitative trait analyses show any effect of the variants on obesity-related traits. However, both the Gly allele of the Arg16Gly variant and the Glu allele of the Gln27Glu variant showed nominal association with systolic blood pressure. Furthermore, there was a nominal association of the Arg16 allele frequency and genotype distribution with type 2 diabetes; however, no influence on quantitative biochemical phenotypes related to type 2 diabetes was found. A nominal association of the Arg/Gly genotype with the metabolic syndrome was also observed (p=0.003). Logistic regression analyses provided no evidence of a synergistic or an additive effect of these variants on obesity, hypertension or diabetes.

CONCLUSIONS/INTERPRETATION

After studying 7,808 middle-aged white subjects, we were unable to demonstrate any consistent associations between two common amino acid polymorphisms of the beta2-adrenergic receptor and obesity, hypertension or type 2 diabetes.

Association of a beta-2 adrenoceptor (ADRB2) gene variant with a blunted in vivo lipolysis and fat oxidation

BACKGROUND AND AIMS

Obesity is associated with a blunted beta-adrenoceptor-mediated lipolysis and fat oxidation. We investigated whether polymorphisms in codon 16, 27 and 164 of the beta (2)-adrenoceptor gene (ADRB2) and exon 10 of the G protein beta (3)-subunit gene (GNB3) are associated with alterations in in vivo lipolysis and fat oxidation.

DESIGN AND METHODS

Sixty-five male and 43 female overweight and obese subjects (body mass index (BMI) range: 26.1-48.4 kg/m(2)) were included. Energy expenditure (EE), respiratory quotient (RQ), circulating free fatty acid (FFA) and glycerol levels were determined after stepwise infusion of increasing doses of the non-selective beta-agonist isoprenaline (ISO).

RESULTS

In women, the Arg16 allele of the ADRB2 gene was associated with a blunted increase in circulating FFA, glycerol and a decreased fat oxidation during ISO stimulation. In men, the Arg16 allele was significantly associated with a blunted increase in FFA but not in glycerol or fat oxidation.

CONCLUSION

These results suggest that genetic variation in the ADRB2 gene is associated with disturbances in in vivo beta-adrenoceptor-mediated lipolysis and fat oxidation during beta-adrenergic stimulation in overweight and obese subjects; these effects are influenced by gene-gender interactions.

Adrenergic receptor polymorphisms and autonomic nervous system function in human obesity

Adrenergic receptors (ARs) are cell-surface G-protein-coupled receptors for catecholamines. They are essential components of the sympathetic nervous system, organized within the autonomic nervous system (ANS), which controls various physiological functions, including energy homeostasis and metabolism of glucose and lipids. An impairment of ANS function in metabolism is considered to be one of the pathological states associated with human obesity and related metabolic diseases; thus, alterations in AR function might be implicated in the pathophysiology of these diseases. Several studies have suggested an association between obesity phenotypes and some AR polymorphisms. In vitro and human clinical studies indicate that some of these polymorphisms have functional and pathophysiological significance, including the linkage to ANS function. This review summarizes present knowledge of AR polymorphisms related to human obesity, and their association with ANS function.

Genetics of obesity

Considerable attention is currently being paid to the secular changes in food intake and physical activity that underlie the increase in the prevalence of obesity that is apparent in many societies. While this is laudable it would be unwise to view these environmental factors in isolation from the biological factors that normally control body weight and composition and the compelling evidence that inter-individual differences in susceptibility to obesity have strong genetic determinants. This is particularly important, as it is only in the past decade that we have begun to obtain substantive information regarding the molecular constituents of pathways controlling mammalian energy balance and therefore, for the first time, are in a position to achieve a better mechanistic understanding of this disease. Population-based association and linkage studies have highlighted a number of loci at which genetic variation is associated with obesity and related phenotypes and the identification and characterization of monogenic obesity syndromes has been particularly fruitful. While there is widespread acceptance that hereditary factors might predispose to human obesity, it is frequently assumed that such factors would influence metabolic rate or the selective partitioning of excess calories into fat. However, it is notable that, thus far, all monogenic defects causing human obesity actually disrupt hypothalamic pathways and have a profound effect on satiety and food intake. To conclude, the evidence we have to date suggests that the major impact of genes on human obesity is just as likely (or perhaps more likely) to directly impact on hunger, satiety and food intake rather than metabolic rate or nutrient partitioning. At the risk of oversimplification, it seems that from an aetiological/genetic standpoint, human obesity appears less a metabolic than a neuro-behavioural disease.

Genetic effects on obesity assessed by bivariate genome scan: the Mexican-American coronary artery disease study

OBJECTIVE

To identify the genetic determinants of obesity using univariate and bivariate models in a genome scan.

RESEARCH METHODS AND PROCEDURES

We evaluated the genetic and environmental effects and performed a genome-wide linkage analysis of obesity-related traits in 478 subjects from 105 Mexican-American nuclear families ascertained through a proband with documented coronary artery disease. The available obesity traits include BMI, body surface area (BSA), waist-to-hip ratio (WHR), and trunk fat mass as percentage of body weight. Heritability estimates and multipoint linkage analysis were performed using a variance components procedure implemented in SOLAR software.

RESULTS

The heritability estimates were 0.62 for BMI, 0.73 for BSA, 0.40 for WHR, and 0.38 for trunk fat mass as percentage of body weight. Using a bivariate genetic model, we observed significant genetic correlations between BMI and other obesity-related traits (all p < 0.01). Evidence for univariate linkage was observed at 252 to approximately 267 cM on chromosome 2 for three obesity-related traits (except for WHR) and at 163 to approximately 167 cM on chromosome 5 for BMI and BSA, with the maximum logarithm of the odds ratio score of 3.12 (empirical p value, 0.002) for BSA on chromosome 2. Use of the bivariate linkage model yielded an additional peak (logarithm of the odds ratio = 3.25, empirical p value, 0.002) at 25 cM on chromosome 7 for the pair of BMI and BSA.

DISCUSSION

The evidence for linkage on chromosomes 2q36-37 and 5q36 is supported both by univariate and bivariate analysis, and an additional linkage peak at 7p15 was identified by the bivariate model. This suggests that use of the bivariate model provides additional information to identify linkage of genes responsible for obesity-related traits.

The human obesity gene map: the 2005 update

This paper presents the 12th update of the human obesity gene map, which incorporates published results up to the end of October 2005. Evidence from single-gene mutation obesity cases, Mendelian disorders exhibiting obesity as a clinical feature, transgenic and knockout murine models relevant to obesity, quantitative trait loci (QTL) from animal cross-breeding experiments, association studies with candidate genes, and linkages from genome scans is reviewed. As of October 2005, 176 human obesity cases due to single-gene mutations in 11 different genes have been reported, 50 loci related to Mendelian syndromes relevant to human obesity have been mapped to a genomic region, and causal genes or strong candidates have been identified for most of these syndromes. There are 244 genes that, when mutated or expressed as transgenes in the mouse, result in phenotypes that affect body weight and adiposity. The number of QTLs reported from animal models currently reaches 408. The number of human obesity QTLs derived from genome scans continues to grow, and we now have 253 QTLs for obesity-related phenotypes from 61 genome-wide scans. A total of 52 genomic regions harbor QTLs supported by two or more studies. The number of studies reporting associations between DNA sequence variation in specific genes and obesity phenotypes has also increased considerably, with 426 findings of positive associations with 127 candidate genes. A promising observation is that 22 genes are each supported by at least five positive studies. The obesity gene map shows putative loci on all chromosomes except Y. The electronic version of the map with links to useful publications and relevant sites can be found at http://obesitygene.pbrc.edu.

The Glu27 genotypes of the beta2-adrenergic receptor are predictors for severe coronary artery disease

Background

The role of the Beta2-adrenoceptor (beta2-AR) Gln27Glu polymorphism in the manifestation of cardiovascular diseases is still unclear.

Methods

In the present study, we evaluated the potential relevance of the c.79 C>G (p.Gln27Glu) polymorphism of this receptor gene for coronary artery disease (CAD) and its associated risk factors in Saudi Arabs. Genotyping was performed by PCR using the confronting two-pair primer (PCR-CTPP) method.

Results

In the general population group (BD) (n = 895), 68.5% were homozygous wild-type C/C, 28.3% were heterozygous C/G and 3.2% were homozygous mutant G/G. Among the CAD patients (n = 773), 50.6% were homozygous wild-type C/C, 43.6% were heterozygous C/G and 5.8% were homozygous mutant G/G, while in the angiographed control group (CON) (n = 528), 71.8% were C/C, 24.4% C/G and 3.8% G/G genotypes. These results indicate that both the C/G (p = < .001) and G/G (p = .005) genotypes are significantly associated with CAD, when compared to the CON group. In addition, C/G (p = < .001) and G/G (p = < .001) were significantly associated with CAD, when compared to the BD group. Furthermore, stepwise logistic regression showed that the genotype [C/G (p < .001) and G/G (p < .001)] increase the risk of CAD.

Conclusion

These results shows that the Gln27Glu genotypes (homo- or heterozygous) of the beta2-AR may be independent predictors of severe CAD.

Association of β2 adrenergic receptor polymorphisms and related haplotypes with triglyceride and LDL-cholesterol levels

Adrenergic receptors regulate lipid mobilization, energy expenditure and glycogen breakdown. The beta(2) adrenergic receptor (beta(2)-AR) gene may constitute a potential candidate gene to explain part of the genetic predisposition to human obesity and correlated traits. With regard to the association between beta(2)-AR gene polymorphisms and obesity-related metabolic disorders, published reports give conflicting results. We investigated the role of three polymorphisms, and related haplotypes of the beta(2)-AR in the obesity and related traits in a cohort of overweight/obese subjects. We characterized one single nucleotide polymorphism (SNP) in the promoter region (5'LC-Cys19Arg) and two in the coding region (Gly16Arg and Gln27Glu) of the beta(2)-AR in 642 consecutively recruited overweight/obese subjects in whom extensive clinical and biochemical analysis was performed. The effect of the polymorphisms on quantitative variables was investigated using multiple linear regression analysis. 5'LC-Cys19 homozygous showed higher triglyceride and LDL-cholesterol levels compared to 5'LC-Arg19 homozygous (P=0.03 and P=0.01, respectively). Similar increase in triglyceride and LDL-cholesterol levels was observed for Arg/Arg genotype compared to Gly/Gly genotype of Gly16Arg polymorphism (P=0.02 and P=0.01, respectively) and for Gln/Gln genotype compared to Glu/Glu genotype of the Gln27Glu polymorphism (P=0.01 and P=0.03, respectively). The 5'LC-Cys(19)Arg(16)Gln(27) haplotype determined a significant increase in triglyceride and LDL-cholesterol levels compared to 5'LC-Arg(19)Gly(16)Glu(27) haplotype (P=0.05 and P=0.02, respectively). Our findings provide additional weight to previous observations on the influence of these three genetic variants on lipid phenotypes; particularly on the increase of triglycerides and LDL-cholesterol levels in overweight/obese subjects carrying the 5'LC-Cys(19)Arg(16)Gln(27) haplotype.

Association between β-adrenergic receptor polymorphisms and their G-protein-coupled receptors with body mass index and obesity in women: a report from the NHLBI-sponsored WISE study

OBJECTIVES

The beta-adrenergic receptor (betaAR) genes are candidate genes for obesity because of their roles in energy homeostasis and promotion of lipolysis in human adipose tissue. Objective is to determine the association between obesity and polymorphisms in genes of the beta(1)AR (ADRB1), beta(2)AR (ADRB2), beta(3)AR (ADRB3), Gs protein alpha (GNAS1), to which all three beta-receptors couple and the G protein beta3 subunit (GNB3), to which beta(3)ARs couple.

DESIGN

A case-control genetic association study.

SUBJECTS

A total of 643 black or white women enrolled in Women's Ischemia Syndrome Evaluation (WISE) study.

MEASUREMENTS

Genotypes were determined by PCR with single primer extension. Associations between genotype and body mass index (BMI), waist-to-hip ratio (WHR), waist circumference, and obesity were made.

RESULTS

Polymorphisms in the three betaAR genes, GNAS1, and GNB3 were not associated with BMI, WHR, waist circumference, or obesity. Linear and logistic regression analyses found no contribution of either genotype or haplotype with anthropometric measurements or obesity.

CONCLUSIONS

Our study suggests that among American women with suspected coronary heart disease, polymorphisms in the betaARs and their G-protein-coupled receptors do not contribute to increased BMI, WHR, waist circumference, or obesity. Given that 50% of all women die from coronary heart disease, and a higher percentage have heart disease during their lifetime, our results are likely generalizable to many American women.

beta2-adrenergic receptor polymorphisms and salbutamol-stimulated energy expenditure

The beta-adrenergic system is involved in the control of energy metabolism and expenditure. The beta2-adrenergic receptor (beta2-AR) gene shows polymorphisms that have been associated with obesity in several studies. In vitro and in vivo studies suggest differences in beta2-AR-mediated function between these polymorphisms. The aim of this study was to investigate the influence of genetic variation in codon 16 of the beta2-AR gene on energy metabolism in humans. Thirty-four subjects were recruited [Gly16Gly (n = 13), Gly16Arg (n = 16), or Arg16Arg (n = 5)]. The beta2-AR was stimulated with two doses of salbutamol (50 and 100 ng/kg fat-free mass per minute) after blockade of the beta1-adrenergic receptors with atenolol. Energy expenditure and plasma substrate and hormone concentrations were measured. The increase in energy expenditure (DeltaEE) was significantly different among groups in which the Arg16Arg group showed the lowest increase (P < 0.05 vs. Gly carriers). In a multiple regression model, variations in the increase in nonesterified fatty acid concentration during salbutamol infusion (partial r = 0.51) and the polymorphism contributed significantly to the variation in DeltaEE. Thirty-five percent of the variation in DeltaEE was explained by these two factors. We conclude that subjects with the Arg16Arg polymorphism of the beta2-AR gene have a reduced thermogenic response to beta2-adrenergic stimulation. Although this relatively small study needs confirmation, the findings support a role for this polymorphism in the development and maintenance of overweight and obesity.

The genetics of human obesity

Obesity is an important cause of morbidity and mortality in developed countries, and is also becoming increasingly prevalent in the developing world. Although environmental factors are important, there is considerable evidence that genes also have a significant role in its pathogenesis. The identification of genes that are involved in monogenic, syndromic and polygenic obesity has greatly increased our knowledge of the mechanisms that underlie this condition. In the future, dissection of the complex genetic architecture of obesity will provide new avenues for treatment and prevention, and will increase our understanding of the regulation of energy balance in humans.

Association between beta-1 and beta-2 adrenergic receptor gene polymorphisms and the response to beta-blockade in patients with stable congestive heart failure

Previous studies have clearly demonstrated the beneficial effect of beta-blockers in patients with stable congestive heart failure (CHF). beta-blockers improve left ventricular ejection fraction (LVEF) and reduce cardiac mortality. However, there is an interindividual variability in the response to these agents. Two studies have suggested a possible impact of some functional betaAR gene polymorphisms on the effects of beta-blockade. The objective of the study is to analyse the association between genetic variations in the beta1 or the beta2 adrenoreceptor (AR) gene and the effects of beta-blockade in patients with stable CHF. We studied 199 consecutive patients with stable CHF not treated with beta-blockers. Before introduction of beta-blockers and 3 months after the maximal tolerated dose was reached, patients underwent an echocardiography and a radionuclide angiography. The beta1ARGly389Arg, beta1ARSer49Gly, beta2ARGly16Arg, beta2ARGln27Glu and beta2ARThr164Ile polymorphisms were determined: beta-blockade resulted in a significant decrease in heart rate, a significant increase in LVEF (from 30+/-10% to 40+/-13%, P<0.0001). There was no association between the five polymorphisms and heart rate or LVEF, either before or after beta-blockade. Heart rate and LVEF responses to beta-blockade were not associated with the beta1AR or the beta2AR polymorphisms. betaAR polymorphisms did not explain the interindividual variability in the response to beta-blockers.

Fatty acid metabolism in obesity and type 2 diabetes mellitus

Disturbances in pathways of lipolysis and fatty acid handling are of importance in the aetiology of obesity and type 2 diabetes mellitus. There is evidence that a lowered catecholamine-mediated lipolytic response may play a role in the development and maintenance of increased adipose tissue stores. Increased adipose tissue stores, a disturbed insulin-mediated regulation of lipolysis and subnormal skeletal muscle non-esterified fatty acid (NEFA) uptake under conditions of high lipolytic rate may increase circulating NEFA concentrations, which may promote insulin resistance and cardiovascular complications. In addition, a disturbance of NEFA uptake by adipose tissue postprandially is also a critical determinant of plasma NEFA concentration. Furthermore, evidence is increasing that insulin-resistant muscle is characterised by a lowered ability to oxidise fatty acids. A dysbalance between fatty acid uptake and fatty acid oxidation may in turn be a factor promoting accumulation of lipid intermediates and triacylglycerols within skeletal muscle, which is strongly associated with skeletal muscle insulin resistance. The present review describes the reported disturbances in pathways of lipolysis and skeletal muscle fatty acid handling, and discusses underlying mechanisms and metabolic consequences of these disturbances.

The glutamine 27 glutamic acid polymorphism of the beta2-adrenoceptor gene is associated with abdominal obesity and greater risk of impaired glucose tolerance in men but not in women: a population-based study in Spain

OBJECTIVE

Given the important role of the beta2-adrenoceptor (beta2-AR) in lipid mobilization and the lack of studies in Southern European countries, the aim of this study was to investigate the role of the glutamine 27 glutamic acid (Gln27Glu) beta2-AR polymorphism in the susceptibility to obesity and its metabolic complications in a population-based nationwide multicentre study in Spain, especially focusing on the hypothetical influence of gender.

DESIGN

Cross-sectional population-based study.

PATIENTS

We studied 666 nonrelated adults (47.9% men and 52.1% women), aged 35-64 years, chosen randomly from a nationwide population-based survey of obesity, and related conditions including insulin resistance and cardiovascular risk factors.

MEASUREMENTS

Body mass index (BMI), waist-to-hip ratio (WHR), sagittal abdominal diameter (SAD), systolic and diastolic blood pressure, fasting and 2-h post-glucose load glycaemic levels, total cholesterol, high density lipoprotein (HDL)- and low density lipoprotein (LDL)-cholesterol, triglycerides, insulin, proinsulin and leptin plasma levels were measured. Beta2-AR Gln27Glu genotypes were determined by restriction fragment length polymorphism (RFLP)-polymerase chain reaction (PCR).

RESULTS

Glu27 homozygous obese men had significantly higher BMI and SAD mean values than both heterozygous and Gln27 homozygous obese men. Two-hour post-load plasma glucose concentration was higher in Glu27 homozygous than in Gln27 homozygous in the whole population and only in men when stratified by gender. No differences according to the genotype were found for the rest of the parameters studied, including homeostasis model assessment (HOMA), insulin, proinsulin and leptin levels, but for total and LDL-cholesterol these increased in men. We did not find differences in the anthropometrical and biochemical parameters according to the genotype in women. Multivariate logistic regression analysis showed that Glu27 homozygosity after adjustment for SAD was associated with type 2 diabetes mellitus.

CONCLUSIONS

Our results suggest that the glutamic acid 27 allele of the beta2-adrenoceptor may be a risk factor in men but not in women for the accumulation of visceral fat and for its association with the development of type 2 diabetes mellitus.

Association studies of genetic polymorphisms in central obesity: a critical review

During the past decade, mutations affecting liability to central obesity have been discovered at a phenomenal rate, and despite few consistently replicated findings, a number of intriguing results have emerged in the literature. Association studies have been proposed to identify the genetic determinants of complex traits such as central obesity. The advantages of the association method include its relative robustness to genetic heterogeneity and the ability to detect much smaller effect sizes than is detectable using feasible sample sizes in linkage studies. However, the current literature linking central obesity to genetic variants is teeming with reports of associations that either cannot be replicated or for which corroboration by linkage has been impossible to find. Explanations for this lack of reproducibility are well rehearsed, and typically include poor study design, incorrect assumptions about the underlying genetic architecture, and simple overinterpretation of data. These limitations create concern about the validity of association studies and cause problems in establishing robust criteria for undertaking association studies. In this article, the current status of the literature of association studies for genetic dissection of central obesity is critically reviewed.

Pharmacology and physiology of human adrenergic receptor polymorphisms

Adrenergic receptors are expressed on virtually every cell type in the body and are the receptors for epinephrine and norepinephrine within the sympathetic nervous system. They serve critical roles in maintaining homeostasis in normal physiologic settings as well as pathologic states. These receptors are also targets for therapeutically administered agonists and antagonists. Recent studies have shown that at least seven adrenergic receptor subtypes display variation in amino acid sequence in the human population due to common genetic polymorphisms. Variations in potential regulatory domains in noncoding sequence are also present. Here, we review the consequences of these polymorphisms in terms of signaling, human physiology and disease, and response to therapy.

Obesity risk is associated with carbohydrate intake in women carrying the Gln27Glu beta2-adrenoceptor polymorphism

Interindividual differences in the response to dietary intake are, in some cases, genotype dependent. Moreover, genotype-environment interactions may appear when the impact of lifestyle factors (e.g., diet) on a phenotype (e.g., BMI > 30 kg/m(2)) differs by genotype. A case-control study (obese subjects vs. normal weight controls) was conducted to assess a possible effect modification on obesity risk of the Gln27Glu polymorphism for the beta(2)-adrenoceptor gene depending on dietary intake. The sample included 159 subjects with BMI > 30 kg/m(2) and 154 controls with BMI < 25 kg/m(2). The allele frequency for the Glu27 polymorphism, as assessed by the polymerase chain reaction-restriction fragment length polymorphism methodology, was 0.40 in cases (obese) and 0.37 in controls (lean), which was similar to that of other Caucasian populations. The dietary intake was estimated by using a previously validated food frequency questionnaire. Obesity incidence was not directly affected by the polymorphism [odds ratio (OR) = 1.40; P = 0.246]. However, a significant interaction (effect modification) between carbohydrate (CHO) intake and the presence of the Glu27 variant in the probability of obesity was apparent. Thus, females with the polymorphism and a higher CHO intake [>49% energy (E)] had a higher obesity risk (OR = 2.56, P = 0.051). The product-term introduced in the logistic model to assess effect modification revealed a marginally significant interaction (P = 0.058) between both factors. Furthermore, a high intake of CHO (E > 49%) was associated with higher insulin levels among women carrying the Gln27Glu polymorphism (P < 0.01). This gene-nutrient interaction emphasizes the importance of examining the outcome of some obesity-related mutations depending on lifestyle (including diet) and may explain the heterogeneity of findings from previous studies.

Effects of beta2-adrenergic receptor gene variants on adiposity: the HERITAGE Family Study

We investigated whether the Arg16Gly and Gln27Glu polymorphisms of the beta2-adrenergic receptor gene were associated with body-fat and fat-distribution phenotypes measured before and in response to a 20-week endurance-training program. BMI, fat mass (FAT), percentage of body fat (%FAT), sum of eight skinfolds (SF8), and abdominal fat areas assessed by computed tomography were measured in adult sedentary white and black participants of the HERITAGE Family Study. Evidence of gene-by-obesity interaction was found in whites for several adiposity phenotypes measured before training. Analyses performed separately in nonobese and obese subjects revealed that obese men carrying the Glu27 allele have lower fat accumulation (BMI, FAT, and %FAT) than noncarriers. Among white obese women, Gly16Gly homozygotes had a lower fat accumulation (BMI, FAT, and SF8) than Arg16Gly and Arg16Arg carriers. In response to endurance training, white women with the Arg16Arg genotype exhibited a greater reduction in BMI, FAT, and %FAT. Results observed in blacks were mostly negative. These results suggest that polymorphisms in the beta2-adrenergic receptor gene influence the amount of body fat in white obese men (Gln27Glu) and women (Arg16Gly), as well as the changes in adiposity in response to endurance training in white women (Arg16Gly).

Basal fat oxidation and after a peak oxygen consumption test in obese women with a beta2 adrenoceptor gene polymorphism

The Glu27Glu genotype in the beta2-adrenergic receptor (ADRB2) has been linked to a higher fat deposition and obesity in females. Also, in our population, it has been described that physically active women carrying the Glu allele had a higher BMI as compared to non-carriers performing the same level of activity. Since exercise may counterbalance a gene predisposition to obesity, we tested the hypothesis of a potential different metabolic response among ADRB2 Gln27Gln versus Glu27Glu obese women when submitted to a peak oxygen consumption test on a treadmill. In our study, 10 obese women with the Gln27Gln genotype were compared to 9 matched obese women bearing the Glu27Glu genotype. The ADRB2 polymorphism was identified by PCR-RFLP, fat oxidation was determined by indirect calorimetry and blood measurements were carried out following conventional procedures. The ADRB2 Glu27Glu subjects had lower plasma glycerol levels (P = 0.026), while plasma triglycerides (P <0.001) and the insulin:glucose ratio were higher (P = 0.046) as compared to the Gln27Gln group along the peak oxygen consumption trial intervention. There was a significantly lower fat oxidation (P = 0.024) in the Glu27Glu obese women during the recovery compared to Gln27Gln obese individuals. These data suggest that exercise would not benefit equally the two ADRB2 polymorphism homozygous groups, since both lipolysis and fat oxidation promoted by a peak oxygen consumption test appear to be blunted in the polymorphic Glu27Glu obese group.

The human obesity gene map: the 2002 update

This is the ninth update of the human obesity gene map, incorporating published results through October 2002 and continuing the previous format. Evidence from single-gene mutation obesity cases, Mendelian disorders exhibiting obesity as a clinical feature, quantitative trait loci (QTLs) from human genome-wide scans and various animal crossbreeding experiments, and association and linkage studies with candidate genes and other markers is reviewed. For the first time, transgenic and knockout murine models exhibiting obesity as a phenotype are incorporated (N = 38). As of October 2002, 33 Mendelian syndromes relevant to human obesity have been mapped to a genomic region, and the causal genes or strong candidates have been identified for 23 of these syndromes. QTLs reported from animal models currently number 168; there are 68 human QTLs for obesity phenotypes from genome-wide scans. Additionally, significant linkage peaks with candidate genes have been identified in targeted studies. Seven genomic regions harbor QTLs replicated among two to five studies. Attempts to relate DNA sequence variation in specific genes to obesity phenotypes continue to grow, with 222 studies reporting positive associations with 71 candidate genes. Fifteen such candidate genes are supported by at least five positive studies. The obesity gene map shows putative loci on all chromosomes except Y. More than 300 genes, markers, and chromosomal regions have been associated or linked with human obesity phenotypes. The electronic version of the map with links to useful sites can be found at http://obesitygene.pbrc.edu.

Beta(2)-adrenergic receptor gene polymorphism, age, and cardiovascular phenotypes

Previous studies suggest that variants of the beta(2)-adrenergic receptor (ADRB2) may differently affect functional responses to adrenergic stimulation, thereby possibly modulating cardiovascular and metabolic phenotypes. We examined the hypothesis that G/R16 and Q/E27 polymorphism of ADRB2, or their haplotypes, may modulate blood pressure, cardiovascular structure, and function or metabolic cardiovascular risk factors in the general population. We examined a random sample of the general population (n=571; age, 35 to 64 years). Neither clinic nor 24-hour ambulatory blood pressure was significantly associated with ADRB2 genotypes in the overall population. Cardiac structure and function were also not influenced by ADRB2 polymorphism. After adjustment for potential confounders, association of the R16 allele with higher systolic blood pressure was observed in the subgroup of younger people (below age of 50 years). Haplotype analysis showed that higher blood pressure values were more specifically associated with the presence of R16-Q27. Younger people carrying the R16-Q27 haplotype also showed a trend toward lower heart rate, higher BMI, lower glycemia, and higher trygliceridemia, which is consistent with the hypothesis of a genetic predisposition to reduced cardiovascular and metabolic response to ADRB2 stimulation. This study does not provide evidence of a major role of ADRB2 gene variability in blood pressure modulation. However, association of ADRB2 polymorphism with cardiovascular and metabolic effects can be observed in younger subjects, before the development of age-related decline of ADRB2-mediated activity. Our study emphasizes the necessity of taking into account (patho)-physiological changes related to aging (in this case, decreased efficiency of ADRB2 signaling) when analyzing phenotypic effects of genetic variants.