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TCF7L2 rs7903146 polymorphism and diabetic nephropathy association is not independent of type 2 diabetes — a study in a south Indian population and meta-analysis
Związek między polimorfizmem rs7903146 genu TCF7L2 a nefropatią cukrzycową nie jest niezależny od cukrzycy typu 2 — badanie populacji Indii Południowych i metaanaliza
1Department of Biomedical Sciences, Sri Ramachandra University, Chennai, India
2Sickle Cell Institute Chhattisgarh, Raipur, India
LVKS Bhaskar M.D., Ph.D., Department of Biomedical Sciences, Sri Ramachandra University, Porur, Chennai- 600116, India, tel.: +91 44 247 68 027, fax: +91-44-24767008, e-mail: lvksbhaskar@gmail.com
Abstract
Diabetic nephropathy (DN) is a chronic microangiopathic complication of both type 1 (T1DM) and type 2 diabetes mellitus (T2DM). The TCF7L2 gene has been reported to be associated with type 2 diabetes risk. We aimed to investigate the impact of TCF7L2 gene on the susceptibility of T2DM and DN in a south Indian population. Plus to evaluate the association of rs7903146 in the TCF7L2 gene with T2DM in the Indian population. The subjects recruited for this included 55 diabetic cases with diabetic nephropathy, 68 diabetic cases without nephropathy, and 82 non-diabetic healthy controls. Genomic DNA was isolated from blood and genotyping of TCF7L2 rs7903146 was performed by PCR-RFLP analysis. A literature survey was carried out into the effect of rs7903146 on genetic susceptibility to T2DM in Indian populations and we then performed a meta-analysis in order to evaluate its association with T2DM. Analysis of TCF7L2 rs7903146 in normal controls and diabetics with or without nephropathy demonstrated that the ʻT’ allele is associated with both diabetes (p = 0.049) and DN (p = 0.024), but this association is not independent of T2DM. Meta-analysis showed that the mutant allele and genotypes are associated with T2DM in Indian populations. In summary, a significant association exists between the ʻT’ allele and DN, but this association is not independent of T2DM. Pooled meta-analysis of studies on rs7903146 and T2DM confirmed that rs7903146 is significantly associated with susceptibility to T2DM in Indian populations.
(Endokrynol Pol 2014; 65 (4): 298–305)
Key words: TCF7L2 gene; SNP; diabetic nephropathy
Streszczenie
Nefropatia cukrzycowa (DN, diabetic nephropathy) jest przewlekłym powikłaniem o charakterze mikroangiopatii występującym zarówno w cukrzycy typu 1 (T1DM, type 1 diabetes mellitus), jak i typu 2 (T2DM, type 2 diabetes mellitus). Gen TCF7L2 jest związany z ryzykiem cukrzycy typu 2. Badanie przeprowadzono w celu dokonania oceny wpływu genu TCF7L2 na podatność na zachorowanie na T2DM i DN w populacji Indii Południowych oraz oceny związku między występowaniem polimorfizmu rs7903146 genu TCF7L2 i T2DM w populacji południowej części Indii. Do badania włączono 55 przypadków chorych na cukrzycę z nefropatią cukrzycową, 68 przypadków cukrzycy bez nefropatii i 82 osoby niechorujące na cukrzycę jako grupę kontrolną. Genomowe DNA izolowano z krwi i przeprowadzono genotypowanie polimorfizmu rs7903146 genu TCF7L2 metodą analizy PCR-RFLP Przeprowadzono również przegląd literatury pod kątem danych dotyczących wpływu występowania polimorfizmu rs7903146 na genetyczną podatność na T2DM w populacji hinduskiej, a następnie przeprowadzono metaanalizę w celu oceny jego związku z T2DM. Analiza polimorfizmu rs7903146 genu TCF7L2 u zdrowych osób z grupy kontrolnej oraz u chorych na cukrzycę z nefropatią i bez nefropatii wykazała, że allel T jest związany zarówno z cukrzycą (p = 0,049), jak i DN (p = 0,024), jednak ten związek nie jest niezależny od T2DM. Metaanaliza wykazała, że zmutowane allele i genotypy są związane z T2DM w populacji hinduskiej.
Podsumowując, istnieje istotny związek między allelem T i DN, jednak związek ten nie jest niezależny od T2DM. Metaanaliza danych z badań dotyczących polimorfizmu rs7903146 i T2DM potwierdziła, że obecność polimorfizmu rs7903146 jest istotnie związana z podatnością na zachorowanie na T2DM w populacji hinduskiej.
(Endokrynol Pol 2014; 65 (4): 298–305)
Słowa kluczowe: gen TCF7L2; SNP; nefropatia cukrzycowa
Introduction
Diabetic nephropathy (DN) is a chronic microangiopathic complication of both type 1 (T1DM) and type 2 diabetes mellitus (T2DM) and is the primary cause of end stage renal disease (ESRD) [1]. Diabetes is characterised by hyperglycaemia resulting from the impairment of insulin secretion, insulin sensitivity, or both. Type 2 diabetes is the most common form of diabetes, affecting 90% of all people with diabetes. The prevalence of type 2 diabetes continues to rise, with an increasing number of patients at risk of serious diabetes-related microvascular and macrovascular complications [2]. Both longitudinal and cross-sectional studies have demonstrated that type 2 diabetes is influenced by several behavioural as well as lifestyle factors [3]. Multiple lines of evidence indicate that type 2 diabetes is a highly inherited trait and different approaches such as candidate gene and linkage studies have been made to identify type 2 diabetes genes [4–6]. Genome wide association studies (GWAS) have paved the way for researchers to identify more genes that have a relatively low effect on type 2 diabetes susceptibility [7, 8].
Transcription factor 7-like 2 is the key transcriptional factor regulating glucose metabolism through the Wnt signalling pathway. Wnt signalling has also been reported to be critical for the development of the pancreas and islets during embryonic growth. Furthermore, regulation of Wnt signalling’s timing and stimulus is crucial for the development of the pancreas [9]. The gene TCF7L2 located on chromosome 10q25.3 which encodes the transcription factor-4 (TCF-4) has been identified as a major T2DM susceptibility gene. TCF7L2 rs7903146 SNP is associated with type 2 diabetes and may operate via impaired glucagon-like peptide 1 (GLP1) secretion, which is stimulated more by fat than by carbohydrate ingestion. Moreover, the association between TCF7L2 variants and T2DM is supported by several prospective mechanisms such as decreased P-cell mass, liver insulin resistance and altered chromatin state in ʻT’ allele carriers [10, 11]. However, causative links between polymorphisms in or near the TCF7L2 gene and overt type 2 diabetes are uncertain, because of the fact that the polymorphisms have not yet been proven to correlate with the risk for type 2 diabetes in prospective follow-up studies.
Thus, the objective of this study was to investigate the association of the TCF7L2 SNPs with SNP rs7903146 with well characterised DN. In particular, we investigated whether the association between TCF7L2 polymorphisms and DN is independent or dependent of diabetes. Further, we analysed the studies conducted so far on TCF7L2 gene rs7903146 in diverse populations of India, using meta-analysis to assess the possible heterogeneity in the allele frequency and the nature as well as the magnitude of its association with T2DM.
Material and methods
Subjects and methods
One hundred and twenty three unrelated individuals visiting outpatient clinics at Sri Ramachandra University Hospital, Chennai were diagnosed as type 2 diabetes according to the World Health Organisation criteria [12]. All participants underwent detailed clinical evaluation followed by biochemical investigations such as serum creatinine, fasting and postprandial blood glucose and 24-h urinary albumin excretion. Among them, 55 patients had overt nephropathy, as indicated by persistent urine albuminuria ( > 300 mg/L) in two consecutive measurements. Sixty eight individuals with normoalbuminuria indicated by urinary albumin excretion rate of < 20 μg/min even after ten years of diabetes were considered as controls. Eighty two age- and sex-matched healthy subjects were selected as controls. Individuals with hypertension, congestive heart defects and chronic renal disease were excluded from the study. This study was approved by the institutional ethics committee of Sri Ramachandra University. Informed written consent was obtained from all the study participants prior to the commencement of the study. Three ml of blood sample was collected from each participant, genomic DNA was isolated from lymphocytes by standard techniques, and we used a published protocol to genotype the TCF7L2 rs7903146 SNP [13]. Briefly, the rs7903146 was genotyped by amplifying 188 bp intron region of TCF7L2 gene by using forward primer 5' ACA ATT AGA GAG CTA AGC ACT TTT TAG GTA 3' and reverse primer 5' GTG AAG TGC CCA AGC TTC TC 3' followed by the digestion of PCR product with RsaI enzyme. The rs7903146 ʻT’ allele was characterised by the presence of a 188 bp fragment, which was digested further to 159 and 29 bp fragments in rs7903146 ‘C’ allele carriers.
A comprehensive search of the electronic databases: PubMed, Embase, and ISI Web of Science was done using the terms: ʻtranscription factor 7-like 2/TCF7L2’, ʻrs7903146’ and ʻtype 2 diabetes mellitus/T2D/T2DM’. Papers pertaining to Indian populations with sufficient data retrieved up to April 2013 were considered for estimating an odds ratio (OR) and 95% confidence interval (CI) in the meta-analysis. All the studies included in the meta-analysis are listed in Table I. The data collected from the eligible studies included the study reference, total number of cases and controls, and numbers of genotypes in both cases and controls.
Table I. Main characteristics of the studies included in the meta-analysis
Tabela I. Charakterystyka badań włączonych do metaanalizy
| Study reference | Total samples | Control | Case | ||||
|---|---|---|---|---|---|---|---|
| CC | TC | TT | CC | TC | TT | ||
| Humphries et al., 2006 [43] | 1,137 | 163 | 111 | 26 | 366 | 375 | 96 |
| Chandak et al., 2007 [32] | 1,354 | 205 | 160 | 34 | 391 | 423 | 141 |
| Bodhini et al., 2007 [35] | 2,069 | 555 | 391 | 92 | 462 | 455 | 114 |
| Mahurkar et al., 2008 (Dravidian) [44] | 592 | 130 | 104 | 25 | 175 | 126 | 32 |
| Mahurkar et al., 2008 (Indo-European) [44] | 547 | 207 | 160 | 35 | 78 | 53 | 14 |
| Sanghera et al., 2008 [34] | 1,081 | 236 | 224 | 77 | 191 | 261 | 92 |
| Rees et al., 2008 [45] | 1,260 | 222 | 166 | 44 | 352 | 360 | 116 |
| Gupta et al., 2010 [46] | 356 | 62 | 78 | 21 | 55 | 96 | 44 |
| Mukhopadhyaya et al., 2010 [47] | 80 | 5 | 19 | 16 | 17 | 21 | 2 |
| Uma Jyothi et al., 2013 [36] | 1,379 | 393 | 194 | 34 | 344 | 328 | 86 |
| Present study | 150 | 43 | 35 | 4 | 25 | 36 | 7 |
Statistical analysis
TCF7L2 rs7903146 allele frequencies of the present study and ten eligible case control studies were determined by direct gene counting. The genotype distribution of this SNP in all studies was evaluated for Hardy-Weinberg equilibrium by using a HWSIM program [14]. The strength of the association between TCF7L2 variant alleles and their interaction in causing diabetic nephropathy and T2DM was calculated using chi square analysis. The OR and corresponding 95% CI limits were also calculated. For TCF7L2 rs7903146, the meta-analysis examined the association between the carriers of the rare T allele and T2DM risk compared to that for CC genotype (CC vs. TC+TT). The pooled OR estimate of each study was calculated by the fixed-effects model [15]. The odds ratio and confidence interval was graphically presented as a forest plot. An estimate of potential publication bias was carried out by the funnel plot. Funnel plot asymmetry was assessed by the method of Egger’s linear regression test [16]. The data was analysed using comprehensive meta-analysis software. For a worldwide comparison in a wider context, we have also extracted 20 kb up and downstream SNPs around rs7903146 from the HapMap data (The International HapMap Consortium) [17].
Figure 1. Schematic representation of the article selection process
Rycina 1. Schemat przedstawiający proces selekcji artykułów
Results
Association study
The distribution of TCF7L2 rs7903146 genotypes among DN, diabetic control and normal controls is documented in Table II. The genotype frequency distribution in all three groups followed Hardy Weinberg equilibrium (Table II). The frequency of ʻT’ allele was 31.9%, 36.8% and 26.2% in diabetic nephropathy, diabetic control, and normal control respectively. The results of association between different groups are also documented in Table II. The frequency of TT genotype was slightly higher in DN cases than the controls and increased the risk of nephropathy (p = 0.021, OR 4.30, 95% CI 1.00–21.44). The ‘T’ allele is associated with both diabetes (p = 0.049, OR 1.64, 95% CI 0.97–2.76) and diabetic nephropathy (p = 0.024, OR 1.81, 95% CI 1.04–3.13). The distribution of both allele and genotypes did not show significant differences between diabetes and diabetic nephropathy (Table II).
Table II. Genotype frequencies and association statistics for the rs7903146 in diabetic nephropathy, T2DM control and normal control
Tabela II. Częstość występowania poszczególnych genotypów i powiązane statystyki dotyczące polimorfizmu rs7903146 u osób z nefropatią cukrzycową, w grupie chorych na T2DM i grupie kontrolnej obejmującej zdrowe osoby
| Control | Diabetic without nephropathy | Diabetic nephropathy | p value* | p value** | p value*** | |
|---|---|---|---|---|---|---|
| CC | 43 (52.44) | 25 (36.76) | 20 (30.36) | Reference | ||
| CT | 35 (42.63) | 36 (52.94) | 27 (49.09) | 0.097 | 0.173 | 0.869 |
| TT | 4 (4.88) | 7 (10.29) | 8 (14.55) | 0.092 | 0.021 | 0.550 |
| CT+TT | 39 (47.51) | 14 (63.23) | 14 (63.64) | 0.226 | 0.529 | 0.643 |
| C | 121 (73.8) | 86 (63.2) | 67 (60.9) | Reference | ||
| T | 43 (26.2) | 50 (36.8) | 43 (39.1) | 0.049 | 0.024 | 0.708 |
| HWE p-value | 0.350 | 0.253 | 0.818 | – | – | – |
*Control i/s. diabetic without nephropathy, **Control i/s. diabetic nephropathy, ***Diabetic without nephropathy i/s. diabetic nephropathy
Meta-analysis
Meta-analysis of 11 studies showed that the mutant allele is associated with T2DM in both fixed effect (P < 0.001, OR = 1.336, 95% CI = 1.255-1.422) and random effect (P = 0.004, OR = 1.254, 95% CI = 1.075–1.463) (Fig. 2). Similar to the allelic meta-analysis, the pooled odds ratio for mutant genotypes (dominant model) showed a statistically significant association with T2DM adopting both fixed effect (P < 0.001, OR = 1.451, 95% CI = 1.336–1.576) and random effect (P < 0.001, OR = 1.370, 95% CI = 1.150–1.832) (Fig. 2). The heterogeneity test and sensitivity analysis showed a true heterogeneity between studies ʻT’ allele in the allelic model (Pheterogeneity < 0.001, χ2 = 35.36, df = 10, I-squared = 74.5%) and dominant model (Pheterogeneity = 0.003, χ2 = 25.43, df = 10, I-squared = 64.6%). The comparison of heterogeneity between studies demonstrated that both allelic and dominant model show variations in study outcomes between studies.
Figure 2. Forest plot of the fixed and random-effects meta-analysis of 11 studies of rs7903146 for T2DM (A. dominant model, B. allelic model). Point estimates, 95% confidence intervals (CI), and study weights are provided for each study
Rycina 2. Wykres typu forest plot efektów stałych i losowych w metaanalizie 11 badań polimorfizmu rs7903146 u osób z T2DM (A. model dominujący, B. model alleliczny). Dla wszystkich badań przedstawiono estymacje punktowe, 95% przedziały ufności i wagi
The funnel plots generated using standard error and precision values for both allelic and dominant models using both fixed and random effect models are depicted in Figure 3. The shape of the funnel plots was symmetrical, suggesting that there was no evidence for publication bias for rs7903146 polymorphism. The other measures used for assessing the publication bias in allelic and dominant models showed absence of publication bias (Table III). The classic fail-safe ʻN’ value of 136 (P < 0.001, Z = 1.96) for allelic model and 130 (P < 0.001, Z = 1.96) for dominant model, indicated that 136 and 130 null studies (for allelic and dominant models respectively) would be required to convert the combined ʻP’ value as a non-significant P > 0.05. The Orwin’s fail-safe ʻN’ value to bring observed Odds Ratio of 1.34 to 1.11 is 15 for allelic model, indicating a minimum of 15 null studies would be needed to bring the effect size to null. Similarly, Orwin’s fail-safe ʻN’ value to bring the observed Odds Ratio of 1.45 to 1.11 is 23 for dominant model, indicating a minimum of 23 null studies would be needed to bring the effect size to null. Furthermore, the Duval and Tweedie’s ʻtrim and fill’ procedure also failed to show publication bias.
Figure 3. Egger’s funnel plot as a test for publication bias for rs7903146 (A. dominant model, B. allelic model). The precision of each study (standard error of the log odds ratio [OR]) is plotted against each study’s effect estimate (OR)
Rycina 3. Wykres lejkowy Eggera w ocenie stronniczości publikacji dotyczących polimorfizmu rs7903146 (A. model dominujący; B. model alleliczny). Przedstawiono dokładność poszczególnych badań (błąd standardowy logarytmu ilorazu szans w zależności od ich oszacowanego efektu (OR)
Table III. Measures of publication bias in allelic and dominant models
Tabela III. Pomiar stronniczości publikacji w modelach allelicznym i dominującym
| Publication bias test | Allelic model | Dominant model |
|---|---|---|
| Classic fail-safe ‘N’ | ||
| Observed studies p value | P < 0.001 | P < 0.001 |
| Observed studies Z value | Z = 1.96 | Z = 1.96 |
| Number of missing studies to bring p > alpha | 136 | 130 |
| Orwin’s fail-safe ʻN’ | ||
| OR | 1.34 | 1.45 |
| Number of null studies required | 15 | 23 |
| Begg and Mazumdar rank correlation test: | ||
| Kendall’ tau | –0.145 | –0.11 |
| One-tailed | 0.267 | 0.32 |
| Two-tailed | 0.533 | 0.64 |
| Egger’s regression test: | ||
| Intercept value | –2.99 | –2.45 |
| ʻt’ value | 1.72 | 1.75 |
| One-tailed | 0.059 | 0.057 |
| Two-tailed | 0.119 | 0.119 |
| df | 9 | 9 |
Discussion
Analysis of TCF7L2 rs7903146 in normal controls and diabetics with or without nephropathy demonstrated that the ʻT’ allele is associated with both diabetes and DN, but this association is not independent of T2DM. The meta-analysis conducted using the 11 studies also showed a significant association between the mutant allele and T2DM in Indian populations. Furthermore, comparison on heterogeneity between studies confirmed that both the allelic and dominant models exhibited heterogeneity. No evidence or publication bias was observed. Although the role of TCF7L2 in the regulation of microvascular complications such as DN is not fully known, there have been several studies reporting the association of this gene with DN [18, 19]. Another study showed that the TCF7L2 gene was associated only with lower estimated glomerular filtration rate (eGFR) but not with albuminuria, indicating a shared genetic risk for T2DM and DN [20]. In contrast to this, no influence of this gene in the pathogenesis of diabetes-induced microvascular complications such as neuropathy, nephropathy and retinopathy has been observed [21].
The first report on a strong genetic association between variants of the TCF7L2 gene and risk of type 2 diabetes was found in Icelandic individuals, a Danish cohort, and a cohort of the US population [22]. The subsequent genome-wide association analysis on T2DM showed a strong signal for TCF7L2 in the French population [23]. This prompted inclusion of TCF7L2 gene variants in a large number of association studies in various populations world-wide [24–29]. Furthermore, a number of meta-analyses supported this robust finding [30, 31]. The replication studies of TCF7L2 gene variants among Indian populations also showed a strong association of TCF7L2 with T2DM [32–36].
Investigations on transcriptional regulation by applying chromatin immunoprecipitation and sequencing techniques in a colorectal cancer cell line revealed overexpression of TCF7L2. This provided the first evidence for its central node for T2DM susceptibility [37]. Later, several studies using pancreatic cells and a rat insulin-producing cell line (Ins-1) have indicated a potential role of TCF7L2 in human T2DM [38–40]. A recent study demonstrated that the liver-specific TCF4 overexpression increases hepatic glucose production, indicating TCF7L2 directly activates metabolic genes [41]. To date, most studies with TCF7L2 have genotyped either the one or two most associated SNPs reported in the original study [22], and ignored the remaining polymorphisms of the TCF7L2 gene. The rs7903146 also showed variations among the world populations with the highest ʻT’ allele frequency in HapMap populations of African (YRI, MKK, ASW and LWK) and European (CEU and TSI) followed by Mexican (MEX) ancestry and south Asian populations (GIH). East Asian populations (CHB, CHD and JPT) exhibited slightly fewer ʻT’ allele frequencies than the rest of the world populations (Table SI).
Table SI. Genotype, allele frequencies and Hardy-Weinberg equilibrium for TCF7L2 rs7903146 in HapMap populations
Tabela SI. Genotypy, częstość występowania alleli i prawo Hardy’ego-Weinberga dla polimorfizmu rs7903146 genu TCF7L2 w populacji HapMap
| C/C | C/T | T/T | T allele | HWp | |
|---|---|---|---|---|---|
| ASW | 23 (41.1) | 28 (50.0) | 5 (8.9) | 38 (33.9) | 0.339 |
| CEU | 62 (54.9) | 39 (34.5) | 12 (10.6) | 63 (27.9) | 0.132 |
| CHB | 130 (94.9) | 7 (5.1) | 0 (0.0) | 7 (2.6) | 0.759 |
| CHD | 101 (92.7) | 8 (7.3) | 0 (0.0) | 8 (3.7) | 0.691 |
| GIH | 52 (51.5) | 42 (41.6) | 7 (6.9) | 56 (27.7) | 0.705 |
| JPT | 106 (93.8) | 6 (5.3) | 1 (0.9) | 8 (3.5) | 0.018 |
| LWK | 58 (52.7) | 43 (39.1) | 9 (8.2) | 61 (27.7) | 0.796 |
| MEX | 32 (55.2) | 22 (37.9) | 4 (6.9) | 30 (25.9) | 0.934 |
| MKK | 77 (49.4) | 63 (40.4) | 16 (10.3) | 95 (30.4) | 0.561 |
| TSI | 44 (43.1) | 42 (41.2) | 16 (15.7) | 74 (36.3) | 0.269 |
| YRI | 76 (51.7) | 63 (42.9) | 8 (5.4) | 79 (26.9) | 0.273 |
Analysis of 20 kb up and downstream SNPs around rs7903146 from the HapMap data demonstrated that the European (CEU and TSI) and Mexican (MEX) populations formed a single large LD block. Unlike in Caucasians, the African populations exhibited weak LD and formed two small LD blocks. In East Asian populations (CHB, CHD and JPT) and south Asian populations (GIH), the LD is fragmented (Fig. S1). Although the functional role of this intronic SNP (rs7903146) is still unknown, the variant risk allele is associated with impaired insulin secretion, reduction of total islet numbers, and quantitative as well as qualitative morphological changes in human islets [42]. Furthermore, carriers of risk variants at TCF7L2 are more likely to fail sulfonulyurea therapy than metformin and more likely to be on insulin therapy rather than diet alone. Thus, the screening of the entire gene leads to a complete understanding of the variants of exons and the surrounding region with a stronger effect on the risk of disease.
Figure S1. Linkage disequilibrium profiles in different populations studied in International HapMap Project. Colour coding represents the D'/LOD values and the values in cells are r2 multiplied by 100
Rycina S1. Nierównowaga sprzężeń w różnych populacjach badanych w ramach projektu HapMap. Kolorami oznaczono wartości D'/LOD, a liczby w komórkach odpowiadają współczynnikom r2 pomnożonym przez 100
In conclusion, we suggest that TCF7L2 is a potent gene in not just causing T2DM, but also DN. This study could be extended to a larger number of diabetes-induced nephropathic individuals to gain more evidence. Thus it may prove to be a strong predictive classifier to provide an index of ʻat risk’ status, including probability estimates to T2DM likelihood and nephropathic complications thereafter. These studies can further aid in translational research, as categorising diabetic individuals based on their genetic makeup will help personalise medication and improve treatment options.
Author’s contribution
All authors contributed equally to the article.
Acknowledgements
The authors would like to thank Sri Ramachandra University for providing the Chancellor’s Summer Research Fellowship and necessary facilities. This study was approved by the Institutional Ethics Committee on 10 January 2013 (CSP/13/JAN/26/32).
References
1. He F., Xia X., Wu X.F. et al. Diabetic retinopathy in predicting diabetic nephropathy in patients with type 2 diabetes and renal disease: a metaanalysis. Diabetológia 2013; 56: 457–466.
2. Donaghue K.C., Chiarelli F., Trotta D. et al. Microvascular and macrovascular complications associated with diabetes in children and adolescents. Pediatr Diabetes 2009; 10 (Suppl. 12): 195–203.
3. Hu F.B. Globalization of diabetes: the role of diet, lifestyle, and genes. Diabetes Care 2011; 34: 1249–1257.
4. Praveen E.P., Sahoo J., Khurana M.L. et al. Insulin sensitivity and beta-cell function in normoglycemic offspring of individuals with type 2 diabetes mellitus: Impact of line of inheritance. Indian J Endocrinol Metab 2012; 16: 105–111.
5. Everett M. They say it runs in the family: diabetes and inheritance in Oaxaca, Mexico. Soc Sci Med 2011; 72: 1776–1783.
6. Mills J.L., Irving R.R., Choo-Kang E.G. et al. Multigenerational inheritance and clinical characteristics of three large pedigrees with early-onset type 2 diabetes in Jamaica. Rev Panam Salud Publica 2010; 27: 435–441.
7. Torres J.M., Cox N.J., Philipson L.H. Genome wide association studies for diabetes: perspective on results and challenges. Pediatr Diabetes 2013; 14: 90–96.
8. Wheeler E., Barroso I. Genome-wide association studies and type 2 diabetes. Brief Funct Genomics 2011; 10: 52–60.
9. Heiser P.W., Lau J., Taketo M.M. et al. Stabilization of beta-catenin impacts pancreas growth. Development 2006; 133: 2023–2032.
10. Pearson E.R. Translating TCF7L2: from gene to function. Diabetologia 2009; 52: 1227–1230.
11. Gaulton K.J., Nammo T., Pasquali L. et al. A map of open chromatin in human pancreatic islets. Nat Genet 2010; 42: 255–259.
12. Alberti K.G., Zimmet P.Z. Definition, diagnosis and classification of diabetes mellitus and its complications. Part 1: diagnosis and classification of diabetes mellitus provisional report of a WHO consultation. Diabet Med 1998; 15: 539–553.
13. Sousa A.G., Marquezine G.F., Lemos P.A. et al. TCF7L2 polymorphism rs7903146 is associated with coronary artery disease severity and mortality. PLoS One 2009; 4: e7697.
14. Cubells J.F., Kobayashi K., Nagatsu T. et al. Population genetics of a functional variant of the dopamine beta-hydroxylase gene (DBH). Am J Med Genet 1997; 74: 374–379.
15. Helfenstein U. Data and models determine treatment proposals — an illustration from meta-analysis. Postgrad Med J 2002; 78: 131–134.
16. Egger M., Davey Smith G., Schneider M. et al. Bias in meta-analysis detected by a simple, graphical test. BMJ 1997; 315: 629–634.
17. The International HapMap Project. Nature 2003; 426: 789–796.
18. Maeda S., Osawa N., Hayashi T. et al. Genetic variations associated with diabetic nephropathy and type II diabetes in a Japanese population. Kidney Int 2007; Suppl.: S43–48.
19. Sale M.M., Smith S.G., Mychaleckyj J.C. et al. Variants of the transcription factor 7-like 2 (TCF7L2) gene are associated with type 2 diabetes in an African-American population enriched for nephropathy. Diabetes 2007; 56: 2638–2642.
20. Franceschini N., Shara N.M., Wang H. et al. The association of genetic variants of type 2 diabetes with kidney function. Kidney Int 2012; 82: 220–225.
21. Buchbinder S., Rudofsky G. Jr., Humpert P.M. et al. The DG10S478 variant in the TCF7L2 gene is not associated with microvascular complications in type 2 diabetes. Exp Clin Endocrinol Diabetes 2008; 116: 211–214.
22. Grant S.F., Thorleifsson G., Reynisdottir I. et al. Variant of transcription factor 7-like 2 (TCF7L2) gene confers risk of type 2 diabetes. Nat Genet 2006; 38: 320–323.
23. Sladek R., Rocheleau G., Rung J. et al. A genome-wide association study identifies novel risk loci for type 2 diabetes. Nature 2007; 445: 881–885.
24. Florez J.C., Jablonski K.A., Bayley N. et al. TCF7L2 polymorphisms and progression to diabetes in the Diabetes Prevention Program. N Engl J Med 2006; 355: 241–250.
25. Karns R., Zhang G., Jeran N. et al. Replication of genetic variants from genome-wide association studies with metabolic traits in an island population of the Adriatic coast of Croatia. Eur J Hum Genet 2011; 19: 341–346.
26. Lin Y., Li P., Cai L. et al. Association study of genetic variants in eight genes/loci with type 2 diabetes in a Han Chinese population. BMC Med Genet 2010; 11: 97.
27. Cruz M., Valladares-Salgado A., Garcia-Mena J. et al. Candidate gene association study conditioning on individual ancestry in patients with type 2 diabetes and metabolic syndrome from Mexico City. Diabetes Metab Res Rev 2010; 26: 261–270.
28. Ezzidi I., Mtiraoui N., Cauchi S. et al. Contribution of type 2 diabetes associated loci in the Arabic population from Tunisia: a case-control study. BMC Med Genet 2009; 10: 33.
29. Mayans S., Lackovic K., Lindgren P. et al. TCF7L2 polymorphisms are associated with type 2 diabetes in northern Sweden. Eur J Hum Genet 2007; 15: 342–346.
30. Cauchi S., El Achhab Y., Choquet H. et al. TCF7L2 is reproducibly associated with type 2 diabetes in various ethnic groups: a global metaanalysis. J Mol Med (Berl) 2007; 85: 777–782.
31. Tong Y., Lin Y., Zhang Y., Yang J., Liu H., Zhang B. Association between TCF7L2 gene polymorphisms and susceptibility to type 2 diabetes mellitus: a large Human Genome Epidemiology (HuGE) review and meta-analysis. BMC Med Genet 2009; 10: 15.
32. Chandak G.R., Janipalli C.S., Bhaskar S. et al. Common variants in the TCF7L2 gene are strongly associated with type 2 diabetes mellitus in the Indian population. Diabetologia 2007; 50: 63–67.
33. Chauhan G., Spurgeon C.J., Tabassum R. et al. Impact of common variants of PPARG, KCNJ11, TCF7L2, SLC30A8, HHEX, CDKN2A, IGF2BP2, and CDKAL1 on the risk of type 2 diabetes in 5,164 Indians. Diabetes 2010; 59: 2068–2074.
34. Sanghera D.K., Nath S.K., Ortega L. et al. TCF7L2 polymorphisms are associated with type 2 diabetes in Khatri Sikhs from North India: genetic variation affects lipid levels. Ann Hum Genet 2008; 72: 499–509.
35. Bodhini D., Radha V., Dhar M. et al. The rs12255372(G/T) and rs7903146(C/T) polymorphisms of the TCF7L2 gene are associated with type 2 diabetes mellitus in Asian Indians. Metabolism 2007; 56: 1174–1178.
36. Uma Jyothi K., Jayaraj M., Subburaj K.S. et al. Association of TCF7L2 gene polymorphisms with T2DM in the population of Hyderabad, India. PLoS One 2013; 8: e60212.
37. Zhao J., Schug J., Li M. et al. Disease-associated loci are significantly over-represented among genes bound by transcription factor 7-like 2 (TCF7L2) in vivo. Diabetologia 2010; 53: 2340–2346.
38. Lyssenko V., Lupi R., Marchetti P. et al. Mechanisms by which common variants in the TCF7L2 gene increase risk of type 2 diabetes. J Clin Invest 2007; 117: 2155–2163.
39. Shu L., Sauter N.S., Schulthess F.T. et al. Transcription factor 7-like 2 regulates beta-cell survival and function in human pancreatic islets. Diabetes 2008; 57: 645–653.
40. Liu Z., Habener J.F. Glucagon-like peptide-1 activation of TCF7L2-dependent Wnt signaling enhances pancreatic beta cell proliferation. J Biol Chem 2008; 283: 8723–8735.
41. Boj S.F., van Es J.H., Huch M. et al. Diabetes risk gene and Wnt effector Tcf7l2/TCF4 controls hepatic response to perinatal and adult metabolic demand. Cell 2012; 151: 1595–1607.
42. Le Bacquer O., Kerr-Conte J., Gargani .S et al. TCF7L2 rs7903146 impairs islet function and morphology in non-diabetic individuals. Diabetologia 2012; 55: 2677–2681.
43. Humphries S.E., Gable D., Cooper J.A. et al. Common variants in the TCF7L2 gene and predisposition to type 2 diabetes in UK European Whites, Indian Asians and Afro-Caribbean men and women. J Mol Med (Berl) 2006; 84: 1005–1014.
44. Mahurkar S., Bhaskar S., Reddy D.N. et al. TCF7L2 gene polymorphisms do not predict susceptibility to diabetes in tropical calcific pancreatitis but may interact with SPINK1 and CTSB mutations in predicting diabetes. BMC Med Genet 2008; 9: 80.
45. Rees S.D., Bellary S., Britten A.C. et al. Common variants of the TCF7L2 gene are associated with increased risk of type 2 diabetes mellitus in a UK-resident South Asian population. BMC Med Genet 2008; 9: 8.
46. Gupta V., Khadgawat R., Ng H.K. et al. A validation study of type 2 diabetes-related variants of the TCF7L2, HHEX, KCNJ11, and ADIPOQ genes in one endogamous ethnic group of north India. Ann Hum Genet 2010; 74: 361–368.
47. Mukhopadhyaya P.N., Acharya A., Chavan Y. et al. Metagenomic study of single-nucleotide polymorphism within candidate genes associated with type 2 diabetes in an Indian population. Genet Mol Res 2010; 9: 2060–2068.
