The common genetic variant upstream of INSIG2 gene is not associated with obesity in Indian population

Common Genetic Variant of insig2 Gene rs7566605 Polymorphism Is Associated with Severe Obesity in North India

Background:

Obesity is a very common disorder resulting from an imbalance between food intake and energy expenditure, and it has a substantial impact on the development of chronic diseases. The aim of this study was to examine the association of INSIG2 (rs7566605) gene polymorphism with obesity and obesity associated phenotypes in North Indian subjects.

Methods:

The variants were investigated for association in 642 obese and non-obese individuals. The genotyping of INSIG2 (rs7566605) single nucleotide polymorphism was analyzed by the TaqMan allelic discrimination protocol.

Results:

A significant association was observed for INSIG2 (rs7566605) single nucleotide polymorphism with obesity and obesity-related phenotypes. Furthermore, a significant relationship was found between the rs7566605 and insulin, homeostasis model of assessment-insulin resistance, the percentage of body fat, fat mass, leptin, and adiponectin.

Conclusion:

The present study observed significant association between INSIG2 (rs7566605) single nucleotide polymorphism and obesity, as well as obesity-associated phenotypes in North Indian population.

Obesity and genomics: role of technology in unraveling the complex genetic architecture of obesity

Obesity is a complex and multifactorial disease that occurs as a result of the interaction between "obesogenic" environmental factors and genetic components. Although the genetic component of obesity is clear from the heritability studies, the genetic basis remains largely elusive. Successes have been achieved in identifying the causal genes for monogenic obesity using animal models and linkage studies, but these approaches are not fruitful for polygenic obesity. The developments of genome-wide association approach have brought breakthrough discovery of genetic variants for polygenic obesity where tens of new susceptibility loci were identified. However, the common SNPs only accounted for a proportion of heritability. The arrival of NGS technologies and completion of 1000 Genomes Project have brought other new methods to dissect the genetic architecture of obesity, for example, the use of exome genotyping arrays and deep sequencing of candidate loci identified from GWAS to study rare variants. In this review, we summarize and discuss the developments of these genetic approaches in human obesity.

Association of INSIG2 polymorphism with overweight and LDL in children

Background

Dyslipidemia and overweight are common issues in children. Identifying genetic markers of risk could lead to targeted interventions. A polymorphism of SNP rs7566605 near insulin-induced gene 2 (INSIG2) has been identified as a strong candidate gene for obesity, through its feedback control of lipid synthesis.

Objective

To identify polymorphisms in INSIG2 which are associated with overweight (BMI ≥ 85% for age) and dyslipidemia in children. Hypothesis: The C allele of rs7566605 would be significantly associated with BMI and LDL.

Design/Methods

We genotyped 15 SNPs in/near INSIG2 in 1,058 healthy children (53% non-Hispanic white (NHW), 37% overweight) participating in a school based study. Genotype was compared with BMI and lipid markers, adjusting for age, gender, and puberty.

Results

We found a significant association between the SNP rs12464355 and LDL in NHW children, p < 0.001. The G allele is protective (lower LDL). A different SNP was associated with overweight in NHW: rs17047757. SNP rs7566605 was not associated with overweight or lipid levels.

Conclusions

We identified novel genetic associations between INSIG2 and both overweight and LDL in NHW children. Polymorphisms in INSIG2 may be important in the development of obesity through its effects on lipid regulation.

Gender-Specific Effect of -102G>A Polymorphism in Insulin Induced Gene 2 on Obesity in Chinese Children

Background. Insulin induced gene 2 (INSIG2) encodes a protein that has a biological effect on regulation of adipocyte metabolism and body weight. This study aimed to investigate the association of INSIG2 gene -102G>A polymorphism with obesity related phenotypes in Chinese children and test gender-specific effects. Methods. The 2,030 independent individuals aged from 7 to 18 years, including 705 obese cases and 1,325 nonobese controls, were recruited from local schools. We measured the obesity-related phenotypes and detected the serum lipids. We genotype -102G>A polymorphism by using the matrix-assisted laser desorption/ionization time-of-flight mass spectrometry (MALDI-TOF MS). Results. In all individuals, we found that the GG/GA genotype of INSIG2 -102G>A polymorphism was associated with risk of severe obesity (OR = 1.62, 95% CI: 1.11-2.36, and P = 0.012) under the dominant model. The association with severe obesity existed only in boys (OR = 1.91, 95% CI: 1.15-3.17, P = 0.012). The GG/GA genotype of -102G>A polymorphism was also associated with higher waist circumference (β = 2.61 cm, P = 0.031) in boys. No similar association was found in girls. The polymorphism was not associated with other obesity-related phenotypes, neither in all individuals nor in gender-specific population. Conclusions. This study identified a gender-specific effect of INSIG2 -102G>A polymorphism on risk of severe obesity and waist circumference in Chinese boys.

Genetic association study with metabolic syndrome and metabolic-related traits in a cross-sectional sample and a 10-year longitudinal sample of chinese elderly population

Background

The metabolic syndrome (MetS) has been known as partly heritable, while the number of genetic studies on MetS and metabolic-related traits among Chinese elderly was limited.

Methods

A cross-sectional analysis was performed among 2 014 aged participants from September 2009 to June 2010 in Beijing, China. An additional longitudinal study was carried out among the same study population from 2001 to 2010. Biochemical profile and anthropometric parameters of all the participants were measured. The associations of 23 SNPs located within 17 candidate genes (MTHFR, PPARγ, LPL, INSIG, TCF7L2, FTO, KCNJ11, JAZF1, CDKN2A/B, ADIPOQ, WFS1, CDKAL1, IGF2BP2, KCNQ1, MTNR1B, IRS1, ACE) with overweight and obesity, diabetes, metabolic phenotypes, and MetS were examined in both studies.

Results

In this Chinese elderly population, prevalence of overweight, central obesity, diabetes, dyslipidemia, hypertension, and MetS were 48.3%, 71.0%, 32.4%, 75.7%, 68.3% and 54.5%, respectively. In the cross-sectional analyses, no SNP was found to be associated with MetS. Genotype TT of SNP rs4402960 within the gene IGF2BP2 was associated with overweight (odds ratio (OR)  = 0.479, 95% confidence interval (CI): 0.316-0.724, p = 0.001) and genotype CA of SNP rs1801131 within the gene MTHFR was associated with hypertension (OR = 1.560, 95% CI: 1.194–2.240, p = 0.001). However, these associations were not observed in the longitudinal analyses.

Conclusions

The associations of SNP rs4402960 with overweight as well as the association of SNP rs1801131 with hypertension were found to be statistically significant. No SNP was identified to be associated with MetS in our study with statistical significance.

The gene-gene interaction of INSIG-SCAP-SREBP pathway on the risk of obesity in Chinese children

Background. Childhood obesity has become a global public health problem in recent years. This study aimed to explore the association of genetic variants in INSIG-SCAP-SREBP pathway with obesity in Chinese children. Methods. A case-control study was conducted, including 705 obese cases and 1,325 nonobese controls. We genotyped 15 single nucleotide polymorphisms (SNPs) of five genes in INSIG-SCAP-SREBP pathway, including insulin induced gene 1 (INSIG1), insulin induced gene 2 (INSIG2), SREBP cleavage-activating protein gene (SCAP), sterol regulatory element binding protein gene 1 (SREBP1), and sterol regulatory element binding protein gene 2 (SREBP2). We used generalized multifactor dimensionality reduction (GMDR) and logistic regression to investigate gene-gene interactions. Results. Single polymorphism analyses showed that SCAP rs12487736 and rs12490383 were nominally associated with obesity. We identified a 3-locus interaction on obesity in GMDR analyses (P = 0.001), involving 3 genetic variants of INSIG2, SCAP, and SREBP2. The individuals in high-risk group of the 3-locus combinations had a 79.9% increased risk of obesity compared with those in low-risk group (OR = 1.799, 95% CI: 1.475–2.193, P = 6.61 × 10⁻⁹). Conclusion. We identified interaction of three genes in INSIG-SCAP-SREBP pathway on risk of obesity, revealing that these genes affect obesity more likely through a complex interaction pattern than single gene effect.

Controversial association results for INSIG2 on body mass index may be explained by interactions with age and with MC4R

Among the single-nucleotide polymorphisms (SNPs) previously reported to be associated with body mass index (BMI) and obesity, we focus on a common risk variant rs7566605 upstream of the insulin-induced gene 2 (INSIG2) gene and a rare protective variant rs2229616 on the melanocortin-4 receptor (MC4R) gene. INSIG2 is involved in adipogenesis and MC4R effects hormonal appetite control in response to the amount of adipose tissue. The influence of rs2229616 (MC4R) on BMI and obesity has been confirmed repeatedly and insight into the underlying mechanism provided. However, a main effect of rs7566605 (INSIG2) is under debate because of inconsistent replications of association. Interaction of rs7566605 with age may offer an explanation. SNP-age and SNP-SNP interaction models were tested on independent individuals from three population-based longitudinal cohorts, restricting the analysis to an observed age of 25-74 years. KORA S3/F3, KORA S4/F4 (Augsburg, Germany, 1994-2005, 1999-2008), and Framingham-Offspring data (Framingham, USA, 1971-2001) were analysed, with a total sample size of N=6926 in the joint analysis. The effect of interaction between rs7566605 and age on BMI and obesity status is significant and consistent across studies. This new evidence for rs7566605 (INSIG2) complements previous research. In addition, the interaction effect of rs7566605 with the MC4R variant rs2229616 on BMI was observed. This effect size was three times larger than that in a previously reported single-locus main effect of rs2229616. This leads to the conclusion that SNP-age or SNP-SNP interactions can mask genetic effects for complex diseases if left unaccounted for.

INSIG2 variants, dietary patterns and metabolic risk in Samoa

BACKGROUND/OBJECTIVES

Association of insulin-induced gene 2 (INSIG2) variants with obesity has been confirmed in several but not all follow-up studies. Differences in environmental factors across populations may mask some genetic associations and therefore gene-environment interactions should be explored. We hypothesized that the association between dietary patterns and components of the metabolic syndrome could be modified by INSIG2 variants.

SUBJECTS/METHODS

We conducted a longitudinal study of adiposity and cardiovascular disease risk among 427 and 290 adults from Samoa and American Samoa (1990-1995). Principal component analysis on food items from a validated food frequency questionnaire was used to identify neotraditional and modern dietary patterns. We explored gene-dietary pattern interactions with the INSIG2 variants rs9308762 and rs7566605.

RESULTS

Results for American Samoans were mostly nonsignificant. In Samoa, the neotraditional dietary pattern was associated with lower triglycerides, body mass index (BMI), waist circumference, systolic and diastolic blood pressure and fasting glucose (all P-for-trend<0.05). The modern pattern was significantly associated with higher triglycerides, BMI, waist circumference and lower high-density lipoprotein-cholesterol (all P-for-trend<0.05). A significant interaction for triglycerides was found between the modern pattern and the rs9308762 polymorphism (P=0.04). Those from Samoa consuming the modern pattern have higher triglycerides if they are homozygous for the rs9308762 C allele.

CONCLUSIONS

The common INSIG2 variant rs9308762 was associated with poorer metabolic control and a greater sensitivity of trigylcerides to a modern dietary pattern. Environmental factors need to be taken into account when assessing genetic associations across and within populations.

Association of polymorphisms in 9p21 region with CAD in North Indian population: replication of SNPs identified through GWAS

Coronary artery disease (CAD) is one of the leading causes of death worldwide that is influenced by both environmental as well as genetic factors. Several recent genome-wide association studies (GWAS) have reported the association of multiple single nucleotide polymorphisms (SNPs) mainly in the 9p21 region with CAD. However, the association of these SNPs with CAD has not been rigorously tested in Indian population, which accounts for the largest incidences of CAD in the world. Herein, we genotyped six such SNPs (rs10116277, rs10757274, rs1333040, rs2383206, rs2383207 and rs1994016) identified through GWAS, in 754 individuals (311 angiography-confirmed CAD patients and 443 treadmill test controls) recruited mainly from North India to evaluate if these SNPs were associated with CAD. The minor allele frequency of these six SNPs was comparable to that reported in the respective GWAS. We found that three of these SNPs (rs10116277, rs1333040 and rs2383206) present at the locus 9p21 were significantly associated with CAD even after controlling for the confounding factors such as age, sex, body mass index, homocysteine, hypertension, diabetes, smoking, diet, etc. In conclusion, the locus 9p21 found to be significantly associated with cardiovascular diseases in the Caucasian populations seems to be also important in North Indian population.

The INSIG2 rs7566605 polymorphism is not associated with body mass index and breast cancer risk

Background

The single nucleotide polymorphism rs7566605, located in the promoter of the INSIG2 gene, has been the subject of a strong scientific effort aimed to elucidate its possible association with body mass index (BMI). The first report showing that rs7566605 could be associated with body fatness was a genome-wide association study (GWAS) which used BMI as the primary phenotype. Many follow-up studies sought to validate the association of rs7566605 with various markers of obesity, with several publications reporting inconsistent findings. BMI is considered to be one of the measures of choice to evaluate body fatness and there is evidence that body fatness is related with an increased risk of breast cancer (BC).

Methods

we tested in a large-scale association study (3,973 women, including 1,269 invasive BC cases and 2,194 controls), nested within the EPIC cohort, the involvement of rs7566605 as predictor of BMI and BC risk.

Results and Conclusions

In this study we were not able to find any statistically significant association between this SNP and BMI, nor did we find any significant association between the SNP and an increased risk of breast cancer overall and by subgroups of age, or menopausal status.

Fine Mapping of the Insulin-Induced Gene 2 Identifies a Variant Associated With LDL Cholesterol and Total Apolipoprotein B Levels

Background—

In a whole-genome scan, a single nucleotide polymorphism (SNP) (rs7566605) upstream of the insulin-induced gene 2 ( INSIG2 ) was shown to influence body mass index and obesity in the Framingham Heart Study, with replication of these results in an additional 4 of 5 studies. However, other studies could not replicate the association. Because INSIG2 plays an important role in cholesterol biosynthesis, we hypothesized that human INSIG2 variants might play a role in the regulation of plasma lipid and lipoprotein levels.

Methods and Results—

We selected tagging SNPs spanning >100 kb of INSIG2 locus and sequenced 18 434 base pairs to discover novel SNPs. Thirty-two SNPs were genotyped in 645 individuals from the Quebec Family Study. Two SNPs (rs10490626 and rs12464355) were associated with plasma low-density lipoprotein cholesterol (LDL-C) ( P <0.0015) and total apolipoprotein B (apoB) levels ( P <0.014), whereas no association was found between any SNP and body mass index. We replicated the finding of rs10490626 for both LDL-C and total apoB in additional study samples, including 758 individuals from Saguenay–Lac St. Jean, Quebec ( P =0.040 for LDL-C, P =0.044 for apoB), 3247 Europeans ( P =0.028 for LDL-C, P =0.030 for apoB), and 1695 South Asians ( P =0.0036 for LDL-C, P =0.034 for apoB) from the INTERHEART study (for LDL-C, the combined 2-sided P =6.2×10 −5 and for total apoB, P =0.0011). Furthermore, we identified a variant in the human sorbin and SH 3 -domain–containing-1 gene that was associated with INSIG2 mRNA levels, and this SNP was shown to act in combination with rs10490626 to affect LDL-C ( P =0.022) in the Quebec Family Study and in INTERHEART South Asians ( P =0.019) and Europeans ( P =0.052).

Conclusion—

These results suggest that INSIG2 genetic variants may have a more direct role in lipid and lipoprotein metabolism than in obesity.

Association of an INSIG2 obesity allele with cardiovascular phenotypes is gender and age dependent

Background

The INSIG2 gene has been implicated in cholesterol metabolism and a single nucleotide polymorphism (SNP) near INSIG2 has been shown to be associated with obesity. We sought to determine the relationship of the INSIG2 SNP to cardiovascular disease (CVD) related phenotypes.

Methods and Results

Nine hundred forty six patients undergoing percutaneous coronary intervention (PCI) in wave 5 of the multicenter NHLBI Dynamic Registry were genotyped using RT-PCR/TaqMan/allelic discrimination for the rs7566605 SNP near the INSIG2 gene. Clinical variables analyzed include demographics, medical history, and procedural details. The prevalence of peripheral vascular disease (PVD) was significantly higher in older men (≥65 years) who were either homozygous or carriers of the obesity/lipid risk allele ("C") compared to non-carriers (odds ratio 3.4, p = 0.013) using a logistic regression model incorporating history of hypercholesterolemia, history of hypertension, cerebrovascular disease, history of diabetes, and BMI. A similar relationship with cerebrovascular disease was found in older (>65) women (odds ratio 3.4, p = 0.013). The INSIG2 SNP was not associated with BMI, nor with other clinical variables.

Conclusion

Age and gender may influence the association of the INSIG2 obesity SNP with PVD and cerebrovascular disease in patients with pre-existing CVD.

Large effects on body mass index and insulin resistance of fat mass and obesity associated gene (FTO) variants in patients with polycystic ovary syndrome (PCOS)

Background

The polycystic ovary syndrome (PCOS), a common endocrine disorder in women of child-bearing age, mainly characterised by chronic anovulation and hyperandrogenism, is often associated with insulin resistance (IR) and obesity. Its etiology and the role of IR and obesity in PCOS are not fully understood. We examined the influence of validated genetic variants conferring susceptibility to obesity and/or type 2 diabetes mellitus (T2DM) on metabolic and PCOS-specific traits in patients with PCOS.

Methods

We conducted an association study in 386 patients with PCOS (defined by the Rotterdam-criteria) using single nucleotide polymorphisms (SNPs) in or in proximity to the fat mass and obesity associated gene (FTO), insulin-induced gene-2 (INSIG2), transcription factor 7-like 2 gene (TCF7L2) and melanocortin 4 receptor gene (MC4R). To compare the effect of FTO obesity risk alleles on BMI in patients with PCOS to unselected females of the same age range we genotyped 1,971 females from the population-based KORA-S4 study (Kooperative Gesundheitsforschung im Raum Augsburg, Survey 4).

Results

The FTO risk allele was associated with IR traits and measures of increased body weight. In addition, the TCF7L2 SNP was associated with body weight traits. For the SNPs in the vicinity of INSIG2 and MC4R and for the other examined phenotypes there was no evidence for an association. In PCOS the observed per risk allele effect of FTO intron 1 SNP rs9939609 on BMI was +1.56 kg/m², whereas it was +0.46 kg/m² in females of the same age range from the general population as shown previously.

Conclusion

The stronger effect on body weight of the FTO SNP in PCOS might well have implications for the etiology of the disease.

Two-stage testing strategies for genome-wide association studies in family-based designs

The analysis of genome-wide association studies (GWAS) poses statistical hurdles that have to be handled efficiently in order for the study to be successful. The two largest impediments in the analysis phase of the study are the multiple comparisons problem and maintaining robustness against confounding due to population admixture and stratification. For quantitative traits in family-based designs, Van Steen (1) proposed a two-stage testing strategy that can be considered a hybrid approach between family-based and population-based analysis. By including the population-based component into the family-based analysis, the Van Steen algorithm maximizes the statistical power, while at the same time, maintains the original robustness of family-based association tests (FBATs) (2-4). The Van Steen approach consists of two statistically independent steps, a screening step and a testing step. For all genotyped single nucleotide polymorphisms (SNPs), the screening step examines the evidence for association at a population-based level. Based on support for a potential genetic association from the screening step, the SNPs are prioritized for testing in the next step, where they are analyzed with a FBAT (3). By exploiting population-based information in the screening step that is not utilized in family-based association testing step, the two steps are statistically independent. Therefore, the use of the population-based data for the purposes of screening does not bias the FBAT statistic calculated in the testing step. Depending on the trait type and the ascertainment conditions, Van Steen-type testing strategies can achieve statistical power levels that are comparable to those of population-based studies with the same number of probands. In this chapter, we review the original Van Steen algorithm, its numerous extensions, and discuss its advantages and disadvantages.

Meta-analysis of the INSIG2 association with obesity including 74,345 individuals: does heterogeneity of estimates relate to study design?

The INSIG2 rs7566605 polymorphism was identified for obesity (BMI≥30 kg/m²) in one of the first genome-wide association studies, but replications were inconsistent. We collected statistics from 34 studies (n = 74,345), including general population (GP) studies, population-based studies with subjects selected for conditions related to a better health status (‘healthy population’, HP), and obesity studies (OB). We tested five hypotheses to explore potential sources of heterogeneity. The meta-analysis of 27 studies on Caucasian adults (n = 66,213) combining the different study designs did not support overall association of the CC-genotype with obesity, yielding an odds ratio (OR) of 1.05 (p-value = 0.27). The I² measure of 41% (p-value = 0.015) indicated between-study heterogeneity. Restricting to GP studies resulted in a declined I² measure of 11% (p-value = 0.33) and an OR of 1.10 (p-value = 0.015). Regarding the five hypotheses, our data showed (a) some difference between GP and HP studies (p-value = 0.012) and (b) an association in extreme comparisons (BMI≥32.5, 35.0, 37.5, 40.0 kg/m² versus BMI<25 kg/m²) yielding ORs of 1.16, 1.18, 1.22, or 1.27 (p-values 0.001 to 0.003), which was also underscored by significantly increased CC-genotype frequencies across BMI categories (10.4% to 12.5%, p-value for trend = 0.0002). We did not find evidence for differential ORs (c) among studies with higher than average obesity prevalence compared to lower, (d) among studies with BMI assessment after the year 2000 compared to those before, or (e) among studies from older populations compared to younger. Analysis of non-Caucasian adults (n = 4889) or children (n = 3243) yielded ORs of 1.01 (p-value = 0.94) or 1.15 (p-value = 0.22), respectively. There was no evidence for overall association of the rs7566605 polymorphism with obesity. Our data suggested an association with extreme degrees of obesity, and consequently heterogeneous effects from different study designs may mask an underlying association when unaccounted for. The importance of study design might be under-recognized in gene discovery and association replication so far.

A polymorphism of the INSIG2 gene was identified as being associated with obesity in one of the first genome-wide association studies. However, this association has since then been highly debated upon inconsistent subsequent reports. We collected association information from 34 studies including a total of 74,000 participants. In a meta-analysis of the 27 studies including 66,000 Caucasian adults, we found no overall association of this polymorphism rs7566605 with obesity, comparing subjects with a body-mass-index (BMI)≥30 kg/m² with normal BMI subjects (BMI<30 kg/m²). Our data suggested an association of this polymorphism with extreme obesity (e.g., BMI≥37.5 kg/m²) compared to normal controls. Such an association with extreme obesity might induce heterogeneous effects from different study designs depending on the proportion of extreme obesity included by the design. However, further studies would be required to substantiate this finding. The importance of study design might be under-recognized in gene discovery and association replication so far.

Single nucleotide polymorphisms in homocysteine metabolism pathway genes: association of CHDH A119C and MTHFR C677T with hyperhomocysteinemia

BACKGROUND

An elevated level of homocysteine (hyperhomocysteinemia) has been implicated as an independent risk factor for cardiovascular diseases. Deficiency of dietary factors like vitamin B(12), folate, and genetic variations can cause hyperhomocysteinemia. The prevalence of hyperhomocysteinemia in the Indian population is likely to be high because most Indians adhere to a vegetarian diet, deficient in vitamin B(12). In the

BACKGROUND

deficiency, variations in genes involved in homocysteine metabolism might have a greater impact on homocysteine levels.

METHODS AND RESULTS

We genotyped 44 nonsynonymous single-nucleotide polymorphisms (nsSNPs) from 11 genes involved in homocysteine metabolism and found only 14 to be polymorphic. These 14 nsSNPs were genotyped in 546 individuals recruited from a tertiary care center in New Delhi, India, and it was found that choline dehydrogenase (CHDH A119C) and methylenetetrahydrofolate reductase (MTHFR C677T) were significantly associated with plasma total homocysteine levels (P=0.009 and P=0.001, respectively). These 2 SNPs were further genotyped in 330 individuals recruited from the same center, and the association remained significant even after increasing the sample size. Furthermore, we found the possibility of a significant interaction between vegetarian diet and the 2 polymorphisms that could explain the variation of homocysteine levels. We also genotyped all the polymorphic nsSNPs in apparently healthy individuals recruited from 24 different subpopulations (based on their linguistic lineage) spread across the country to determine their basal frequencies. The frequencies of these SNPs varied significantly between linguistic groups.

CONCLUSIONS

Vegetarian diet along with CHDH A119C and MTHFR C677T play an important role in modulating the homocysteine levels in Indian population.

INSIG2 SNPs associated with obesity and glucose homeostasis traits in Hispanics: the IRAS Family Study

The genome-wide association study by Herbert et al. identified the INSIG2 single-nucleotide polymorphism (SNP) rs7566605 as contributing to increased BMI in ethnically distinct cohorts. The present study sought to further clarify the matter, by testing whether SNPs of INSIG2 influenced quantitative adiposity or glucose homeostasis traits in Hispanics of the Insulin Resistance Atherosclerosis Family Study (IRASFS). Using a tagging SNP approach, rs7566605 and 31 additional SNPs were genotyped in 1,425 IRASFS Hispanics. SNPs were tested for association with six adiposity measures: BMI, waist circumference (WAIST), waist-to-hip ratio (WHR), subcutaneous adipose tissue (SAT), visceral adipose tissue (VAT), and VAT to SAT ratio (VSR). SNPs were also tested for association with fasting glucose (GFAST), fasting insulin (FINS), and three measures obtained from the frequently sampled intravenous glucose tolerance test: insulin sensitivity (S(I)), acute insulin response (AIR), and disposition index (DI). Most prominent association was observed with direct computed tomography (CT)-measured adiposity phenotypes, including VAT, SAT, and VSR (P values range from 0.007 to 0.044 for rs17586756, rs17047718, rs17047731, rs9308762, rs12623648, and rs11673900). Multiple SNP associations were observed with all glucose homeostasis traits (P values range from 0.001 to 0.031 for rs17047718, rs17047731, rs2161829, rs10490625, rs889904, and rs12623648). Using BMI as a covariate in evaluation of glucose homeostasis traits slightly reduced their association. However, association with adiposity and glucose homeostasis phenotypes is not significant following multiple comparisons adjustment. Trending association after multiple comparisons adjustment remains suggestive of a role for genetic variation of INSIG2 in obesity, but these results require validation.

Possible role for ENPP1 polymorphism in obesity but not for INSIG2 and PLIN variants

Previous studies have suggested that ENPP1, INSIG2, and PLIN may be linked with a higher risk for obesity or with increased phenotypic measures of obesity. We selected polymorphisms in these candidate genes based on their prior associations with obesity risk or obesity parameters. K121Q (rs1044498) in ENPP1, rs7566605 in INSIG2, and rs894160 in PLIN were genotyped by Taqman assays in a Belgian sample of 1,078 obese subjects (body mass index (BMI) > 30 kg/m(2)) and 323 lean controls (18.5 < BMI < 25 kg/m(2)). BMI, waist circumference, and waist-to-hip ratio (WHR) were assessed by standard methods while a computerized tomography-scan was used to measure visceral (VFA), subcutaneous (SFA), and total (TFA) abdominal fat areas. Presence of the rare allele was not significantly different between cases and controls for the three variants that were tested, while only WHR was associated with ENPP1 in obese subjects. Our data thus indicate that K121Q, rs7566605, and rs894160 are not major contributing factors for obesity.

Absence of association between the INSIG2 gene polymorphism (rs7566605) and obesity in the European Youth Heart Study (EYHS)

The first genome-wide association study for BMI identified a polymorphism, rs7566605, 10 kb upstream of the insulin-induced gene 2 (INSIG2) transcription start site, as the most significantly associated variant in children and adults. Subsequent studies, however, showed inconsistent association of this polymorphism with obesity traits. This polymorphism has been hypothesized to alter INSIG2 expression leading to inhibition of fatty acid and cholesterol synthesis. Hence, we investigated the association of the INSIG2 rs7566605 polymorphism with obesity- and lipid-related traits in Danish and Estonian children (930 boys and 1,073 girls) from the European Youth Heart Study (EYHS), a school-based, cross-sectional study of pre- and early pubertal children. The association between the polymorphism and obesity traits was tested using additive and recessive models adjusted for age, age-group, gender, maturity and country. Interactions were tested by including the interaction terms in the model. Despite having sufficient power (98%) to detect the previously reported effect size for association with BMI, we did not find significant effects of rs7566605 on BMI (additive, P = 0.68; recessive, P = 0.24). Accordingly, the polymorphism was not associated with overweight (P = 0.87) or obesity (P = 0.34). We also did not find association with waist circumference (WC), sum of four skinfolds, or with total cholesterol, triglycerides, low-density lipoprotein, or high-density lipoprotein. There were no gender-specific (P = 0.55), age-group-specific (P = 0.63) or country-specific (P = 0.56) effects. There was also no evidence of interaction between genotype and physical activity (P = 0.95). Despite an adequately powered study, our findings suggest that rs7566605 is not associated with obesity-related traits and lipids in the EYHS.

Lack of association between a common polymorphism near the INSIG2 gene and BMI, myocardial infarction, and cardiovascular risk factors

Epidemiological studies revealed an increasing prevalence of and a steep increase in obesity, a risk factor for cardiovascular disease. Because significant influence of a polymorphism, rs7566605, near the INSIG2 gene on BMI has been shown in the general population and in obesity cohorts, we hypothesized that this polymorphism might also act through an elevated BMI on the development of coronary artery disease (CAD) or myocardial infarction (MI). We pursued two strategies: First, the polymorphism rs7566605 was investigated for association with BMI, CAD/MI, and cardiovascular risk factors in a large German cohort at high risk for CAD and MI (n = 1,460 MI patients) as compared to unrelated healthy controls (n = 1,215); second, we extended our analyses on the families of MI patients and performed family-based association testing (n = 5,390 individuals). The polymorphism rs7566605 was analyzed using TaqMan technology. No deviation from Hardy-Weinberg equilibrium could be observed, and the call rate was 98.2%. No significant associations of rs7566605 with CAD/MI, BMI, and classical cardiovascular risk factors could be detected in the full sample size or in the subgroups. A total of 6,878 individuals were investigated in a population of German MI patients and their family members. Although the number of individuals was large enough, no influence of the rs7566605 INSIG2 polymorphism was detected on BMI and CAD/MI. We therefore conclude that in our sample the SNP rs7566605 near the INSIG2 gene does not influence BMI and is not associated directly with CAD/MI or indirectly through cardiovascular risk factors.

The INSIG2 rs7566605 genetic variant does not play a major role in obesity in a sample of 24,722 individuals from four cohorts

Background

In a genome-wide association study performed in the Framingham Offspring Cohort, individuals homozygous for the rs7566605 C allele located upstream of insulin-induced gene 2 (INSIG2) were reported to incur an increased risk of obesity. This finding was later replicated in four out of five populations examined. The goal of the study reported here was to assess the role of the INSIG2 single nucleotide polymorphism (SNP) in susceptibility to obesity in the prospective longitudinal Atherosclerosis Risk in Communities (ARIC) study (n = 14,566) and in three other cohorts: the Coronary Artery Risk Development in Young Adults (CARDIA) study (n = 3,888), the Genetic Epidemiology Network of Arteriopathy (GENOA) study (n = 4,766), and extremely obese and lean individuals ascertained at the University of Ottawa (n = 1,502). The combined study sample is comprised of 24,722 white, African-American, and Mexican-American participants.

Methods

Differences in mean body mass index (BMI) and other anthropometric measures including weight, waist circumference, and waist-to-hip ratio were assessed by a general linear model in individuals categorized by INSIG2 rs7566605 genotype. Multivariable logistic regression was used to predict the risk of obesity (BMI ≥ 30 kg/m²).

Results

There was no discernable variation in the frequencies of the three INSIG2 SNP genotypes observed between white, Hispanic, and African-American obese individuals and non-obese study subjects. When the relationship between rs7566605 and BMI considered either as a categorical variable or a continuous variable was examined, no significant association with obesity was found for participants in any of the four study populations or in a combined analysis (p = 0.38) under a recessive genetic model. There was also no association between the INSIG2 polymorphism and the obesity-related quantitative traits except for a reduced waist-to-hip ratio in white ARIC study participants homozygous for the C allele, and an increased waist-to-hip ratio in African-Americans in the ARIC cohort with the same genotype (p = 0.04 and p = 0.01, respectively). An association with waist-to-hip ratio was not seen when the combined study sample was analyzed (p = 0.74).

Conclusion

These results suggest that the INSIG2 rs7566605 variant does not play a major role in determining obesity risk in a racially and ethnically diverse sample of 24,722 individuals from four cohorts.

Association between the insulin-induced gene 2 (INSIG2) and weight gain in a German sample of antipsychotic-treated schizophrenic patients: perturbation of SREBP-controlled lipogenesis in drug-related metabolic adverse effects?

Atypical antipsychotics are nowadays the most widely used drugs to treat schizophrenia and other psychosis. Unfortunately, some of them can cause major metabolic adverse effects, such as weight gain, dyslipidemia and type 2 diabetes. The underlying lipogenic mechanisms of the antipsychotic drugs are not known, but several studies have focused on a central effect in the hypothalamic control of appetite regulation and energy expenditure. In a functional convergent genomic approach we recently used a cellular model and demonstrated that orexigenic antipsychotics that induce weight gain activate the expression of lipid biosynthesis genes controlled by the sterol regulatory element-binding protein (SREBP) transcription factors. We therefore hypothesized that the major genes involved in the SREBP activation of fatty acids and cholesterol production (SREBF1, SREBF2, SCAP, INSIG1 and INSIG2) would be strong candidate genes for interindividual variation in drug-induced weight gain. We genotyped a total of 44 HapMap-selected tagging single nucleotide polymorphisms in a sample of 160 German patients with schizophrenia that had been monitored with respect to changes in body mass index during antipsychotic drug treatment. We found a strong association (P=0.0003-0.00007) between three markers localized within or near the INSIG2 gene (rs17587100, rs10490624 and rs17047764) and antipsychotic-related weight gain. Our finding is supported by the recent involvement of the INSIG2 gene in obesity in the general population and implicates SREBP-controlled lipogenesis in drug-induced metabolic adverse effects.

Studies of CTNNBL1 and FDFT1 variants and measures of obesity: analyses of quantitative traits and case-control studies in 18,014 Danes

Background

A genome-wide scan in unrelated US Caucasians identified rs7001819 upstream of farnesyl-diphosphate farnesyltransferase 1 (FDFT1) and multiple variants within catenin (cadherin-associated protein), β-like 1 (CTNNBL1) to associate strongly with body mass index (BMI). The most significantly associating variants within CTNNBL1 including rs6013029 and rs6020846 were additionally confirmed to associate with morbid obesity in a French Caucasian case-control sample. The aim of this study was to investigate the impact of these three variants on obesity, through analyses of obesity-related quantitative traits, and case-control studies in large study samples of Danes.

Methods

The FDFT1 rs7001819, CTNNBL1 rs6013029 and rs6020846 were genotyped, using TaqMan allelic discrimination, in a combined study sample comprising 18,014 participants ascertained from; the population-based Inter99 cohort (n = 6,514), the ADDITION Denmark screening study cohort (n = 8,662), and a population-based sample (n = 680) and a type 2 diabetic patients group (n = 2,158) from Steno Diabetes Center.

Results

Both CTNNBL1 variants associated with body weight and height with per allele effect sizes of 1.0 [0.3–0.8] kg and 0.6 [0.2–0.9] cm, respectively, for the rs6020846 G-allele. No association was observed with BMI and waist circumference. In case-control studies neither of the CTNNBL1 variants showed association with overweight, obesity or morbid obesity (rs6013029: Odds Ratio (OR)_overweight = 1.02 [0.90–1.16], OR_obesity = 1.09 [0.95–1.25], OR_{morbidobesity} = 1.26 [0.91–1.74]; rs6020846: OR_overweight = 1.05 [0.93–1.18], OR_obesity= 1.13 [1.00–1.28], OR_{morbidobesity} = 1.17 [0.86–1.61]). However, in meta-analyses of the present and the previous study, both the rs6013029 T-allele and the rs6020846 G-allele increased the risk of developing morbid obesity (rs6013029: OR_combined = 1.36 [1.12–1.64], p = 0.002; rs6020846: OR_combined = 1.26 [1.06–1.51], p = 0.01), and obesity (rs6013029: OR_combined = 1.17 [1.04–1.31], p = 0.007; rs6020846: OR_combined = 1.17 [1.05–1.30], p = 0.004).

The FDFT1 rs7001819 C-allele showed no association with obesity-related quantitative measures or dichotomous measures of overweight, obesity and morbid obesity.

Conclusion

CTNNBL1 variants associated with body weight and height, and confer the risk of developing obesity in meta-analyses combining the present and a previous study. FDFT1 rs7001819 showed no association with obesity, neither when analysing quantitative traits nor when performing case-control studies of obesity.

Association of a genetic polymorphism in ectonucleotide pyrophosphatase/phosphodiesterase 1 with hepatitis C virus infection and hepatitis C virus core antigen levels in subjects in a hyperendemic area of Japan

BACKGROUND

The clinical course of chronic hepatitis C virus (HCV) infection is strongly associated with insulin resistance and obesity. The K121Q polymorphism in the ectonucleotide pyrophosphatase/phosphodiesterase (ENPP)-1 gene and the rs7566605 genotype located near insulin-induced gene 2 have been shown to be associated with insulin resistance and obesity. This study examined whether the K121Q polymorphism in ENPP1 or the rs7566605 genotype is associated with the clinical course of HCV infection.

METHODS

The relationships between the clinical characteristics of 469 anti-HCV antibody-seropositive subjects (353 were positive for HCV core antigen or RNA, whereas 116 were negative for HCV RNA) and the polymorphisms were analyzed.

RESULTS

No significant differences in body mass index, plasma glucose level, serum insulin level, and other biochemical markers were observed between subgroups of subjects with different genotypes at the K121Q polymorphism or rs7566605. The frequency of the homozygous wild-type genotype at K121Q in HCV carriers, however, was significantly higher than that in subjects who were negative for HCV RNA (84.5% vs. 75.9%; P < 0.05). Moreover, in HCV carriers, HCV core antigen levels in subjects homozygous for the wild-type genotype at K121Q were significantly higher than in heterozygous carriers of K121Q (5358 fmol/l vs. 4002 fmol/l; P = 0.04). In contrast, the rs7566605 genotype was not associated with hepatitis C viremia or with the HCV core antigen level.

CONCLUSIONS

The K121Q variant of ENPP1 may be associated with hepatitis C viremia and core antigen levels in HCV carriers.

INSIG2 is Associated with Lower Gain in Weight-for-Length Between Birth and Age 6 Months

Researchers have described the association of a common DNA polymorphism, rs7566605, near INSIG2 (insulin-induced gene 2) with obesity in multiple independent populations that include subjects ages 11-60 years.1 To our knowledge, no studies have examined the association of this polymorphism with weight status during early childhood. We explored the association of the rs7566605 polymorphism with weight-for-length among 319 children at 6 months and 3 years participating in Project Viva, a pre-birth cohort study. In contrast to studies of older individuals, CC homozygosity was associated with lower gain in weight-for-length z-score between birth and age 6 months than GG homozygosity or GC heterozygosity. At age 3, we did not find an association. The association of INSIG2 gene with obesity may change direction with age.

INSIG2 gene polymorphism is associated with increased subcutaneous fat in women and poor response to resistance training in men

Background

A common SNP upstream of the INSIG2 gene, rs7566605 (g.-10,1025G>C, Chr2:118,552,255, NT_022135.15), was reported to be associated with obesity (Body Mass Index, [BMI]) in a genome-wide association scan using the Framingham Heart Study but has not been reproduced in other cohorts. As BMI is a relatively insensitive measure of adiposity that is subject to many confounding variables, we sought to determine the relationship between the INSIG2 SNP and subcutaneous fat volumes measured by MRI in a young adult population.

Methods

We genotyped the INSIG2 SNP rs7566605 in college-aged population enrolled in a controlled resistance-training program, (the Functional Polymorphism Associated with Human Muscle Size and Strength, FAMuSS cohort, n = 752 volunteers 18–40 yrs). In this longitudinal study, we examined the effect of the INSIG2 polymorphism on subcutaneous fat and muscle volumes of the upper arm measured by magnetic resonance imaging (MRI) before and after 12 wks of resistance training. Gene/phenotype associations were tested using an analysis of covariance model with age and weight as covariates. Further, the % variation in each phenotype attributable to genotype was determined using hierarchical models and tested with a likelihood ratio test.

Results

Women with a copy of the C allele had higher levels of baseline subcutaneous fat (GG: n = 139; 243473 ± 5713 mm³ vs. GC/CC: n = 181; 268521 ± 5003 mm³; p = 0.0011); but men did not show any such association. Men homozygous for the G ancestral allele showed a loss of subcutaneous fat, while those with one or two copies of the C allele gained a greater percentage of subcutaneous fat with resistance training (GG: n = 103; 1.02% ± 1.74% vs. GC/CC: n = 93; 6.39% ± 1.82%; p = 0.035).

Conclusion

Our results show that the INSIG2 rs7566605 polymorphism underlies variation in subcutaneous adiposity in young adult women and suppresses the positive effects of resistance training on men. This supports and extends the original finding that there is an association between measures of obesity and INSIG2 rs7566605 and further implicates this polymorphism in fat regulation.

Association of the common genetic variant upstream of INSIG2 gene with obesity related phenotypes in Chinese children and adolescents

OBJECTIVE

To study the association between the rs7566605 variant of INSIG2 and obesity-related phenotypes in Chinese children and adolescents.

METHODS

The study sample consisted of two independent cohorts of Chinese children and adolescents. Anthropometric indices, lipids, blood pressure, fasting glucose, insulin and percentage of fat mass were determined. PCR with restriction fragment length polymorphism analysis was performed for genotyping the rs7566605 variant.

RESULTS

In each of the two independent cohorts, no significant association was observed between rs7566605 and obesity under additive, dominant or recessive model. We also did not detect any difference in the genotype frequency between all the obese children and controls. Furthermore, we did not find evidence of an association between body composition indices and metabolic phenotypes in all children. However, the triglyceride level of CC homozygotes was significantly higher than that of GG+GC genotypes in obese children (P=0.022). Additionally, we observed a non-significant trend of severe obesity in a post-hoc test.

CONCLUSION

INSIG2 rs7566605 variant is not associated Chinese childhood obesity in two independent cohorts. Further study is needed to verify the effect of rs7566605 on triglyceride in obese children.

Assessing gene-treatment interactions at the FTO and INSIG2 loci on obesity-related traits in the Diabetes Prevention Program

AIMS/HYPOTHESIS

The single nucleotide polymorphism (SNP) rs9939609 in the fat mass and obesity associated gene (FTO) and the rs7566605 SNP located 10 kb upstream of the insulin-induced gene 2 gene (INSIG2) have been proposed as risk factors for common obesity.

METHODS

We tested for genotype-treatment interactions on changes in obesity-related traits in the Diabetes Prevention Program (DPP). The DPP is a randomised controlled trial of 3,548 high-risk individuals from 27 participating centres throughout the USA who were originally randomised to receive metformin, troglitazone, intensive lifestyle modification or placebo to prevent the development of type 2 diabetes. Measures of adiposity from computed tomography were available in a subsample (n = 908). This report focuses on the baseline and 1 year results.

RESULTS

The minor A allele at FTO rs9939609 was positively associated with baseline BMI (p = 0.003), but not with baseline adiposity or the change at 1 year in any anthropometric trait. For the INSIG2 rs7566605 genotype, the minor C allele was associated with more subcutaneous adiposity (second and third lumbar vertebrae [L2/3]) at baseline (p = 0.04). During follow-up, CC homozygotes lost more weight than G allele carriers (p = 0.009). In an additive model, we observed nominally significant gene-lifestyle interactions on weight change (p = 0.02) and subcutaneous (L2/3 [p = 0.01] and L4/5 [p = 0.03]) and visceral (L2/3 [p = 0.02]) adipose areas. No statistical evidence of association with physical activity energy expenditure or energy intake was observed for either genotype.

CONCLUSIONS/INTERPRETATION

Within the DPP study population, common variants in FTO and INSIG2 are nominally associated with quantitative measures of obesity, directly and possibly by interacting with metformin or lifestyle intervention.

Non-replication of genome-wide based associations between common variants in INSIG2 and PFKP and obesity in studies of 18,014 Danes

Background

The INSIG2 rs7566605 and PFKP rs6602024 polymorphisms have been identified as obesity gene variants in genome-wide association (GWA) studies. However, replication has been contradictory for both variants. The aims of this study were to validate these obesity-associations through case-control studies and analyses of obesity-related quantitative traits. Moreover, since environmental and genetic factors may modulate the impact of a genetic variant, we wanted to perform such interaction analyses. We focused on physical activity as an environmental risk factor, and on the GWA identified obesity variants in FTO (rs9939609) and near MC4R (rs17782313) as genetic risk factors.

Materials and Methods

The four variants were genotyped in a combined study sample comprising a total of 18,014 subject ascertained from, the population-based Inter99 cohort (n = 6,514), the ADDITION screening cohort (n = 8,662), a population-based study sample (n = 680) and a type 2 diabetic patient group (n = 2,158) from Steno Diabetes Center.

Results

No association with overweight, obesity or obesity-related measures was shown for either the INSIG2 rs7566605 or the PFKP rs6602024 variants. However, an interaction between the INSIG2 rs7566605 variant and the level of self-reported physical activity (p_Int = 0.004) was observed. A BMI difference of 0.53 (SE 0.42) kg/m² was found when comparing physically passive homozygous C-allele carriers with physically passive G-allele carriers. No interactions between the two variants and FTO rs9939609 and MC4R rs17782313 were observed.

Conclusions

The INSIG2 rs7566605 and PFKP rs6602024 polymorphisms play no apparent role in the development of common forms of obesity in the Danish population. However, if replicated, the INSIG2 rs7566605 may influence the level of BMI in combination with the level of physical activity.

INSIG2 gene rs7566605 polymorphism is associated with severe obesity in Japanese

The single nucleotide polymorphism (SNP) rs7566605 in the upstream region of the insulin-induced gene 2 (INSIG2) is associated with the obesity phenotype in many Caucasian populations. In Japanese, this association with the obesity phenotype is not clear. To investigate the relationship between rs7566605 and obesity in Japanese, we genotyped rs7566605 from severely obese subjects [n = 908, body mass index (BMI) ≥ 30 kg/m²] and normal-weight control subjects (n = 1495, BMI < 25 kg/m²). A case–control association analysis revealed that rs7566605 was significantly associated with obesity in Japanese. The P value in the minor allele recessive mode was 0.00020, and the odds ratio (OR) adjusted for gender and age was 1.61 [95% confidential interval (CI) = 1.24–2.09]. Obesity-associated phenotypes, which included the level of BMI, plasma glucose, hemoglobin A1c, total cholesterol, triglycerides, high-density lipoprotein (HDL) cholesterol, and blood pressure, were not associated with the rs7566605 genotype. Thus, rs7566605 in the upstream region of the INSIG2 gene was found to be associated with obesity, i.e., severe obesity, in Japanese.

New insights into the genetics of body weight

PURPOSE OF REVIEW

These last months, the wave of genome-wide association scans finally reached the shores of body weight and obesity complex trait. In parallel, thanks to the increasing sequencing and genotyping capacities, large studies on rare mutations can now be carried out.

RECENT FINDINGS

In this review, I tried to cover the most recent findings in genome-wide association analyses, the outcome of conclusions subsequently not replicated, and the weight of rare mutations with strong effects on common obesity. The strongest predictor of obesity, FTO, is responsible for 1% of the total heritability, and results from other genome-wide scans do not provide, so far, any clue of other variants of this effect size. Thus, monogenic obesity studies might well reinstall the importance of rare nonsynonymous mutations of already known genes, especially melanocortin-4 receptor gene, in the general population. Nevertheless, additional genome-wide association analyses and replication are expected to confirm these first intuitions.

SUMMARY

Initial results both support the common variant-common disease hypothesis because at least one such variant exists in FTO, and also tone down its importance because such variants may be fewer than expected. Moreover, having a polymorphism associated with body weight is clearly not the end but rather the beginning of a long search for the gene function and pathway.

INSIG2 polymorphism is neither associated with BMI nor with phenotypes of lipoprotein metabolism

OBJECTIVE

A previous epidemiological study showed an association of the insulin-induced gene 2 (INSIG2) gene with BMI. Additionally, experimental investigations in animals and cell culture provided evidence that this gene might be involved in lipoprotein and free fatty acid (FFA) metabolism. Therefore, the aim of this study was to examine the association between the rs7566605 variant near the INSIG2 gene and BMI and to extend it to other quantitative measures of obesity, as well as parameters of lipoprotein and FFA metabolism.

METHODS AND PROCEDURES

We genotyped rs7566605 in a group of severely obese white patients (n = 1,026) with an average BMI of 46.0 kg/m(2) and a control group (n = 818) from Utah, as well as in the Salzburg Atherosclerosis Prevention Program in Subjects at High Individual Risk (SAPHIR) study from Austria, which is based on a healthy working population (n = 1,696).

RESULTS

We observed no difference in the genotype frequency of rs7566605 of INSIG2 between obese subjects and population-based controls from Utah. Furthermore, we did not find evidence of an association with measures of body composition (BMI, waist, waist-to-hip ratio, percentage body fat, amount of visceral and subcutaneous abdominal adipose fat) or lipoprotein metabolism (total cholesterol, low-density lipoprotein (LDL) and high-density lipoprotein (HDL) cholesterol, triglycerides, and FFAs) in the Utah study population or in the independent SAPHIR study.

DISCUSSION

Our results do not support an association of the INSIG2 gene with the regulation of body weight or parameters related to lipoprotein metabolism.

Progress in the genetics of common obesity: size matters

PURPOSE OF REVIEW

Over the past two decades serious efforts has been invested in the search for genes that predispose to common obesity, but progress has been slow and success limited. Genome-wide association, however, has revived optimism. Here we review recent advances in the field of obesity genetics and discuss the most important findings of candidate gene, genome-wide linkage studies and genome-wide association studies. We conclude by speculating about the way forward in the near future.

RECENT FINDINGS

Although large-scale candidate gene studies have placed MC4R more firmly on the human obesity map, the major breakthrough in obesity genetics was the discovery of FTO through genome-wide association. Variants located in the first intron of FTO were unequivocally associated with a 1.67-fold increased risk for obesity and a 0.40-0.66 kg/m2 increase in body mass index.

SUMMARY

Genome-wide association promises to enhance greatly our understanding of the genetic basis of common obesity, although candidate gene studies will remain a valuable approach because they allow more detailed analyses of biologically relevant candidates. A key factor contributing to continued success lies in large-scale data integration through international collaboration, which will provide the sample sizes required to identify genetic association with conclusive evidence.

Evidence of an influence of a polymorphism near the INSIG2 on weight loss during a lifestyle intervention in obese children and adolescents

OBJECTIVE

Homozygotes for the C-allele of the single nucleotide polymorphism (SNP) rs7566605, located approximately 10 kb upstream of insulin-induced gene 2 (INSIG2), showed a slightly increased risk of becoming obese. The aim of this study was to analyze whether children homozygous for the C-allele lose less weight in an intervention than children with the GG- or GC-genotype.

RESEARCH DESIGN AND METHODS

We genotyped rs7566605 in 293 obese children (mean age 10.8 years, 45% male, mean BMI 28.1 kg/m(2)) who presented for a 1-year intervention. The reduction of SD score (SDS) BMI was compared based on an intention-to-treat analysis between the children with different genotypes. Blood pressure, triglycerides, insulin and glucose concentrations, and total, HDL, and LDL cholesterol were measured before and after intervention.

RESULTS

After 1 year, obese children with the CC-genotype had reduced their SDS BMI to a lower extent than obese children with GC- or GG-genotypes (recessive model P = 0.007). There was no evidence for an association of rs7566605 with the cardiovascular risk factor profile (nominal P > 0.1).

CONCLUSIONS

CC-homozygotes at SNP rs7566605 in the vicinity of INSIG2 lost less weight in this lifestyle intervention. This finding further implicates this polymorphism in weight regulation.

Regulation of Fto/Ftm gene expression in mice and humans

Two recent, large whole-genome association studies (GWAS) in European populations have associated a approximately 47-kb region that contains part of the FTO gene with high body mass index (BMI). The functions of FTO and adjacent FTM in human biology are not clear. We examined expression of these genes in organs of mice segregating for monogenic obesity mutations, exposed to underfeeding/overfeeding, and to 4 degrees C. Fto/Ftm expression was reduced in mesenteric adipose tissue of mice segregating for the Ay, Lep ob, Lepr db, Cpe fat, or tub mutations, and there was a similar trend in other tissues. These effects were not due to adiposity per se. Hypothalamic Fto and Ftm expression were decreased by fasting in lean and obese animals and by cold exposure in lean mice. The fact that responses of Fto and Ftm expression to these manipulations were almost indistinguishable suggested that the genes might be coregulated. The putative overlapping regulatory region contains at least two canonical CUTL1 binding sites. One of these nominal CUTL1 sites includes rs8050136, a SNP associated with high body mass. The A allele of rs8050136 preferentially bound CUTL1[corrected] in human fibroblast DNA. 70% knockdown of CUTL1 expression in human fibroblasts decreased FTO and FTM expression by 90 and 65%, respectively. Animals and humans with various genetic interruptions of FTO or FTM have phenotypes reminiscent of aspects of the Bardet-Biedl obesity syndrome, a confirmed "ciliopathy." FTM has recently been shown to be a ciliary basal body protein.

No association between INSIG2 Gene rs7566605 polymorphism and being overweight in Japanese population

Obesity is a complex trait reflecting numerous genetic and environmental factors. Recently, a common genetic polymorphism (rs7566605) associated with a higher BMI was found in proximity to the insulin induced protein 2 (INSIG2 ) gene, with replication in four unrelated populations living in Western countries. We investigated the susceptibility to the polymorphism amongst the general Japanese population (n = 1976). The frequency of appearance of the single-nucleotide polymorphism (SNP) in the Japanese (G allele; 0.652, C allele; 0.348) was not different from that found in subjects of European origin as reported previously. However, the BMI levels in each of these genotypes did not differ significantly (GG; 23 +/- 3, GC; 24 +/- 3, CC; 24 +/- 3 kg/m(2), P = 0.906). In a separate analysis according to sex (male; P = 0.462, female; P = 0.879), age decade (40s; P = 0.057, 50s; P = 0.998, 60s; P = 0.622, 70s; 0.425, respectively), and tertiles of the BMI (1st; P = 0.409, 2nd; P = 0.088, 3rd; P = 0.780), the differences did not achieve statistical significance. The frequency of obesity did not differ among the genotypes (25 kg/m(2); 30.3, 30.8, 28.2%, P = 0.729, 30 kg/m(2); 2.9, 3.8, 2.8%, P = 0.549). No associations were also observed for related plasma markers; high-molecular weight (HMW) adiponectin (P = 0.510), high-sensitive C-reactive protein (P = 0.788), resistin (P = 0.937) and homeostasis of minimal assessment of insulin resistance (P = 0.634). These results indicate a lack of association between SNP rs7566605 and being overweight among the Japanese (in the middle-aged and elderly population).