The insulin gene VNTR is associated with fasting insulin levels and development of juvenile obesity

Association of tyrosine hydroxylase 01 (TH01) microsatellite and insulin gene (INS) variable number of tandem repeat (VNTR) with type 2 diabetes and fasting insulin secretion in Mexican population

PURPOSE

A variable number of tandem repeats (VNTR) in the insulin gene (INS) control region may be involved in type 2 diabetes (T2D). The TH01 microsatellite is near INS and may regulate it. We investigated whether the TH01 microsatellite and INS VNTR, assessed via the surrogate marker single nucleotide polymorphism rs689, are associated with T2D and serum insulin levels in a Mexican population.

METHODS

We analyzed a main case-control study (n = 1986) that used univariate and multivariate logistic regression models to calculate the risk conferred by TH01 and rs689 loci for T2D development; rs689 results were replicated in other case-control (n = 1188) and cross-sectional (n = 1914) studies.

RESULTS

TH01 alleles 6, 8, 9, and 9.3 and allele A of rs689 were independently associated with T2D, with differences between sex and age at diagnosis. TH01 alleles with ≥ 8 repeats conferred an increased risk for T2D in males compared with ≤ 7 repeats (odds ratio, ≥ 1.46; 95% confidence interval, 1.1-1.95). In females, larger alleles conferred a 1.5-fold higher risk for T2D when diagnosed ≥ 46 years but conferred protection when diagnosed ≤ 45 years. Similarly, rs689 allele A was associated with T2D in these groups. In males, larger TH01 alleles and the rs689 A allele were associated with a significant decrease in median fasting plasma insulin concentration with age in T2D cases; the reverse occurred in controls.

CONCLUSION

Larger TH01 alleles and rs689 A allele may potentiate insulin synthesis in males without T2D, a process disabled in those with T2D.

Stimulated Insulin Secretion Predicts Changes in Body Composition Following Weight Loss in Adults with High BMI

BACKGROUND

The aim of obesity treatment is to promote loss of fat relative to lean mass. However, body composition changes with calorie restriction differ among individuals.

OBJECTIVES

The goal of this study was to test the hypothesis that insulin secretion predicts body composition changes among young and middle-age adults with high BMI (in kg/m2) following major weight loss.

METHODS

Exploratory analyses were conducted with pre-randomization data from 2 large feeding trials: the Framingham, Boston, Bloomington, Birmingham, and Baylor study (FB4; n = 82, 43.9% women, BMI ≥27) and the Framingham State Food Study [(FS)2; n = 161, 69.6% women, BMI ≥25]. Participants in the 2 trials consumed calorie-restricted moderate-carbohydrate or very-low-carbohydrate diets to produce 12-18% weight loss in ∼14 wk or 10-14% in ∼10 wk, respectively. We determined insulin concentration 30 min after a 75-g oral glucose load (insulin-30) as a measure of insulin secretion and HOMA-IR as a measure of insulin resistance at baseline. Body composition was determined by DXA at baseline and post-weight loss. Associations were analyzed using general linear models with adjustment for covariates.

RESULTS

In FB4, higher insulin-30 was associated with a smaller decrease in fat mass (0.441 kg per 100 μIU/mL increment in baseline insulin-30; P = 0.005; -1.20-kg mean difference between the first compared with the fifth group of insulin-30) and a larger decrease in lean mass (-0.465 kg per 100 μIU/mL; P = 0.004; 1.27-kg difference). Participants with higher insulin-30 lost a smaller proportion of weight loss as fat (-3.37% per 100 μIU/mL; P = 0.003; 9.20% difference). Greater HOMA-IR was also significantly associated with adverse body composition changes. Results from (FS)2 were qualitatively similar but of a smaller magnitude.

CONCLUSIONS

Baseline insulin dynamics predict substantial individual differences in body composition following weight loss. These findings may inform understanding of the pathophysiological basis for weight regain and the design of more effective obesity treatment. Registered at clinicaltrials.gov as NCT03394664 and NCT02068885.

The carbohydrate-insulin model: a physiological perspective on the obesity pandemic

According to a commonly held view, the obesity pandemic is caused by overconsumption of modern, highly palatable, energy-dense processed foods, exacerbated by a sedentary lifestyle. However, obesity rates remain at historic highs, despite a persistent focus on eating less and moving more, as guided by the energy balance model (EBM). This public health failure may arise from a fundamental limitation of the EBM itself. Conceptualizing obesity as a disorder of energy balance restates a principle of physics without considering the biological mechanisms that promote weight gain. An alternative paradigm, the carbohydrate-insulin model (CIM), proposes a reversal of causal direction. According to the CIM, increasing fat deposition in the body-resulting from the hormonal responses to a high-glycemic-load diet-drives positive energy balance. The CIM provides a conceptual framework with testable hypotheses for how various modifiable factors influence energy balance and fat storage. Rigorous research is needed to compare the validity of these 2 models, which have substantially different implications for obesity management, and to generate new models that best encompass the evidence.

Insulin: too much of a good thing is bad

BACKGROUND

Insulin shares a limited physiological concentration range with other endocrine hormones. Not only too low, but also too high systemic insulin levels are detrimental for body functions.

MAIN BODY

The physiological function and clinical relevance of insulin are usually seen in association with its role in maintaining glucose homeostasis. However, insulin is an anabolic hormone which stimulates a large number of cellular responses. Not only too low, but also excess insulin concentrations are detrimental to the physiological balance. Although the glucoregulatory activity of insulin is mitigated during hyperinsulinemia by dampening the efficiency of insulin signaling ("insulin resistance"), this is not the case for most other hormonal actions of insulin, including the promotion of protein synthesis, de novo lipogenesis, and cell proliferation; the inhibition of lipolysis, of autophagy-dependent cellular turnover, and of nuclear factor E2-related factor-2 (Nrf2)-dependent antioxidative; and other defense mechanisms. Hence, there is no general insulin resistance but selective impairment of insulin signaling which causes less glucose uptake from the blood and reduced activation of endothelial NO synthase (eNOS). Because of the largely unrestricted insulin signaling, hyperinsulinemia increases the risk of obesity, type 2 diabetes, and cardiovascular disease and decreases health span and life expectancy. In epidemiological studies, high-dose insulin therapy is associated with an increased risk of cardiovascular disease. Randomized controlled trials of insulin treatment did not observe any effect on disease risk, but these trials only studied low insulin doses up to 40 IU/day. Proof for a causal link between elevated insulin levels and cardiovascular disease risk comes from Mendelian randomization studies comparing individuals with genetically controlled low or high insulin production.

CONCLUSIONS

The detrimental actions of prolonged high insulin concentrations, seen also in cell culture, argue in favor of a lifestyle that limits circadian insulin levels. The health risks associated with hyperinsulinemia may have implications for treatment regimens used in type 2 diabetes.

Pancreatic β-cells in type 1 and type 2 diabetes mellitus: different pathways to failure

Loss of functional β-cell mass is the key mechanism leading to the two main forms of diabetes mellitus - type 1 diabetes mellitus (T1DM) and type 2 diabetes mellitus (T2DM). Understanding the mechanisms behind β-cell failure is critical to prevent or revert disease. Basic pathogenic differences exist in the two forms of diabetes mellitus; T1DM is immune mediated and T2DM is mediated by metabolic mechanisms. These mechanisms differentially affect early β-cell dysfunction and eventual fate. Over the past decade, major advances have been made in the field, mostly delivered by studies on β-cells in human disease. These advances include studies of islet morphology and human β-cell gene expression in T1DM and T2DM, the identification and characterization of the role of T1DM and T2DM candidate genes at the β-cell level and the endoplasmic reticulum stress signalling that contributes to β-cell failure in T1DM (mostly IRE1 driven) and T2DM (mostly PERK-eIF2α dependent). Here, we review these new findings, focusing on studies performed on human β-cells or on samples obtained from patients with diabetes mellitus.

INSULIN AND INSULIN RECEPTOR GENE POLYMORPHISMS AND SUSCEPTIBILITY TO NONALCOHOLIC FATTY LIVER DISEASE

ABSTRACT BACKGROUND: Nonalcoholic fatty liver disease (NAFLD) is an increasing global health concern defined by excessive hepatic fat content in the absence of excessive alcohol consumption. OBJECTIVE: Given the pivotal role of insulin resistance in NAFLD, we hypothesized that insulin (INS) and insulin receptor (INSR) gene polymorphisms may be associated with NAFLD risk. METHODS: A total of 312 subjects, including 153 cases with biopsy-proven NAFLD and 159 controls were enrolled in this case-control study. Four polymorphisms in INS (rs3842752, rs689) and INSR (rs1052371, rs1799817) genes were genotyped using PCR-RFLP method. RESULTS: The cases with NAFLD were older and had higher BMI, systolic blood pressure, diastolic blood pressure, as well as higher serum levels of aspartate aminotransferase, alanine aminotransferase, and gamma glutamyl transferase than the controls (P<0.001). The “TT” genotype of INSR rs1799817 compared with “CC” genotype occurred more frequently in the controls than the cases with NAFLD and the difference remained significant after adjustment for confounding factors (P=0.018; OR=0.10, 95%CI=0.02-0.76). However, no significant difference was found for INS rs3842752, INS rs689, and INSR rs1052371 gene polymorphisms between the cases with NAFLD and the controls either before or after adjustment for the confounders. CONCLUSION: These findings corroborate the hypothesis that genetic polymorphisms related to insulin resistance play a role in NAFLD susceptibility. Specifically, the INSR rs1799817 “TT” genotype had a protective effect for NAFLD. However, our results remain to be validated in other studies.

Development of Obesity: The Driver and the Passenger

Obesity has reached epidemic proportions and is one of the greatest challenges for public health in the twenty-first century. The macronutrient composition of diets, in particular the amount and ratio of carbohydrates, fat and protein, have received considerable attention in recent decades due to its potential relevance to the development of obesity and weight loss. The effects of various macronutrients on body weight regulation are still under debate. High-carbohydrate diets, and particularly high-fat diets, have been blamed for the increase in the prevalence of obesity. This paper shows that neither fat nor carbohydrates are fattening per se. Mixed diets with substantial amounts of fat and high-glycemic carbohydrates, like current WDs, are required to promote weight gain and obesity. High-glycemic carbohydrates are the active partner (the "driver"), which promotes fat storage through its insulinogenic effect, while fat is the passive partner (the "passenger") on the way to obesity. Elevated insulin levels (postprandial, but more importantly due to hypersecretion and hyperinsulinemia) promote fat storage and play a key role in obesogenesis and the obesity epidemic. Furthermore, mixed diets high in high-glycemic carbohydrates and fat promote fetal programming, with long-term adverse impacts on the offspring, including insulin hypersecretion, (childhood) obesity and metabolic diseases. Maternal obesity and high weight gain during pregnancy have also been linked to deleterious effects on fetal programming. As the global obesity epidemic increasingly affects women of reproductive age, a significant percentage of fetuses will experience fetal programming with a tendency towards obesity - a self-reinforcing process that further fuels the epidemic. A change in lifestyle and diet composition is needed to prevent or limit the development of obesity and related diseases.

Low-Carb and Ketogenic Diets in Type 1 and Type 2 Diabetes

Low-carb and ketogenic diets are popular among clinicians and patients, but the appropriateness of reducing carbohydrates intake in obese patients and in patients with diabetes is still debated. Studies in the literature are indeed controversial, possibly because these diets are generally poorly defined; this, together with the intrinsic complexity of dietary interventions, makes it difficult to compare results from different studies. Despite the evidence that reducing carbohydrates intake lowers body weight and, in patients with type 2 diabetes, improves glucose control, few data are available about sustainability, safety and efficacy in the long-term. In this review we explored the possible role of low-carb and ketogenic diets in the pathogenesis and management of type 2 diabetes and obesity. Furthermore, we also reviewed evidence of carbohydrates restriction in both pathogenesis of type 1 diabetes, through gut microbiota modification, and treatment of type 1 diabetes, addressing the legitimate concerns about the use of such diets in patients who are ketosis-prone and often have not completed their growth.

How Western Diet And Lifestyle Drive The Pandemic Of Obesity And Civilization Diseases

Westernized populations are plagued by a plethora of chronic non-infectious degenerative diseases, termed as "civilization diseases", like obesity, diabetes, cardiovascular diseases, cancer, autoimmune diseases, Alzheimer's disease and many more, diseases which are rare or virtually absent in hunter-gatherers and other non-westernized populations. There is a growing awareness that the cause of this amazing discrepancy lies in the profound changes in diet and lifestyle during recent human history. This paper shows that the transition from Paleolithic nutrition to Western diets, along with lack of corresponding genetic adaptations, cause significant distortions of the fine-tuned metabolism that has evolved over millions of years of human evolution in adaptation to Paleolithic diets. With the increasing spread of Western diet and lifestyle worldwide, overweight and civilization diseases are also rapidly increasing in developing countries. It is suggested that the diet-related key changes in the developmental process include an increased production of reactive oxygen species and oxidative stress, development of hyperinsulinemia and insulin resistance, low-grade inflammation and an abnormal activation of the sympathetic nervous system and the renin-angiotensin system, all of which play pivotal roles in the development of diseases of civilization. In addition, diet-related epigenetic changes and fetal programming play an important role. The suggested pathomechanism is also able to explain the well-known but not completely understood close relationship between obesity and the wide range of comorbidities, like type 2 diabetes mellitus, cardiovascular disease, etc., as diseases of the same etiopathology. Changing our lifestyle in accordance with our genetic makeup, including diet and physical activity, may help prevent or limit the development of these diseases.

The Carbohydrate-Insulin Model of Obesity: Beyond "Calories In, Calories Out"

Despite intensive research, the causes of the obesity epidemic remain incompletely understood and conventional calorie-restricted diets continue to lack long-term efficacy. According to the carbohydrate-insulin model (CIM) of obesity, recent increases in the consumption of processed, high-glycemic-load carbohydrates produce hormonal changes that promote calorie deposition in adipose tissue, exacerbate hunger, and lower energy expenditure. Basic and genetic research provides mechanistic evidence in support of the CIM. In animals, dietary composition has been clearly demonstrated to affect metabolism and body composition, independently of calorie intake, consistent with CIM predictions. Meta-analyses of behavioral trials report greater weight loss with reduced-glycemic load vs low-fat diets, though these studies characteristically suffer from poor long-term compliance. Feeding studies have lacked the rigor and duration to test the CIM, but the longest such studies tend to show metabolic advantages for low-glycemic load vs low-fat diets. Beyond the type and amount of carbohydrate consumed, the CIM provides a conceptual framework for understanding how many dietary and nondietary exposures might alter hormones, metabolism, and adipocyte biology in ways that could predispose to obesity. Pending definitive studies, the principles of a low-glycemic load diet offer a practical alternative to the conventional focus on dietary fat and calorie restriction.

Fetal growth is associated with CpG methylation in the P2 promoter of the IGF1 gene

Background

There are many reasons to think that epigenetics is a key determinant of fetal growth variability across the normal population. Since IGF1 and INS genes are major determinants of intrauterine growth, we examined the methylation of selected CpGs located in the regulatory region of these two genes.

Methods

Cord blood was sampled in 159 newborns born to mothers prospectively followed during their pregnancy. A 142-item questionnaire was filled by mothers at inclusion, during the last trimester of the pregnancy and at the delivery. The methylation of selected CpGs located in the promoters of the IGF1 and INS genes was measured in cord blood mononuclear cells collected at birth using bisulfite-PCR-pyrosequencing.

Results

Methylation at IGF1 CpG-137 correlated negatively with birth length (r = 0.27, P = 3.5 × 10⁻⁴). The same effect size was found after adjustment for maternal age, parity, and smoking: a 10% increase in CpG-137 methylation was associated with a decrease of length by 0.23 SDS.

Conclusion

The current results suggest that the methylation of IGF1 CpG-137 contributes to the individual variation of fetal growth by regulating IGF1 expression in fetal tissues.

Electronic supplementary material

The online version of this article (10.1186/s13148-018-0489-9) contains supplementary material, which is available to authorized users.

The association of insertions/deletions (INDELs) and variable number tandem repeats (VNTRs) with obesity and its related traits and complications

BACKGROUND

Despite the fact that insertions/deletions (INDELs) are the second most common type of genetic variations and variable number tandem repeats (VNTRs) represent a large portion of the human genome, they have received far less attention than single nucleotide polymorphisms (SNPs) and larger forms of structural variation like copy number variations (CNVs), especially in genome-wide association studies (GWAS) of complex diseases like polygenic obesity. This is exemplified by the vast amount of review papers on the role of SNPs and CNVs in obesity, its related traits (like anthropometric measurements, biochemical variables, and eating behavior), and its related complications (like hypertension, hypertriglyceridemia, hypercholesterolemia, and insulin resistance-collectively known as metabolic syndrome). Hence, this paper reviews the types of INDELs and VNTRs that have been studied for association with obesity and its related traits and complications. These INDELs and VNTRs could be found in the obesity loci or genes from the earliest GWAS and candidate gene association studies, like FTO, genes in the leptin-proopiomelanocortin pathway, and UCP2/3. Given the important role of the brain serotonergic and dopaminergic reward system in obesity susceptibility, the association of INDELs and VNTRs in these neurotransmitters' metabolism and transport genes with obesity is also reviewed. Next, the role of INS VNTR in obesity and its related traits is questionable, since recent large-scale studies failed to replicate the earlier positive associations. As obesity results in chronic low-grade inflammation of the adipose tissue, the proinflammatory cytokine gene IL1RA and anti-inflammatory cytokine gene IL4 have VNTRs that are implicated in obesity. A systemic proinflammatory state in combination with activation of the renin-angiotensin system and decreased nitric oxide bioavailability as found in obesity leads to endothelial dysfunction. This explains why VNTR and INDEL in eNOS and ACE, respectively, could be predisposing factors of obesity. Finally, two novel genes, DOCK5 and PER3, which are involved in the regulation of the Akt/MAPK pathway and circadian rhythm, respectively, have VNTRs and INDEL that might be associated with obesity.

SHORT CONCLUSION

In conclusion, INDELs and VNTRs could have important functional consequences in the pathophysiology of obesity, and research on them should be continued to facilitate obesity prediction, prevention, and treatment.

Relationship of insulin dynamics to body composition and resting energy expenditure following weight loss

OBJECTIVE

To examine associations of baseline insulin dynamics with changes in body composition and resting energy expenditure (REE) following weight loss.

METHODS

Twenty-one participants with overweight or obesity achieved 10-15% weight loss and then received 3 weight loss maintenance diets (high-carbohydrate, moderate-carbohydrate, and low-carbohydrate) in random order, each for 4 weeks. Body composition was measured at baseline and after weight loss. Insulin 30 min after glucose consumption (insulin-30; insulin response), C-peptide deconvolution analysis, HOMA, hepatic insulin sensitivity (IS), and REE were assessed at baseline and after each maintenance diet.

RESULTS

Insulin-30, but not maximal insulin secretion, hepatic IS, or HOMA, predicted changes in fat mass (standardized β = 0.385, 1.7 kg difference between 10th and 90th centile of insulin-30, P = 0.04) after weight loss. Insulin-30 (β = -0.341, -312 kcal day(-1) , P = 0.008), maximal insulin secretion (β = -0.216, -95 kcal day(-1) , P = 0.0002), HOMA (β = -0.394, -350 kcal day(-1) , P = 0.002), and hepatic IS (β = 0.217, 225 kcal day(-1) , P = 0.0003) predicted change in REE during weight loss maintenance, independent of changes in body composition. The inverse relationship between insulin-30 and REE was substantially attenuated when the low-carbohydrate diet was consumed first.

CONCLUSIONS

These findings distinguish a novel phenotype, characterized by high insulin response, at risk for weight regain, and identify a dietary approach to ameliorate this risk.

VNTR Polymorphism of the Insulin Gene and Childhood Overweight in a General Population

OBJECTIVE

The VNTR polymorphism 5' of the insulin gene has been related to obesity in a previous study on children with early onset of severe obesity. Our purpose was to analyze the association between this polymorphism and adiposity variability in an unselected population of children and adolescents in northern France.

RESEARCH METHODS AND PROCEDURES

In 293 nuclear families from the Fleurbaix Laventie Ville Santé study, we genotyped the INS VNTR polymorphism in 431 children and adolescents (8 to 18 years of age) and their parents. Overweight was defined according to the international definition in both children and adults. A transmission disequilibrium test in families with an overweight offspring was performed. The prevalence of overweight was compared according to genotype. The effect of the genotype on BMI and waist circumference was tested with a linear regression model, adjusting for age, gender, and Tanner stage.

RESULTS

There was an undertransmission of class III alleles from heterozygous parents to their overweight offspring (p < 0.002). Overweight was associated with class I alleles in children and adolescents (12% I/I, I/III vs. 3% III/III; p < 0.08). Those with a class III/III genotype had a 1 kg/m(2) lower mean BMI (p = 0.04) and 3 cm lower waist circumference (p = 0.02) than those bearing one or two class I alleles. No association of adiposity or obesity with class I alleles was found in parents.

DISCUSSION

INS VNTR polymorphism seems to contribute to differences in adiposity level in the general population of children and adolescents.

Prenatal famine and genetic variation are independently and additively associated with DNA methylation at regulatory loci within IGF2/H19

Both the early environment and genetic variation may affect DNA methylation, which is one of the major molecular marks of the epigenome. The combined effect of these factors on a well-defined locus has not been studied to date. We evaluated the association of periconceptional exposure to the Dutch Famine of 1944-45, as an example of an early environmental exposure, and single nucleotide polymorphisms covering the genetic variation (tagging SNPs) with DNA methylation at the imprinted IGF2/H19 region, a model for an epigenetically regulated genomic region. DNA methylation was measured at five differentially methylated regions (DMRs) that regulate the imprinted status of the IGF2/H19 region. Small but consistent differences in DNA methylation were observed comparing 60 individuals with periconceptional famine exposure with unexposed same-sex siblings at all IGF2 DMRs (P(BH)<0.05 after adjustment for multiple testing), but not at the H19 DMR. IGF2 DMR0 methylation was associated with IGF2 SNP rs2239681 (P(BH) = 0.027) and INS promoter methylation with INS SNPs, including rs689, which tags the INS VNTR, suggesting a mechanism for the reported effect of the VNTR on INS expression (P(BH) = 3.4 × 10(-3)). Prenatal famine and genetic variation showed similar associations with IGF2/H19 methylation and their contributions were additive. They were small in absolute terms (<3%), but on average 0.5 standard deviations relative to the variation in the population. Our analyses suggest that environmental and genetic factors could have independent and additive similarly sized effects on DNA methylation at the same regulatory site.

A pilot study of discontinuous, insulin-like growth factor 1-dosing growth hormone treatment in young children with FGFR3 N540K-mutated hypochondroplasia

OBJECTIVE

To assess the growth promoting effect of a recombinant growth hormone (rGH) treatment protocol adjusted on insulin-like growth factor 1 (IGF-1) dosing in children affected by the most severe forms of FGFR3 N540K-mutated hypochondroplasia.

STUDY DESIGN

Midterm results of an open-label, single-center, nonrandomized, 2003-2020 pilot trial to final stature, including 6 children (mean age, 2.6 ± 0.7 years; mean height SDS, -3.0 ± 0.5) with the N540K mutation of FGFR3 gene who received an rGH dosage titrated to an IGF-1 level close to 1.5 SDS of the normal range. rGH therapy was interrupted 1 day per week, 1 month per year, and 6 months every 2 years.

RESULTS

The mean height SDS increased by 1.9 during the 6.1 ± 0.9-year study period, reaching -0.8 to -1.3 at age 8.7 ± 1 years. The mean±SDS baseline IGF-1 value was -1.6 ± 0.5 before rGH treatment and 1.4±0.3 during the last year of observation. The average cumulative rGH dose was 0.075 ± 0.018 mg/kg/day (range, 0.059-0.100 mg/kg/day). Trunk/leg disproportion was improved.

CONCLUSION

IGF-1-dosing rGH treatment durably improves growth and reduces body disproportion in children with severe forms of hypochondroplasia.

Genetic correlates of early accelerated infant growth associated with juvenile-onset type 1 diabetes

OBJECTIVE

We previously showed that accelerated growth predisposing to development of childhood-onset type 1 diabetes (T1D) is restricted to the first year after birth. We assessed whether this phenomenon of increased early growth is associated with variants of two genes, insulin-like growth factor-1 (IGF1) and insulin variable number of tandem repeats (INS-VNTR), whose products are components of the growth axis.

PATIENTS AND METHODS

Patients and their siblings were genotyped for the INS-VNTR and for an IGF1 microsatellite. We tested for difference in first year growth, i.e., increased weight standard deviation score (SDS), a reliable measure of especially first year growth, between carriers and non-carriers of these gene variants, using a repeated measurement and regression analysis.

RESULTS

In patients, growth did not differ between carriers and non-carriers of the INS-VNTR*III allele, while carriership of this allele in siblings was positively associated with increased first year growth. In both patients and siblings, non-carriership of the IGF1*194 allele was positively associated with growth. Birth size was not associated with either variant.

CONCLUSIONS/DISCUSSION

Non-carriership of the IGF1*194 allele was positively associated with accelerated first year growth in both patients and siblings, independent of disease. This IGF1 variant may therefore contribute to increased first year growth, but cannot explain the association of first year growth with diabetes. An effect on growth of the INS-VNTR was detected in healthy siblings, but not in patients, suggesting that disease supersedes a growth effect of INS-VNTR.

The insulin gene variable number of tandemrepeats (INS VNTR) genotype and sleep disordered breathing in childhood obesity

Aim of our study is to verify the association between the genetic predisposition to hyperinsulinism due to the presence of the insulin gene (INS) I/I genotype and the development of sleep-related breathing disorders (SRBD) in obese children and adolescents. Two hundred and fifty-six obese children and adolescents (125 girls) have been investigated. As initial screening all subjects' mothers filled out the Sleep Disturbances Scale for Children (SDSC). The Sleep-Disordered Breathing (SDB) scale has been taken into account. Successively, a subgroup of 34 patients belonging to the first (14 children) and the last (20 children) SDB score quintiles underwent an overnight polysomnography and the apnea-hypopnea index (AHI) was evaluated. All subjects were genotyped for the INS VNTR and fasting insulin levels were evaluated. The population was divided into two groups according to the genotype: the first group was comprehensive of patients homozygotes for class I allele and the second group was composed by class III allele heterozygotes and homozygotes patients. Subjects I/I showed statistically signifIcant higher insulin levels (p<0.001) and SDB scores (p<0.001). Moreover, in the subgroup of patients investigated with polysomnography, class I homozygous subjects showed higher AHI compared to those patients carrying class III allele (p<0.001). Our data support the hypothesis that INS VNTR is associated with the development of SDB among obese children and adolescents.

A single-nucleotide polymorphism in a methylatable Foxa2 binding site of the G6PC2 promoter is associated with insulin secretion in vivo and increased promoter activity in vitro

OBJECTIVE

The G6PC2 gene encoding islet-specific glucose-6-phosphatase related protein (IGRP) has a common promoter variant, rs573225 (-231G/A), located within a Foxa binding site. We tested the cis-regulatory effects of rs573225 on promoter activity and its association with insulin response to oral glucose.

RESEARCH DESIGN AND METHODS

Functional effects of rs573225 were explored in transfected INS-1 and HIT-T beta-cell lines. A total of 734 young obese subjects of European ancestry were genotyped for rs573225. Insulin and glucose levels were measured in response to oral glucose, and the insulinogenic index (IGI) of insulin secretion was calculated.

RESULTS

In vitro, the G allele showed a higher affinity for binding Foxa2 transcription factor and increased G6PC2 promoter activity. Foxa2 binding is modified if the C adjacent to the G allele is methylated. IGI was associated with rs573225 by linear regression analysis and was 30% greater in AA or AG than in GG obese children. rs573225 was also associated with fasting glucose.

CONCLUSIONS

rs573225 is a functional cis-regulatory (epi)-single-nucleotide polymorphism (SNP) of G6PC2 associated with glucose-insulin homeostasis in obese children, likely to explain the results of recent genome-wide association studies in nondiabetic adults.

The association between low birth weight and type 2 diabetes: contribution of genetic factors

BACKGROUND

Low birth weight has been associated with an increased risk of type 2 diabetes in adulthood. Poor fetal nutrition has been suggested to explain this association. Our objective was to determine whether genetic factors contribute to the association between low birth weight and subsequent risk of type 2 diabetes.

METHODS

We retrieved information from original birth records on same-sex Swedish twins with known zygosity, born from 1926 to 1958. We used regression models to investigate whether birth weight was associated with risk of type 2 diabetes in the cohort of twins overall, and in case-control analyses within disease-discordant dizygotic and monozygotic twin pairs.

RESULTS

Of 18,230 twins, 592 (3.2%) had type 2 diabetes. The rate of type 2 diabetes consistently increased with decreasing birth weight, from 2.4% among twins with birth weights of 3500 g or more to 5.3% among those with birth weights less than 2000 g. In the cohort analysis, in which twins are analyzed as independent individuals, the adjusted odds ratio (95% confidence interval) of type 2 diabetes per 500-g decrease in birth weight was 1.44 (1.28-1.63). When we compared the diseased twin with the healthy cotwin, the corresponding odds ratios were 1.38 (1.02-1.85), among dizygotic twins, and 1.02 (0.63-1.64), among monozygotic twins.

CONCLUSIONS

Low birth weight is associated with type 2 diabetes in adulthood. The difference in this association between monozygotic and dizygotic twin pairs suggests that genetic mechanisms play an important role in this association.

INS VNTR is not associated with childhood obesity in 1,023 families: a family-based study

Previous studies have described genetic associations of the insulin gene variable number tandem repeat (INS VNTR) variant with childhood obesity and associated phenotypes. We aimed to assess the contribution of INS VNTR genotypes to childhood obesity and variance of insulin resistance, insulin secretion, and birth weight using family-based design. Participants were either French or German whites. We used transmission disequilibrium tests (TDTs) for assessing binary traits and quantitative pedigree disequilibrium tests for assessing continuous traits. In contrast to previous findings, we did not observe any familial association with childhood obesity (T = 50%, P = 0.77) in the 1,023 families tested. In French obese children, INS VNTR did not associate with fasting insulin levels (P = 0.23) and class I allele showed only borderline association with increased insulin secretion index at 30 min (P = 0.03). INS VNTR did not associate with birth weight in obese children (P = 0.98) and TDT analyses in 350 French families with history of low birth weight (LBW) showed no association with this condition (P = 0.92). In summary, our study, the largest performed so far, does not support the previously reported associations between INS VNTR and childhood obesity, insulin resistance, or birth weight, and does not suggest any major role for this variant in modulating these traits.

Mismatch base pair detection by fluorescence spectral change upon addition of metal cation--toward efficient analysis of single nucleotide polymorphism

Addition of mercury (II) cation to fluorescent-labeled duplex involving a T:T mismatch base pair and silver (I) cation to fluorescent-labeled duplex involving a C:C mismatch base pair significantly changed the fluorescence intensity, but no significant change in the fluorescence intensity was observed for duplexes involving the other base pairs. The fluorescence spectral change upon addition of the metal cation can discriminate T:T and C:C mismatch base pairs from the other base pairs. Our results certainly support the idea that the fluorescence spectral change upon addition of the metal cation could be a convenient strategy for the mismatch base pair detection by the heteroduplex analysis, and may eventually lead to progress in single nucleotide polymorphism genotyping.

A novel interaction between dietary composition and insulin secretion: effects on weight gain in the Quebec Family Study

BACKGROUND

Clinical trials of low-fat diets characteristically produce small mean long-term weight loss but a large interindividual variation in response. This variation has been attributed to psychological and behavioral factors, although biological differences may also play a role.

OBJECTIVE

The objective was to determine whether physiologic differences in insulin secretion explain differences in weight gain among individuals consuming low- and high-fat diets.

DESIGN

Of 276 individuals followed in the Quebec Family Study for a mean of 6 y, we compared those in the lowest with those in the highest dietary fat tertiles. We performed oral-glucose-tolerance tests at baseline and examined the insulin concentration at 30 min (insulin-30) as a proxy measure of insulin secretion. Six-year changes in body weight and waist circumference were the primary endpoints. We determined the associations between insulin-30 and the primary endpoints by linear regression analysis, with adjustment for potentially confounding factors.

RESULTS

Mean changes in body weight and waist circumference did not differ significantly between the lowest- and highest-fat diet groups. However, these endpoints were strongly associated with insulin-30, especially among individuals consuming the lowest-fat diet. Insulin-30 at baseline was significantly associated with 6-y weight gain (r = 0.51, P < 0.0001) and change in waist circumference (r = 0.55, P < 0.0001) in the lowest diet fat, group [corrected], but not in the highest diet fat group (r = 0.18, P = 0.086 and r = 0.20, P = 0.058, respectively) [corrected] Individuals in the highest insulin-30 and lowest dietary fat group gained 1.8 kg more than did those in the highest insulin-30 and highest dietary fat group (51%; P = 0.034); they gained 4.5 kg more than did those in the lowest insulin-30 and lowest dietary fat group (6.5-fold; P = 0.0026).

CONCLUSION

A proxy measure of insulin secretion strongly predicts changes in body weight and waist circumference over 6 y in adults, especially among those consuming lower-fat diets, which demonstrates the existence of a novel diet-phenotype interaction.

Epigenetic regulation and fetal programming

Fetal programming encompasses the role of developmental plasticity in response to environmental and nutritional signals during early life and its potential adverse consequences (risk of cardiovascular, metabolic and behavioural diseases) in later life. The first studies in this field highlighted an association between poor fetal growth and chronic adult diseases. However, environmental signals during early life may lead to adverse long-term effects independently of obvious effects on fetal growth. Adverse long-term effects reflect a mismatch between early (fetal and neonatal) environmental conditions and the conditions that the individual will confront later in life. The mechanisms underlying this risk remain unclear. However, experimental data in rodents and recent observations in humans suggest that epigenetic changes in regulatory genes and growth-related genes play a significant role in fetal programming. Improvements in our understanding of the biochemical and molecular mechanisms at play in fetal programming would make it possible to identify biomarkers for detecting infants at high risk of adult-onset diseases. Such improvements should also lead to the development of preventive and therapeutic strategies.

Association analysis indicates that a variant GATA-binding site in the PIK3CB promoter is a Cis-acting expression quantitative trait locus for this gene and attenuates insulin resistance in obese children

OBJECTIVE

In search of functional polymorphisms associated with the genetics of insulin resistance, we studied a variant in the promoter of PIK3CB, the gene coding for the catalytic p110beta subunit of phosphatidylinositol (PI) 3-kinase, a major effector of insulin action.

RESEARCH DESIGN AND METHODS

The rs361072 C/T variant was selected among single nucleotide polymorphisms of the PIK3CB region because we suspected that its common C allele (allelic frequency approximately 50% in Europeans) could create a GATA-binding motif and was genotyped in five cohorts of obese (n = 1,876) and two cohorts of nonobese (n = 1,490) European children. To estimate insulin resistance in these children, the homeostasis model assessment for insulin resistance (HOMA-IR) index was measured in strict nutritional conditions. GATA-binding and functional effects of rs361072 were explored in transfected cell lines and in lymphocytes from obese children.

RESULTS

The rs361072 C/T variant was associated with HOMA-IR in the obese children cohorts (1.7 x 10(-12) < P < 2 x 10(-4) for C/C vs. T/T using regression analysis). HOMA-IR averaged 3.3 +/- 0.1 in C/C and 4.5 +/- 0.2 in T/T obese children (P = 4.5 x 10(-6) by ANOVA). C/T patients had intermediate values. As shown by the interaction between BMI and genotype (P = 2.1 x 10(-9)), the association of rs361072 with HOMA-IR depended on BMI and was only marginal in nonobese children (P = 0.04). At the molecular level, the C allele of rs361072 was found to create a GATA-binding site able to increase transcription of PIK3CB.

CONCLUSIONS

We postulate that the C allele of rs361072 is a causal variant capable of attenuating insulin resistance in obese children through increased expression of p110beta.

A single-nucleotide polymorphism in the p110beta gene promoter is associated with partial protection from insulin resistance in severely obese adolescents

OBJECTIVE

Severe juvenile obesity causes metabolic and cardiovascular complications in adulthood. The catalytic p110beta subunit of phosphatidyl-inositol-3 kinase is a major effector of insulin action. We studied the p110beta gene as a candidate gene for association with insulin resistance (IR) and fasting glycemia in severely obese children.

METHODS

We conducted an association study in 580 severely obese European children (body mass index > 99.6th centile) and 606 nonobese control children, in whom glucose and insulin were measured in the fasting state. The homeostasis model assessment insulin resistance index was used to estimate IR.

RESULTS

We found that a single-nucleotide polymorphism (rs361072) located in the promoter of the p110beta gene was associated with fasting glucose (P = 0.0002), insulin (P = 2.6 10(-8)), and homeostasis model assessment insulin resistance index (P =1 10(-9)) in the severely obese children. The effect of rs361072 was marginal or not significant in nonobese children.

CONCLUSIONS

The C allele of rs361072 attenuates IR in superobese children.

Childhood obesity and insulin resistance

Insulin resistance (IR) in childhood has importance to the understanding and prevention of the growing epidemic of insulin resistance syndrome (IRS) in adults with attendant obesity, type 2 diabetes (T2DM), atherosclerotic diseases, hypertension, gout, non-alcoholic, steato-hepatitis (NASH), gall bladder disease, nephropathy, polycystic ovarian disease (PCOS), infertility and premature senility. The severity of IR and its' complications in children unfortunately and usually progresses in their pubertal transition to adulthood; affected young children are more likely than adults to have underlying causal monogenic disorders; the sequence of natural history and events give insights into disease pathogeneses, and optimal life style choices that last are best made during the early formative years. Some features of IR in children discussed herein are: a strong tendency to low birth weight for gestational age, adverse effects of adrenarche and therapeutic steroid therapy, predisposition to premature pubarche, acanthosis nigricans, tall stature despite pituitary GH suppression, allergic diathesis, hyperandrogenism and PCOS, dyslipidemia and fatty liver disease, and diagnosis by clinical and biochemical markers of IR including insulin regulated hepatic hormonal binding proteins such as IGFBP-1. The national preoccupation with the "metabolic syndrome" T2DM and obesity, should be appropriately directed to an improved understanding of IR in children and their management, if the looming health crisis in affected adults is to be seriously addressed. The nation is facing its' first generation of children who will be less healthy and die younger than the previous generation (Marks (2005) Presentation to the American Association of Diabetes Educators 32nd Annual Meeting and Exhibition, August 10-13, Washington, DC).

Growth hormone therapy for short children born small for gestational age

Children born small for gestational age may demonstrate continued growth retardation, resulting in persistent short stature. In the majority of the cases, this is linked with abnormal growth hormone secretion and also abnormal insulin-like growth factor levels. This review discusses the treatment of such children with recombinant human growth hormone. It illustrates the importance of starting therapy early, the dose-dependent response, and the advantages of continuous therapy and describes safety considerations.

Association between small for gestational age and paternally inherited 5' insulin haplotypes

OBJECTIVE

To test the association between small for gestational age and polymorphisms in the insulin gene in newborns and their mothers, as well as the effect of the parental transmission of haplotypes.

SUBJECTS

Pairs of healthy African-American full-term newborns (N=207) and mothers were recruited from Memphis TN and Jackson MS with birth weights ranging from 2210 to 4735 g.

METHODS

Six single nucleotide polymorphisms (SNPs) located in the insulin (INS) and insulin-like growth factor 2 (IGF2) genes were genotyped in mothers and newborns. Haplotypes composed of three SNPs in the 5' region of the INS-IGF2 locus were computationally inferred. Odds ratios for risk of small for gestational age (SGA) birth were calculated for individual SNPs and inferred haplotypes in the newborns and in the mothers using logistic regression. For 162 mother--newborn pairs the parental transmission of the haplotypes could be inferred, and the risks for SGA birth were calculated for the three common haplotypes in this sample.

RESULTS

Three INS SNPs exhibited significant association with risk for SGA birth. The SNP alleles associated with increased risk for SGA were opposite in the maternal and newborn genomes, implying opposing influences on the rate of fetal growth. Consistent with these results, haplotypes composed of complementary nucleotide sequences (CAC at rs3842738, rs689 and rs3842748, respectively, in the newborn versus GTG in the mother) were significantly associated with risk for SGA birth. In analyses of haplotypes according to parental transmission, the same trend in risk for SGA was observed for both maternally and paternally transmitted haplotypes, although a significant difference in risk was observed only for paternally transmitted haplotypes.

CONCLUSION

Polymorphisms near the 5' end of the INS-IGF2 locus are significantly associated with risk for SGA birth with a major effect due to the paternally transmitted haplotype, which is preferentially expressed due to imprinting.

Markers of insulin resistance are associated with fatness and fitness in school-aged children: the European Youth Heart Study

AIMS/HYPOTHESIS

Our aim was to examine the association between markers of insulin resistance and: (1) body fat and waist circumference, taking into account cardiorespiratory fitness in school-aged children; and (2) cardiorespiratory fitness at differing levels of body fat and waist circumference.

SUBJECTS AND METHODS

This was a cross-sectional study of 873 children aged 9.6 +/- 0.4 years from Estonia and Sweden. Weight, height and waist circumference were measured. Body fat was expressed as the sum of five skinfold thicknesses. Cardiorespiratory fitness was estimated by a maximal cycle-ergometer test. The studied markers of insulin resistance were fasting insulin and glucose, and homeostasis model assessment (HOMA).

RESULTS

HOMA and fasting insulin were positively associated with body fat and waist circumference after adjusting for cardiorespiratory fitness, age, pubertal status and study location. HOMA and fasting insulin were negatively associated with cardiorespiratory fitness in children in the third (highest) tertile of body fat and waist circumference after controlling for sex, age, pubertal status and study location. Fasting glucose was negatively associated with cardiorespiratory fitness in children in the third (highest) tertile of waist circumference, but it was not associated when body fat was taken into account.

CONCLUSIONS/INTERPRETATION

In school-aged children, HOMA and fasting insulin are significantly associated with body fat and waist circumference. In addition, cardiorespiratory fitness explains a significant proportion of the HOMA and fasting insulin variance in those children with high levels of body fat and waist circumference. The findings suggest that the deleterious consequences ascribed to high fatness could be counteracted by having high levels of cardiorespiratory fitness.

Obesity and polymorphisms in genes regulating human adipose tissue

Obesity is the result of an imbalance between food intake and energy expenditure resulting in the storing of energy as fat. Adipose tissue contains the largest store of energy in the body and plays important roles in regulating energy partitioning. Developments in genomics, in particular microarray-based expression profiling, have provided scientists with a number of new candidate genes whose expression in adipose tissue is regulated by obesity. Integrating expression profiles with genome-wide linkage and/or association analyses is a promising strategy to identify new genes underlying susceptibility to obesity. This article provides a comprehensive review of adipose-tissue-expressed genes implicated in predisposition to human obesity. The authors consider the following genes of particular interest: peroxisome proliferator-activated receptor gamma and, potentially, INSIG2 acting in adipogenesis; the adrenoreceptors beta 2 and 3, as well as hormone-sensitive lipase acting on lipolysis; uncoupling protein 2 acting in mitochondria energy expenditure; and among secreted molecules the cytokine tumor necrosis factor alpha and the hormone leptin. With the rapid development in genome research, we predict that additional alleles in genes regulating adipose tissue function will be established as risk factors for common obesity in the coming years. This has important implications for the prevention of obesity and may also offer new therapeutic targets.

Insulin resistance-related genes and advanced left-sided colorectal adenoma

BACKGROUND

Insulin resistance has been linked with colorectal neoplasia through a number of mechanistic and observational studies. Allelic variants of genes encoding components of the insulin pathway, including insulin (INS), insulin receptor (INSR), and insulin receptor substrate-1 and insulin receptor substrate-2 (IRS1 and IRS2) have been associated with hyperinsulinemia and insulin resistance and may, therefore, predict susceptibility to colorectal neoplasia.

METHODS

We investigated whether single nucleotide polymorphisms (SNP) in the INS, INSR, IRS1, and IRS2 genes are associated with risk of advanced left-sided colorectal adenoma, a cancer precursor. We analyzed 20 SNPs in a largely Caucasian study population comprising 766 cases with advanced adenomas of the distal colon and 771 controls, all of whom had undergone flexible sigmoidoscopy as part of the screening arm of the Prostate, Lung, Colorectal and Ovarian Cancer Screening Trial.

RESULTS

Overall, we found limited evidence for a role of gene variants of the insulin signaling pathway and prevalence of advanced colorectal adenoma. We observed a statistically significant interaction between INSR genotypes and body mass index (BMI) with colorectal adenoma prevalence (P value for global test = 0.003) and suggestion of an interaction between INSR genotypes and glycemic load (P value for global test = 0.06); however, exploration of the interaction of BMI and glycemic load with the individual SNPs in INSR did not suggest a single SNP that may explain the significance of these global tests of interaction and did not yield any consistent patterns.

CONCLUSION

These findings do not provide strong evidence for associations between polymorphic variation in genes of the insulin signaling pathway and advanced left-sided colorectal adenoma. Evidence for interaction between INSR variants and BMI and glycemic load for risk of advanced left-sided colorectal adenoma requires independent confirmation, and genotyping of INSR across a broader region and at greater density may be necessary to fully elucidate the nature of these interactions.

Type 2 diabetes TCF7L2 risk genotypes alter birth weight: a study of 24,053 individuals

The role of genes in normal birth-weight variation is poorly understood, and it has been suggested that the genetic component of fetal growth is small. Type 2 diabetes genes may influence birth weight through maternal genotype, by increasing maternal glycemia in pregnancy, or through fetal genotype, by altering fetal insulin secretion. We aimed to assess the role of the recently described type 2 diabetes gene TCF7L2 in birth weight. We genotyped the polymorphism rs7903146 in 15,709 individuals whose birth weight was available from six studies and in 8,344 mothers from three studies. Each fetal copy of the predisposing allele was associated with an 18-g (95% confidence interval [CI] 7-29 g) increase in birth weight (P=.001) and each maternal copy with a 30-g (95% CI 15-45 g) increase in offspring birth weight (P=2.8x10-5). Stratification by fetal genotype suggested that the association was driven by maternal genotype (31-g [95% CI 9-48 g] increase per allele; corrected P=.003). Analysis of diabetes-related traits in 10,314 nondiabetic individuals suggested the most likely mechanism is that the risk allele reduces maternal insulin secretion (disposition index reduced by ~0.15 standard deviation; P=1x10-4), which results in increased maternal glycemia in pregnancy and hence increased offspring birth weight. We combined information with the other common variant known to alter fetal growth, the -30G-->A polymorphism of glucokinase (rs1799884). The 4% of offspring born to mothers carrying three or four risk alleles were 119 g (95% CI 62-172 g) heavier than were the 32% born to mothers with none (for overall trend, P=2x10-7), comparable to the impact of maternal smoking during pregnancy. In conclusion, we have identified the first type 2 diabetes-susceptibility allele to be reproducibly associated with birth weight. Common gene variants can substantially influence normal birth-weight variation.

Insulin gene VNTR, CTLA-4 +49A/G and HLA-DQB1 alleles distinguish latent autoimmune diabetes in adults from type 1 diabetes and from type 2 diabetes group

Recent research has underlined the need to explore pathogenic, genetic and clinical spectrum of adult onset autoimmune diabetes, also known as latent autoimmune diabetes in adults (LADA). We aimed to investigate whether genetic factors that are associated with type 1 diabetes (T1D) susceptibility, namely HLA-DQB1 alleles, cytotoxic T-lymphocyte antigen 4 gene (CTLA-4) and insulin gene (INS) polymorphisms, are also associated with an atypical subset of patients diagnosed with type 2 diabetes (T2D). The case-control study included 70 T1D, 305 T2D and 252 nondiabetic controls. The T2D group was divided into atypical T2D (LADA, n = 61) or typical T2D (n = 244) subgroups based on the presence of at least one pancreas-specific antibody. Our data suggested that HLA-DQB1 alleles of all three risk classes, INS variable number of tandem repeat (VNTR) I/I and CTLA-4 +49 GG or AG genotypes, were independent risk factors for developing LADA and could be used as a diagnostic tool to discriminate between LADA and T2D. Additionally, there was an increased association between LADA and CTLA-4 diabetes-susceptibility genotypes and decreased association with INS VNTR and high-risk HLA-DQB1 alleles, compared with T1D. Our study suggested the need for further investigation into the genetic background and functional genomics of LADA in comparison with T1D and T2D.

Increased prevalence of VNTR III of the insulin gene in women with gestational diabetes mellitus (GDM)

OBJECTIVE

The VNTR polymorphism in the promoter region of the insulin gene (INS-VNTR) affects transcription rate and has been associated with insulin resistance and DM2. Gestational diabetes mellitus (GDM) is a multifactorial disorder, where both impaired insulin secretion and action may be involved. The aim of the study was to examine the distribution of the INS-VNTRs in women with GDM and to investigate possible associations with features of beta cell function and glycaemic control in this population.

METHODS

One hundred and sixty-one women with GDM and 111 normal pregnant women (n) were genotyped for INS-VNTR during the 24th-32nd pregnancy week. Glucose and insulin levels were determined during the diagnostic OGTT. The majority of the previous GDM women were also examined at 3-6 months post-partum.

RESULTS

VNTR class III/III genotype was significantly more frequent in the GDM group 8.7% versus 2.7%, p=0.02 giving an OR of 3.97 (1.1-14.29). An increased frequency of the VNTR class III allele was found in those GDM women who required insulin for treatment compared to those controlled with diet alone (12.4% versus 4%, p<0.001). Basal insulin levels tended to be lower in GDM women homozygous for the class III allele without reaching statistical significance (p=0.09).

CONCLUSIONS

The INS-VNTR class III is more frequent in women who develop GDM, and may be associated with decreased ability of the beta cell to meet the increased insulin requirements as reflected by the need for insulin supplementation for adequate glycaemic control.

Gene-diet interactions in childhood obesity: paucity of evidence as the epidemic of childhood obesity continues to rise

Childhood obesity is growing rapidly worldwide. Although there have been enormous advances in the genetic underpinnings of obesity in recent years, the pathways that lead to obesity are still not completely understood. One of the ongoing challenges is the lack of a comprehensive definition of the obese phenotype that encompasses intermediary phenotypic expressions of biological and behavioral nature. Interactions between genetic and environmental factors, including nutrient exposures and dietary behaviors, can influence the development of the obese phenotype. Specifically, genes play a decisive role in the etiology of childhood obesity under the permissive circumstances of an obesogenic environment (increase in energy intake with a decrease in physical activity). Like many diseases, the causes of obesity are complex and their investigation requires novel approaches. Given the many contributors to obesity (weight gain, weight loss, weight maintenance, variability in body composition), as well as the dynamic nature of this issue, genomic tools must continue to be employed to evaluate all dimensions of the obesity phenotype, such as biochemical characteristics, susceptibility markers, nutrient intake, feeding practices and gene-environment interactions. Fundamental knowledge of the types of genes involved and available gene-diet interaction studies in children's obesity are reviewed. Although there is a paucity of existing literature in this specific domain of childhood obesity, ongoing investigations utilizing large cohorts have potential for providing the knowledge needed for targeted interventions in the future.

Effect of the melanocortin-3 receptor C17A and G241A variants on weight loss in childhood obesity

BACKGROUND

The central melanocortin system is critical for the long-term regulation of energy homeostasis. Melanocortin-3 receptor (MC3R) knock-out mice, despite being hypophagic, have increased fat mass and higher feed efficiency than do their wild-type littermates.

OBJECTIVE

The aim was to evaluate whether, in childhood obesity, MC3R variants are associated with changes in fatness reduction as a consequence of a weight-reduction program.

DESIGN

Molecular screening of the MC3R coding region in 184 obese children, 77 girls and 107 boys [x (+/-SEM) body mass index (BMI; in kg/m(2)) z score: 3.3 +/- 2.3; age 9.2 +/- 2 y], was performed. BMI was evaluated at baseline and after 6 and 12 mo of the weight loss program.

RESULTS

No new mutations were found. Two previously described polymorphisms, C17A (Thr6Lys) and G241A (Val81Ile), were observed in 20 patients in almost complete linkage disequilibrium. No significant differences in BMI z scores were observed at baseline of the weight-loss program between the genotypes; however, at follow-up, heterozygotes showed a significantly higher BMI z score (P = 0.03). When the patients were divided according to the amount of weight lost, a higher prevalence of heterozygotes was observed among subjects who lowered their BMI z score <1.5 (P = 0.03).

CONCLUSION

These results suggest a gene-diet interaction between the MC3R C17A and G241A variants and a weight loss program for the ability to lose weight in childhood obesity.

A study of association between common variation in the growth hormone-chorionic somatomammotropin hormone gene cluster and adult fasting insulin in a UK Caucasian population

Background

Reduced growth during infancy is associated with adult insulin resistance. In a UK Caucasian cohort, the CSH1.01 microsatellite polymorphism in the growth hormone-chorionic somatomammotropin hormone gene cluster was recently associated with increases in adult fasting insulin of approximately 23 pmol/l for TT homozygote males compared to D1D1 or D2D2 homozygotes (P = 0.001 and 0.009; n = 206 and 92, respectively), but not for females. TT males additionally had a 547-g lower weight at 1 year (n = 270; P = 0.008) than D2D2 males. We sought to replicate these data in healthy UK Caucasian subjects. We genotyped 1396 subjects (fathers, mothers and children) from a consecutive birth study for the CSH1.01 marker and analysed genotypes for association with 1-year weight in boys and fasting insulin in fathers.

Results

We found no evidence for association of CSH1.01 genotype with adult male fasting insulin concentrations (TT/D1D1 P = 0.38; TT/D2D2 P = 0.18) or weight at 1 year in boys (TT/D1D1 P = 0.76; TT/D2D2 P = 0.85). For fasting insulin, our data can exclude the previously observed effect sizes as the 95 % confidence intervals for the differences observed in our study exclude increases in fasting insulin of 9.0 and 12.6 pmol/l for TT relative to D1D1 and D2D2 homozygotes, respectively. Whilst we have fewer data on boys' 1-year weight than the original study, our data can exclude a reduction in 1-year weight greater than 557 g for TT relative to D2D2 homozygotes.

Conclusion

We have not found association of the CSH1.01 genotype with fasting insulin or weight at 1 year. We conclude that the original study is likely to have over-estimated the effect size for fasting insulin, or that the difference in results reflects the younger age of subjects in this study relative to those in the previous study.

Insulin gene variable number of tandem repeats (INS VNTR) genotype and metabolic syndrome in childhood obesity

OBJECTIVE

The insulin variable number of tandem repeats (VNTR) polymorphism located in the insulin gene promoter (INS VNTR) has been associated with insulin levels in obese children. Hyperinsulinemia is a pivotal factor in the development of metabolic syndrome, an emerging complication in childhood obesity. With the present study, we aimed to test the associations between INS VNTR and the metabolic syndrome in juvenile-onset obesity.

SUBJECTS AND METHODS

We screened for the INS VNTR in 320 obese children (152 girls; mean age, 11.2 +/- 2.3 yr; mean z-score body mass index, 3.6 +/- 1.1). All of them underwent a standard oral glucose tolerance test; baseline measurements included blood pressure and plasma lipid and fasting insulin levels. By using the data derived from the oral glucose tolerance test, the whole-body insulin sensitivity and the insulinogenic index were calculated.

RESULTS

The prevalence of metabolic syndrome reached 39%. No differences in INS VNTR genotype distribution were observed between obese subjects and 200 lean, age- and sex-matched children (P = 0.7). Among obese subjects, the prevalence of the metabolic syndrome was significantly higher in subjects with the I/I genotype (P = 0.006); the risk for developing the metabolic syndrome was significantly higher in subjects carrying the I/I genotype (odds ratio, 2.5; 95% confidence interval, 1.5-3.9). Obese subjects homozygous for the class I allele showed higher insulin levels and insulinogenic index but lower whole-body insulin sensitivity.

CONCLUSIONS

We conclude that the I variant of the insulin promoter, when expressed in homozygotes, can predispose obese children to develop the metabolic syndrome.