Common variants near MC4R are associated with fat mass, weight and risk of obesity

From monogenic to polygenic obesity: recent advances

The heritability of obesity and body weight in general is high. A small number of confirmed monogenic forms of obesity-the respective mutations are sufficient by themselves to cause the condition in food abundant societies-have been identified by molecular genetic studies. The elucidation of these genes, mostly based on animal and family studies, has led to the identification of important pathways to the disorder and thus to a deeper understanding of the regulation of body weight. The identification of inborn deficiency of the mostly adipocyte-derived satiety hormone leptin in extremely obese children from consanguineous families paved the way to the first pharmacological therapy for obesity based on a molecular genetic finding. The genetic predisposition to obesity for most individuals, however, has a polygenic basis. A polygenic variant by itself has a small effect on the phenotype; only in combination with other predisposing variants does a sizeable phenotypic effect arise. Common variants in the first intron of the 'fat mass and obesity associated' gene (FTO) result in an elevated body mass index (BMI) equivalent to approximately +0.4 kg/m(2) per risk allele. The FTO variants were originally detected in a genome wide association study (GWAS) pertaining to type 2 diabetes mellitus. Large meta-analyses of GWAS have subsequently identified additional polygenic variants. Up to December 2009, polygenic variants have been confirmed in a total of 17 independent genomic regions. Further study of genetic effects on human body weight regulation should detect variants that will explain a larger proportion of the heritability. The development of new strategies for diagnosis, treatment and prevention of obesity can be anticipated.

Prevalence of loss-of-function FTO mutations in lean and obese individuals

OBJECTIVE

Single nucleotide polymorphisms (SNPs) in intron 1 of fat mass- and obesity-associated gene (FTO) are strongly associated with human adiposity, whereas Fto(-/-) mice are lean and Fto(+/-) mice are resistant to diet-induced obesity. We aimed to determine whether FTO mutations are disproportionately represented in lean or obese humans and to use these mutations to understand structure-function relationships within FTO.

RESEARCH DESIGN AND METHODS

We sequenced all coding exons of FTO in 1,433 severely obese and 1,433 lean individuals. We studied the enzymatic activity of selected nonsynonymous variants.

RESULTS

We identified 33 heterozygous nonsynonymous variants in lean (2.3%) and 35 in obese (2.4%) individuals, with 8 mutations unique to the obese and 11 unique to the lean. Two novel mutations replace absolutely conserved residues: R322Q in the catalytic domain and R96H in the predicted substrate recognition lid. R322Q was unable to catalyze the conversion of 2-oxoglutarate to succinate in the presence or absence of 3-methylthymidine. R96H retained some basal activity, which was not enhanced by 3-methylthymidine. However, both were found in lean and obese individuals.

CONCLUSIONS

Heterozygous, loss-of-function mutations in FTO exist but are found in both lean and obese subjects. Although intron 1 SNPs are unequivocally associated with obesity in multiple populations and murine studies strongly suggest that FTO has a role in energy balance, it appears that loss of one functional copy of FTO in humans is compatible with being either lean or obese. Functional analyses of FTO mutations have given novel insights into structure-function relationships in this enzyme.

Single gold nanoparticles counter: an ultrasensitive detection platform for one-step homogeneous immunoassays and DNA hybridization assays

In this paper, we present for the first time a single gold nanoparticle counter (SGNPC) in solution based on the photon bursting in a highly focused laser beam (less than 1 fL) due to the plasmon resonance scattering and Brownian motion of gold nanoparticles (GNPs). The photon burst intensity of single 36 nm GNPs is several tens to hundreds times stronger than that of quantum dots (QDs) and organic dyes. The relationship between the photon burst counts and GNPs concentration shows an excellent linearity. The linear range is over 4 orders of magnitude, and the detection limit of GNPs (36 nm) is 17 fM. On the basis of this single nanoparticle technique, we developed an ultrasensitive and highly selective detection platform for homogeneous immunoassay and DNA hybridization assays using GNPs as probes, which were 2-5 orders of magnitude more sensitive than current homogeneous methods. We used this technology to construct homogeneous sandwich immunoassays for cancer biomarkers, such as carcinoembryonic antigen (CEA) and alpha fetal protein (AFP), and aptamer recognition for thrombin. The detection limits are 130 fM for CEA, 714 fM for AFP and 2.72 pM for thrombin. Our method was successfully applied for direct determination of CEA, AFP and thrombin levels in sera from healthy subjects and cancer patients. In homogeneous DNA hybridization detection, we chose methylenetetrahydrofolate reductase (MTHFR) gene as a target. This assay successfully distinguished DNA sequences with single base mismatches, and the detection limits for the target were at 1 fM level.

European lactase persistence genotype shows evidence of association with increase in body mass index

The global prevalence of obesity has increased significantly in recent decades, mainly due to excess calorie intake and increasingly sedentary lifestyle. Here, we test the association between obesity measured by body mass index (BMI) and one of the best-known genetic variants showing strong selective pressure: the functional variant in the cis-regulatory element of the lactase gene. We tested this variant since it is presumed to provide nutritional advantage in specific physical and cultural environments. We genetically defined lactase persistence (LP) in 31 720 individuals from eight European population-based studies and one family study by genotyping or imputing the European LP variant (rs4988235). We performed a meta-analysis by pooling the β-coefficient estimates of the relationship between rs4988235 and BMI from the nine studies and found that the carriers of the allele responsible for LP among Europeans showed higher BMI (P = 7.9 × 10⁻⁵). Since this locus has been shown to be prone to population stratification, we paid special attention to reveal any population substructure which might be responsible for the association signal. The best evidence of exclusion of stratification came from the Dutch family sample which is robust for stratification. In this study, we highlight issues in model selection in the genome-wide association studies and problems in imputation of these special genomic regions.

A multilevel linear mixed model of the association between candidate genes and weight and body mass index using the Framingham longitudinal family data

Obesity has become an epidemic in many countries and is one of the major risk conditions for disease including type 2 diabetes, coronary heart disease, stroke, dyslipidemia, and hypertension. Recent genome-wide association studies have identified two genes (FTO and near MC4R) that were unequivocally associated with body mass index (BMI) and obesity. For the Genetic Analysis Workshop 16, data from the Framingham Heart Study were made available, including longitudinal anthropometric and metabolic traits for 7130 Caucasian individuals over three generations, each with follow-up data at up to four time points. We explored the associations between four single-nucleotide polymorphisms (SNPs) on FTO (rs1121980, rs9939609) or near MC4R (rs17782313, rs17700633) with weight and BMI under an additive model. We applied multilevel linear mixed model for continuous outcomes, using the Affymetrix 500k genome-wide genotype data for the four SNPs. The results of the multilevel modeling in the entire sample indicated that the minor alleles of the four SNPs were associated with higher weight and higher BMI. The most significant associations were between rs9939609 and weight (p = 4.7 × 10^-6) and BMI (p = 8.9 × 10^-8). The results also showed that, for SNPs at FTO, the homozygotes for the minor allele had the most pronounced increase in weight and BMI, while the common allele homozygotes gained less weight and BMI during the follow-up period. Linkage disequilibrium (LD) between the two FTO SNPs was strong (D' = 0.997, r² = 0.875) but their haplotype was not significantly associated with either weight or BMI. The two SNPs near MC4R were in weak LD (D' = 0.487, r² = 0.166).

Genome-wide association scans for secondary traits using case-control samples

Genome-wide association studies (GWAS) require considerable investment, so researchers often study multiple traits collected on the same set of subjects to maximize return. However, many GWAS have adopted a case-control design; improperly accounting for case-control ascertainment can lead to biased estimates of association between markers and secondary traits. We show that under the null hypothesis of no marker-secondary trait association, naïve analyses that ignore ascertainment or stratify on case-control status have proper Type I error rates except when both the marker and secondary trait are independently associated with disease risk. Under the alternative hypothesis, these methods are unbiased when the secondary trait is not associated with disease risk. We also show that inverse-probability-of-sampling-weighted (IPW) regression provides unbiased estimates of marker-secondary trait association. We use simulation to quantify the Type I error, power and bias of naïve and IPW methods. IPW regression has appropriate Type I error in all situations we consider, but has lower power than naïve analyses. The bias for naïve analyses is small provided the marker is independent of disease risk. Considering the majority of tested markers in a GWAS are not associated with disease risk, naïve analyses provide valid tests of and nearly unbiased estimates of marker-secondary trait association. Care must be taken when there is evidence that both the secondary trait and tested marker are associated with the primary disease, a situation we illustrate using an analysis of the relationship between a marker in FGFR2 and mammographic density in a breast cancer case-control sample.

A genome-wide association study reveals variants in ARL15 that influence adiponectin levels

The adipocyte-derived protein adiponectin is highly heritable and inversely associated with risk of type 2 diabetes mellitus (T2D) and coronary heart disease (CHD). We meta-analyzed 3 genome-wide association studies for circulating adiponectin levels (n = 8,531) and sought validation of the lead single nucleotide polymorphisms (SNPs) in 5 additional cohorts (n = 6,202). Five SNPs were genome-wide significant in their relationship with adiponectin (P< or =5x10(-8)). We then tested whether these 5 SNPs were associated with risk of T2D and CHD using a Bonferroni-corrected threshold of P< or =0.011 to declare statistical significance for these disease associations. SNPs at the adiponectin-encoding ADIPOQ locus demonstrated the strongest associations with adiponectin levels (P-combined = 9.2x10(-19) for lead SNP, rs266717, n = 14,733). A novel variant in the ARL15 (ADP-ribosylation factor-like 15) gene was associated with lower circulating levels of adiponectin (rs4311394-G, P-combined = 2.9x10(-8), n = 14,733). This same risk allele at ARL15 was also associated with a higher risk of CHD (odds ratio [OR] = 1.12, P = 8.5x10(-6), n = 22,421) more nominally, an increased risk of T2D (OR = 1.11, P = 3.2x10(-3), n = 10,128), and several metabolic traits. Expression studies in humans indicated that ARL15 is well-expressed in skeletal muscle. These findings identify a novel protein, ARL15, which influences circulating adiponectin levels and may impact upon CHD risk.

The role of obesity-associated loci identified in genome-wide association studies in the determination of pediatric BMI

The prevalence of obesity in children and adults in the United States has increased dramatically over the past decade. Besides environmental factors, genetic factors are known to play an important role in the pathogenesis of obesity. A number of genetic determinants of adult BMI have already been established through genome-wide association (GWA) studies. In this study, we examined 25 single-nucleotide polymorphisms (SNPs) corresponding to 13 previously reported genomic loci in 6,078 children with measures of BMI. Fifteen of these SNPs yielded at least nominally significant association to BMI, representing nine different loci including INSIG2, FTO, MC4R, TMEM18, GNPDA2, NEGR1, BDNF, KCTD15, and 1q25. Other loci revealed no evidence for association, namely at MTCH2, SH2B1, 12q13, and 3q27. For the 15 associated variants, the genotype score explained 1.12% of the total variation for BMI z-score. We conclude that among 13 loci that have been reported to associate with adult BMI, at least nine also contribute to the determination of BMI in childhood as demonstrated by their associations in our pediatric cohort.

Additive effects of genetic variation in GCK and G6PC2 on insulin secretion and fasting glucose

OBJECTIVE

Glucokinase (GCK) and glucose-6-phosphatase catalytic subunit 2 (G6PC2) regulate the glucose-cycling step in pancreatic beta-cells and may regulate insulin secretion. GCK rs1799884 and G6PC2 rs560887 have been independently associated with fasting glucose, but their interaction on glucose-insulin relationships is not well characterized.

RESEARCH DESIGN AND METHODS

We tested whether these variants are associated with diabetes-related quantitative traits in Mexican Americans from the BetaGene Study and attempted to replicate our findings in Finnish men from the METabolic Syndrome in Men (METSIM) Study.

RESULTS

rs1799884 was not associated with any quantitative trait (corrected P > 0.1), whereas rs560887 was significantly associated with the oral glucose tolerance test 30-min incremental insulin response (30' Deltainsulin, corrected P = 0.021). We found no association between quantitative traits and the multiplicative interaction between rs1799884 and rs560887 (P > 0.26). However, the additive effect of these single nucleotide polymorphisms was associated with fasting glucose (corrected P = 0.03) and 30' Deltainsulin (corrected P = 0.027). This additive association was replicated in METSIM (fasting glucose, P = 3.5 x 10(-10) 30' Deltainsulin, P = 0.028). When we examined the relationship between fasting glucose and 30' Deltainsulin stratified by GCK and G6PC2, we noted divergent changes in these quantitative traits for GCK but parallel changes for G6PC2. We observed a similar pattern in METSIM.

CONCLUSIONS

Our data suggest that variation in GCK and G6PC2 have additive effects on both fasting glucose and insulin secretion.

Human genetics illuminates the paths to metabolic disease

Metabolic diseases represent a growing threat to world-wide public health. In general, these disorders result from the interaction of heritable factors with environmental influences. Here, I will focus on two important metabolic disorders, namely type 2 diabetes and obesity, and explore the extent to which human molecular genetic research has illuminated our understanding of their underlying pathophysiological mechanisms.

Targeting microRNAs in obesity

Obesity is a serious health problem worldwide associated with an increased risk of life-threatening diseases such as type 2 diabetes, atherosclerosis, and certain types of cancer. Fundamental for the development of novel therapeutics for obesity and its associated metabolic syndromes is an understanding of the regulation of fat cell development. Recent computational and experimental studies have shown that microRNAs (miRNAs) play a role in metabolic tissue development, lipid metabolism and glucose homeostasis. In addition, many miRNAs are dysregulated in metabolic tissues from obese animals and humans, which potentially contributes to the pathogenesis of obesity-associated complications. In this review we summarize the current state of understanding of the roles of miRNAs in metabolic tissues under normal development and obese conditions, and discuss the potential use of miRNAs as therapeutic targets.

Mendelian randomization in nutritional epidemiology

Nutritional epidemiology aims to identify dietary and lifestyle causes for human diseases. Causality inference in nutritional epidemiology is largely based on evidence from studies of observational design, and may be distorted by unmeasured or residual confounding and reverse causation. Mendelian randomization is a recently developed methodology that combines genetic and classical epidemiological analysis to infer causality for environmental exposures, based on the principle of Mendel's law of independent assortment. Mendelian randomization uses genetic variants as proxies for environmental exposures of interest. Associations derived from Mendelian randomization analysis are less likely to be affected by confounding and reverse causation. During the past 5 years, a body of studies examined the causal effects of diet/lifestyle factors and biomarkers on a variety of diseases. The Mendelian randomization approach also holds considerable promise in the study of intrauterine influences on offspring health outcomes. However, the application of Mendelian randomization in nutritional epidemiology has some limitations.

Obesity genotype score and cardiovascular risk in women with type 2 diabetes mellitus

OBJECTIVE

To investigate the associations between obesity-predisposing genetic variants, cardiovascular biomarkers, and cardiovascular disease (CVD) risk in women with preexisting type 2 diabetes mellitus.

METHODS AND RESULTS

We genotyped polymorphisms at nine established obesity loci in 1,395 women with diabetes from the Nurses' Health Study: 449 women developed CVD, and 946 women did not develop CVD. A genetic risk score (GRS) was derived by summing risk alleles for each individual. Four polymorphisms (rs9939609 [FTO], rs11084753 [KCTD15], rs10838738 [MTCH2], and rs10938397 [GNPDA2]) showed nominally significant associations with CVD. The GRS combining all obesity loci was linearly related to CVD risk (P = 0.013 for trend). The odds ratio was 1.08 per risk allele (95% confidence interval, 1.02-1.15; P = 0.01) after adjustment for body mass index and other conventional risk factors. Women with the highest quartile of GRS had 53% (95% confidence interval, 6%-122%) increased CVD risk, compared with those in the lowest quartile of GRS (P = 0.024). In addition, a higher GRS was associated with lower adiponectin levels (P = 0.02). Further adjustment for body mass index and other covariates did not change the association (P = 0.006). A higher GRS was also correlated with lower levels of high-density lipoprotein (P = 0.01).

CONCLUSIONS

Obesity-predisposing variants may jointly affect CVD risk among women with diabetes.

Early life influences on obesity risk: maternal overnutrition and programming of obesity

While adult lifestyle factors undoubtedly contribute to the incidence of obesity and its attendant disorders, mounting evidence suggests that programming of obesity may occur following over-nutrition during development. As hypothalamic control of appetite and energy expenditure is set early in life and can be perturbed by certain exposures, such as undernutrition and altered metabolic and hormonal signals, in utero exposure to maternal obesity-related changes may contribute to programming of obesity in offspring. Data from animal studies indicate both intrauterine and postnatal environments are critical determinants of the development of pathways regulating energy homeostasis. This review summarizes recent evidence of the impact of maternal obesity on subsequent obesity risk, paying particular attention to the hypothalamic regulation of appetite and markers of metabolic control. The extraordinary rise in the rates of maternal obesity underlines an urgent need to investigate the mechanisms contributing to its transgenerational effects.

Postprandial responses in hunger and satiety are associated with the rs9939609 single nucleotide polymorphism in FTO

BACKGROUND

The common rs9939609 single nucleotide polymorphism (SNP) in the fat mass and obesity-associated (FTO) gene is associated with adiposity, possibly by affecting satiety responsiveness.

OBJECTIVE

The objective was to determine whether postprandial responses in hunger and satiety are associated with rs9939609, taking interactions with other relevant candidate genes into account.

DESIGN

Sixty-two women and 41 men [age: 31 +/- 14 y; body mass index (in kg/m(2)): 25.0 +/- 3.1] were genotyped for 5 SNPs in FTO, DNMT1, DNMT3B, LEP, and LEPR. Individuals received fixed meals provided in energy balance. Hunger and satiety were determined pre- and postprandially by using visual analog scales.

RESULTS

A general association test showed a significant association between postprandial responses in hunger and satiety with rs9939609 (P = 0.036 and P = 0.050, respectively). Individuals with low postprandial responses in hunger and satiety were overrepresented among TA/AA carriers in rs9939609 (FTO) compared with TT carriers (dominant and additive model: P = 0.013 and P = 0.020, respectively). Moreover, multifactor dimensionality reduction showed significant epistatic interactions for the postprandial decrease in hunger involving rs9939609 (FTO), rs992472 (DNMT3B), and rs1137101 (LEPR). Individuals with a low postprandial decrease in hunger were overrepresented among TA/AA (dominant), CC/CA (recessive), and AG/GG (dominant) carriers in rs9939609 (FTO), rs992472 (DNMT3B), and rs1137101 (LEPR), respectively (n = 39), compared with TT, AA, and/or AA carriers in these SNPs, respectively (P = 0.00001). Each SNP had an additional effect.

CONCLUSIONS

Our results confirm a role for FTO in responsiveness to hunger and satiety cues in adults in an experimental setting. The epistatic interaction suggests that DNA methylation, an epigenetic process, affects appetite.

Genetic variation in the hypothalamic pathways and its role on obesity

Over recent decades, the prevalence of obesity has increased dramatically worldwide. Although this epidemic is mainly attributable to modern (western) lifestyle, multiple twin and adoption studies indicate the significant role of genes in the individual's predisposition to becoming obese. As the hypothalamus plays a central role in controlling body weight, its regulatory circuits may represent a crucial system in the pathogenesis of the disorder. Genetic variations in genes in the hypothalamic pathways may therefore contribute to the susceptibility for obesity in humans and animals. We summarize current knowledge on the physiological role of the hypothalamus in body-weight regulation and review genetic studies on the hypothalamic candidate genes in relation to obesity. Together, data from functional and genetic studies as well as the new, common, obesity loci identified in genome-wide association scans support an important role for the hypothalamic genes in predisposing to obesity. However, findings are still inconclusive for many candidate genes. To improve our understanding of the genetic architecture of common obesity, we suggest that specific obesity phenotypes should be considered and different analytical approaches used. Such studies should consider multiple genes from the same physiological pathways, together with environmental risk factors.

Genetic basis of beta-cell dysfunction in man

Although the genetic causes of monogenic disorders have been successfully identified in the past, the success in dissecting the genetics of complex polygenic diseases has until now been limited. With the introduction of whole genome wide association studies (WGAS) in 2007, the picture has been dramatically changed. Today we know of about 20 genetic variants increasing the risk of type 2 diabetes (T2D). Most of them seem to influence the capacity of beta-cells to increase insulin secretion to meet the demands imposed by an increase in body weight and insulin resistance. This probably represents only the tip of the iceberg, and over the next few years refined tools will provide a more complete picture of the genetic complexity of T2D. This will not only include the current dissection of common variants increasing the susceptibility of the disease but also rare variants with stronger effects, copy number variations and epigenetic effects like DNA methylation and histone acetylation. For the first time, we can anticipate with some confidence that the genetics of a complex disease like T2D really can be dissected.

Multicenter dizygotic twin cohort study confirms two linkage susceptibility loci for body mass index at 3q29 and 7q36 and identifies three further potential novel loci

OBJECTIVE

To identify common loci and potential genetic variants affecting body mass index (BMI, kg m(-2)) in study populations originating from Europe.

DESIGN

We combined genome-wide linkage scans of six cohorts from Australia, Denmark, Finland, the Netherlands, Sweden and the United Kingdom with an approximately 10-cM microsatellite marker map. Variance components linkage analysis was carried out with age, sex and country of origin as covariates.

SUBJECTS

The GenomEUtwin consortium consists of twin cohorts from eight countries (Australia, Denmark, the Netherlands, Finland, Italy, Norway, Sweden and the United Kingdom) with a total data collection of more than 500,000 monozygotic and dizygotic (DZ) twin pairs. Variance due to early-life events and the environment is reduced within twin pairs, which makes DZ pairs highly valuable for linkage studies of complex traits. This study totaled 4401 European-originated twin families (10,535 individuals) from six countries (Australia, Denmark, the Netherlands, Finland, Sweden and the United Kingdom).

RESULTS

We found suggestive evidence for a quantitative trait locus on 3q29 and 7q36 in the combined sample of DZ twins (multipoint logarithm of odds score (MLOD) 2.6 and 2.4, respectively). Two individual cohorts showed strong evidence independently for three additional loci: 16q23 (MLOD=3.7) and 2p24 (MLOD=3.4) in the Dutch cohort and 20q13 (MLOD=3.2) in the Finnish cohort.

CONCLUSION

Linkage analysis of the combined data in this large twin cohort study provided evidence for suggestive linkage to BMI. In addition, two cohorts independently provided significant evidence of linkage to three new loci. The results of our study suggest a smaller environmental variance between DZ twins than full siblings, with a corresponding increase in heritability for BMI as well as an increase in linkage signal in well-replicated regions. The results are consistent with the possibility of locus heterogeneity for some genomic regions, and indicate a lack of major common quantitative trait locus variants affecting BMI in European populations.

Replication in genome-wide association studies

Replication helps ensure that a genotype-phenotype association observed in a genome-wide association (GWA) study represents a credible association and is not a chance finding or an artifact due to uncontrolled biases. We discuss prerequisites for exact replication; issues of heterogeneity; advantages and disadvantages of different methods of data synthesis across multiple studies; frequentist vs. Bayesian inferences for replication; and challenges that arise from multi-team collaborations. While consistent replication can greatly improve the credibility of a genotype-phenotype association, it may not eliminate spurious associations due to biases shared by many studies. Conversely, lack of replication in well-powered follow-up studies usually invalidates the initially proposed association, although occasionally it may point to differences in linkage disequilibrium or effect modifiers across studies.

A genome-wide meta-analysis identifies 22 loci associated with eight hematological parameters in the HaemGen consortium

The number and volume of cells in the blood affect a wide range of disorders including cancer and cardiovascular, metabolic, infectious and immune conditions. We consider here the genetic variation in eight clinically relevant hematological parameters, including hemoglobin levels, red and white blood cell counts and platelet counts and volume. We describe common variants within 22 genetic loci reproducibly associated with these hematological parameters in 13,943 samples from six European population-based studies, including 6 associated with red blood cell parameters, 15 associated with platelet parameters and 1 associated with total white blood cell count. We further identified a long-range haplotype at 12q24 associated with coronary artery disease and myocardial infarction in 9,479 cases and 10,527 controls. We show that this haplotype demonstrates extensive disease pleiotropy, as it contains known risk loci for type 1 diabetes, hypertension and celiac disease and has been spread by a selective sweep specific to European and geographically nearby populations.

Pathogenesis of adolescent idiopathic scoliosis in girls - a double neuro-osseous theory involving disharmony between two nervous systems, somatic and autonomic expressed in the spine and trunk: possible dependency on sympathetic nervous system and hormones with implications for medical therapy

Anthropometric data from three groups of adolescent girls - preoperative adolescent idiopathic scoliosis (AIS), screened for scoliosis and normals were analysed by comparing skeletal data between higher and lower body mass index subsets. Unexpected findings for each of skeletal maturation, asymmetries and overgrowth are not explained by prevailing theories of AIS pathogenesis. A speculative pathogenetic theory for girls is formulated after surveying evidence including: (1) the thoracospinal concept for right thoracic AIS in girls; (2) the new neuroskeletal biology relating the sympathetic nervous system to bone formation/resorption and bone growth; (3) white adipose tissue storing triglycerides and the adiposity hormone leptin which functions as satiety hormone and sentinel of energy balance to the hypothalamus for long-term adiposity; and (4) central leptin resistance in obesity and possibly in healthy females. The new theory states that AIS in girls results from developmental disharmony expressed in spine and trunk between autonomic and somatic nervous systems. The autonomic component of this double neuro-osseous theory for AIS pathogenesis in girls involves selectively increased sensitivity of the hypothalamus to circulating leptin (genetically-determined up-regulation possibly involving inhibitory or sensitizing intracellular molecules, such as SOC3, PTP-1B and SH2B1 respectively), with asymmetry as an adverse response (hormesis); this asymmetry is routed bilaterally via the sympathetic nervous system to the growing axial skeleton where it may initiate the scoliosis deformity (leptin-hypothalamic-sympathetic nervous system concept = LHS concept). In some younger preoperative AIS girls, the hypothalamic up-regulation to circulating leptin also involves the somatotropic (growth hormone/IGF) axis which exaggerates the sympathetically-induced asymmetric skeletal effects and contributes to curve progression, a concept with therapeutic implications. In the somatic nervous system, dysfunction of a postural mechanism involving the CNS body schema fails to control, or may induce, the spinal deformity of AIS in girls (escalator concept). Biomechanical factors affecting ribs and/or vertebrae and spinal cord during growth may localize AIS to the thoracic spine and contribute to sagittal spinal shape alterations. The developmental disharmony in spine and trunk is compounded by any osteopenia, biomechanical spinal growth modulation, disc degeneration and platelet calmodulin dysfunction. Methods for testing the theory are outlined. Implications are discussed for neuroendocrine dysfunctions, osteopontin, sympathoactivation, medical therapy, Rett and Prader-Willi syndromes, infantile idiopathic scoliosis, and human evolution. AIS pathogenesis in girls is predicated on two putative normal mechanisms involved in trunk growth, each acquired in evolution and unique to humans.

Life course variations in the associations between FTO and MC4R gene variants and body size

The timing of associations between common genetic variants for weight or body mass index (BMI) across the life course may provide insights into the aetiology of obesity. We genotyped variants in FTO (rs9939609) and near MC4R (rs17782313) in 1240 men and 1239 women born in 1946 and participating in the MRC National Survey of Health and Development. Birth weight was recorded and height and weight were measured or self-reported repeatedly at 11 time-points between ages 2 and 53 years. Hierarchical mixed models were used to test whether genetic associations with weight or BMI standard deviation scores (SDS) changed with age during childhood and adolescence (2–20 years) or adulthood (20–53 years). The association between FTO rs9939609 and BMI SDS strengthened during childhood and adolescence (rate of change: 0.007 SDS/A-allele/year; 95% CI: 0.003–0.010, P < 0.001), reached a peak strength at age 20 years (0.13 SDS/A-allele, 0.08–0.19), and then weakened during adulthood (−0.003 SDS/A-allele/year, −0.005 to −0.001, P = 0.001). MC4R rs17782313 showed stronger associations with weight than BMI; its association with weight strengthened during childhood and adolescence (0.005 SDS/C-allele/year; 0.001–0.008, P = 0.006), peaked at age 20 years (0.13 SDS/C-allele, 0.07–0.18), and weakened during adulthood (−0.002 SDS/C-allele/year, −0.004 to 0.000, P = 0.05). In conclusion, genetic variants in FTO and MC4R showed similar biphasic changes in their associations with BMI and weight, respectively, strengthening during childhood up to age 20 years and then weakening with increasing adult age. Studies of the aetiology of obesity spanning different age groups may identify age-specific determinants of weight gain.

Association between leptin receptor (LEPR) and brain-derived neurotrophic factor (BDNF) gene variants and obesity: a case-control study

INTRODUCTION

Human and animal studies provide evidence for a relevant role of the leptin receptor (LEPR) and the brain-derived neurotrophic factor (BDNF) genes in energy homeostasis.

AIM

To assess the association between human LEPR and BDNF genetic variants with adult obesity.

DESIGN AND METHODS

Case-control study in Pamplona (Navarra, Spain) with adult obese subjects (n = 159) and normal weight controls (n = 154). Four common polymorphisms of the LEPR gene (Lys109Arg, Gln223Arg, Ser343Ser, Lys656Asn) and 17 variants of the BDNF gene, including the Val66Met variant, were genotyped.

RESULTS

No significant case-control differences were found in allele/genotype frequencies after adjusting for relevant co-variates. Haplotype analysis did not detect any significant association between LEPR or BDNF variants and obesity. No associations were found between LEPR variants and serum leptin levels.

CONCLUSIONS

Our results do not support a major role of LEPR or BDNF common polymorphisms in multifactorial adult obesity.

Association between obesity and polymorphisms in SEC16B, TMEM18, GNPDA2, BDNF, FAIM2 and MC4R in a Japanese population

There is evidence that the obesity phenotype in the Caucasian populations is associated with variations in several genes, including neuronal growth regulator 1 (NEGR1), SEC16 homolog B (SCE16B), transmembrane protein 18 (TMEM18), ets variant 5 (ETV5), glucosamine-6-phosphate deaminase 2 (GNPDA2), prolactin (PRL), brain-derived neurotrophic factor (BDNF), mitochondrial carrier homolog 2 (MTCH2), Fas apoptotic inhibitory molecule 2 (FAIM2), SH2B adaptor protein 1 (SH2B1), v-maf musculoaponeurotic fibrosarcoma oncogene homolog (MAF), Niemann-Pick disease, type C1 (NPC1), melanocortin 4 receptor (MC4R) and potassium channel tetramerisation domain containing 15 (KCTD15). To investigate the relationship between obesity and these genes in the Japanese population, we genotyped 27 single-nucleotide polymorphisms (SNPs) in 14 genes from obese subjects (n=1129, body mass index (BMI) > or =30 kg m(-2)) and normal-weight control subjects (n=1736, BMI <25 kg m(-2)). The SNP rs10913469 in SEC16B (P=0.000012) and four SNPs (rs2867125, rs6548238, rs4854344 and rs7561317) in the TMEM18 gene (P=0.00015), all of which were in almost absolute linkage disequilibrium, were significantly associated with obesity in the Japanese population. SNPs in GNPDA2, BDNF, FAIM2 and MC4R genes were marginally associated with obesity (P<0.05). Our data suggest that some SNPs identified by genome-wide association studies in the Caucasians also confer susceptibility to obesity in Japanese subjects.

Common variants near MC4R in relation to body fat, body fat distribution, metabolic traits and energy expenditure

OBJECTIVE

Common variants near melanocortin receptor 4 (MC4R) have been related to fatness and type 2 diabetes. We examined the associations of rs17782313 and rs17700633 in relation to body fat, body fat distribution, metabolic traits, weight development and energy expenditure.

METHODS

Obese young men (n = 753, BMI > or = 31.0 kg m(-2)) and a randomly selected group (n = 874) identified from a population of 174 800 men were re-examined in three surveys at mean ages 35, 46 and 49 years (S-35, S-46 and S-49). Measurements were available at upto eight times from birth to adulthood. Logistic regression analysis was used to assess odds ratio (OR) for the presence of the carrier allele for a given difference in phenotypic values.

RESULTS

Rs17782313 minor C-allele was associated with overall, abdominal and peripheral fatness (range of OR = 1.06-1.14 per z-score units) at all three surveys, although only consistently significant at S-35 and S-46. Rs17700633 minor A-allele was also associated with the fatness measures, but significantly so only at S-49 for overall and abdominal fatness (range of OR = 1.03-1.15 per z-score units), and peripheral fatness (OR = 1.15-1.20 per z-score units). There were only few significant associations with metabolic traits. The rs17782313 C-allele and the rs17700633 A-allele were both associated with lower high-density lipoprotein cholesterol (range of OR = 0.64-0.84 per mol l(-1)), significantly at S-46. The rs17700633 A-allele was significantly associated with insulin (OR = 1.25 per 50 pmol l(-1)), leptin (OR = 1.42 per 10 ng microl(-1)) and insulin sensitivity (OR = 0.81 per model unit). The rs17782313 C-allele and the rs17700633 A-allele were both associated with BMI in childhood and adolescence (range of OR = 1.04-1.17 per z-score units), significant for the rs17782313 C-allele at the age of 13-19 years and for rs17700633 A-allele at age 7, 10, 13 and 19 years. No significant associations were found for energy expenditure.

CONCLUSION

Near MC4R variants appear to contribute to body fat, body fat distribution, some metabolic traits, weight development during childhood, but not to energy expenditure.

Single nucleotide polymorphisms in obesity-related genes and all-cause and cause-specific mortality: a prospective cohort study

Background

The aim of this study was to examine the associations between 16 specific single nucleotide polymorphisms (SNPs) in 8 obesity-related genes and overall and cause-specific mortality. We also examined the associations between the SNPs and body mass index (BMI) and change in BMI over time.

Methods

Data were analyzed from 9,919 individuals who participated in two large community-based cohort studies conducted in Washington County, Maryland in 1974 (CLUE I) and 1989 (CLUE II). DNA from blood collected in 1989 was genotyped for 16 SNPs in 8 obesity-related genes: monoamine oxidase A (MAOA), lipoprotein lipase (LPL), paraoxonase 1 and 2 (PON1 and PON2), leptin receptor (LEPR), tumor necrosis factor-α (TNFα), and peroxisome proliferative activated receptor-γ and -δ (PPARG and PPARD). Data on height and weight in 1989 (CLUE II baseline) and at age 21 were collected from participants at the time of blood collection. All participants were followed from 1989 to the date of death or the end of follow-up in 2005. Cox proportional hazards regression was used to obtain the relative risk (RR) estimates and 95% confidence intervals (CI) for each SNP and mortality outcomes.

Results

The results showed no patterns of association for the selected SNPs and the all-cause and cause-specific mortality outcomes, although statistically significant associations (p < 0.05) were observed between PPARG rs4684847 and all-cause mortality (CC: reference; CT: RR 0.99, 95% CI 0.89, 1.11; TT: RR 0.60, 95% CI 0.39, 0.93) and cancer-related mortality (CC: reference; CT: RR 1.01, 95% CI 0.82, 1.25; TT: RR 0.22, 95% CI 0.06, 0.90) and TNFα rs1799964 and cancer-related mortality (TT: reference; CT: RR 1.23, 95% CI 1.03, 1.47; CC: RR 0.83, 95% CI 0.54, 1.28). Additional analyses showed significant associations between SNPs in LEPR with BMI (rs1137101) and change in BMI over time (rs1045895 and rs1137101).

Conclusion

Findings from this cohort study suggest that the selected SNPs are not associated with overall or cause-specific death, although several LEPR SNPs may be related to BMI and BMI change over time.

The liver and the waistline: Fifty years of growth

Fifty years of the Gastroenterological Society of Australia have witnessed the changing appearance of Australians. Asian immigration has transformed the dominant urban culture from European to Eurasian, with some unique Australian attributes. Meanwhile, global conditions have altered body shape, and our sports-proud country is now fat! Thus, as in North America, Europe, China, and affluent Asia-Pacific countries, prosperity and lifestyle, cheap processed foods coupled with reduced physical activity have created an epidemic of over-nutrition resulting in overweight/obesity. Additional genetic factors are at the core of the apple shape (central obesity) that typifies over-nourished persons with metabolic syndrome. Indigenous Australians, once the leanest and fittest humans, now have exceedingly high rates of obesity and type 2 diabetes, contributing to shorter life expectancy; Asian Australians are also at higher risk. Like non-steroidal anti-inflammatory drugs (NSAIDs) and cigarette smoking, obesity now contributes much to gastrointestinal morbidity and mortality (gastroesophageal reflux disease, cancers, gallstones, endoscopy complications). This review focuses on Australian research about fatty liver, particularly roles of central obesity/insulin resistance in non-alcoholic fatty liver disease/steatohepatitis (NAFLD/NASH). The outputs include many highly cited original articles and reviews and the first book on NAFLD. Studies have identified community prevalence, clinical outcomes, association with insulin resistance, metabolic syndrome and hypoadiponectinemia, developed and explored animal models for mechanisms of inflammation and fibrosis, conceptualized etiopathogenesis, and demonstrated that NASH can be reversed by lowering body weight and increasing physical activity. The findings have led to development of regional guidelines on NAFLD, the first internationally, and should now inform daily practice of gastroenterologists.

Pathomechanisms of type 2 diabetes genes

Type 2 diabetes mellitus is a complex metabolic disease that is caused by insulin resistance and beta-cell dysfunction. Furthermore, type 2 diabetes has an evident genetic component and represents a polygenic disease. During the last decade, considerable progress was made in the identification of type 2 diabetes risk genes. This was crucially influenced by the development of affordable high-density single nucleotide polymorphism (SNP) arrays that prompted several successful genome-wide association scans in large case-control cohorts. Subsequent to the identification of type 2 diabetes risk SNPs, cohorts thoroughly phenotyped for prediabetic traits with elaborate in vivo methods allowed an initial characterization of the pathomechanisms of these SNPs. Although the underlying molecular mechanisms are still incompletely understood, a surprising result of these pathomechanistic investigations was that most of the risk SNPs affect beta-cell function. This favors a beta-cell-centric view on the genetics of type 2 diabetes. The aim of this review is to summarize the current knowledge about the type 2 diabetes risk genes and their variants' pathomechanisms.

Genetics of inflammatory bowel disease: implications for disease pathogenesis and natural history

Epidemiological data, detailed molecular studies and recent genome-wide association studies strongly suggest that ulcerative colitis (UC) and Crohn's disease (CD) are related polygenic diseases that share some susceptibility loci, but differ at others. To date, there are more than 50 confirmed inflammatory bowel disease genes/loci, a number that is widely anticipated to at least double in the next 2 years. Germline variation in IL23R, IL12B, JAK2 and STAT3 is associated with inflammatory bowel disease susceptibility, consistent with the newly described role for IL23 signaling and Th17 cells in disease pathogenesis. Several genes involved in different aspects of bacterial handling are defective only in CD, including NOD2 and the autophagy genes ATG16L1 and IRGM. IL10 and ECM1 are associated with UC, while inherited variation at the HLA region is related to an inflammatory colonic phenotype. The application of genome-wide association studies to inflammatory bowel disease has been successful in defining the genetic architecture of CD and UC and in delivering genuinely novel and important insights into disease pathogenesis. This has unearthed a plethora of attractive targets for the development of future therapeutics. Insights into the natural history of these complex diseases will follow and may enable appropriate patient selection for early aggressive therapy with the view to modifying the disease course.

Genome-wide association study and follow-up analysis of adiposity traits in Hispanic Americans: the IRAS Family Study

We investigated candidate genomic regions associated with computed tomography (CT)-derived measures of adiposity in Hispanics from the Insulin Resistance Atherosclerosis Study Family Study (IRASFS). In 1,190 Hispanic individuals from 92 families 3 from the San Luis Valley, Colorado and San Antonio, Texas, we measured CT-derived visceral adipose tissue (VAT), subcutaneous adipose tissue (SAT), and visceral:subcutaneous ratio (VSR). A genome-wide association study (GWAS) was completed using the Illumina HumanHap 300 BeadChip (approximately 317K single-nucleotide polymorphisms (SNPs)) in 229 individuals from the San Antonio site (stage 1). In total, 297 SNPs with evidence for association with VAT, SAT, or VSR, adjusting for age and sex (P<0.001), were genotyped in the remaining 961 Hispanic samples. The entire Hispanic cohort (n=1,190) was then tested for association, adjusting for age, sex, site of recruitment, and admixture estimates (stage 2). In stage 3, additional SNPs were genotyped in four genic regions showing evidence of association in stage 2. Several SNPs were associated in the GWAS (P<1x10(-5)) and were confirmed to be significantly associated in the entire Hispanic cohort (P<0.01), including: rs7543757 for VAT, rs4754373 and rs11212913 for SAT, and rs4541696 and rs4134351 for VSR. Numerous SNPs were associated with multiple adiposity phenotypes. Targeted analysis of four genes whose SNPs were significant in stage 2 suggests candidate genes for influencing the distribution (RGS6) and amount of adiposity (NGEF). Several candidate loci, including RGS6 and NGEF, are associated with CT-derived adipose fat measures in Hispanic Americans in a three-stage genetic association study.

Impact of variation near MC4R on whole-body fat distribution, liver fat, and weight loss

Polymorphisms near the melanocortin-4 receptor (MC4R) gene locus are associated with body weight. Recent studies have shown that they influence insulin sensitivity and incidence of the metabolic syndrome. Thus, we hypothesized that the candidate single-nucleotide polymorphism (SNP) rs17782313 near MC4R additionally influences body fat distribution and its change during lifestyle intervention. To test this, 343 German subjects were genotyped for SNP rs17782313. Body composition was assessed using magnetic resonance technique. Subjects were characterized by an oral glucose tolerance test (OGTT). A subgroup of 242 subjects participated in a 9-month lifestyle intervention. In the overall cohort, the C allele was associated with a higher BMI (P=0.0013), but had no impact on glucose tolerance or insulin sensitivity (all P>or=0.10). There was an effect of the SNP on total body fat (P=0.022) and nonvisceral fat (P=0.017), but not on liver fat and visceral fat (all P>or=0.33). In the subgroup undergoing lifestyle intervention, SNP rs17782313 had no impact on changes in body weight or fat distribution. Despite an association with BMI and nonvisceral adipose tissue, the SNP rs17782313 did not influence visceral adipose tissue. Thus, this candidate SNP for human obesity may preferentially affect the accumulation of subcutaneous adipose tissue. Furthermore, the variation near MC4R has no effect on success of weight loss during lifestyle intervention.

Genetic variation and effects on human eating behavior

Feeding is a physiological process, influenced by genetic factors and the environment. In recent years, many studies have been performed to unravel the involvement of genetics in both eating behavior and its pathological forms: eating disorders and obesity. In this review, we provide a condensed introduction on the neurological aspects of eating and we describe the current status of research into the genetics of eating behavior, primarily focused on specific traits such as taste, satiation, and hunger. This is followed by an overview on the genetic studies done to unravel the heritable background of obesity and eating disorders. We examine the discussion currently taking place in the field of genetics of complex disorders and phenotypes on how to perform good and powerful studies, with the use of large-scale whole-genome association studies as one of the possible solutions. In the final part of this review, we give our view on the latest developments, including endophenotype approaches and animal studies. Studies of endophenotypes of eating behavior may help to identify core traits that are genetically influenced. Such studies would yield important knowledge on the underlying biological scaffold on which diagnostic criteria for eating disorders could be based and would provide information to influence eating behavior toward healthier living.

Association of variants in the PCSK1 gene with obesity in the EPIC-Norfolk study

Recently, the rs6232 (N221D) and rs6235 (S690T) SNPs in the PCSK1 gene were associated with obesity in a meta-analysis comprising more than 13 000 individuals of European ancestry. Each additional minor allele of rs6232 or rs6235 was associated with a 1.34- or 1.22-fold increase in the risk of obesity, respectively. So far, only one relatively small study has aimed to replicate these findings, but could not confirm the association of the rs6235 SNP and did not study the rs6232 variant. In the present study, we examined the associations of the rs6232 and rs6235 SNPs with obesity in a population-based cohort consisting of 20 249 individuals of European descent from Norfolk, UK. Logistic regression and generalized linear models were used to test the associations of the risk alleles with obesity and related quantitative traits, respectively. Neither of the SNPs was significantly associated with obesity, BMI or waist circumference under the additive genetic model (P > 0.05). However, we observed an interaction between rs6232 and age on the level of BMI (P = 0.010) and risk of obesity (P = 0.020). The rs6232 SNP was associated with BMI (P = 0.021) and obesity (P = 0.022) in the younger individuals [less than median age (59 years)], but not among the older age group (P = 0.81 and P = 0.68 for BMI and obesity, respectively). In conclusion, our data suggest that the PCSK1 rs6232 and rs6235 SNPs are not major contributors to common obesity in the general population. However, the effect of rs6232 may be age-dependent.

Is the thrifty genotype hypothesis supported by evidence based on confirmed type 2 diabetes- and obesity-susceptibility variants?

AIMS/HYPOTHESIS

According to the thrifty genotype hypothesis, the high prevalence of type 2 diabetes and obesity is a consequence of genetic variants that have undergone positive selection during historical periods of erratic food supply. The recent expansion in the number of validated type 2 diabetes- and obesity-susceptibility loci, coupled with access to empirical data, enables us to look for evidence in support (or otherwise) of the thrifty genotype hypothesis using proven loci.

METHODS

We employed a range of tests to obtain complementary views of the evidence for selection: we determined whether the risk allele at associated 'index' single-nucleotide polymorphisms is derived or ancestral, calculated the integrated haplotype score (iHS) and assessed the population differentiation statistic fixation index (F (ST)) for 17 type 2 diabetes and 13 obesity loci.

RESULTS

We found no evidence for significant differences for the derived/ancestral allele test. None of the studied loci showed strong evidence for selection based on the iHS score. We find a high F (ST) for rs7901695 at TCF7L2, the largest type 2 diabetes effect size found to date.

CONCLUSIONS/INTERPRETATION

Our results provide some evidence for selection at specific loci, but there are no consistent patterns of selection that provide conclusive confirmation of the thrifty genotype hypothesis. Discovery of more signals and more causal variants for type 2 diabetes and obesity is likely to allow more detailed examination of these issues.

New insights into nutrition and cognitive neuroscience

Nutrition can affect the brain throughout the life cycle, with profound implications for mental health and degenerative disease. Many aspects of nutrition, from entire diets to specific nutrients, affect brain structure and function. The present short review focuses on recent insights into the role of nutrition in cognition and mental health and is divided into four main sections. First, the importance of nutritional balance and nutrient interactions to brain health are considered by reference to the Mediterranean diet, energy balance, fatty acids and trace elements. Many factors modulate the effects of nutrition on brain health and inconsistencies between studies can be explained in part by differences in early environment and genetic variability. Thus, these two factors are considered in the second and third parts of the present review. Finally, recent findings on mechanisms underlying the actions of nutrition on the brain are considered. These mechanisms involve changes in neurotrophic factors, neural pathways and brain plasticity. Advances in understanding the critical role of nutrition in brain health will help to fulfil the potential of nutrition to optimise brain function, prevent dysfunction and treat disease.

Macronutrient-specific effect of FTO rs9939609 in response to a 10-week randomized hypo-energetic diet among obese Europeans

BACKGROUND

The A risk allele of rs9939609 of the fat mass- and obesity-associated gene (FTO) increases body fat mass.

OBJECTIVE

To examine whether FTO rs9939609 affects obese individuals' response to a high-fat, low-carbohydrate (CHO) (HF) or low-fat, high-CHO (LF), hypo-energetic diet and whether the effect of the FTO variant depends on dietary fat and CHO content.

DESIGN

In a 10-week, European, multi-centre dietary intervention study 771 obese women and men were randomized to either LF (20-25% of energy (%E) from fat, 60-65%E from CHO) or HF (40-45%E from fat, 40-45%E from CHO), hypo-energetic diet (measured resting metabolic rate multiplied by 1.3-600 kcal day(-1)). Body weight, fat mass (FM), fat-free mass (FFM), waist circumference (WC), resting energy expenditure (REE), fasting fat oxidation as % of REE (FatOx), insulin release (HOMA-beta) and a surrogate measure of insulin resistance (HOMA-IR) were measured at baseline and after the intervention. In all, 764 individuals were genotyped for FTO rs9939609.

RESULTS

For A-allele carriers the drop-out rate was higher on HF than LF diet (in AT, P=0.002; in AT/AA combined, P=0.003). Among those individuals completing the intervention, we found no effect of FTO rs9939609 genotype on Deltaweight, DeltaFM, DeltaFFM, DeltaWC or DeltaFatOx. However, participants with TT had a smaller reduction in REE on LF than on HF diet (75 kcal/24 h; interaction: P=0.0055). These individuals also showed the greatest reduction in HOMA-beta and HOMA-IR (interaction: P=0.0083 and P=0.047).

CONCLUSION

The FTO rs9939609 may interact with the macronutrient composition in weight loss diets in various ways; carriers of the A allele on LF diet appear to have a lower risk for drop out, and TT individuals have a smaller decrease in REE and greater decrease in HOMA-beta and HOMA-IR on LF than on HF diet.

Prognostic significance of FTO genotype in the development of obesity in Japanese: the J-SHIPP study

OBJECTIVE

Susceptibility of fat mass and obesity-associated (FTO) gene polymorphisms to obesity has been reported in various populations. Polymorphisms in the melanocortin 4 receptor (MC4R) gene were recently explored as another susceptible locus. However, prognostic significance of these genetic variations has not been fully elucidated. Here, we investigated the involvement of FTO rs9939609 and MC4R rs17782313 polymorphisms in the development of obesity. Association with type 2 diabetes mellitus (T2DM) was also investigated.

SUBJECTS

We analyzed 2806 community-dwelling middle-aged to elderly subjects (61+/-14 years). Clinical parameters were obtained from the subjects' personal health records, evaluated at their annual medical check-up.

RESULTS

FTO genotype was significantly associated with current body mass index (BMI; TT 23.2+/-3.2, TA 23.7+/-3.2, AA 24.4+/-3.2 kg m(-2), P=2.5 x 10(-6)) and frequency of obesity (26.6, 32.0, 43.0% respectively, P=2.0 x 10(-4)). Age- and sex-adjusted odds ratio for obesity was 1.30 (P=0.004) in TA and 2.07 (P=0.002) in AA genotype. During the 9.4 years comprising the follow-up period, 214 new cases of obesity were diagnosed among 1718 subjects whose retrospective data were available. A allele frequency of the FTO genotype was significantly higher in subjects who developed obesity (22.2, 15.8%, P=0.001), Age-, sex- and initial BMI-adjusted odds ratio for the development of obesity was 1.46 (95% confidence interval, 1.04-2.04) (P=0.031). However, association studies and meta-analysis of T2DM did not actively support the involvement of FTO genotype. No significant differences were observed between the MC4R genotype and BMI (P=0.015), and the frequency of obesity (P=0.284).

CONCLUSION

FTO genotype is an independent risk factor for future development of obesity.

Genetic variations in regulatory pathways of fatty acid and glucose metabolism are associated with obesity phenotypes: a population-based cohort study

BACKGROUND

As nuclear receptors and transcription factors have an important regulatory function in adipocyte differentiation and fat storage, genetic variation in these key regulators and downstream pathways may be involved in the onset of obesity.

OBJECTIVE

To explore associations between single nucleotide polymorphisms (SNPs) in candidate genes from regulatory pathways that control fatty acid and glucose metabolism, and repeated measurements of body mass index (BMI) and waist circumference in a large Dutch study population.

METHODS

Data of 327 SNPs across 239 genes were analyzed for 3575 participants of the Doetinchem cohort, who were examined three times during 11 years, using the Illumina Golden Gate assay. Adjusted random coefficient models were used to analyze the relationship between SNPS and obesity phenotypes. False discovery rate q-values were calculated to account for multiple testing. Significance of the associations was defined as a q-value < or = 0.20.

RESULTS

Two SNPs (in NR1H4 and SMARCA2 in women only) were significantly associated with both BMI and waist circumference. In addition, two SNPs (in SIRT1 and SCAP in women only) were associated with BMI alone. A functional SNP, in IL6, was strongly associated with waist.

CONCLUSION

In this explorative study among participants of a large population-based cohort, five SNPs, mainly located in transcription mediator genes, were strongly associated with obesity phenotypes. The results from whole genome and candidate gene studies support the potential role of NR1H4, SIRT1, SMARCA2 and IL6 in obesity. Although replication of our findings and further research on the functionality of these SNPs and underlying mechanism is necessary, our data indirectly suggest a role of GATA transcription factors in weight control.

A common genetic variant in the 15q24 nicotinic acetylcholine receptor gene cluster (CHRNA5-CHRNA3-CHRNB4) is associated with a reduced ability of women to quit smoking in pregnancy

Maternal smoking during pregnancy is associated with low birth weight and adverse pregnancy outcomes. Women are more likely to quit smoking during pregnancy than at any other time in their lives, but some pregnant women continue to smoke. A recent genome-wide association study demonstrated an association between a common polymorphism (rs1051730) in the nicotinic acetylcholine receptor gene cluster (CHRNA5-CHRNA3-CHRNB4) and both smoking quantity and nicotine dependence. We aimed to test whether the same polymorphism that predisposes to greater cigarette consumption would also reduce the likelihood of smoking cessation in pregnancy. We studied 7845 pregnant women of European descent from the South-West of England. Using 2474 women who smoked regularly immediately pre-pregnancy, we analysed the association between the rs1051730 risk allele and both smoking cessation during pregnancy and smoking quantity. Each additional copy of the risk allele was associated with a 1.27-fold higher odds (95% CI 1.11-1.45) of continued smoking during pregnancy (P = 0.0006). Adjustment for pre-pregnancy smoking quantity weakened, but did not remove this association [odds ratio (OR) 1.20 (95% CI 1.03-1.39); P = 0.018]. The same risk allele was also associated with heavier smoking before pregnancy and in the first, but not the last, trimester [OR for smoking 10+ cigarettes/day versus 1-9/day in first trimester = 1.30 (95% CI 1.13-1.50); P = 0.0003]. To conclude, we have found strong evidence of association between the rs1051730 variant and an increased likelihood of continued smoking in pregnancy and have confirmed the previously observed association with smoking quantity. Our data support the role of genetic factors in influencing smoking cessation during pregnancy.

Identification of genetic loci involved in diabetes using a rat model of depression

While diabetic patients often present with comorbid depression, the underlying mechanisms linking diabetes and depression are unknown. The Wistar Kyoto (WKY) rat is a well-known animal model of depression and stress hyperreactivity. In addition, the WKY rat is glucose intolerant and likely harbors diabetes susceptibility alleles. We conducted a quantitative trait loci (QTL) analysis in the segregating F(2) population of a WKY x Fischer 344 (F344) intercross. We previously published QTL analyses for depressive behavior and hypothalamic-pituitary-adrenal (HPA) activity in this cross. In this study we report results from the QTL analysis for multiple metabolic phenotypes, including fasting glucose, post-restraint stress glucose, postprandial glucose and insulin, and body weight. We identified multiple QTLs for each trait and many of the QTLs overlap with those previously identified using inbred models of type 2 diabetes (T2D). Significant correlations were found between metabolic traits and HPA axis measures, as well as forced swim test behavior. Several metabolic loci overlap with loci previously identified for HPA activity and forced swim behavior in this F(2) intercross, suggesting that the genetic mechanisms underlying these traits may be similar. These results indicate that WKY rats harbor diabetes susceptibility alleles and suggest that this strain may be useful for dissecting the underlying genetic mechanisms linking diabetes, HPA activity, and depression.

Gender in childhood obesity: family environment, hormones, and genes

BACKGROUND

The prevalence of obesity among children in the United States represents a pool of latent morbidity. Though the prevalence of obesity has increased in both boys and girls, the causes and consequences differ between the sexes. Thus, interventions proposed to treat and prevent childhood obesity will need to account for these differences.

OBJECTIVE

This review examines gender differences in the presentation of obesity in children and describes environmental, hormonal, and genetic factors that contribute to observed gender differences.

METHODS

A search of peer-reviewed, published literature was performed with PubMed for articles published from January 1974 through October 2008. Search terms used were obesity, sex, gender, hormones, family environment, body composition, adiposity, and genes. Studies of children aged 0 to 18 years were included, and only articles published in English were reviewed for consideration. Articles that illustrated gender differences in either the presentation or underlying mechanisms of obesity in children were reviewed for content, and their bibliographies were used to identify other relevant literature.

RESULTS

Gender differences in childhood obesity have been understudied partially because of how we define the categories of overweight and obesity. Close examination of studies revealed that gender differences were common, both before and during puberty. Boys and girls differ in body composition, patterns of weight gain, hormone biology, and the susceptibility to certain social, ethnic, genetic, and environmental factors.

CONCLUSION

Our understanding of how gender differences in pediatric populations relate to the pathogenesis of obesity and the subsequent development of associated comorbid states is critical to developing and implementing both therapeutic and preventive interventions.