Mapping of the OB receptor to 1p in a region of nonconserved gene order from mouse and rat to human

Genetic predisposition of LEPR (rs1137101) gene polymorphism related to type 2 diabetes mellitus - a meta-analysis

Background: Type 2 diabetes mellitus (T2DM) is a multifaceted disease appropriate to elevated blood glucose levels resulting from decreased insulin and beta-cell activity. Using a case-control methodology, researchers have examined the relationship between polymorphisms in LEPR and T2DM in a population from south India.Materials and Methods: We conducted a genetic analysis of 311 participants, and results were accomplished using a case-control study, a meta-analysis of previous studies on LEPR was conducted, and type 2 diabetes genotype distribution across various geographical regions Malaysians, Chinese Han, Kuwait, Iran, Mongolia, and Han Chinese, Greece, Saudi, India (North India, Punjabi), (South India, Tamilnadu). The study involved 254 prospective investigations, and nine association studies were preferred according to preset criteria. Studies were assessed for quality using the Hardy-Weinberg equilibrium (HWE) and the Newcastle-Ottawa Scale (NOS). An analysis of the genetic models was conducted to determine their relationship, statistical analysis was utilized to calculate odds ratios (ORs) and matching 95% confidence intervals (CIs).Results: The LEPR-rs1137101 polymorphism in the case-control study was associated with a significant increase in the risk of type 2 diabetes. A meta-analysis revealed a connection between LEPR gene polymorphism (rs1137101) and type 2 diabetes risk. Investigators might gain a more profound thought on the significance of the identified genetic variation and its impact on the chance of developing type 2 diabetes by verifying and strengthening previously reported findings. The model of fixed effects was chosen due to the low heterogeneity, and significant associations were observed in the allelic (OR = 0.79, 95% CI [0.70-0.87]), homozygote (OR = 0.58, 95% CI [0.46-0.72]), dominant (OR = 0.66, 95% CI [0.56-0.79]), and recessive (OR = 0.83, 95% CI [0.71-0.96]) genetic models. A Begg's funnel plot and Egger's test indicated no publication bias. These findings suggest that the rs1137101 variant in the LEPR gene has been linked to a higher risk of T2DM.Conclusions: A larger sample size, however, is required for further research, and consideration of potential confounding factors is needed to validate these associations. Understanding the implications of LEPR gene polymorphisms in T2DM susceptibility may contribute to personalized treatment strategies for patients with T2DM.

Trajectory of leptin and leptin receptor in vertebrates: Structure, function and their regulation

The present review provides a comparative insight into structure, function and control of leptin system in fishes, herptiles, birds and mammals. In general, leptin acts as an anorexigenic hormone since its administration results in decrease of food intake in vertebrates. Nonetheless, functional paradox arises in fishes from contradictory observations on level of leptin during fasting and re-feeding. In addition, leptin is shown to modulate metabolic functions in fishes, reptiles, birds and mammals. Leptin also regulates reproductive and immune functions though more studies are warranted in non-mammalian vertebrates. The expression of leptin and its receptor is influenced by numerous factors including sex steroids, stress and stress-induced catecholamines and glucocorticoids though their effect in non-mammalian vertebrates is hard to be generalized due to limited studies.

Association of LEPR gene polymorphisms with the risk of hepatitis B virus-related liver disease in Guangxi Chinese: A case-control study

BACKGROUND AND OBJECTIVE

Leptin receptor (LEPR) signaling inhibits apoptosis, promotes angiogenesis and proliferation, and plays a critical role in carcinogenesis. Variants of the LEPR gene may be key factors in the growth of human malignant tumors. However, the relationship between LEPR polymorphisms and hepatocellular carcinoma (HCC) has not been thoroughly investigated. Therefore, we further investigated the association between LEPR polymorphisms and the risk of chronic hepatitis B (CHB), hepatitis B virus (HBV)-related liver cirrhosis (LC), and HCC in a southern Guangxi Chinese population.

METHOD

Two LEPR polymorphisms (rs1137100 and rs1137101) were genotyped in 138 CHB patients, 136 patients with LC, 149 HCC patients, and 146 healthy controls using the SNaPshot method.

RESULTS

We did not observe any significant difference in the LEPR rs1137100 and rs1137101 polymorphisms between the groups of healthy controls and patients (all p > 0.05), regardless of genotypes, alleles, or haplotypes.

CONCLUSIONS

Our data suggest that the genetic variants of the LEPR gene are not associated with the risk of HBV-related liver diseases (CHB, LC, and HCC) in the Guangxi population. Further studies are necessary to validate these results.

A meta-analysis of associations of LEPR Q223R and K109R polymorphisms with Type 2 diabetes risk

Background

Leptin receptor (LEPR) plays a pivotal role in the control of body weight, energy metabolism, and insulin sensitivity. Various genetic association studies were performed to evaluate associations of LEPR genetic variants with type 2 diabetes (T2D) susceptibility.

Methods

A comprehensive search was conducted to identify all eligible case-control studies for examining the associations of LEPR single nucleotide polymorphisms (SNPs) Q223R (rs1137101) and K109R (rs1137100) with T2D risk. Odds ratios (OR) and corresponding 95% confidence intervals (CIs) were used to measure the magnitudes of association.

Results

For Q223R, 13 studies (11 articles) consisting of a total of 4030 cases and 2844 controls, and for K109R 7 studies (7 articles) consisting of 3319 cases and 2465 controls were available. Under an allele model, Q223R was not significantly associated with T2D risk (OR = 1.09, 95% CI: 0.80–1.48, P-value = 0.5989), which was consistent with results obtained under four genotypic models (ranges: ORs 1.08–1.20, 95% CIs: 0.58–2.02 to 0.64–2.26; P-values, 0.3650–0.8177, which all exceeded multiplicity-adjusted α = 0.05/5 = 0.01). In addition, no significant association was found between K109R and T2D risk based on either an allele model (OR = 0.93, 95% CI: 0.85–1.03, P-value = 0.1868) or four genotypic models (ranges: ORs 0.81–0.99, 95% CIs: 0.67–0.86 to 0.97–1.26, P-values, 0.0207–0.8804 which all exceeded multiplicity-adjusted α of 0.01). The magnitudes of association for these two SNPs were not dramatically changed in subgroup analyses by ethnicity or sensitivity analyses. Funnel plot inspections as well as Begg and Mazumdar adjusted rank correlation test and Egger linear regression test did not reveal significant publication biases in main and subgroup analyses. Bioinformatics analysis predicted that both missense SNPs were functionally neutral and benign.

Conclusions

The present meta-analysis did not detect significant genetic associations between LEPR Q223R and K109R polymorphisms and T2D risk.

Dietary Interventions, Cardiovascular Aging, and Disease

Recent studies indicate that dietary interventions have the potential to prevent and even treat cardiovascular disease, which is the leading cause of death. Many of these studies have focused on various animal models that are able to recreate one or more conditions or elevate risk factors that characterize the disease. Here, we highlight macronutrient-focused interventions in both mammalian model organisms and humans with emphasis on some of the most relevant and well-established diets known to be associated with cardiovascular disease prevention and treatment. We also discuss more recent dietary interventions in rodents, monkeys, and humans, which affect atherosclerosis and cardiovascular diseases with focus on those that also delay aging.

Obstructive Sleep Apnea Susceptibility Genes in Chinese Population: A Field Synopsis and Meta-Analysis of Genetic Association Studies

BACKGROUND

Epidemiological studies to date have evaluated the association between genetic variants and the susceptibility to obstructive sleep apnea (OSA). However, the results of these studies have been inconclusive. In this current study we performed meta-analysis of genetic association studies (GAS) to pool OSA-susceptible genes in Chinese population, to perform a more precise evaluation of the association.

METHODS

Various databases (i.e., PubMed, EMBASE, HuGE Navigator, Wanfang and CNKI) were searched to identify all eligible GAS-related variants associated with susceptibility to OSA. The generalized odds ratio metric (ORG) and the odds ratio (OR) of the allele contrast were used to quantify the impact of genetic variants on the risk of OSA. Cumulative and recursive cumulative meta-analyses (CMA) were also performed to investigate the trend and stability of effect sizes as evidence was accumulated.

RESULTS

Thirty-two GAS evaluating 13 polymorphisms in 10 genes were included in our meta-analysis. Significant associations were derived for four polymorphisms either for the allele contrast or for the ORG. The variants TNF-α-308G/A, 5-HTTLPR, 5-HTTVNTR, and APOE showed marginal significance for ORG (95% confidence interval [CI]): 2.01(1.31-3.07); 1.31(1.09-1.58); 1.85(1.16-2.95); 1.79(1.10-2.92); and 1.79(1.10-2.92) respectively. In addition, the TNF-α-308G/A, 5-HTTLPR, and 5-HTTVNTR variants showed significance for the allele contrast: 2.15(1.39-3.31); 2.26(1.58-3.24); 1.32(1.12-1.55); and 1.86(1.12-3.08) respectively. CMA showed a trend towards an association, and recursive CMA indicated that more evidence was needed to determine whether this was significant.

CONCLUSIONS

TNF-α, 5-HTT, and APOE genes can all be proposed as OSA-susceptibility genes in Chinese population. Genome-wide association studies (GWAS) are therefore urgently needed to confirm our findings within a larger sample of OSA patients in China.

Lack of mutations in the leptin receptor gene in severely obese children

OBJECTIVE

To analyze the LEPR gene in obese children and to investigate the associations between molecular findings and anthropometric and metabolic features.

SUBJECTS AND METHODS

Thirty-two patients were evaluated regarding anthropometric characteristics, blood pressure, heart rate, serum glucose, insulin, leptin levels, and lipid profile. The molecular study consisted of the amplification and automatic sequencing of the coding region of LEPR in order to investigate new mutations.

RESULTS

We identified a high prevalence of metabolic disorders: impaired fasting glucose in 12.5% of the patients, elevated HOMA-IR in 85.7%, low HDL-cholesterol levels in 46.9%, high triglyceride levels in 40.6%, and hypertension in 58.6% of the patients. The molecular study identified 6 already described allelic variants: rs1137100 (exon-2), rs1137101 (exon-4), rs1805134 (exon-7), rs8179183 (exon-12), rs1805096 (exon-18), and the deletion/insertion of the pentanucleotide CTTTA at 3'untranslated region.

CONCLUSIONS

The frequency of alleles observed in this cohort is similar to that described in the literature, and was not correlated with any clinical feature. The molecular findings in the analysis of the LEPR did not seem to be implicated in the etiology of obesity in these patients.

The association between polymorphisms in the leptin receptor gene and risk of breast cancer: a systematic review and pooled analysis

Many epidemiological studies have found that leptin correlates to body fat extent and breast cancer. Leptin exerts its physiological action through the leptin receptor (LEPR). However, published data on the association between LEPR alleles and breast cancer occurrence have led to in contradictory results. A total of 10 studies were identified to the meta-analysis, including 4,644 cases and 5,485 controls for LEPR rs1137101 polymorphism, 5 studies with 2,759 cases and 4,464 controls for rs1137100 polymorphism, and 2 studies for rs8051542, rs8051542, and rs8051542 polymorphisms. The pooled odds ratios (OR) with 95 % confidence intervals (CI) for breast cancer risk associated with LEPR genotypes were estimated. Elevated breast cancer risk was associated with LEPR rs1137101 polymorphism when all studies were pooled in the meta-analysis (allele contrast model: OR = 0.71, 95 % CI = 0.551-0.997). In the stratified analysis by ethnicity, significantly increased risks were also found among Asians for allele contrast model (OR 0.414, 95 % CI 0.312-0.550) and dominant model (OR 0.537, 95 % CI 0.370-0.781); for Africans, significantly increased risks were also found for allele contrast model (OR 0.716, 95 % CI 0.595-0.861), homozygote codominant (OR 0.537, 95 % CI 0.370-0.781) and dominant model (OR 1.595, 95 % CI 1.207-2.108). And significantly elevated breast cancer risk was associated with LEPR rs1137100 polymorphism for allele contrast (OR = 0.666, 95 % CI = 0.603-0.720) and homozygote codominant models (OR = 0.344, 95 % CI = 0.282-0.421). For LEPR rs8179183, rs4655537, and rs3762274 polymorphisms, no significant associations were detected in all comparison models. This pooled analysis suggested that rs1137101 and rs1137100 polymorphisms were significantly correlated with breast cancer risk and the A allele of LEPR rs1137101 variant and the G allele of LEPR rs1137100 variant were low-penetrant risk factors for developing breast cancer. Further, no significant associations existed between LEPR rs8179183, rs4655537, and rs3762274 polymorphisms and risk of breast cancer.

Effect of LEPR Gln223Arg polymorphism on breast cancer risk in different ethnic populations: a meta-analysis

Leptin and leptin receptor have been implicated in processes leading to breast cancer initiation and progression. An A to G transition mutation in codon 223, in exon 6 of the leptin receptor gene (LEPR) can result in glutamine to arginine substitution (Gln223Arg). A variety of case-control studies have been published evaluating the association between LEPR Gln223Arg polymorphism and breast cancer. However, published studies have yielded contradictory conclusions. This meta-analysis enrolled eight studies to estimate the overall risk of LEPR Gln223Arg polymorphism associated with breast cancer. The pooled ORs were performed for codominant model (Arg/Arg versus Gln/Gln; Arg/Gln versus Gln/Gln), dominant model (Arg/Arg + Arg/Gln versus Gln/Gln), recessive model (Arg/Arg versus Arg/Gln + Gln/Gln). Overall significantly elevated breast cancer risk was found for recessive model (OR 1.32, 95% CI 1.03-1.69) and for genotype Arg/Gln versus Gln/Gln (OR 1.16, 95% CI 1.01-1.34). In the stratified analysis by ethnicity, significantly increased risks were also found among Africans for genotype Arg/Arg versus Gln/Gln: OR 1.86, 95% CI 1.28-2.71, Arg/Gln versus Gln/Gln: OR 1.48, 95% CI 1.10-1.99, dominant model: OR 1.60, 95% CI 1.21-2.11 and recessive model: OR 1.48, 95% CI 1.07-2.05; for Asians, Arg/Arg versus Gln/Gln: OR 6.79, 95% CI 3.42-13.47 and dominant model: OR 2.03, 95% CI 1.42-2.90. However, no significantly increased risk was found among Europeans for all genetic models. In conclusion, the LEPR 223Arg is a low-penetrant risk for developing breast cancer, especially for black African women.

Fine-mapping of obesity-related quantitative trait loci in an F9/10 advanced intercross line

Obesity develops in response to a combination of environmental effects and multiple genes of small effect. Although there has been significant progress in characterizing genes in many pathways contributing to metabolic disease, knowledge about the relationships of these genes to each other and their joint effects upon obesity lags behind. The LG,SM advanced intercross line (AIL) model of obesity has been used to characterize over 70 loci involved in fatpad weight, body weight, and organ weights. Each of these quantitative trait loci (QTLs) encompasses large regions of the genome and require fine-mapping to isolate causative sequence changes and possible mechanisms of action as indicated by the genetic architecture. In this study we fine-map QTLs first identified in the F(2) and F(2/3) populations in the combined F(9/10) advanced intercross generations. We observed significantly narrowed QTL confidence regions, identified many single QTL that resolve into multiple QTL peaks, and identified new QTLs that may have been previously masked due to opposite gene effects at closely linked loci. We also present further characterization of the pleiotropic and epistatic interactions underlying these obesity-related traits.

Metabolic syndrome components in murine models

Animal models have enriched understanding of the physiological basis of metabolic disorders and advanced identification of genetic risk factors underlying the metabolic syndrome (MetS). Murine models are especially appropriate for this type of research, and are an excellent resource not only for identifying candidate genomic regions, but also for illuminating the possible molecular mechanisms or pathways affected in individual components of MetS. In this review, we briefly discuss findings from mouse models of metabolic disorders, particularly in light of issues raised by the recent flood of human genome-wide association studies (GWAS) results. We describe how mouse models are revealing that genotype interacts with environment in important ways, indicating that the underlying genetics of MetS is highly context dependant. Further we show that epistasis, imprinting and maternal effects each contribute to the genetic architecture underlying variation in metabolic traits, and mouse models provide an opportunity to dissect these aspects of the genetic architecture that are difficult if not impossible to ascertain in humans. Finally we discuss how knowledge gained from mouse models can be used in conjunction with comparative genomic methods and bioinformatic resources to inform human MetS research.

Fyn mediates leptin actions in the thymus of rodents

BACKGROUND

Several effects of leptin in the immune system rely on its capacity to modulate cytokine expression and apoptosis in the thymus. Surprisingly, some of these effects are dependent on signal transduction through the IRS1/PI3-kinase, but not on the activation of JAK2. Since all the well known effects of leptin in different cell types and tissues seem to be dependent on JAK2 activation, we hypothesized that, at least for the control of thymic function, another, unknown kinase could mediate the transduction of the leptin signal from the ObR towards the IRS1/PI3-kinase signaling cascade.

METHODOLOGY/PRINCIPAL FINDINGS

Here, by employing immunoblot, real-time PCR and flow citometry we show that the tyrosine kinase, Fyn, is constitutively associated with the ObR in thymic cells. Following a leptin stimulus, Fyn undergoes an activating tyrosine phosphorylation and a transient association with IRS1. All these effects are independent of JAK2 activation and, upon Fyn inhibition, the signal transduction towards IRS1/PI3-kinase is abolished. In addition, the inhibition of Fyn significantly modifies the effects of leptin on thymic cytokine expression.

CONCLUSION/SIGNIFICANCE

Therefore, in the thymus, Fyn acts as a tyrosine kinase that transduces the leptin signal independently of JAK2 activation, and mediates some of the immunomodulatory effects of leptin in this tissue.

The genetics of neutral lipid biosynthesis: an evolutionary perspective

The storage of fatty acids and fatty alcohols in the form of neutral lipids such as triacylglycerol (TAG), cholesteryl ester (CE), and wax ester (WE) serves to provide reservoirs for membrane formation and maintenance, lipoprotein trafficking, lipid detoxification, evaporation barriers, and fuel in times of stress or nutrient deprivation. This ancient process likely originated in actinomycetes and has persisted in eukaryotes, albeit by different molecular mechanisms. A surfeit of neutral lipids is strongly, perhaps causally, related to several human diseases such as diabetes mellitus, obesity, atherosclerosis and nonalcoholic fatty liver disease. Therefore, understanding the metabolic pathways of neutral lipid synthesis and the roles of the enzymes involved may facilitate the development of new therapeutic interventions for these syndromes.

Molecular physiology of weight regulation in mice and humans

Evolutionary considerations relating to efficiency in reproduction, and survival in hostile environments, suggest that body energy stores are sensed and actively regulated, with stronger physiological and behavioral responses to loss than gain of stored energy. Many physiological studies support this inference, and suggest that a critical axis runs between body fat and the hypothalamus. The molecular cloning of leptin and its receptor-projects based explicitly on the search for elements in this axis-confirmed the existence of this axis and provided important tools with which to understand its molecular physiology. Demonstration of the importance of this soma-brain reciprocal connection in body weight regulation in humans has been pursued using both classical genetic approaches and studies of physiological responses to experimental weight perturbation. This paper reviews the history of the rationale and methodology of the cloning of leptin (Lep) and the leptin receptor (Lepr), and describes some of the clinical investigation characterizing this axis.

The role of leptin and ghrelin in the regulation of food intake and body weight in humans: a review

Leptin and ghrelin are two hormones that have been recognized to have a major influence on energy balance. Leptin is a mediator of long-term regulation of energy balance, suppressing food intake and thereby inducing weight loss. Ghrelin on the other hand is a fast-acting hormone, seemingly playing a role in meal initiation. As a growing number of people suffer from obesity, understanding the mechanisms by which various hormones and neurotransmitters have influence on energy balance has been a subject of intensive research. In obese subjects the circulating level of the anorexigenic hormone leptin is increased, whereas surprisingly, the level of the orexigenic hormone ghrelin is decreased. It is now established that obese patients are leptin-resistant. However, the manner in which both the leptin and ghrelin systems contribute to the development or maintenance of obesity is as yet not clear. The purpose of this review is to provide background information on the leptin and ghrelin hormones, their role in food intake and body weight in humans, and their mechanism of action. Possible abnormalities in the leptin and ghrelin systems that may contribute to the development of obesity will be mentioned. In addition, the potentials of leptin and ghrelin as drug targets will be discussed. Finally, the influence of the diet on leptin and ghrelin secretion and functioning will be described.

Relationships among serum leptin, leptin receptor gene polymorphisms, and breast cancer in Korea

Leptin plays an important role in the regulation of body fat homeostasis, and potential associations of leptin receptor gene (LEPR) polymorphisms with obesity have been suggested. Obesity is considered to relate to breast cancer. We assessed the role of leptin in relation to breast cancer. We measured the serum leptin concentrations of 45 Korean pre-treatment patients with breast cancer and 45 age-matched controls. By direct sequencing, we investigated four leptin receptor gene (LEPR) polymorphisms at codons 109, 223, 656, and 1019. There was no significant difference between the mean leptin concentrations of the patient and control groups in both pre- and post-menopausal women. The frequencies of the wild-type for LEPR codons 109, 223, and 1019 were very low. No increased risk estimate was found for the four LEPR polymorphisms. Our results indicate that it is difficult to explain breast cancer on the basis of serum leptin concentrations or polymorphisms in the LEPR gene.

Linkage analysis of chromosome 1 with essential hypertension and blood pressure quantitative traits in Chinese families

Summary Several recent studies have linked human chromosome 1p to essential hypertension (EH) or blood pressure (BP) levels. In an independent population of 148 hypertensive families from China we tested these findings. Thirty highly informative microsatellite markers spanning about 284 cM were genotyped. Qualitative linkage analysis was conducted using non-parametric linkage analysis implemented within the GENEHUNTER 2.0 software, whereas quantitative analysis was performed with the variance-component method integrated in the S.O.L.A.R. 1.7.4. software with an additional Haseman-Elston method using the SAGE/SIBPAL2 program. We observed suggestive linkage between D1S2890 (1p31, 80.9 cM) and hypertension using the multipoint non-parametric linkage analysis (NPL = 2.19, P = 0.01). In the quantitative analysis we didn't observe a significant excess of identity-by-descent allele sharing between the systolic blood pressure levels and the markers. However, the D1S207 microsatellite marker (1p21) which is located about 107 cM from the telomere of 1p showed weak linkage evidence with the diastolic blood pressure levels (LOD = 1.42). These findings suggest linkage of 1p31 with essential hypertension in the ethnic Chinese, and provide a potential clue for future studies involving candidate genes for hypertension.

Association of Ob-R gene polymorphism and insulin resistance in Japanese men

Leptin and its receptors are known to play a role in glucose metabolism. We succeeded in cloning human Ob-R cDNA and revealed 7 single nucleotide polymorphisms (SNPs) (Lys109Arg, Arg223Gln, Ser343Ser, Ser492Thr, Lys656Asn, Ala976Asp, and Pro1019Pro) in the coding region of Ob-Rb. Although these 7 SNPs were not associated with an obese phenotype, several studies have reported that some of them were associated with impaired glucose metabolism. To clarify whether the Arg223Gln and A3057G (Pro1019Pro) polymorphisms influence glucose metabolism in Japanese, 696 Japanese men were genotyped. Individually, the Arg223Gln and the A3057G polymorphisms were not associated with the glucose metabolic parameters. No associations were found between haplotype and clinical parameters. However, in 327 subjects with normal glucose tolerance (NGT), the subjects with Arg/Gln or Gln/Gln + A/A haplotype showed significantly higher serum insulin levels and homeostasis model assessment (HOMA) index than those with Arg/Arg + A/A haplotype and Arg/Gln or Gln/Gln + A/G or G/G haplotype. The subjects with Arg/Gln or Gln/Gln + A/A haplotype showed a significantly lower fasting glucose to insulin (GI) ratio than those with Arg/Arg + A/A haplotype. These results suggest that the Ob-R gene may serve as a modifier gene for insulin resistance in Japanese men.

Leptin receptor polymorphism is associated with serum lipid levels and impairment of cholesterol lowering effect by simvastatin in Japanese men

OBJECTIVE

To investigate whether leptin receptor (Ob-R) Arg223Gln polymorphism influences serum lipid levels and whether this polymorphism affects the efficiency of the cholesterol lowering HMG-CoA reductase inhibitor, simvastatin [Clin. Cardiol. 16 (1993) 317].

DESIGN

Case-control association study.

SUBJECTS

We studied 201 Japanese men without medical care, and 78 Japanese who took simvastatin.

METHODS

Genotyping was performed by polymerase chain reaction-restriction fragment length polymorphism (PCR-RFLP). Serum lipid and leptin levels were determined.

RESULTS

Subjects with the Arg/Arg homozygotes had significantly higher serum total cholesterol (TC) and low density lipoprotein cholesterol (LDL-C) levels than those with the Arg/Gln heterozygotes and Gln/Gln homozygotes (TC: Arg/Arg: 213+/-3, Arg/Gln: 196+/-6, Gln/Gln: 184+/-5, P=0.004 for comparison among three genotypes, P=0.008 for difference between Arg/Arg and Arg/Gln, and P=0.025 for difference between Arg/Arg and Gln/Gln, LDL-C: Arg/Arg: 127+/-3, Arg/Gln: 112+/-6, Gln/Gln: 114+/-8, P=0.027) for comparison among three genotypes and P=0.011 for difference between Arg/Arg and Arg/Gln. Subjects with the Arg/Arg homozygotes had significantly lower serum high density lipoprotein cholesterol (HDL-C) levels than those with the Arg/Gln heterozygotes and Gln/Gln homozygotes (Arg/Arg: 55+/-1, Arg/Gln: 62+/-3, Gln/Gln: 57+/-7, P=0.046) for comparison among three genotypes and P=0.013 for difference between Arg/Arg and Arg/Gln. In addition, in 78 patients with hypercholesterolemia who took 5 mg simvastatin, the TC lowering effect by simvastatin in subjects with the Arg/Arg homozygotes was significantly lower than in those with the Arg/Gln heterozygotes and Gln/Gln homozygotes (the reduction in serum TC levels; 62+/-4 vs. 79+/-6, P=0.044).

CONCLUSIONS

We demonstrate that Ob-R Arg223Gln polymorphism in Japanese men is associated with significant elevation of serum TC and LDL-C levels. Our data also show that the Arg/Arg homozygotes tend to show lowered level of serum HDL-C. Furthermore, this polymorphism tends to show an attenuated response to an HMG-CoA reductase inhibitor in terms of the cholesterol lowering effect. These results suggest that the Ob-R gene may serve as a novel modifier gene for hypercholesterolemia in Japanese men.

The neuronal nicotinic acetylcholine receptor in some hereditary epilepsies

Recent advances in human genetics and in the neurobiology of neurotransmitter receptors and channels have led to the discovery of specific genes associated with hereditary epileptic phenotypes. All the genes identified to date code for ligand- and voltage-gated ion channels. Some clinically rare idiopathic epilepsies are associated with mutations in genes coding for different neuronal nicotinic acetylcholine receptor (AChR) subunits. Distinct alpha subunits are found in the brain and in the peripheral nervous system, and structural, non-alpha subunits like beta2 and beta4 confer different properties to neuronal receptors. Thus, the final properties of the oligomeric AChR depend on the different combinations of alpha and beta subunits. Most mutations found so far occur in the alpha4 chain, the most abundant subunit in the central nervous system. Specifically, the identification of mutations in the alpha4 subunit of neuronal AChR in human benign familial neonatal convulsions (BFNC) and autosomal dominant nocturnal frontal lobe epilepsy (ADNFLE) raise the possibility that the observed gene defects are linked (causatively) with these two diseases or, alternatively, that AChR alpha4 mutants increase the probability of epileptic discharges. We discuss testable hypotheses for unraveling the pathophysiology of these two disorders associated with AChR mutations.

A role for leptin in hemopoieses?

The recent discovery of leptin as a major controller of appetite has led to a detailed analysis of its specific actions in this process as well as any potential role in the etiology of obesity. It has also emerged that leptin has a wider spectrum of biological activities and has been strongly implicated in fertility and reproduction. The structural similarity between leptin and its receptor and cytokine-receptor systems that control hemopoiesis has also prompted investigation of the potential for this hormone to influence blood cell formation. Recent studies have shown that the leptin receptor is expressed on a diverse range of hemopoietic cells. Leptin itself appears to enhance proliferation of hemopoietic cells in vitro, particularly in combination with other cytokines and may augment some mature hemopoietic cell functions. Although only relatively minor hemopoietic deficiencies have been reported in mice lacking leptin or its receptor, these emerging studies suggest that further analysis of leptin actions in hemopoiesis may be warranted.

Leptin and the regulation of body weight

Leptin has received considerable attention as a newly recognized metabolic hormone and for its potential for therapeutic use in the treatment of human obesity. Furthermore, defects in the leptin signal pathway that result in obesity in animal models have raised the possibility of a similar etiology for obesity in humans. This review will summarize the current findings on leptin in both humans and rodents. These findings will be discussed with respect to our view of the physiology and potential for pathophysiology in leptin-mediated regulation of body weight and composition.

Leptin receptor gene variation and obesity: lack of association in a white British male population

Leptin, a hormone secreted by adipocytes, plays a pivotal role in the control of body weight. Rodents with mutations in the leptin receptor gene develop morbid obesity. It is possible, therefore, that leptin receptor gene mutations contribute to human obesity. To test this possibility, we determined the entire coding sequence of the human leptin receptor cDNA from peripheral blood lymphocytes of 22 morbidly obese patients with body-mass index (BMI) between 35.1 and 60.9 kg/m2. We identified five common DNA sequence variants distributed throughout the coding sequence at codons 109, 223, 343, 656 and 1019, one rare silent mutation at codon 986 and one novel alternatively spliced form of transcript. None of the five common variants, including the three that predict amino acid changes, are null mutations causing morbid obesity, because homozygotes for the variant sequences were also found in lean subjects. Furthermore, the frequency of each variant allele and the distribution of genotypes and haplotypes were similar in 190 obese (BMI >28 kg/m2) and 132 lean (BMI <22 kg/m2) white British males selected from a population-based epidemiological survey. In these subjects, there was no evidence for a significant effect of the common variants on obesity or obesity-related phenotypes. These results suggest that mutations in the leptin receptor gene are not a common cause of human obesity.

The rat corpulent (cp) mutation maps to the same interval on (Pgm1-Glut1) rat chromosome 5 as the fatty (fa) mutation

The autosomal recessive obesity mutations fatty (fa) and corpulent (cp) arose in separate rat strains, 13M and Koletsky, respectively. By complementation analysis, the two mutations appear to be in the same gene. The somewhat different phenotypes of fa/fa and cp/cp animals probably reflect the fact that the mutations are segregating on different rat strains. The fa mutation has been mapped to the interval between Pgm1 and Glut1 on rat Chr 5, but cp has not been mapped genetically. We mapped cp in 30 obese progeny of a LA/N-BN cp/+ intercross using microsatellite markers for these flanking genes. Cp maps to the same genetic interval as rat fa and mouse db. Cp is flanked by Glut1 and Pgm1: Pgm1-------- cp -------- Glut1 map distance (cM) 1.67 6.67 Thus, cp and fa map to the same approximately 8 cm interval of the rat genome. In conjunction with the complementation studies alluded to above, these findings indicate that cp and fa are mutations in the same gene (Lepr).

Suggestive linkages between markers on human 1p32-p22 and body fat and insulin levels in the Quebec Family Study

A single-gene rodent mutation (diabetes) and a quantitative trait locus (dietary obese 1) mapped to the mid portion of mouse chromosome 4 have been related to obesity and/or insulin levels. Synteny relationships place their putative human homologs on 1p31 and 1p35-p31, respectively. In 137 sibships of adult brothers and sisters from the Québec Family Study, genetic linkages between seven microsatellite markers from 1p32-p22 and various obesity- and diabetes-related quantitative phenotypes were examined using single locus sibpair linkage analysis. Suggestive linkages were observed between markers D1S476 and body mass index (p = 0.05), fat mass (p = 0.02), the sum of six skinfolds (p = 0.02), the insulin area after an oral glucose tolerance test (p = 0.02), and between the neighboring marker D1S200 and body mass index (p = 0.03), and fat mass (p = 0.009). Suggestive linkages were also observed between the more telomeric markers D1S193 and body mass index (p = 0.03), and between the neighboring marker D1S197 and fasting insulin level (p = 0.05). No linkage was observed with the trunk to extremity skinfolds ratio. These linkages suggest that human homologs of the mouse diabetes or dietary obese 1 and/or other genes in this interval on chromosome 1 play a role in the regulation of body mass, body composition, and insulin levels, but not of subcutaneous fat distribution.

Genomic structure of the human OB receptor and identification of two novel intronic microsatellites

Identification of the OB (leptin) receptor (OBR) as the gene that is defective in diabetes (Leprdb) mice and fatty (Leprfa) rats provides an important candidate gene for the study of the genetics of human obesity. We defined the boundaries of the 18 coding exons for the long form of OBR, and sequenced the immediately adjacent intronic regions. These sequences can be used to generate reagents for genetic analysis (e.g., direct sequencing, single-stranded conformational polymorphism analysis, etc.) of the possible role of OBR in the regulation of adiposity in humans. In addition, we have identified two highly polymorphic intronic microsatellites that can be scored with the polymerase chain reaction.

It's the genes! EST access to human genome content

ESTs or 'expressed sequence tags' are DNA sequences read from both ends of expressed gene fragments. The Merck-WashU EST Project and several other public EST projects are being performed to rapidly discover the complement of human genes, and make them easily accessible. These ESTs are widely used to discover novel members of gene families, to map genes to chromosomes as 'sequence-tagged sites' (STSs), and to identify mutations leading to heritable diseases. Informatic strategies for querying the EST databases are discussed, as well as the strengths and weaknesses of the EST data. There is a compelling need to build on the informatic synthesis of human gene data, and to devise facile methods for determining gene functions.