The W64R variant of the beta3-adrenergic receptor is not associated with type II diabetes or obesity in a large Finnish sample

Association of Type 2 Deiodinase Thr92Ala Polymorphism with Pediatric Obesity in Japanese Children: A Case-Control Study

Genetic factors play critical roles in the onset and progression of obesity. Brown adipose tissue (BAT) activity is also critical for adiposity. The objective of this study was to evaluate the prevalence and effects of BAT gene polymorphisms in pediatric obesity. This case-control study included 270 non-obese and 86 obese children. All participants underwent genotyping for type 2 deiodinase (DIO2) Thr92Ala (rs225014). The prevalence of the homozygous Ala/Ala allele of the DIO2 gene in the obese group was 15.1% versus 6.3% in the non-obese group, resulting in an odds ratio (OR) of 3.393 (p = 0.003). The results of this study indicate that the homozygous Ala/Ala allele of the DIO2 gene is associated with an increased risk of pediatric obesity and suggest that pediatric obesity might be suitable for assessing the association with gene polymorphisms related to BAT, especially DIO2 Thr92Ala.

Effect of the beta-3 adrenergic receptor Trp64Arg and uncoupling protein 1-3826 A>G genotypes on lipid and apolipoprotein levels in overweight/obese and non-obese Chinese subjects

BACKGROUND

The beta-3 adrenergic receptor (β3-AR) Trp64Arg and uncoupling protein 1 (UCP1) -3826 A>G polymorphisms have been reported to be associated with obesity and/or lipid metabolism in some populations. This study examined the possible association of the β3-AR and UCP1 polymorphisms with overweight/obesity or lipid variation in a Southwest Chinese population.

METHODS

A total of 418 Han Chinese (249 overweight/obese and 169 healthy control subjects) in the Chengdu area were studied using PCR-RFLP analysis. Total serum cholesterol (TC) and triglycerides (TGs) were measured using an enzymatic method. High density lipoprotein cholesterol (HDL-C) was determined after sodium phosphotungstate/magnesium chloride precipitation of low-density lipoproteins by polyvinyl sulfate. Serum apolipoproteins were quantified by radial immunodiffusion.

RESULTS

The genotype and allele frequencies of the β3-AR Trp64Arg and UCP1 -3826 A>G polymorphisms in overweight/obese subjects exhibited no significant differences compared to the controls. However, subjects carrying the β3-AR TrpTrp genotype and UCP1 AG genotype had higher TG levels than those carrying the Arg allele and AA genotype, respectively (P<0.05), while controls carrying the β3-AR Arg allele had significantly higher TC and apo AII concentrations than those carrying the TrpTrp genotype (P<0.05). Additionally, subjects carrying the UCP1 AG genotype exhibited elevated apo C-II and apo C-III levels compared to those carrying the AA genotype (P<0.05). We were unable to find an association of the UCP1 and β3-AR polymorphisms with low HDL-cholesterolemia in the overweight/obese subjects.

CONCLUSIONS

The present study provides evidence that the β3-AR Trp64Arg and UCP1 -3826 A>G polymorphisms are associated with TG levels in overweight/obese Chinese subjects and that the two polymorphisms are also associated with certain lipid and apolipoprotein variations, depending on BMI. However, these polymorphisms are not associated with overweight/obesity or low HDL-cholesterolemia in a Chinese population from the Chengdu area.

Higher cardiorespiratory fitness attenuates the risk of atherosclerosis associated with ADRB3 Trp64Arg polymorphism

PURPOSE

β3-Adrenergic receptor (ADRB3) Trp64Arg polymorphism is associated with atherogenic risk factors that include weight gain, insulin resistance, and diabetes. Habitual exercise brings higher cardiorespiratory fitness and results in the amelioration of atherosclerotic risk factors. However, the effects of cardiorespiratory fitness level and ADRB3 Trp64Arg polymorphism on the risk of cardiovascular disease remain unclear. A cross-sectional investigation of 877 Japanese men and women (18-75 years old) was performed to clarify the effects of cardiorespiratory fitness on the relationship between ADRB3 Trp64Arg polymorphism and risk of cardiovascular disease.

METHOD

Common carotid intima-media thickness (ccIMT) and blood lipid profiles were assessed as surrogate markers of atherosclerosis. We measured peak oxygen uptake (V̇O(2peak)) during incremental cycle ergometer exercise testing. Subjects were divided into groups with high (High-Fit) and low (Low-Fit) levels of cardiorespiratory fitness based on the median value of V̇O(2peak) for sex and decade.

RESULTS

Levels of body fat, triglycerides, and plasma glucose were lower and high-density lipoprotein cholesterol levels and V̇O(2peak) were higher in High-Fit subjects than Low-Fit subjects. ADRB3 Trp64Arg polymorphism did not significantly affect ccIMT or blood lipid profiles. In Low-Fit subjects, ccIMT was higher in individuals with the Arg/Arg genotype compared to the Trp/Trp and Trp/Arg genotypes (each P < 0.0001); however, ADRB3 polymorphism had no effect in High-Fit subjects.

CONCLUSION

Higher levels of cardiorespiratory fitness may attenuate the risk of atherosclerosis associated with ADRB3 Trp64Arg polymorphism.

β3Adrenergic Receptor Polymorphism and Obesity-Related Phenotypes in Hypertensive Patients

OBJECTIVES

Obesity is a complex trait that is affected by both environmental and genetic risk factors. The beta(3) adrenergic receptor (ADRB3) is expressed in adipose tissue and plays a role in energy metabolism. A missense mutation on codon 64 of this gene (W64R) is associated with receptor malfunction. Previous studies examining the relation between this polymorphism and obesity produced inconsistent findings. The current study assessed the association between the W64R genotype and obesity-related phenotypes, including body weight, BMI, and serum triglycerides, cholesterol, and glucose.

RESEARCH METHODS AND PROCEDURES

We determined the ADRB3 W64R genotypes and fasting serum lipid and glucose concentrations for 695 hypertensive adults (336 men,359 women) from a rural county in Anhui Province, China. Multivariate linear regression models were fit to detect associations between the genetic polymorphism and obesity-related phenotypes.

RESULTS

The ADRB3 W64R polymorphism was significantly associated with body weight and BMI in men but not in women. After controlling for potential confounding variables, men who were homozygous for the R64 allele were 11.8 kg heavier (p < 0.001) and had a BMI that was 3.7 kg/m(2) greater (p = 0.001) than men who were homozygous for the W64 allele. Serum concentrations of lipids and glucose were found not associated with the genetic polymorphism.

DISCUSSION

The ADRB3 R64 allele was associated with increased body weight and BMI in men but not in women. The genetic association was not modified by triglyceride, cholesterol, blood glucose, or blood pressure levels of the subjects.

Meta-Analysis of the Association of the Trp64Arg Polymorphism in the β3 Adrenergic Receptor with Insulin Resistance

OBJECTIVE

To clarify the possible association between the Trp64Arg polymorphism and insulin resistance (IR).

RESEARCH METHODS AND PROCEDURES

Articles evaluating the effect of the Trp64Arg polymorphism on IR were identified on the MEDLINE and PubMed databases from 1995 to February, 2004. After extraction of relevant data, main and subgroup meta-analyses were performed to assess the differences in IR indices between Trp/Trp and Trp/Arg genotypes.

RESULTS

Forty eligible papers containing 56 subgroups were included in this meta-analysis. Among a total of 12,805 subjects, 21.9% had Trp64Arg mutation: 20.8%, heterozygotes and 1.1%, homozygotes. Significant associations were found between this mutation and some indices of IR. The weighted mean difference in fasting insulin, 120-minute insulin level after oral glucose tolerance test, and homeostasis model assessment between Arg64 and Trp64 was 0.23 [95% confidence interval (CI), 0.05 to 0.42] pM, 0.89 (95% CI, 0.30 to 1.48) pM, and 0.55 (95% CI, 0.14 to 0.96), respectively. Subgroup analysis further indicated that this significant association existed only in the Asian population (p < 0.01) and in the obese (p = 0.02) and diabetes subgroups (p = 0.03).

DISCUSSION

Numerous studies have been conducted to examine the relationship between the beta3-adrenergic receptor Trp64Arg polymorphism and components of IR syndrome. However, the results have been inconsistent and have led to controversy about whether this polymorphism is associated with these clinical features. The current meta-analysis demonstrated the moderate effects of the Trp64Arg polymorphism on IR in the Asian population and in obese and diabetic subgroups.

An association between TRP64ARG polymorphism of the B3 adrenoreceptor gene and some metabolic disturbances

Backgrounds

B3 adrenoreceptors (ADRB3) are abundant in adipose tissue and play the role in its metabolism and lipolysis. Some variants of the ADRB3 gene may predispose subjects for the development obesity and metabolic abnormalities in the setting of modern sedentary lifestyle. ADRB3 gene polymorphism association with metabolic disturbances has never been studied before in the ethnic Kyrgyz population.

Aim

To study an association between Trp64Arg polymorphism of the ADRB3 and metabolic syndrome (MS) components in an ethnic Kyrgyz group.

Materials and methods

213 Ethnic Kyrgyz volunteers over the age of 30 were enrolled in the study. The assessment plan for each individual comprised of general physical and anthropometric exams as well as laboratory tests (glucose, lipid panel, insulin) and genotyping by Trp64Arg polymorphism of the ADRB3. MS diagnosis was consistent with modified ATP III criteria (2005). Logistic regression analysis was performed to test the potential independent association between Arg64 allele with obesity, abdominal obesity (AO) and arterial hypertension (AH).

Results

Trp64Arg polymorphism of the ADRB3 was assessed in 213 individuals (145 men, 68 women) aged 30-73 (mean age 50.7 ± 7.6). Arg64 allele frequency was 0.239; ADRB3 genotype distribution among participants was: Trp64 homozygotes 54.5%, Trp64Arg 43.2% and Arg64 homozygotes 2.3%. There was an association between Trp64Arg и Arg64Arg genotypes and higher BMI, WC and obesity frequency (p < 0.00009), AO (p < 0.01), type 2 diabetes mellitus (DM) (p < 0.005) and lower high density cholesterol (HDL-C) level (p < 0.03). The logistic regression analysis showed the correlation of the Arg64 allele with obesity (OR 3.159; 95% CI 1.789-5.577) and AO (OR 1.973; 95% CI 1.118-3.481). The association between Arg64 allele and AH lost its significance after adjustment for obesity.

Conclusion

Arg64 allele of the ADRB3 gene in the studied group has an association with MS components such as obesity, AO and decreased HDL-C level.

Independent predictive roles of eotaxin Ala23Thr, paraoxonase 2 Ser311Cys and beta-adrenergic receptor Trp64Arg polymorphisms on cardiac disease in Type 2 Diabetes--an 8-year prospective cohort analysis of 1297 patients

AIMS

To examine the independent and joint effects of multiple genetic variants on a cardiac end-point in an 8-year prospective study of a Chinese diabetic cohort.

METHODS

Seventy-seven single nucleotide polymorphisms (SNPs) of 53 candidate genes for inflammation, thrombosis, vascular tone regulation and lipid metabolism were genotyped in 1297 Chinese patients with no prior history of coronary heart disease (CHD) or heart failure at baseline. Cardiac end-point was defined by the occurrence of CHD and/or heart failure.

RESULTS

In Cox regression model, after adjustment for baseline confounding variables including age, sex, smoking status, duration of diabetes, glycaemic control, lipid levels, waist circumference, blood pressure, albuminuria and estimated glomerular filtration rate, genetic variants, including Ala/Ala of SCYA11 (eotaxin) Ala23Thr, Cys/Cys or Cys/Ser of PON2 (paraoxonase 2) Ser311Cys and Arg/Arg of ADRB3 (beta3-adrenergic receptor) Trp64Arg, were independently associated with incident cardiac end-point, with respective hazard ratios (95% confidence interval) of 1.70 (1.10-2.61, P=0.037), 1.42 (1.08-1.88, P=0.013) and 3.84 (1.18-12.50, P=0.025). Analysis of the joint effect of the risk alleles showed significant increased risk of the cardiac end-point with increasing number of risk alleles (P<0.001). The adjusted risk for the cardiac end-point was 4.11 (P=0.002) for patients carrying four risk alleles compared with those carrying one or no risk allele.

CONCLUSIONS

The independent risk conferred by genetic variants encoding pathways such as inflammation and lipid metabolism, not adequately reflected by conventional biomarkers, may identify high-risk individuals for intensified control of modifiable risk factors.

Association of Trp64Arg polymorphism of beta3-adrenergic receptor with insulin resistance in Polish children with obesity

AIM

To establish the influence of the Trp64Arg variant of the beta3-adrenergic receptor (Trp64Arg- beta3AR) on body mass index (BMI) and insulin resistance (IR) in obese children.

METHODS

BMI, presence of the Trp64Arg mutation, plasma glucose and insulin concentrations during an oral glucose tolerance test (OGTT) and IR were determined in 60 obese and 33 normal weight children.

RESULTS

The frequency of Trp64Arg was similar in normal weight and obese children. BMI, glucose and insulin concentrations during an OGTT in children with Trp64Argbeta3AR were not different from those with Trp64Trpbeta3AR. IR was confirmed in 42.8% of children with Trp64Argbeta3AR and in 45.6% of children with Trp64Trpbeta3AR (NS).

CONCLUSIONS

1. The similar frequency of the Trp64Argbeta3AR variant in normal weight and obese children suggests that it is not a susceptibility gene for obesity in Polish children. 2. The presence of the Trp64Argbeta3AR variant does not have an unfavourable influence on BMI, glucose or insulin concentrations during OGTT or on IR frequency in Polish obese children.

Screening of 134 single nucleotide polymorphisms (SNPs) previously associated with type 2 diabetes replicates association with 12 SNPs in nine genes

More than 120 published reports have described associations between single nucleotide polymorphisms (SNPs) and type 2 diabetes. However, multiple studies of the same variant have often been discordant. From a literature search, we identified previously reported type 2 diabetes-associated SNPs. We initially genotyped 134 SNPs on 786 index case subjects from type 2 diabetes families and 617 control subjects with normal glucose tolerance from Finland and excluded from analysis 20 SNPs in strong linkage disequilibrium (r(2) > 0.8) with another typed SNP. Of the 114 SNPs examined, we followed up the 20 most significant SNPs (P < 0.10) on an additional 384 case subjects and 366 control subjects from a population-based study in Finland. In the combined data, we replicated association (P < 0.05) for 12 SNPs: PPARG Pro12Ala and His447, KCNJ11 Glu23Lys and rs5210, TNF -857, SLC2A2 Ile110Thr, HNF1A/TCF1 rs2701175 and GE117881_360, PCK1 -232, NEUROD1 Thr45Ala, IL6 -598, and ENPP1 Lys121Gln. The replication of 12 SNPs of 114 tested was significantly greater than expected by chance under the null hypothesis of no association (P = 0.012). We observed that SNPs from genes that had three or more previous reports of association were significantly more likely to be replicated in our sample (P = 0.03), although we also replicated 4 of 58 SNPs from genes that had only one previous report of association.

Comparison of Body Fat Distribution and Blood Lipid Profiles according to Trp64Arg Polymorphism for the .BETA.3-Adrenergic Receptor Gene in Korean Middle-Aged Women

The aim of this study was to determine whether there was an association between body fat distribution, blood lipid profiles, and beta 3-adrenergic receptor gene polymorphism in Korean middle-aged women. Subjects were grouped according to BMI as obese (> or = 5 BMI, n = 95) or non-obese (BMI<25, n = 93). The Trp64Arg mutation of the beta 3-adrenergic receptor gene was detected by PCR-RFLP. Skinfold thickness, body circumference, intra-abdominal fat area by CT, and blood lipid profiles were also measured. Data were compared using ANOVA, Bonferroni t-test, and Chi-square. Significance for statistical analyses were set at p<0.05. In the obese group, 63.16% were Trp64Trp homozygotes and 36.84% were Trp64Arg heterozygotes, compared to 80.65% who were Trp64Trp homozygotes and 19.35% who were Trp64Arg heterozygotes in the non-obese group. These results indicated a significant (chi-square = 4.943, p<0.05) difference between the two groups. Frequency of the Arg64 allele in the obese group (16.84%) showed a significant (chi-square = 4.185, p<0.05) difference as compared to the non-obese group (9.68%). Skinfold thickness and body circumference of the Trp64Arg heterozygote group showed a consistent increase as compared to the Trp64Trp homozygote group. Visceral fat area and VSR of Trp64Arg heterozygote group showed a higher tendency than Trp64Trp homozygotes in the obese group, but these differences were not statistically significant. In conclusion, the Trp64Arg polymorphism of the beta 3-adrenergic receptor gene is associated with obesity in middle-aged Korean women, but it is difficult to suggest the prominent association of the Trp64Arg polymorphism of the beta 3-adrenergic receptor gene with prevalence of abdominal obesity or dyslipidemia in Korean middle-aged women.

Genetics of Type 2 diabetes

Type 2 diabetes (T2D) has become a health-care problem worldwide, with the rise in disease prevalence being all the more worrying as it not only affects the developed world but also developing nations with fewer resources to cope with yet another major disease burden. Furthermore, the problem is no longer restricted to the ageing population, as young adults and children are also being diagnosed with T2D. In recent years, there has been a surge in the number of genetic studies of T2D in attempts to identify some of the underlying risk factors. In this review, I highlight the main genes known to cause uncommon monogenic forms of diabetes (e.g. maturity-onset diabetes of the young--MODY--and insulin resistance syndromes), as well as describe some of the main approaches used to identify genes involved in the more common forms of T2D that result from the interaction between environmental risk factors and predisposing genotypes. Linkage and candidate gene studies have been highly successful in the identification of genes that cause the monogenic variants of diabetes and, although progress in the more common forms of T2D has been slow, a number of genes have now been reproducibly associated with T2D risk in multiple studies. These are discussed, as well as the main implications that the diabetes gene discoveries will have in diabetes treatment and prevention.

Pharmacogenomics of adrenoceptors

Adrenoceptors (ARs) consist of nine subtypes (alpha(1A)-, alpha(1B)-, alpha(1D)-, beta(1)-, beta(2)-, beta(3)-, alpha(2A)-, alpha(2B)- and alpha(2C)-AR), which are involved in a wide spectrum of physiological functions and are the site of action for a considerable percentage of currently prescribed therapeutics. With the exception of alpha(1D), all AR subtypes are polymorphic with genetic variations in the coding and non-coding regions. This review discusses the biochemical consequences of these genetic variations and their impact in receptor function, disease pathophysiology, and drug response. Pharmacogenomic principles that have been discovered are also discussed.

Lack of relationship between beta3-adrenergic receptor gene polymorphism and gestational diabetes mellitus in a Taiwanese population

The Trp64Arg polymorphism of beta(3)-adrenergic receptor (ADRB3) has been reported to be associated with insulin resistance and gestational diabetes mellitus (GDM). The objective of this study is to investigate whether the ADRB3 Arg variant confers susceptibility to GDM in a Taiwanese population. A total of 299 pregnant women (mean +/- SD, 31.1 +/- 4.2 years) was recruited. Two-hour, 75-g oral glucose tolerance tests (OGTT) were conducted at 24 to 31 weeks gestation (28.3 +/- 1.6 weeks). Forty-one GDM subjects and 258 controls with normal glucose tolerance (NGT) level were genotyped for the ADRB3 Trp64Arg polymorphism. The genotype distribution and allele frequency of ADRB3 did not significantly differ between GDM and NGT subjects (9.8% v 14.5%). Body weight gain during pregnancy was not different between ADRB3 genotypes. However, the GDM subjects with the Arg64 variant had higher fasting (P =.04) and postload 120 minutes (P =.03) insulin levels as compared with the GDM subjects with the Trp64Trp allele. In all subjects, the women with the Arg64 allele (n = 76) had significantly higher level of insulin secretion (the ratio of Deltainsulin(60)/Deltaglucose(60)) during OGTT than those without (n = 223) (P =.03) despite similar plasma levels of glucose and insulin in both genotypes. Our results indicated that the ADRB3 Trp64Arg variant is not related to the development of GDM and has no effect on obesity during pregnancy in a Taiwanese population. However, ADRB3 polymorphism might be a possible determinant of insulin resistance.

Autonomic Nervous System Pharmacogenomics: A Progress Report

Pharmacogenetics, the inherited basis for interindividual differences in drug response, has rapidly expanded with the advent of new molecular tools and the sequencing of the human genome, yielding pharmacogenomics. We review here recent ideas and findings regarding pharmacogenomics of components of the autonomic nervous system, in particular, neuronal nicotinic acetylcholine receptors, postsynaptic receptors with which the parasympathetic and sympathetic neurotransmitters, acetylcholine (ACh) and norepinephrine, respectively, interact. The receptor subtypes that mediate these responses, M(1-3) muscarinic cholinergic receptors (mAChRs), and alpha(1A,B,D)-, alpha(2A,B,C)-, and beta(1,2,3)-adrenergic receptors (AR), show highly variable expression of genetic variants; variants of mAChRs and alpha(1)-ARs are relatively rare, whereas alpha(2)-AR and beta-AR subtype variants are quite common. The largest amount of data is available regarding variants of the latter ARs and represents efforts to associate certain receptor genotypes, most commonly, single nucleotide polymorphisms, with particular phenotypes (e.g., cardiovascular and metabolic responses). In vitro and in vivo studies have yielded inconsistent results; definitive conclusions are limited. We identify several conceptual and methodological problems with available data: sample size, ethnicity, tissue differences, coding versus noncoding variants, limited studies of haplotypes, and interaction among variants. Thus, although progress has been made in identifying genetic variation that influences drug response fo autonomic nervous system components, we are still at the early stages of defining the most critical genetic determinants and their role in human physiology and pharmacology.

Effect of Trp64Arg mutation of the beta3-adrenergic receptor gene and C161T substitution of the peroxisome proliferator activated receptor gamma gene on obesity in Japanese children

OBJECTIVE

Obesity is a multifactorial syndrome influenced by both genetic and behavioral factors. Trp64Arg mutation of the beta3-adrenergic receptor (AR) gene and C161T substitution of the peroxisome proliferator-activated receptor (PPAR) gamma gene have been reported to be associated with obesity or lipid metabolism in adults. However, the effects of these mutations on children have not yet been clarified. For this reason, we studied the effects of Trp64Arg mutation of the beta3-AR gene and C161T substitution of the PPARgamma gene on obesity in Japanese children.

SUBJECTS AND METHODS

In order to determine the effects of Trp64Arg mutation of the beta3-AR gene and C161T substitution of the PPARgamma gene on obesity in children, 105 obese Japanese children were screened by the polymerase chain reaction and restriction fragment-length polymorphism analysis. Plasma lipid, apolipo-protein (apo), glucose, insulin and leptin levels were also determined.

RESULTS

Obese boys with Trp64Arg showed a higher obesity index and lower plasma levels of high-density lipoprotein cholesterol (HDL-C), apoA-I and apoA-II than those of them without the mutation. Obese boys with both mutations showed a higher plasma leptin level than those with only the beta3-AR gene mutation or PPARgamma gene mutation. No significant effect of these mutations was found in obese girls.

CONCLUSION

All of these data suggest that Trp64Arg mutation of the beta3-AR gene might affect obesity and HDL metabolism in obese boys. In contrast, C161T mutation of the PPARgamma gene, by itself, is unlikely to influence obesity, lipid metabolism or plasma leptin levels.

Genetics of obesity

Obesity is a typical common multifactorial disease in which environmental and genetic factors interact. In rare cases of severe obesity with childhood onset, a single gene has a major effect in determining the occurrence of obesity, with the environment having only a permissive role in the severity of the phenotype. Exceptional mutations of the leptin gene and its receptor, pro-opiomelanocortine (POMC), prohormone convertase 1 (PC1) and more frequently, mutations in the melanocortin receptor 4 (1 to 4% of very obese cases) have been described. All these obesity genes encode proteins that are strongly connected as part of the same loop of the regulation of food intake. They all involve the leptin axis and one of its hypothalamic targets; the melanocortin pathway. Pathways of bodyweight regulation involved in monogenic forms of obesity might represent targets for future drug development. Successful leptin protein replacement in a leptin-deficient child has contributed to the validation of the usefulness of gene screening in humans. However, the individual variability in response to leptin treatment might be related to genetic variability. The efficiency of leptin itself or of small-molecule agonists of the leptin receptor should be studied in relation with genetic variations in the leptin gene promoter. The most common forms of obesity are polygenic. Two general approaches have been used to date in the search for genes underlying common polygenic obesity in humans. The first approach focuses on selected genes having some plausible role in obesity on the basis of their known or presumed biological role. This approach yielded putative susceptibility genes with only small or uncertain effects. The second approach attempts to map genes purely by position and requires no presumptions on the function of genes. Genome-wide scans identify chromosomal regions showing linkage with obesity in large collections of nuclear families. Genome-wide scans in different ethnic populations have localized major obesity loci on chromosomes 2, 5, 10, 11 and 20. Susceptibility gene(s) for obesity may be positionally cloned in the intervals of linkage. The candidate gene and positional cloning of major obesity-linked regions approaches are discussed in this paper.

Genetics of insulin resistance

Insulin resistance, defined as the decreased ability of insulin to perform its biological functions, is likely to represent the primary physiologic defect underlying the insulin resistance syndrome (IRS), which includes insulin resistance/hyperinsulinemia, glucose intolerance and/or type 2 diabetes mellitus, visceral obesity, hypertension, and dyslipidemia. This constellation of traits is a leading cause of cardiovascular mortality and morbidity. Insulin sensitivity varies widely among individuals. Although environmental provocations including physical inactivity and caloric excess play an important role in the development of obesity and thus insulin resistance, epidemiologic and family studies show that there are also moderate genetic influences on the development of insulin resistance. Extreme forms of insulin resistance may be caused rarely by mutations in the genes for the insulin receptor and peroxisome proliferator-activated receptor gamma. However, the genetic basis for common more moderate forms of insulin resistance is likely to be polygenic and heterogeneous. Evidence further suggests that gene variants may have phenotypic influences on more than one IRS trait (so-called pleiotrophy), which may explain, in part, the clustering of these traits. This article reviews the evidence that insulin resistance has a genetic basis. Progress to date toward identifying specific gene variants are reviewed. Ultimately, the identification of specific gene variants that influence insulin resistance and other IRS traits will have profound influences on our understanding of the molecular and pathophysiologic basis of these disorders, from which new and more effective preventive and therapeutic interventions will be possible.

Genetics of human obesity

Obesity is a multifactorial condition. Environmental risk factors related to a sedentary life-style and unlimited access to food apply constant pressure in subjects with a genetic predisposition to gain weight. The fact that genetic defects can result in human obesity has been unequivocally established over the past 3 years with the identification of the genetic defects responsible for different monogenic forms of human obesity: the leptin, leptin receptor, pro-opiomelanocortin, pro-hormone convertase-1 and melanocortin-4 receptor genes. The common forms of obesity are, however, polygenic. The examination of specific genes for involvement in the susceptibility to common obesity has not yet yielded convincing results. Approaches involving the candidate genes and the positional cloning of major obesity-linked regions (state-of-the-art future prospects) will be discussed.

Genotype Arg/Arg, but not Trp/Arg, of the Trp64Arg polymorphism of the beta(3)-adrenergic receptor is associated with type 2 diabetes and obesity in a large Japanese sample

OBJECTIVE

Despite a large number of studies, no association of the Trp64Arg polymorphism of the beta(3)-adrenergic receptor gene with obesity and type 2 diabetes has yet to be clearly elucidated. We examined the associations in a large population-based sample.

RESEARCH DESIGN AND METHODS

A total of 1,685 subjects (935 women and 750 men, aged 58.7 +/- 12.4 years) from a cohort population (n = 3,706) of the Funagata Diabetes Study were divided into three groups according to genotypes: Trp/Trp (n = 1,155), Trp/Arg (n = 486), and Arg/Arg (n = 44). Glucose tolerance was diagnosed according to the 1985 World Health Organization criteria. Subjects who had a BMI > or =30 kg/m(2) were considered obese. Associations with the traits related to obesity, diabetes, hypertension, and dyslipidemia were also examined. The chi(2) test and analysis of variance were used for the association studies and to assess the differences in the traits' values, respectively.

RESULTS

More subjects with genotype Arg/Arg were obese and had diabetes (13.6% for each) than those with genotype Trp/Trp (3.29%, P < 0.001; and 4.16%, P = 0.007, respectively) or genotype Trp/Arg (2.06%, P < 0.001; and 5.97%, P = 0.051, respectively). No significant differences in the frequencies of occurrence of these conditions were observed between genotypes Trp/Arg and Trp/Trp. Traits related to obesity, such as percent body fat (28.82 +/- 7.95 vs. 25.93 +/- 7.21, P = 0.038) and BMI (25.07 +/- 3.84 vs. 23.63 +/- 3.18, P = 0.018), were higher in the genotype Arg/Arg than in the genotype Trp/Trp groups.

CONCLUSIONS

Genotype Arg/Arg, but not Trp/Arg, of the beta(3)-adrenergic receptor was associated with both obesity and type 2 diabetes in a large Japanese sample.

Genetic polymorphisms of adrenergic receptors

Recent advances in molecular biology have enhanced the understanding of adrenergic receptors. They have allowed the characterization of the several subtypes of adrenergic receptors expressed and have expanded the research about the potential physiologic functions they mediate. Furthermore, variant forms, or polymorphims, of the genes that code for these receptors are being identified. These genetic variants may or may not result in functional differences in the receptors they encode. There is obvious interest in determining the physiologic and clinical relevance of these polymorphisms. The purpose of this review is to describe these polymorphisms and the often contradictory literature pertaining to their clinical significance. Progress in this area is being made at a rapid pace. As the allele-disease relations become less equivocal, it might be possible to predict individual differences in susceptibility to a disease, disease prognosis, and response to treatment.

Relationship of the Trp64Arg polymorphism of the beta3-adrenoceptor gene to central adiposity and high blood pressure: interaction with age. Cross-sectional and longitudinal findings of the Olivetti Prospective Heart Study

METHODS

The association of the Trp64Arg polymorphism of the beta3-adrenoceptor (beta3-AR) gene with high blood pressure, central adiposity and other features of the metabolic syndrome was investigated in a large unselected sample of a white male working population in Southern Italy (n = 979).

RESULTS

In the whole population, subjects heterozygous for the Trp64Arg mutation (11.2%) were not different from the homozygous Trp64Trp for any of the variables investigated. However, upon stratification for age, among men in the upper tertile of age (> 53 years), the Trp64Arg genotype was associated with higher waist: hip ratio (0.992 +/- 0.021 versus 0.982 +/- 0.037, P< 0.05), serum uric acid (6.34 +/- 1.50 versus 5.75 +/- 1.30 micromol/l, P < 0.05) and systolic blood pressure (144.3 +/- 19.4 versus 136.9 +/- 18.9 mmHg, P< 0.05) compared with the wild-type homozygotes. Accordingly, in the same age group, the carriers of Trp64Arg genotype were more often in the upper tertile of abdominal adiposity (69.7 versus 43.7%, P< 0.02) and serum uric acid (56.3 versus 34.8%, P < 0.02) and were more often hypertensive (68.6 versus 57.6%, P< 0.058) than the Trp64Trp homozygotes. No such differences were observed in younger age groups. No association was found with fasting serum insulin and the homeostasis model assessment (HOMA) index of insulin resistance. Furthermore, in a subgroup of 457 men for whom retrospective 20-year follow-up data were available, the variant genotype was associated with a higher probability of developing overweight (44.7 versus 27.0%, P < 0.05) and a trend to higher blood pressure (52.6 versus 38.4%, P = 0.09) over 20 years.

CONCLUSION

We conclude that the Trp64Arg variant of the beta3-AR receptor predicts a greater tendency to develop abdominal adiposity and high blood pressure with advancing age.

The peripheral sympathetic nervous system in human obesity

The peripheral sympathetic nervous system is a key factor in the regulation of energy balance in humans. Differences in sympathetic nervous system activity may contribute to variations in 24 h energy expenditure between individuals. beta-Adrenoceptors play a more important role than alpha-adrenoceptors in this regulation. The involvement of both beta 1- and beta 2-adrenoceptor subtypes has been demonstrated, the role of the beta 3-adrenoceptor subtype is not yet clear. Normal or increased levels of sympathetic nervous system activity and reduced reactivity appear to be present in established obesity. Furthermore, the sensitivity for beta-adrenoceptor stimulation is impaired in obesity. The blunted reactivity and sensitivity may contribute to the maintenance of the obese state. There are data to suggest that they may also play a role in the aetiology of obesity, because the impairments often remain after weight reduction. Furthermore, a negative correlation between baseline sympathetic nervous system activity and weight gain during follow-up has been found in Pima Indians. Recently, genetic evidence about the involvement of adrenoceptors in obesity has become available. Although the results of association and linkage studies on polymorphisms in the beta 2-, beta 3- and alpha 2-adrenoceptor genes are inconsistent, the functional correlates of some of these polymorphisms (changes in agonist-promoted down-regulation, protein expression levels, lipolytic sensitivity, basal metabolic rate, sympathetic nervous system activity) suggest that they may be important in the aetiology of obesity.

The iterative two-stage population approach to IVGTT minimal modeling: improved precision with reduced sampling. Intravenous glucose tolerance test

The minimal model method is widely used to estimate glucose effectiveness (S(G)) and insulin sensitivity (S(I)) from intravenous glucose tolerance test (IVGTT) data. In the standard protocol (sIVGTT, 0.33 g/kg glucose bolus given at time 0), which allows the simultaneous assessment of beta-cell function, the precision of the individualized estimates often degrades and particularly so in the presence of reduced sampling schedules. Here, we investigated the use of a population approach, the iterative two-stage (ITS) approach, to analyze 16 sIVGTTs in healthy subjects and to obtain refined estimates of S(G) and S(I) in the population and in the individual subjects. The ITS is based on calculation of the population mean and standard deviation of the parameters at each iteration and then use of them as prior information for the individual analyses. Theoretically, the use of a prior in the ITS should improve the precision of the individual estimates. The customary approach (standard two stage, STS), where modeling is performed separately for each individual subject, does not take the population knowledge into account. We used both frequent (FSS, 30 samples) and (quasi-optimally) reduced (RSS, 14 samples) sampling schedules. For the FSS, STS gave estimates (mean +/- SD) for S(G) = 2.66 +/- 1.09 x 10(-2). min(-1) and S(I) = 6.46 +/- 6.99 10(-4). min(-1). microU(-1). ml, with an average precision of 51 (range 5-176) and 33% (3-91), respectively. RSS radically worsened the precision of both S(G) and S(I). However, RSS and ITS gave S(G) = 2.59 +/- 0.73 and S(I) = 6.06 +/- 7.28, with an average precision of 23 (12-42) and 27% (), respectively. In conclusion, population minimal modeling of sIVGTT data improves the precision of individual estimates of glucose effectiveness and insulin sensitivity, as the theory predicts, and, even with reduced sampling, the improvement is substantial.

No association between body mass index and beta(3)-adrenergic receptor variant (W64R) in children with premature pubarche and adolescent girls with hyperandrogenism

OBJECTIVE

To determine if the Trp(64)Arg (W64R) variant of the beta(3)-adrenergic receptor (ADRB3) could be used as a genetic marker to define risk for polycystic ovary syndrom (PCOS) and/or obesity in children and adolescents.

DESIGN

Association study.

SETTING

Academic research environment.

PATIENT(S)

Children referred for evaluation of premature pubic hair (n = 63), adolescent girls referred for evaluation of hirsutism and/or oligomenorrhea (n = 33), and healthy adult controls (n = 67).

INTERVENTION(S)

None.

MAIN OUTCOME MEASURE(S)

Relationship of body mass index (BMI) to presence or absence of W64R variant and frequency of W64R variant in our patient population.

RESULT(S)

Body mass index (kg/m(2)) was determined for 63 children (55 girls and 8 boys) and 33 adolescent girls. Presence or absence of the W64R variant was assayed by polymerase chain reaction (PCR) amplification followed by allele-specific restriction fragment digest. Twelve subjects and 11 healthy controls were found to be heterozygous for the W64R variant. One subject was found to be homozygous for the W64R variant. Allele frequency for the W64R variant was comparable between patients and controls. Among the patients, mean BMI values were not different between carriers and noncarriers.

CONCLUSION(S)

Although other studies suggest that the W64R variant is associated with the development of obesity and insulin resistance, we cannot demonstrate that it has a major effect on BMI in children with premature pubarche or in adolescent girls with hyperandrogenism. Serial observations are necessary to determine if this variant predicts the development of obesity and/or PCOS in adulthood.

The human obesity gene map: the 1999 update

This report constitutes the sixth update of the human obesity gene map incorporating published results up to the end of October 1999. Evidence from the rodent and human obesity cases caused by single gene mutations, Mendelian disorders exhibiting obesity as a clinical feature, quantitative trait loci (QTL) uncovered in human genome-wide scans and in crossbreeding experiments with mouse, rat, pig and chicken models, association and linkage studies with candidate genes and other markers is reviewed. Twenty-five human cases of obesity can now be explained by variation in five genes. Twenty Mendelian disorders exhibiting obesity as one of their clinical manifestations have now been mapped. The number of different QTLs reported from animal models reaches now 98. Attempts to relate DNA sequence variation in specific genes to obesity phenotypes continue to grow, with 89 reports of positive associations pertaining to 40 candidate genes. Finally, 44 loci have linked to obesity indicators in genomic scans and other linkage study designs. The obesity gene map depicted in Figure 1 reveals that putative loci affecting obesity-related phenotypes can be found on all autosomes, with chromosomes 14 and 21 showing each one locus only. The number of genes, markers, and chromosomal regions that have been associated or linked with human obesity phenotypes continues to increase and is now well above 200.