DNA polymorphism in the uncoupling protein 1 (UCP1) gene has no effect on obesity related phenotypes in the Swedish Obese Subjects cohorts

Genotypes of the UCP1 gene polymorphisms and cardiometabolic diseases: A multifactorial study of association with disease probability

Cardiometabolic diseases (CMDs) are complex disorders with a heterogenous phenotype, which are caused by multiple factors including genetic factors. Single nucleotide polymorphisms (SNPs) rs45539933 (p.Ala64Thr), rs10011540 (c.-112A>C), rs3811791 (c.-1766A>G), and rs1800592 (c.-3826A>G) in the UCP1 gene have been analyzed for association with CMDs in many studies providing controversial results. However, previous studies only considered individual UCP1 SNPs and did not evaluate them in an integrated manner, which is a more powerful approach to uncover genetic component of complex diseases. This study aimed to investigate associations between UCP1 genotype combinations and CMDs or CMD risk factors in the context of non-genetic factors. We performed multiple logistic regression analysis and proposed new methodology of testing different combinations of SNP genotypes. We found that probability of CMDs increased in presence of the three-SNP combination of genotypes with minor alleles of c.-3826A>G and p.Ala64Thr and wild allele of c.-112A>C, with increasing age, body mass index (BMI), body fat percentage (BF%) and may differ between sexes and between countries. The combination of genotypes with c.-3826A>G minor allele and wild homozygotes of c.-112A>C and p.Ala64Thr was associated with increased probability of diabetes. While combination of genotypes with minor alleles of all three SNPs reduced the CMD probability. The present results suggest that age, BMI, sex, and UCP1 three-SNP combinations of genotypes significantly contribute to CMD probability. Varying of c.-112A>C alleles in the genotype combination with minor alleles of c.-3826A>G and p.Ala64Thr markedly changes CMD probability.

Prevalence of uncoupling protein one genetic polymorphisms and their relationship with cardiovascular and metabolic health

Contribution of UCP1 single nucleotide polymorphisms (SNPs) to susceptibility for cardiometabolic pathologies (CMP) and their involvement in specific risk factors for these conditions varies across populations. We tested whether UCP1 SNPs A-3826G, A-1766G, Ala64Thr and A-112C are associated with common CMP and their risk factors across Armenia, Greece, Poland, Russia and United Kingdom. This case-control study included genotyping of these SNPs, from 2,283 Caucasians. Results were extended via systematic review and meta-analysis. In Armenia, GA genotype and A allele of Ala64Thr displayed ~2-fold higher risk for CMP compared to GG genotype and G allele, respectively (p<0.05). In Greece, A allele of Ala64Thr decreased risk of CMP by 39%. Healthy individuals with A-3826G GG genotype and carriers of mutant allele of A-112C and Ala64Thr had higher body mass index compared to those carrying other alleles. In healthy Polish, higher waist-to-hip ratio (WHR) was observed in heterozygotes A-3826G compared to AA homozygotes. Heterozygosity of A-112C and Ala64Thr SNPs was related to lower WHR in CMP individuals compared to wild type homozygotes (p<0.05). Meta-analysis showed no statistically significant odds-ratios across our SNPs (p>0.05). Concluding, the studied SNPs could be associated with the most common CMP and their risk factors in some populations.

Association of uncoupling protein (Ucp) gene polymorphisms with cardiometabolic diseases

The hereditary aspect of obesity is a major focus of modern medical genetics. The genetic background is known to determine a higher-than-average prevalence of obesity in certain regions, like Oceania. There is evidence that dysfunction of brown adipose tissue (BAT) may be a risk factor for obesity and type 2 diabetes (T2D). A significant number of studies in the field focus on the UCP family. The Ucp genes code for electron transport carriers. UCP1 (thermogenin) is the most abundant protein of the UCP superfamily and is expressed in BAT, contributing to its capability of generating heat. Single nucleotide polymorphisms (SNPs) of Ucp1-Ucp3 were recently associated with risk of cardiometabolic diseases. This review covers the main Ucp SNPs A-3826G, A-1766G, A-112C, Met229Leu, Ala64Thr (Ucp1), Ala55Val, G-866A (Ucp2), and C-55 T (Ucp3), which may be associated with the development of obesity, disturbance in lipid metabolism, T2D, and cardiovascular diseases.

Role of UCP1 Gene Variants in Interethnic Differences in the Development of Cardio-Metabolic Diseases

Cardio-metabolic diseases (CMDs) comprise a cluster of risk factors that contribute to chronic pathological conditions with adverse consequences for cardiovascular function and metabolic processes. A wide range of CMD prevalence rates among different ethnic groups has been documented. In view of accumulated evidence, there is a trend toward increasing CMD prevalence rates in Eastern Europe and Western Asia. Numerous studies have revealed an association between uncoupling protein 1 (UCP1) gene variants and CMDs. UCP1 activity is essential for brown adipose tissue (BAT)-mediated thermogenesis. Experimental animal studies and epidemiological studies in humans highlight the significance of BAT-mediated thermogenesis in protecting against obesity and maintaining a lean phenotype. We hypothesize that the genetic variation in UCP1 gene expression observed among different ethnic groups could contribute to the ethnic-specific predisposition to CMD development. Constructing such prevalence maps of UCP1 gene variants could contribute significantly into identifying high-risk ethnic groups predisposed to the development of CMDs, and further shaping public health policies by the improvement of existing preventive and management strategies.

Association of the UCP polymorphisms with susceptibility to obesity: case-control study and meta-analysis

This paper describes a case-control study and a meta-analysis performed to evaluate if the following polymorphisms are associated with presence of obesity: -3826A/G (UCP1); -866G/A, Ala55Val and Ins/Del (UCP2) and -55C/T (UCP3). The case-control study enrolled 282 obese and 483 non-obese patients with type 2 diabetes. A literature search was made to identify all studies that evaluated associations between UCP1-3 polymorphisms and obesity. In the case-control study the distributions of the UCP variants did not differ between obese and non-obese groups (P > 0.05). Forty-seven studies were eligible for the meta-analysis and the results showed that the UCP2 -866G/A and UCP3 -55C/T polymorphisms were associated with protection to obesity in Europeans (OR = 0.89, 95% CI 0.82-0.97 and OR = 0.88, 95% CI 0.80-0.97, respectively). The UCP2 Ala55 val polymorphism was associated with obesity in Asians (OR = 1.61, 95% CI 1.13-2.30). The UCP2 Ins/Del polymorphism was associated with obesity mainly in Europeans (OR = 1.19, 95% CI 1.00-1.42). There was no significant association of the UCP1 -3826A/G polymorphism with obesity. In our case-control study we were not able to demonstrate any association between UCP polymorphisms and obesity in T2DM patients; however, in the meta-analysis we detected a significant association of UCP2 -866G/A, Ins/Del, Ala55Val and UCP3 -55C/T polymorphisms with obesity.

Brown adipose tissue in adult humans: a metabolic renaissance

Brown adipose tissue (BAT) plays a key role in energy homeostasis and thermogenesis in animals, conferring protection against diet-induced obesity and hypothermia through the action of uncoupling protein 1 (UCP1). Recent metabolic imaging studies using positron emission tomography computerized tomography (PET-CT) scanning have serendipitously revealed significant depots of BAT in the cervical-supraclavicular regions, demonstrating persistence of BAT beyond infancy. Subsequent cold-stimulated PET-CT studies and direct histological examination of adipose tissues have demonstrated that BAT is highly prevalent in adult humans. BAT activity correlates positively with increment of energy expenditure during cold exposure and negatively with age, body mass index, and fasting glycemia, suggesting regulatory links between BAT, cold-induced thermogenesis, and energy metabolism. Human BAT tissue biopsies express UCP1 and harbor inducible precursors that differentiate into UCP1-expressing adipocytes in vitro. These recent discoveries represent a metabolic renaissance for human adipose biology, overturning previous belief that BAT had no relevance in adult humans. They also have implications for the understanding of the pathogenesis and treatment of obesity and its metabolic sequelae.

The role of the uncoupling protein 1 (UCP1) on the development of obesity and type 2 diabetes mellitus

It is well established that genetic factors play an important role in the development of both type 2 diabetes mellitus (DM2) and obesity, and that genetically susceptible subjects can develop these metabolic diseases after being exposed to environmental risk factors. Therefore, great efforts have been made to identify genes associated with DM2 and/or obesity. Uncoupling protein 1 (UCP1) is mainly expressed in brown adipose tissue, and acts in thermogenesis, regulation of energy expenditure, and protection against oxidative stress. All these mechanisms are associated with the pathogenesis of DM2 and obesity. Hence, UCP1 is a candidate gene for the development of these disorders. Indeed, several studies have reported that polymorphisms -3826A/G, -1766A/G and -112A/C in the promoter region, Ala64Thr in exon 2 and Met299Leu in exon 5 of UCP1 gene are possibly associated with obesity and/or DM2. However, results are still controversial in different populations. Thus, the aim of this study was to review the role of UCP1 in the development of these metabolic diseases.

Implications of nonshivering thermogenesis for energy balance regulation in humans

The incidence of the metabolic syndrome has reached epidemic levels in the Western world. With respect to the energy balance, most attention has been given to reducing energy (food) intake. Increasing energy expenditure is an important alternative strategy. Facultative thermogenesis, which is the increase in energy expenditure in response to cold or diet, may be an effective way to affect the energy balance. The recent identification of functional brown adipose tissue (BAT) in adult humans promoted a renewed interest in nonshivering thermogenesis (NST). The purpose of this review is to highlight the recent insight in NST, general aspects of its regulation, the major tissues involved, and its metabolic consequences. Sustainable NST in adult humans amounts to 15% of the average daily energy expenditure. Calculations based on the limited available literature show that BAT thermogenesis can amount to 5% of the basal metabolic rate. It is likely that at least a substantial part of NST can be attributed to BAT, but it is possible that other tissues contribute to NST. Several studies on mitochondrial uncoupling indicate that skeletal muscle is another potential contributor to facultative thermogenesis in humans. The general and synergistic role of the sympathetic nervous system and the thyroid axis in relation to NST is discussed. Finally, perspectives on BAT and skeletal muscle NST are given.

The polymorphisms of UCP1 genes associated with fat metabolism, obesity and diabetes

Uncoupling protein 1 (UCP1), a 32-kDa protein located in the inner mitochondrial membrane, is abundant in brown adipose tissue, as a proton transporter in mitochondria inner membrane which uncouples oxidative metabolism from ATP synthesis and dissipates energy through the heat. UCP1 has been reported to play important roles for energy homeostasis in rodents and neonate of larger mammals including human. Recently, numerous candidate genes were searched to determine the genetic factors implicated in the pathogenesis of obesity, related metabolic disorders and diabetes. UCP-1, which plays a major role in thermogenesis, was suggested to be one of the candidates. This review summarizes data supporting the existence of brown adipocytes and the role of UCP1 in energy dissipation in adult humans, and the genetic variety association with the fat metabolism, obesity and diabetes.

The uncoupling protein-1 gene -3826A/G polymorphism and hypertension in Japanese subjects

BACKGROUND

The possible effects of the uncoupling protein-1 (UCP-1) gene -3826A/G polymorphism on hypertension (HT) have yet to be elucidated.

METHODS

A total of 578 Japanese subjects (231 males and 347 females, mean age 58.4 years) were enrolled in the study to investigate the association between HT and the -3826A/G polymorphism by genomic PCR and Bcl1-restriction fragment length polymorphism methods.

RESULTS

Multivariate logistic regression analysis for HT, adjusted for genotype (recessive model, AA+AG vs. GG) and other covariates such as cardiovascular risk factors [e.g., smoking, body mass index (BMI), dyslipidemia and diabetes] showed age [odds ratio (OR) 1.11 (95% confidence interval 1.08-1.13)] and BMI [OR 1.13 (1.06-1.21)] as independent significant factors. In the subgroup analysis, as well as age and BMI, GG genotype [OR 2.32 (1.08-4.99)] was also an independent significant factor for HT in males. Similarly, as well as age and BMI, GG genotype [OR 1.89 (1.00-3.57)] was also an independent significant factor for HT in the relatively older subgroup (> or =60 years).

CONCLUSIONS

The results suggest that the GG genotype may be associated with the presence of HT in Japanese males and older subjects. Further investigation is needed to confirm our hypothesis.

Relationship between A-3826G polymorphism in the promoter of the uncoupling protein-1 gene and high-density lipoprotein cholesterol in Japanese individuals: a cross-sectional study

BACKGROUND

A-3826G polymorphism within the promoter region of the uncoupling protein-1 (UCP-1) gene is possibly involved in the pathophysiology of obesity and metabolic disorders. However, the effects of UCP-1 A-3826G polymorphism on high-density lipoprotein cholesterol (HDL-C), a major contributor to atherosclerotic disease, still have not been established.

METHODS

A total of 298 healthy Japanese subjects (144 males and 154 females, mean age: 45.2 years) with a body mass index (BMI) of 20.0-30.0 kg/m(2), regular lifestyles, and receiving no medication were enrolled in the cross-sectional study to estimate the relationship of serum HDL-C levels with UCP-1 A-3826G polymorphism by genomic PCR and Bcl1-restriction fragment length polymorphism analysis. We used 1.04 mmol/L of HDL-C in Japanese males and 1.29 mmol/L in Japanese females as cut-off values of low HDL-cholesterolemia.

RESULTS

The genotype and allele frequencies of UCP-1 A-3826G polymorphism were similar to those previously reported in the Japanese population. In males, HDL-C levels of the GG genotype (1.75+/-0.49 mmol/L) were significantly higher than those found in the AA genotype (1.45+/-0.34 mmol/L, p=0.015). In females, the occurrence rate of low HDL-cholesterolemia was significantly different by genotype: a low prevalence in the GG genotype (15.4% in the AA, 4.8% in the AG, 15.4% in the GG genotype, p=0.022). Logistic regression analysis was used to identify risk factors for low HDL-cholesterolemia, with adjustments for age, gender, smoking, alcohol intake, BMI, hypertriglyceridemia, and genotype. The GG genotype was detected as being a significant associated factor (odds ratio =0.11 [95% confidence interval =0.01-0.90], p=0.01), in addition to BMI and the presence of hypertriglyceridemia.

CONCLUSIONS

These results suggest that the GG genotype may be an independent protective factor associated with low HDL-cholesterolemia in this population, although the role of the UCP-1 A-3826G polymorphism in HDL-C is complex and remains controversial. This hypothesis needs further investigation.

The effects of UCP-1 polymorphisms on obesity phenotypes among Korean female subjects

Three SNPs of UCP-1 including A-3826G, A-1766G, and Ala64Thr (G+1068A) were genotyped among 453 overweight Korean female subjects recruited from an obesity clinic. Four common haplotypes with frequency greater than 0.04 were constructed with three SNPs. For an accurate evaluation of the effects of UCP-1 polymorphism on body fat accumulation, all subjects were tested using computerized tomography to measure the cross-sectional fat tissue areas at abdominal and distal part of the body. By statistical analyses, ht4[GAA] showed a significant association with decreased abdominal fat tissue area (P=0.02, dominant model), fat tissue area at thigh (P=0.008, dominant model), body fat mass (P=0.002, dominant model), and waist-to-hip ratio (P=0.01, dominant model). In addition, ht3[GAG] was associated with the accelerated reduction of waist-to-hip ratio and body fat mass by very low calorie diet among subjects who finished one-month-weight control program (P=0.05-0.006).

The finding of new genetic polymorphism of UCP-1 A-1766G and its effects on body fat accumulation

A-1766G polymorphism, for the first time, has been found in the sequencing of pooled and individual genomic DNA of Korean subjects at the 5' flanking region of the UCP-1 gene. The effects of new polymorphism on body fat were elucidated among 387 Korean female subjects. It was shown that the genotypes AA, AG, and GG were consisted of 57.4%, 37.7%, and 4.9%, respectively, which was in agreement with Hardy-Weinberg equilibrium (P=0.327). The frequency of major A allele was 0.762 and that of minor G allele was 0.238. It is found that the waist-hip ratio (WHR) (P=0.008), body fat mass (P=0.023), and percent body fat (P=0.014) are significantly higher in the AG/GG type compared to the AA type. When the subjects were analyzed using computerized tomography, there were significant increases in the AG/GG type compared to the AA type in the abdominal subcutaneous fat (P=0.015) and the abdominal visceral fat (P=0.013), respectively. A-1766G is approximately 2 kb downstream from the well-known A-3826G polymorphism, and no linkage between them was found (D'=0.929, R(2)=0.283). Three haplotypes (frequency >0.05) were examined from two polymorphisms and studied for their physiological effects. It was found that haplotype [GG] was significantly associated with increased body fat, while haplotype [GA] was associated with decreased body fat.

The effects of uncoupling protein-1 genotype on lipoprotein cholesterol level in Korean obese subjects

Uncoupling protein-1 (UCP-1) plays a major role in thermogenesis, and has been implicated in the pathogenesis of obesity and metabolic disorders. The purpose of this study was to estimate the effects of A-3826G polymorphism of the UCP-1 gene on the plasma lipid profiles in 190 Korean obese subjects with a body mass index (BMI) more than 30 kg/m2. Height, weight, BMI, wait-to-hip ratio (WHR), obesity index, and body composition were measured and genotype of UCP-1 was analyzed by polymerase chain reaction (PCR) restriction fragment length polymorphism (RFLP) method. Serum concentrations of fasting glucose, total cholesterol, high-density lipoprotein (HDL) cholesterol, and triglyceride were measured. The frequencies of UCP-1 genotypes were AA type, 22.1%; AG type, 53.7%; and GG type, 24.2%; and the frequency of G allele was 0.51. Among many parameters, diastolic blood pressure (DBP) (P = .023) and low-density lipoprotein (LDL) cholesterol (P = .011) were significantly higher in AG and GG types compared with AA type, whereas HDL cholesterol was significantly lower in GG type compared with other types (P < .05). Atherogenic index was significantly higher in GG type compared with AA type (P = 0.027). LDL-to-HDL cholesterol ratio was significantly increased in the order of AA < AG < GG types (P = .001). When the subjects were divided into a normal group and a hyper-LDL cholesterolemia group by LDL cholesterol level of 3.626 mmol/L (140 mg/dL), the frequency of hyper-LDL cholesterolemia was significantly higher in GG type compared with other types by Fisher's exact (chi-square) test (P = .05). When logistic regression analysis was conducted to find the risk factors of hyper-LDL cholesterolemia, the odds ratio was 4.115 (P = .03) for GG type of UCP-1 gene. These results suggest that the GG type of the UCP-1 gene has a strong association with increased LDL cholesterol level and might be a significant risk factor for hyper-LDL cholesterolemia among Korean obese subjects.

Putative role of polymorphisms in UCP1-3 genes for diabetic nephropathy

Increased production of reactive oxygen species (ROS) has been suggested as a cause of diabetic complications. Uncoupling proteins (UCPs) have been ascribed a role in reducing the formation of ROS, and genetic variation in genes encoding for UCPs could thus be putative candidate genes for diabetic nephropathy. To test this hypothesis we searched for association between the A-->G (-3862) variant in UCP1, the insertion/deletion (I/D) polymorphism in exon 8 in UCP2, and the C-->T (-55) polymorphism in UCP3 and diabetic nephropathy in 218 diabetic patients with normal urinary albumin excretion rate (AER), 216 with micro- or macroalbuminuria, and in 106 control subjects without a family history of diabetes. We did not find any association between the different polymorphisms and diabetic nephropathy, nor did we observe any difference in AER among carriers of different UCP1-3 genotypes. We could, however, confirm the reported association between BMI and the UCP3 -55 C-->T polymorphism; patients carrying the T allele had higher BMI than patients homozygous for the C allele (26.4+/-4.2 vs. 25.3+/-4.3 kg/m(2); P=.01). We conclude that studied polymorphisms in the UCP1-3 genes do not play a major role in the development of micro- or macroalbuminuria in Scandinavian diabetic patients.

Estudios sobre la obesidad en genes candidatos

There are more than 430 chromosomic regions with gene variants involved in body weight regulation and obesity development. Polymorphisms in genes related to energy expenditure--uncoupling proteins (UCPs), related to adipogenesis and insulin resistance--hormone-sensitive lipase (HLS), peroxisome proliferator-activated receptor gamma (PPAR gamma), beta adrenergic receptors (ADRB2,3), and alfa tumor necrosis factor (TNF-alpha), and related to food intake--ghrelin (GHRL)--appear to be associated with obesity phenotypes. Obesity risk depends on two factors: a) genetic variants in candidate genes, and b) biographical exposure to environmental risk factors. It is necessary to perform new studies, with appropriate control groups and designs, in order to reach relevant conclusions with regard to gene/environmental (diet, lifestyle) interactions.

Effects of uncoupling protein 1 and beta3-adrenergic receptor gene polymorphisms on body size and serum lipid concentrations in Japanese women

OBJECTIVES

To investigate whether the -3826 A-G point mutation of the uncoupling protein 1 (UCP1) gene and the Trp64Arg mutation of the beta3-adrenergic receptor (beta3-AR) gene are associated with increased susceptibility to weight gain and hyperlipidemia in postmenopausal women.

METHODS

We genotyped 312 Japanese women for UCP1 and beta3-AR gene polymorphisms, and investigated their effects on anthropometrical parameters, serum lipid concentrations, and their changes after 4 years.

RESULTS

Although body mass index (BMI), serum triglyceride, total cholesterol, and low-density lipoprotein levels were significantly higher and high-density lipoprotein levels significantly lower in postmenopausal (n=182) than in premenopausal (n=99) women, there was no significant difference in these parameters between carriers and non-carriers of the G allele in the postmenopausal women. In the premenopausal women, BMI and the 4-year change in body weight (BW) of carriers of the G allele were significantly higher than those of non-carriers of the G allele (P=0.022 and 0.048, respectively). In the postmenopausal women, the 4-year change in the level of serum triglyceride of carriers of the G allele was significantly higher (P=0.049), and the change of high-density lipoprotein was significantly lower (P=0.020) than those of non-carriers of the G allele. The beta3-AR polymorphism showed no apparent affect on these parameters.

CONCLUSIONS

The -3826 A-G polymorphism of the UCP1 gene is associated with an increase in BW of premenopausal women and with the 4-year changes in serum triglyceride and high-density lipoprotein levels in postmenopausal women.

Uncoupling protein 1 and 3 polymorphisms are associated with waist-to-hip ratio

Body weight regulation is a complex phenotype also depending on the action of uncoupling proteins (UCPs) that mediate the "uncoupling" of respiration leading to the dissipation of energy as heat. This study investigated whether genetic variants in the genes encoding UCP-1 and UCP-3 are associated with different obesity-related phenotypes in 162 whites with a wide range of body mass index. All subjects were genotyped for the polymorphisms UCP-1 A-3826G, UCP-1 Ala64Thr, and UCP-3 C-55T using a PCR-based restriction method with appropriate enzymes. The frequencies of the UCP-1 3826G, UCP-1 64Thr, and UCP-3 55T alleles were 27.2%, 12.0%, and 22.8%, respectively. No significant associations were observed between polymorphism and body mass index or obesity. However, after adjustment for gender, age, body mass index, and diabetes mellitus the waist-to-hip ratio was significantly associated with UCP-1 Ala64Thr ( P=0.003) and UCP-3 C-55T ( P=0.02) but not with UCP-1 A-3826G. The higher waist-to-hip ratios associated with the UCP-1 64Thr and UCP-3 55T alleles were due to higher waist circumference in these allele carriers. In conclusion, central obesity in whites as reflected by an increased waist-to-hip ratio is associated with the UCP-1 Ala64Thr and UCP-3 C-55T polymorphisms. To what extent these genotypes contribute to the overall cardiovascular risk remains to be elucidated.

Genetic factors as predictors of weight gain in young adult Dutch men and women

OBJECTIVE

To investigate the association between DNA polymorphisms in several candidate genes for obesity and weight gain. Polymorphisms in these genes may contribute to weight gain through effects on energy intake, energy expenditure or adipogenesis.

DESIGN AND METHODS

From two large cohorts in The Netherlands (total 17,500 adult men and women), we compared 286 subjects aged 20-40 y who gained an average of 12.8 kg (range 5.5-47 kg) during a mean follow-up of 6.8 y with 296 subjects who remained relatively constant over the same period with respect to occurrence of several polymorphisms in candidate genes of obesity and some lifestyle factors. Subjects who were dieting, were high alcohol consumers, were pregnant, changed their smoking status recently, or those who suffered from serious illnesses were excluded. Polymorphisms were determined in the LEPR-gene (LEPR Lys109Arg, LEPR Gln223Arg, LEPR Lys656Asn), in the UCP1 gene (A-G mutation at position-3826 5' region), in the UCP2 gene (Ala55Val, 45 bp Ins/Del), in the PPARG2 gene (Pro12Ala) and in the ADRB2 gene (Gly16Arg and Gln27Glu).

RESULTS

With the exception of the Gly16Arg polymorphism in the ADRB2 gene in men (P = 0.04) and women (P = 0.05), and the Lys109Arg polymorphism in the LEPR gene in women, no statistically significant differences in the genotype and allele frequencies were observed between weight gainers and non-weight gainers. Weight gainers differed in some aspects of dietary habits and physical activity patterns: weight gainers consumed relatively more savory snacks and were less active during leisure time compared with non-weight gainers.

CONCLUSION

Only variations in the ADRB2 gene and LEPR gene, may contribute to susceptibility to weight gain. None of the other studied genetic markers were clearly associated with weight gain. Further research is necessary to establish the role of lifestyle factors, or interactions between genes or between genes and lifestyle factors on weight gain with age.

Reward deficiency syndrome: a biogenetic model for the diagnosis and treatment of impulsive, addictive, and compulsive behaviors

The dopaminergic system, and in particular the dopamine D2 receptor, has been implicated in reward mechanisms. The net effect of neurotransmitter interaction at the mesolimbic brain region induces "reward" when dopamine (DA) is released from the neuron at the nucleus accumbens and interacts with a dopamine D2 receptor. "The reward cascade" involves the release of serotonin, which in turn at the hypothalmus stimulates enkephalin, which in turn inhibits GABA at the substania nigra, which in turn fine tunes the amount of DA released at the nucleus accumbens or "reward site." It is well known that under normal conditions in the reward site DA works to maintain our normal drives. In fact, DA has become to be known as the "pleasure molecule" and/or the "antistress molecule." When DA is released into the synapse, it stimulates a number a DA receptors (D1-D5) which results in increased feelings of well-being and stress reduction. A consensus of the literature suggests that when there is a dysfunction in the brain reward cascade, which could be caused by certain genetic variants (polygenic), especially in the DA system causing a hypodopaminergic trait, the brain of that person requires a DA fix to feel good. This trait leads to multiple drug-seeking behavior. This is so because alcohol, cocaine, heroin, marijuana, nicotine, and glucose all cause activation and neuronal release of brain DA, which could heal the abnormal cravings. Certainly after ten years of study we could say with confidence that carriers of the DAD2 receptor A1 allele have compromised D2 receptors. Therefore lack of D2 receptors causes individuals to have a high risk for multiple addictive, impulsive and compulsive behavioral propensities, such as severe alcoholism, cocaine, heroin, marijuana and nicotine use, glucose bingeing, pathological gambling, sex addiction, ADHD, Tourette's Syndrome, autism, chronic violence, posttraumatic stress disorder, schizoid/avoidant cluster, conduct disorder and antisocial behavior. In order to explain the breakdown of the reward cascade due to both multiple genes and environmental stimuli (pleiotropism) and resultant aberrant behaviors, Blum united this hypodopaminergic trait under the rubric of a reward deficiency syndrome.

The human uncoupling protein-1 gene (UCP1): present status and perspectives in obesity research

Energy expenditure through brown adipose tissue thermogenesis contributes either to maintenance of body temperature in a cold environment or to wasted food energy, i.e. cold-induced or diet-induced thermogenesis. Both mechanisms are due to a specific and unique protein: the uncoupling protein-1. Uncoupling protein-1 is exclusively expressed in mitochondria of brown adipocytes where it uncouples respiration from ATP synthesis, dissipating the proton gradient as heat. In humans, although uncoupling protein-1 can be detected, the inability to quantify brown adipose tissue makes it difficult to argue for a role for uncoupling protein-1 in thermogenesis and energy expenditure. This review summarizes data supporting the existence of brown adipocytes and the role of UCP1 in energy dissipation in adult humans. Understanding the mechanisms which regulate transcription and expression of the human UCP1 gene will facilitate the identification of molecules able to increase the levels of this protein in order to modulate energy expenditure in adult humans.

Promising new approaches to the management of obesity

The pathophysiology of obesity is complex with many different pathways involved. A better understanding of these weight-regulating mechanisms has lead to the identification of new targets for anti-obesity agents. Most attention has been given to the centrally acting neuropeptides regulating food intake. Leptin, playing a key-role, exerts its action through several neuropeptides such as neuropeptide Y, alpha-melanocyte stimulating hormone and agouti related protein. Cocaine- and amphetamine-regulated transcript peptide and the orexins are the latest discovered peptides acting at the level of the hypothalamus. Targets for new drugs acting on peptides secreted from the periphery are cholecystokinin and glucagon-like peptide 1. Another potential target in the treatment of obesity is increasing energy expenditure via beta3 adrenoceptors or uncoupling proteins. These new pharmacological agents in development could be valuable adjuncts to more traditional treatment strategies such as dietary treatment, behavioural/psychological counselling and physical activity.

Associations between uncoupling protein 2, body composition, and resting energy expenditure in lean and obese African American, white, and Asian children

BACKGROUND

Little is known about genes that affect childhood body weight.

OBJECTIVE

The objective of this study was to examine the association between alleles of the mitochondrial uncoupling protein 2 (UCP2) gene and obesity because UCP2 may influence energy expenditure.

DESIGN

We related UCP2 genotype to body composition and resting energy expenditure in 105 children aged 6-10 y. Overweight children and nonoverweight children of overweight parents were genotyped for a 45-base pair deletion/insertion (del/ins) in 3'-untranslated region of exon 8 and for an exon 4 C to T transition.

RESULTS

Eighty-nine children were genotyped for the exon 8 allele: 50 children had del/del, 33 had del/ins, and 6 had ins/ins. Mean (+/-SD) body mass index (BMI; in kg/m(2)) was greater for children with del/ins (24.1 +/- 5.9) than for children with del/del (20.4 +/- 4.8; P < 0.001). BMI of ins/ins children (23.7 +/- 7.8) was not significantly different from that of del/ins children. A greater BMI in del/ins children was independent of race and sex. Body composition was also different according to UCP2 genotype. All body circumferences and skinfold thicknesses examined were significantly greater in del/ins than in del/del children. Body fat mass as determined by dual-energy X-ray absorptiometry was also greater in del/ins than in del/del children (P < 0.005). For 104 children genotyped at exon 4, no significant differences in BMI or body composition were found among the 3 exon 4 genotypes. Neither resting energy expenditure nor respiratory quotient were different according to UCP2 exon 4 or exon 8 genotype.

CONCLUSIONS

The exon 8 ins/del polymorphism of UCP2 appears to be associated with childhood-onset obesity. The UCP2/UCP3 genetic locus may play a role in childhood body weight.

Obesity--a genetic disease of adipose tissue?

Although the rapid increase in the prevalence of obesity in many countries suggests that environmental factors (mainly overeating and physical inactivity) play the most important role in the development of overweight, it is very likely that genetic factors also contribute. It appears that one major gene in combination with one or several minor genes constitute the genetic components behind excess accumulation of body fat in most obese individuals. However, monogenic obesity has been described in a few families due to changes in leptin, leptin receptor, prohormone convertase, pro-opiomelanocortin or melanocortin-4 receptor. None of the monogenic variants is of great importance for common human obesity; the latter genes are unknown so far. Results from genomic scans suggest that major obesity genes are located on chromosomes 2, 10, 11 and 20. Studies of candidate genes indicate that the minor obesity genes control important functions of adipose tissue, and that structural variance in these genes may alter adipose tissue function in a way that promotes obesity. Such genes are beta 2- and beta 3-adrenoceptors, hormone-sensitive lipase, tumour necrosis factor alpha, uncoupling protein-1, low-density lipoprotein receptor, and peroxisome proliferator activator receptor gamma-2. Some of these genes may promote obesity by gene-gene interactions (for example beta 3-adrenoceptors and uncoupling protein-1) or gene-environment interactions (for example beta 2-adrenoceptors and physical activity). Some are important for obesity only among women (for example beta 2- and beta 3-adrenoceptors, low-density lipoprotein receptor and tumour necrosis factor alpha). Few 'non-adipose' genes have so far shown a firm association to common human obesity, which could suggest that the important genes for the development of excess body fat also control adipose tissue function.

The human obesity gene map: the 1998 update

An update of the human obesity gene map incorporating published results up to the end of October 1998 is presented. Evidence from the human obesity cases caused by single gene mutations; other Mendelian disorders exhibiting obesity as a clinical feature; quantitative trait loci uncovered in human genome-wide scans and in crossbreeding experiments with mouse, rat, and pig models; association and case-control studies with candidate genes; and linkage studies with genes and other markers is reviewed. The most noticeable changes from the 1997 update is the number of obesity cases due to single gene mutations that increased from three cases due to mutations in two genes to 25 cases due to 12 mutations in seven genes. A look at the obesity gene map depicted in Figure 1 reveals that putative loci affecting obesity-related phenotypes are found on all but chromosome Y of the human chromosomes. Some chromosomes show at least three putative loci related to obesity on both arms (1, 2, 3, 6, 7, 8, 9, 11, 17, 19, 20, and X) and several on one chromosome arm only (4q, 5q, 10q, 12q, 13q, 15q, 16p, and 22q). The number of genes and other markers that have been associated or linked with human obesity phenotypes is increasing very rapidly and now approaches 200.