obesity has been associated with many common medical conditions , such as type 2 diabetes , hypertension , cardiovascular disease , stroke , and physical disabilities . the prevalence of obesity has been increasing quickly in the world , not only in developed countries but also in developing countries , being a serious public health problem . obesity has familial predisposition and high heredity , indicating the role of genetic factors in pathogenesis of obesity . reported that a common variation ( rs7566605 ) located 10  kb upstream of insulin induced gene 2 ( insig2 ) was associated with obesity in the first obesity genome - wide association study ( gwas ) in 2006 . the association between rs7566605 and obesity was reported in different populations [ 35 ] , but there were negative reports about this polymorphism and obesity [ 610 ] . a meta - analysis study declared that rs7566605 was associated with severe obesity ( bmi  32.5 , 35.0 , 37.5 , 40.0 ) . in the previous study of our research group , the frequency of rs7566605 cc genotype frequency in severe obese group ( bmi  97th percentile ) was higher than that of normal - weight group . these evidences showed that the upstream region of insig2 gene might be involved in weight regulation [ 11 , 12 ] . krapivner and colleagues   screened insig2 gene in search of the functional polymorphism which was responsible for the relationship of rs7566605 and bmi . they discovered a novel variation , -102g > a ( rs76335892 ) in putative promoter region , which was associated with bmi in 1590 middle - aged caucasian men . in the subsequent research , -102g > a polymorphism was shown to affect the binding of nuclear factor to the promoter region of insig2 . in a following report , hubek and colleagues   found -102g > a was associated with high - density lipoprotein cholesterol ( hdl - c ) only in caucasian female . so whether the -102g > a polymorphism is associated with bmi or related phenotypes is not clear . and it is unknown whether the effect is gender - specific , which awaits further investigation . considering varied genetic background across populations with different ethnicity , , we did not find any study exploring the relationship between -102g > a polymorphism and obesity in chinese population . compared with adults , children have higher bmi or obesity heritability and most obese children are only obese without complications , which help to identify the genetic effects on obesity . in addition , the effect of -102g > a polymorphism has not been studied in children population . therefore , we performed the present study , aiming to investigate the association of -102g > a polymorphism with obesity - related phenotypes in chinese children and test gender - specific effects . we conducted the study in 2,030 children and adolescents from two independent study groups , including 1,218 boys and 812 girls , 705 obese cases , and 1,325 nonobese controls . the first study group came from the study on adolescent lipids , insulin resistance , and candidate genes ( alir ) . the second study group was from the comprehensive prevention project for overweight and obese adolescents ( cpooa ) with physical exercise and healthy nutrition as instruments . the ascertainment strategies in two studies have been previously described in detail [ 12 , 15 ] . the method of cluster sampling was adopted , to recruit nonobese subjects from some classes of each grade in the same schools . we used the uniform bmi percentile criteria for obese and nonobese children , which were determined in a representative chinese population . according to the criteria , the children and adolescents with an age- and gender - specific bmi  95th percentile are defined as obese , whereas those with a bmi between 15th and 95th percentile are nonobese . we excluded the individuals with heart , lung , liver , kidney disease , and cardiovascular or metabolic disease by asking the medical history . two studies were approved by the ethic committee of peking university health science center . written informed consent was provided by all participants and , in the case of minors , their parents . anthropometric measurements , including height , weight , waist , and hip circumference , were determined according to standard protocols . the body fat percentage was determined by bioelectrical impedance analysis ( genius-220 , jawon , korea ) . fasting venous blood samples were taken for measurement of total cholesterol , triglyceride , low - density lipoprotein cholesterol ( ldl - c ) , and high - density lipoprotein cholesterol ( hdl - c ) using a biochemical autoanalyzer ( hitachi 7060 , tokyo , japan ) . the -102g > a genotype was assayed by using matrix - assisted laser desorption / ionization time - of - flight mass spectrometry ( maldi - tof ms ) . primers , including a pair of amplification primers and an extension primer , were designed with spectrodesigner software ( sequenom , san diego , ca ) . a multiplex polymerase chain reaction was performed , and unincorporated double stranded nucleotide triphosphate bases were dephosphorylated with shrimp alkaline phosphatase followed by primer extension . the purified primer extension reaction was spotted onto a 384-element silicon chip ( spectrochip , sequenom ) and assayed in maldi - tof ms . the resulting spectra were processed with massarray typer ( sequenom , san diego , ca ) . our study groups came from two independent studies , that is , alir study and cpooa study . the genotypes of the -102g > a polymorphism were in hardy - weinberg equilibrium ( hwe ) among nonobese children ( p = 0.540 ) of the alir study but not in those of the cpooa study ( p < 0.001 ) . we performed the genotyping of all the subjects twice by using arms - pcr and maldi - tof ms , respectively . except for one sample which was not successfully genotyped by maldi - tof ms , the genotyping results were exactly the same for the results of the two genotyping methods . for validity of genotypes , allele assignments were made by at least two experienced individuals independently . so the deviation from hwe in the cpooa study was not due to any genotyping error . the differences in general characteristics between obese and nonobese subjects were tested with chi - square ( categorical variables ) or t - test ( continuous variables ) . the logistic regression model ( lrm ) was used to examine the effect of -102g > a on obesity . the multiple linear regression ( mlr ) was performed to examine the effect of -102g > a on bmi or other obesity - related phenotypes ( waist and hip circumferences , skinfold thickness , body fat percentage , serum lipids , etc . ) . lrm and mlr were performed under the dominant model adjusted for gender , age , age square , and study population . chicago , usa ) . the criterion for statistical significance was set at p < 0.05 . as the original paper of -102g > a polymorphism just reported its association with bmi ( subjects homozygous for the -102a allele had greater decreases in bmi compared with -102 g allele carriers ) , the effect size of the -102g > a polymorphism on risk of obesity was not available . with the assumed or of 1.4 for obesity , the power for detecting association was estimated to be 84% , given the minor allele frequency ( 10% in the original paper ) , the sample size ( 1325 controls and 705 cases ) , and the alpha level of 0.05 under the dominant model . power calculations were performed using the method for gene study of case - control ( unmatched ) in quanto software ( university of southern california , los angeles , ca ) . the general characteristics of the study groups were shown in table 1 . in total populations , there are more boys in obese group than in nonobese group ( 68.7% versus 55.4% , p < 0.001 ) . the mean age was similar between nonobese group and obese subjects ( p = 0.497 ) . the levels of bmi , waist circumference , hip circumference , total cholesterol , triglyceride , ldl - c , and skinfold thickness were higher in obese group ( p  0.001 ) , while the hdl - c level was lower in obese group , compared with controls ( p < 0.001 ) . table 1(b ) showed the general characteristics of the study groups in boys or girls . the age difference was not significant between nonobese group and obese subjects in both boys and girls . except for the total cholesterol levels in girls , the other phenotypes were significantly different between nonobese group and obese subjects in both girls and boys . in all the 2030 samples , 2029 were genotyped successfully for the -102g > a polymorphism . there were 1877 ( 92.5% ) children and adolescents being homozygous carriers of g - allele , 142 ( 7.0% ) heterozygous and 10 ( 0.5% ) homozygous carriers of a - allele . the a - allele frequency was 3.99% . considering the number of aa genotype carriers was small , we performed the following analyses under dominant genetic model . as shown in table 2 , the percentage of ga / aa genotype carriers in all 2029 subjects was marginally higher in obese group ( 8.8% versus 6.8% , p = 0.063 ) and significantly higher in severely obese group ( 10.1% versus 6.8% , p = 0.015 ) , compared with the nonobese group . adjusted for covariates such as gender , age , age square , and study population , the ga / aa genotype was still marginally associated with high risk of obesity ( or = 1.41 , 95% ci : 0.9982.00 , p = 0.051 , table 2 ) . we found a stronger association between ga / aa genotype and increased risk to be severely obese ( or = 1.62 , 95% ci : 1.112.36 , p = 0.012 ) . subsequently , we stratified the population by gender and found the ga / aa genotype was significantly associated with risk of severe obesity only in boys ( or = 1.91 , 95% ci : 1.153.17 , p = 0.012 ) . the association with increased risk of obesity in boys was marginal ( or = 1.57 , 95% ci : 0.9962.46 , p = 0.052 ) . in addition , we analyzed the relationship between the -102g > a polymorphism and quantitative obesity - related phenotypes . a gender - specific association of -102g > a polymorphism with waist circumference was found in boys (  = 2.61  cm , p = 0.013 , table 3 ) . we did not find the association between -102g > a polymorphism and waist circumference in girls . in the subsequent analyses we did not find any association of the polymorphism with hip circumference , whr , lipids levels ( total cholesterol , triglyceride , ldl - c , and hdl - c ) , body fat percentage , or skinfold thickness ( p > 0.05 , table 3 ) . the results were similar in nonobese participants ( p > 0.05 , data not shown ) . to our knowledge , this is the first study to investigate the association between -102g > a polymorphism and obesity - related phenotypes in chinese children . we found a gender - specific effect of -102g > a polymorphism on severe obesity and waist circumference only in boys . the -102g > a was found to be associated with bmi in the discovery study . the present data did not support evidence for its association with bmi but showed an association for severe obesity compared to nonobese group ( p = 0.012 ) . in the previous investigation , the association between insig2 upstream polymorphism rs7566605 and obesity or severe obesity did not reach significant statistic level in our population . the association of -102g > a with severe obesity suggested that the proximal promoter region might impact the function of insig2 gene . of note , the association for severe obesity was only observed in boys in the further gender - stratified analyses . additionally , the -102g > a polymorphism was associated with waist circumference and tended to affect hip circumference and whr levels in boys . taken together , it appears that the -102g > a polymorphism affects both general and central obesity in chinese boys . there are evidences for difference in body composition , hormones , and genetic and environmental factors between boys and girls [ 18 , 19 ] . it was previously reported that the effects of some obesity - related gene variants have gender - specific effects [ 20 , 21 ] , including a male - specific effect of the near - insig2 variant ( rs7566605 , upstream -102g > a ) on waist - hip ratio in norway adolescents and adults . in line with the norway research , the effects of -102g > a polymorphism on severe obesity and waist circumstance in the present study were significant only in boys . it is interesting that two previous reports observed different gender - specific effect of -102g > a polymorphism in european populations [ 13 , 14 ] . further investigation is required to examine how gender influences the association between -102g > a polymorphism and obesity - related phenotypes . in the discovery study , krapivner and colleagues   found -102g - allele was significantly associated with elevated bmi ; that is , the gg genotype carriers had the highest bmi compared with ga or aa genotypes carriers . hubek and colleagues   conducted another study on -102g > a polymorphism in european white people , discovering that -102g > a polymorphism may affect the hdl - c level in young women . hdl - c level of gg homozygotes was higher than that of the a - allele carriers . they did not find similar association in males and older women , which indicated that gender and age may influence the effect of -102g > a polymorphism on serum lipids . the level of hdl - c is usually higher in normal - weight individuals than that in obese group . .   indicated that the gg homozygotes carriers of -102g > a had higher hdl - c levels and a - allele may be a risk factor for obesity . the present study found a - allele is a risk factor for obesity and waist circumference , which was supported by hubek et al . 's results . however , the results of krapivner and colleagues   suggested gg genotype is a risk factor for obesity ; that is , a - allele is a protective factor for obesity . the inconsistency may be explained by the differences in race , age , and gender of study subjects , demonstrating the value of conducting genetic studies in different ethnic populations . insig2 is an important protein in sterol regulatory element binding protein ( srebp ) activation - related lipid regulation pathway . insig2 could combine with the complex of srebp and srebp cleavage - activating protein ( scap ) to block the transport of srebps from endoplasmic reticulum to golgi apparatus and then affect lipid synthesis . for obesity is associated with lipid metabolism , insig2 may influence the development of obesity by regulating lipid synthesis . they found the differentiation process of adipocyte is accompanied by increasing expression of insig2 , while the expression of insig2 seems to be associated with -102g > a polymorphism . they demonstrated that the -102g > a polymorphism could affect the binding of nuclear factors to the promoter of insig2 , resulting in changes in the expression of insig2 in adipose tissue , ultimately leading to changes in lipid metabolism . based on krapivner 's functional study , we consider that -102a allele can lead to less expression of insig2 , and theoretically there will be less insig2 protein to block the activation of srebp , ultimately leading to increase of lipid synthesis , which supported -102a allele is a risk factor of obesity . the strength of the study was that we conducted the study in children . compared with adults , children have higher bmi or obesity heritability and most obese children are only obese without complications , which help to identify the genetic effects on obesity . our finding of the association of -102g > a with severe obesity and waist circumference in boys provided evidence for gender disparity of the insig2 gene effects , which will be helpful for identifying genetic factors related to childhood obesity and developing early prevention strategy . secondly , we provided evidence for gender - specific effect of -102g > a in a chinese population different from previous studies . however , the limitation of the present study is that we did not analyze interaction between the polymorphism and environmental factors , such as exercise and diet for limited sample size . and the mechanism underlying the gender - specific effect is unknown , which awaits further functional studies . the third limitation is that the findings of the present study need further replication in other independent population groups . statistical power analysis revealed that the present study had power around 80% to detect the association of -102g > a polymorphism with severe obesity in total population and boys ( 76% and 81% , resp . ) , but the power was lower in girls for lower or ( 17% ) . but our results indicated that the or of -102g > a for obesity in girls is probably lower than that in boys , which need further confirmation by large sample studies . in conclusion , the study identified a gender - specific effect of insig2 -102g > a polymorphism on risk of severe obesity and waist circumference in chinese boys .
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 : 1.112.36 , and p = 0.012 ) under the dominant model . 
 the association with severe obesity existed only in boys ( or = 1.91 , 95% ci : 1.153.17 , p = 0.012 ) . 
 the gg / ga genotype of -102g > a polymorphism was also associated with higher waist circumference (  = 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 .