Journal of Clinical Endocrinology & Metabolism, doi:10.1210/jc.2006-2514
The Journal of Clinical Endocrinology & Metabolism Vol. 92, No. 5 1956-1960
Copyright © 2007 by The Endocrine Society
TCF7L2 Gene Polymorphisms Confer an Increased Risk for Early Impairment of Glucose Metabolism and Increased Height in Obese Children
Antje Körner,
Janin Berndt,
Michael Stumvoll,
Wieland Kiess and
Peter Kovacs
University Hospital for Children and Adolescents (A.K., W.K.) and Department of Internal Medicine III (J.B., M.S., P.K.), University of Leipzig, 04317 Leipzig, Germany
Address all correspondence and requests for reprints to: Dr. Antje Körner, University Hospital for Children and Adolescents, University of Leipzig, Oststrasse 21-25, 04317 Leipzig, Germany. E-mail: antje.koerner{at}medizin.uni-leipzig.de.
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Abstract
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Context: Variants in the transcription factor 7-like2 (TCF7L2) gene have been associated with an increased risk for type 2 diabetes in adults. To evaluate whether the five reported risk variants confer a higher risk for obesity and early impairment of glucose metabolism in children, we genotyped these risk variants of the TCF7L2 gene in a representative cohort of 1029 Caucasian children and an independent cohort of 283 obese children.
Results: Applying a case control design, we observed a significantly lower prevalence of the rs11196205 and rs7895340 risk alleles in the obese (n = 283) compared with lean (n = 672) children (0.40 vs. 0.45; P = 0.02). There was, however, no statistically significant relationship between these genotypes and quantitative traits of obesity in either a normal representative cohort (n = 1029) or an obesity cohort. Obese children were significantly taller than lean children. This increase in height was independently associated with risk variants of the TCF7L2 gene, whereas in the normal representative cohort height appeared to be decreased in carriers of the minor alleles. In the obese cohort, three risk alleles (rs7901695, rs7903146, and rs1225572) were significantly associated with higher fasting and 120-min blood glucose levels independent of sex, age, pubertal stage, and body mass index. Fasting and peak insulin levels and HOMA-IR appeared with a similar tendency but were not statistically significant.
Conclusions: Our data indicate for the first time that TCF7L2 gene variants confer an increased risk for early impairment of glucose metabolism in obese children, which is consistent with adult studies identifying TCF7L2 as a major diabetes susceptibility gene.
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Introduction
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THE TCF7L2 GENE ENCODES for a transcription factor that is involved in the regulation of cellular proliferation and differentiation (1). Variants in the TCF7L2 gene have been associated with an increased risk for type 2 diabetes (2). The relative risks for diabetes of 1.45 for heterozygous to 2.41 for homozygous carriers of the gene variants was appreciably greater than for most identified genetic factors so far, accounting for a population attributable risk of 21% (2). The strongest associations with type 2 diabetes were reported for the rs7903146 variant with a clear gene dosis effect (3). Subsequent independent studies in distinct ethnic populations of European (4, 5, 6, 7, 8), Caucasian, Afro-American, Amish U.S. American (9, 10, 11, 12), and Indian (13, 14), as well as genetically more diverse West African cohorts (15), all in adults, convincingly confirmed the initial findings and extended the knowledge by showing that these risk alleles actually predict the progression from impaired glucose tolerance to diabetes prospectively in adults (10).
Considering these data that suggest TCF7L2 as a major candidate gene for the predisposition to type 2 diabetes (3), we hypothesized that carriers of those at-risk variants have an earlier age of onset than noncarriers. Children represent an interesting population for identifying such primary genetic determinants involved in the susceptibility to complex polygenic diseases because, unlike in adults, phenotypes are less influenced by comorbidities, their treatment, and environmental factors. In addition, the detailed evaluation of parameters of glucose and insulin metabolism at early stages of metabolic impairment may help to understand the sequence of events leading to overt pathology and diabetes.
To test this hypothesis, we genotyped the five TCF7L2 gene risk variants in two independent cohorts of Caucasian children and analyzed their association with early onset obesity and parameters of glucose metabolism.
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Subjects and Methods
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Study populations
Normal representative cohort (schoolchildren cohort).
The Leipzig Schoolchildren Project investigated anthropometric and clinical parameters in 2675 children aged 7.5 to 18.5 yr in 1999 to 2000 (16). Schools were chosen to cover representative local areas within Leipzig and suburbs (hence, social distribution) and an even distribution of school types to establish a representative cohort of German Caucasian children. DNA was available in 1033 children. Four children were excluded from the analysis due to non-Caucasian background, history of hereditary pancreatitis, GH, and metformin treatment, respectively.
Lean control group.
All children with a body mass index (BMI) between –1.0 SD score (SDS) and +1.0 SDS were selected from the schoolchildren cohort to serve as a lean control group (n = 672).
Leipzig obesity cohort.
A total of 283 Caucasian children and adolescents with a BMI of at least 1.88 SDS were consecutively recruited from our obesity clinic. All obese children had a detailed metabolic work-up, including an oral glucose tolerance test, lipid profiles, and blood pressure measurements. This group also included 16 overweight subjects. Children with secondary or syndromal forms of obesity were not included.
A careful history and physical exam including anthropometric measurements were obtained in all subjects. For standardization of height and BMI, reference percentiles for central Germany were applied. Data are given as absolute values and/or SDS (17). Consensus guidelines of the German Working Group for Pediatric Obesity were applied for the classification of overweight (BMI between 1.28 and 1.88 SDS) and obesity (BMI 
1.88 SDS) (18).
Characteristics of study populations are given in Table 1
. Written informed consent was obtained from all guardians and children older 12 yr. Both studies were approved by the ethical committee of the University of Leipzig.
Genotyping of TCF7L2 variants
Genotyping of all five variants (rs7901695, rs7903146, rs12255372, rs11196205, and 7895340) described by Grant et al. (2) was performed using the TaqMan allelic discrimination assay (Applied Biosystems, Inc., Foster City, CA) on ABI PRISM 7500 sequence detector (Applied Biosystems, Inc.). To assess genotyping reproducibility, a random approximately 10% selection of the samples were regenotyped in all single nucleotide polymorphisms (SNPs) with 100% concordance. Genotype data for all SNPs were consistent with Hardy-Weinberg equlibrium in all cohorts and subcohorts. Allelic frequencies for cohorts are given in Table 1
, and genotype distribution is given in Tables 2 and 3.
Statistical analyses
To compare allelic frequencies between obese and lean healthy controls, we used logistic regression. We tested for associations of genetic variants and anthropometric and metabolic characteristics using generalized linear regression models under the additive mode of inheritance that is mulitplicative on the odds ratio (OR) scale and the dominant/recessive mode. All analyses were adjusted for age, sex, pubertal stage, and height SDS. Statistical analyses were performed using the SPSS software package (version 11.5) (SPSS, Inc., Chicago, IL) and Statistica7.1 (StatSoft, Tulsa, OK).
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Results
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We genotyped the five initially reported SNPs (2) in a representative cohort of 1029 Caucasian children and an independent cohort of 283 obese children with detailed metabolic testing. Anthropometric data and frequencies of the minor alleles are given in Table 1.
Association of TCF7L2 genotypes with parameters of obesity and height
In the entire reference population of Caucasian children (schoolchildren cohort) there was no significant association of any of the SNPs with BMI SDS or other surrogate markers of obesity such as waist to hip ratio (WHR) or skinfolds.
To maximize discriminative power for BMI, we compared frequencies of the minor risk alleles in independent cohorts of obese and lean children applying a case control design. Although there were no differences in the three SNPs more adjacent to the microsatellite diabetes-risk marker DG10S478 (2), we identified a significantly lower minor-allele frequency for rs11196205 and for rs7895340 in obese children (Table 1) conferring a lower risk for obesity with OR = 0.78 (0.63–0.96) and OR = 0.78 (0.63–0.97). The same results were obtained if children younger than 8 yr were excluded from the obesity cohort to approximate the age range in the lean control group. Results were concordant irrespective of the genetic model (additive/dominant) applied.
Analysis of height according to genotype revealed a significant association of lower height with the minor alleles of the SNPs rs7903146, rs12255372, and rs11196205 (Table 3) in the representative schoolchildren cohort. In obese children, in contrast, the minor alleles of the SNPs rs7903146, rs11196205, and rs7895340 were associated with taller stature (Table 3).
Association of TCF7L2 genotypes with metabolic parameters
In obese children, three risk alleles were significantly associated with higher fasting as well as 120-min blood glucose levels independent of sex, age, pubertal stage, height, and BMI in the additive and dominant model of inheritance (Fig. 1), whereas differences for the remaining SNPs did not reach statistical significance (Table 2). Although similar tendencies appeared for insulin secretion and insulin resistance parameters, differences were not significant (Table 2). There was also no significant relationship between the SNPs and intermediate metabolic traits (leptin, liver enzymes, and cholesterol levels), blood pressure, or detailed anthropometric parameters (WHR) (data not shown).
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FIG. 1. Association of TCF7L2 risk alleles with parameters of glucose metabolism in obese children. The effects of genetic variants on parameters of glucose metabolism determined by oral glucose tolerance test were evaluated using generalized linear regression models applying the additive (#) and dominant (*) model of inheritance as indicated. The analysis was adjusted for age, sex, pubertal stage, and BMI SDS. Data are shown as mean ± SEM. BG, Blood glucose level; SDS, SD score for sex and age according to German references.
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Discussion
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Gene variants in the transcription factor TCF7L2 have been identified and replicated to be associated with an increased risk for developing type 2 diabetes in adults (2, 5, 10). We provide evidence that in obese children the risk genotypes of the TCF7L2 gene are associated with an increase in fasting as well as stim-ulated blood glucose levels when applying the dominant and additive model of inheritance. The tendency was similar across all SNPs investigated, although it did not reach statistical significance for the rs11196205 and rs7895340. The latter SNPs were, however, not as closely associated with the diabetes risk markers in previous studies in adults (2, 9) and showed the weakest correlation with the DG10S478 microsatellite marker, associated with diabetes in the initial study (2). These data indicate that TCF7L2 variants confer a higher risk for early impairment of glucose metabolism emerging as soon as in childhood and adolescence, although we cannot directly predict the progression to overt diabetes from our data. Studies in nondiabetic subjects may, however, help to understand the mechanisms involved in this progression. Although most studies in adults did not identify an association of TCF7L2 variants with measures of insulin resistance (6, 7, 9, 10), several studies did observe a defect in insulin secretion (6, 10, 12) or a trend for decreased fasting insulinemia (19) in subjects carrying the risk alleles. The conclusion from these data was that the polymorphisms affect the capacity of pancreatic ß-cells to secrete insulin rather than aggravating insulin resistance. This was further supported by expression data suggesting a putative role of TCF7L2 in ß-cell differentiation (19). In contrast to these findings in adults, in our cohort of obese children we observed hyperinsulinemia in the majority of children that was not decreased by carrying the risk alleles. This may not necessarily contradict the observations in adults where the decreased insulin levels in response to hyperglycemia in more advanced states of disease may indeed reflect progressing ß-cell failure. Potential limitations of our study are, in fact, the young age of the children, which may not have allowed them to progress to a more severe phenotype, and the relatively small sample size of obese children.
Considering that TCF7L2, as a transcription factor, regulates genes involved in proliferation and differentiation, one may hypothesize that early onset obesity through increased or dysregulated adipogenesis may constitute one underlying mechanism (20, 21). In support of this hypothesis, our preliminary analyses in human adipocytes showed an increased expression of TCF7L2 during early stages of adipocyte differentiation (our unpublished observations) that precedes the expression of classical adipocyte markers such as adiponectin and leptin (22), thus a pattern compatible with transcription factor regulating adipogenesis.
Comparing lean and obese children, the risk alleles of rs11196205 and rs7895340 were less prevalent in the obese cohort, which would be indicative for a decreased obesity risk. There was, however, no relationship between risk genotypes and quantitative traits of obesity in the schoolchildren or obesity cohort. This lack of effect may be attributable to insufficient numbers of overweight (10.0%) and obese (3.9%) children in the schoolchildren cohort. We can, however, not exclude that this finding is accidental. Studies in adults also did not find an association of TCF7L2 variants with obesity (6) or reported a tendency for negative association with BMI (10, 19). These studies did, however, not investigate rs11196205 and rs7895340 that may lie in linkage disequilibrium with nearby genetic markers of obesity.
Obese children were significantly taller than lean children. This increase in height may be phenomenal for the constitutional (growth) acceleration frequently seen in obese children, which has been discussed as potentially accelerating diabetes manifestation along with autoimmunity and insulin resistance in the "accelerator hypothesis" (23). When we analyzed the possible relationship of TCF7L2 variants with height, we indeed identified an effect on increased height SDS for most risk variants in obese children, whereas in the normal representative cohort height was decreased in carriers of the minor allele, if significant at all. Another potential mechanism is the hypothesis that TCF7L2 may directly or indirectly regulate growth through effects on the differentiation of pituitary cell lines including GH-secreting cells (24) or peripheral chondrogenic cell lines, as can be suspected from the expression pattern in embryonic limb formation (25). It will now be of interest to investigate whether TCF7L2 variants are related to final adult height to differentiate between constitutional acceleration and potential primary effects on growth.
In summary, our data suggest for the first time that TCF7L2 gene polymorphisms may confer an increased risk for early impairment of glucose metabolism in obese children, which is consistent with adult studies that established TCF7L2 as a major diabetes susceptibility gene. Longitudinal studies in pediatric cohorts will be desirable to confirm these findings and to specify potential effects of TCF7L2 variants on anthropometric parameters of obesity and height.
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Acknowledgments
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We thank all the children and their parents who participated in this study. We also gratefully acknowledge the help of the study nurses and technical assistants in performing these investigations.
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Footnotes
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This work was supported by a grant from the Deutsche Forschungsgemeinschaft (DFG) KFO 152: "Atherobesity," project KO 3512/1–1 (TP 1) and BE 1264/10–1 (TP5), from the German Diabetes Association to A.K., and from the European Community integrated project grant "PIONEER." The Leipzig Schoolchildren project was supported by unrestricted grants from Pfizer Pharma GmbH and Novo Nordisk GmbH (to W.K.). Part of the study was supported by a research grant from the German Hypertension Association (to A.K.).
First Published Online February 20, 2007
Abbreviations: BMI, Body mass index; OR, odds ratio; SDS, SD score; SNP, single nucleotide polymorphism; WHR, waist to hip ratio.
Received November 15, 2006.
Accepted February 14, 2007.
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Abstract
Introduction
