No major contribution of TCF7L2 sequence variants to maturity onset of diabetes of the young (MODY) or neonatal diabetes mellitus in French white subjects

Clinical signs of type 1 diabetes are associated with type 2 diabetes marker transcription factor 7-like 2 polymorphism

AIMS/INTRODUCTION

We aimed to assess the distribution of transcription factor 7-like 2 gene TCF7L2 (rs7903146) polymorphism and to find possible associations between TCF7L2 and the characteristics of type 1 diabetes.

MATERIALS AND METHODS

We studied 190 newly diagnosed type 1 diabetes patients (median age 12.7 years, range 2.0-72.5) and 246 controls (median age 23.8 years, range 1.4-81.5) for TCF7L2 single nucleotide polymorphism. We determined anti-islet autoantibodies, random C-peptide levels, diabetes associated HLA DR/DQ haplotypes and genotypes in all patients.

RESULTS

There were no differences in the distribution of TCF7L2 single nucleotide polymorphism between patients and controls. However, patients with in type 1 diabetes, after adjusting for age and sex, subjects carrying C allele were at risk for a C-peptide level lower than 0.5 nmol/L (OR 5.65 [95% CI: 1.14-27.92]) and for zinc transporter 8 autoantibody positivity (5.22 [1.34-20.24]). Participants without T allele were associated with a higher level of islet antigen-2 autoantibodies (3.51 [1.49-8.27]) and zinc transporter 8 autoantibodies (2.39 [1.14-4.99]).

CONCLUSIONS

The connection of TCF7L2 polymorphism with zinc transporter 8 and islet antigen-2 autoantibodies and C-peptide levels in patients supports the viewpoint that TCF7L2 is associated with the clinical signs and autoimmune characteristics of type 1 diabetes. The mechanisms of the interaction between the TCF7L2 risk genotype and anti-islet autoantibodies need to be studied further.

Polymorphisms of TCF7L2 gene in South Brazilian women with polycystic ovary syndrome: a cross-sectional study

OBJECTIVE

To assess whether TCF7L2 single nucleotide polymorphisms rs7903146 C/T and rs11196236 C/T are associated with polycystic ovary syndrome (PCOS) in South Brazilian women.

DESIGN

Cross-sectional study.

METHODS

Two hundred PCOS patients and 102 non-hirsute, ovulatory controls were genotyped by real-time PCR. Haplotypes were constructed from the combination of both polymorphisms. Frequencies were inferred using the PHASE 2.1.1 software.

RESULTS AND CONCLUSIONS

The distribution of rs7903146 (PCOS, 54.4% CC; 28.5% CT; 17.1% TT; controls, 51.0% CC; 37.0% CT; 12.0% TT) and rs11196236 (PCOS, 4.3% CC; 33.5% CT; 62.2% TT; controls, 3.2% CC; 35.5% CT; 61.3% TT) was similar between the groups. rs7903146 and rs11196236 were not in linkage disequilibrium (|D'|=0.34; r(2)=0.07). PCOS participants were younger, with higher age-adjusted BMI, waist circumference, blood pressure, triglycerides, insulin, homeostasis model assessment index to estimate insulin resistance and total testosterone, and lower HDL-C and sex hormone binding globulin vs controls. In PCOS, no differences between genotypes and haplotypes were found for clinical and metabolic variables. However, for each T (rs7903146) and T (rs11196236) allele added to the haplotypes, a variation of 5.87 cm in waist (P trend=0.01), 10.7 mg/dl in total cholesterol (P trend=0.03), and 10.3 mg/dl in LDL-C (P trend=0.01) was recorded. TCF7L2 variants are probably not implicated in PCOS development in South Brazilian women.

Revision of the ADA-classification of diabetes mellitus type 2 (DMT2): the importance of maturity onset diabetes (MOD), and senile diabetes (DS)

The changing social and economic conditions and the increase of the life span induced a progressive increase of the general prevalence of DMT2, particularly in the elderly population of the highly evoluted countries. Up to now 18 genetic loci have been identified, each of them consisting of several single nucleotide polymorphisms (SNPs). The evidence that the DMT2 is regulated by a high number of genes, demonstrate the pathogenetic complexity of this disease. The onset of diabetes mellitus (DM) in medium age is a consequence of the breakdown of the glycemic homeostasis in correlation with the genetic factors, such as the variants of the TCF7L2, obesity, etc., and the environmental factors, such as the life-style, the evolution of chronic-degenerative diseases, etc. In case of DM that onsets in old age we have to add the deterioration of the anti-aging defense mechanisms, characterized by the antagonistic action of the genes of longevity and aging. One can observe several clinical and therapeutic differences; therefore, the authors of this review propose the reinsertion of three forms into the DMT2 correlated with the age of onset and with the actual age of the subjects: the maturity onset diabetes (MOD), the maturity onset diabetes in elderly (MODE), and the senile diabetes (DS).

Single nucleotide transcription factor 7-like 2 (TCF7L2) gene polymorphisms in antiislet autoantibody-negative patients at onset of diabetes

CONTEXT

There is controversy as to whether type 2 diabetes genetic susceptibility contributes to type 1 diabetes, and it is not known what proportion of islet autoantibody-negative new onset subjects have type 2 diabetes risk alleles.

OBJECTIVES

We designed this study to evaluate whether two type 2 diabetes-associated single nucleotide polymorphisms (SNPs) of transcription factor 7-like 2 (TCF7L2) gene are associated with the development of islet autoantibody-negative diabetes vs. islet autoantibody-positive diabetes in young patients and whether these SNPs are associated with specific clinical phenotypes.

DESIGN

Autoantibody against glutamic acid decarboxylase 65, islet cell antibody 512bdc (form of IA-2), insulin, ZnT8 transporter, and cytoplasmic islet cell antibody were assayed in patients with new onset diabetes seen at the Barbara Davis Center using sera obtained within 2 wk of diagnosis. We genotyped two noncoding variants in the TCF7L2 gene, rs12255372 and rs7903146, in diabetic subjects and normal controls.

RESULTS

A total of 140 patients (15.7%) were negative for all islet autoantibodies among 893 subjects less than age 25 at the onset of diabetes. The allele and genotype frequencies of two SNPs showed that these are associated (odds ratio up to 4) with the development of diabetes in the autoantibody-negative diabetic cohort, but not in the autoantibody-positive diabetic cohort.

CONCLUSION

TCF7L2 type 2 diabetes susceptibility alleles are associated with islet autoantibody-negative but not autoantibody-positive new onset diabetes in young patients.

Exon sequencing and association analysis of polymorphisms in TCF7L2 with type 2 diabetes in a Chinese population

AIMS/HYPOTHESIS

Recently, variants in the transcription factor 7-like 2 (TCF7L2) gene have been found to be consistently associated with type 2 diabetes in different populations. In this study, we hypothesized that TCF7L2 also contributed to genetic susceptibility for type 2 diabetes in a Chinese population.

METHODS

We looked for new variants by direct sequencing of all exons and intron-exon junctions of TCF7L2 in 100 Chinese type 2 diabetic patients, and then we genotyped five single nucleotide polymorphisms (SNPs) by Snapshot technology in 1,000 Chinese individuals.

RESULTS

By sequencing, we identified six SNPs (c.1,637C>A; c.1,674C>G; c.1,709G>A; c.1,846C>G; c.1,888C>T; and c.1,876T>G), and three of them led to non-synonymous polymorphisms (c.1,637C>A, His-->Gln or Pro-->Thr; c.1,674C>G, Pro-->Arg; and c.1,709G>A, Ala-->Thr). All of them are rare except c.1,637C>A, which had a frequency of 0.23 for the minor A allele in 98 sequenced individuals. In a case-control study, one of the newly discovered SNPs (c.1,637C>A), together with four reported ones (rs7903146, rs12255372, rs290487 and rs3814573) were genotyped. Comparison between allele and genotype frequencies of these SNPs in patients and controls showed marginal association for rs7903146 and rs290487 with type 2 diabetes (p = 0.063, OR 1.982, 95% CI 1.128-3.485; p = 0.071, OR 1.237, 95% CI 0.983-1.557, respectively). No association was found for rs12255372, rs3814573, c.1,637C>A and type 2 diabetes (p = 0.278-1.000).

CONCLUSIONS/INTERPRETATION

With the current sample size, we did not find any mutation in the coding sequence of TCF7L2 that confers a genetic risk for type 2 diabetes in a Chinese population, and did not replicate some of the major positive results obtained in other populations.

Glucokinase (GCK) and other susceptibility genes for β-cell dysfunction: the candidate approach

There are well-documented examples in the literature of where determining the genetic aetiology of a disorder has provided insights into important regulatory pathways and protein interactions, and, more recently, has led to improved treatment options for patients. The studies of monogenic forms of β-cell dysfunction are no exception. Naturally occurring mutations in the gene for the β-cell enzyme glucokinase (GCK) result in both hyper- and hypo-glycaemia. Over 200 mutations have been described, and careful study of the mutational mechanisms for a number of these has provided important insights into glucokinase regulation. Increased understanding of post-translational regulatory mechanisms holds the promise of novel pharmacotherapeutic options for the treatment of T2DM (Type 2 diabetes mellitus). It is well established that common genetic variation in genes involved in monogenic forms of β-cell dysfunction contributes to susceptibility to T2DM. Recent genome-wide scans for association have identified a number of novel T2DM susceptibility genes which probably influence β-cell mass and/or function. Their identification allows the investigation of the role of rare mutations in monogenic β-cell dysfunction. Current results indicate the importance of these genes in pancreatic development and suggest that mutations which result in a severe functional defect could be lethal.

TCF7L2 genetic defect and type 2 diabetes

After two decades of limited success, the genetic architecture of type 2 diabetes (T2D) is finally being revealed. Within only 2 years, an avalanche of studies identified several genes expressed in pancreatic beta cells and involved in the control of insulin secretion, such as transcription factor 7-like 2 (TCF7L2), a key element of the Wnt signaling pathway. In Europeans, genome-wide association scans showed that TCF7L2 has been the most important locus predisposing to T2D so far. For the first time, a gene is consistently involved in T2D susceptibility in all major ethnic groups. At the individual level, carrying the TCF7L2 risk allele increases T2D risk 50%. However, at the population level, the attributable risk is lower than 25% and varies with the allele frequency. The presence of the TCF7L2 rs7903146 risk allele increases TCF7L2 gene expression in beta cells, possibly impairing glucagon-like peptide-1-induced insulin secretion and/or the production of new mature beta cells. The tremendous association of TCF7L2 polymorphisms with T2D provides new insights into future genetic predisposition tests but remains the tip of the T2D genetic iceberg.

Genetics of type 2 diabetes

Identification and characterization of genetic variants that either cause or predispose to diabetes are a major focus of biomedical research. As of early 2007, the molecular basis of most forms of monogenic diabetes resulting from beta-cell dysfunction is known and, in particular, there has been recent success in delineating the genetic aetiology of neonatal diabetes. Finding genes predisposing to more common, multifactorial forms of type 2 diabetes represents a far greater challenge, and only a handful of robust, well-replicated examples have been established. Nevertheless, 2006 heralded identification of the most important type 2 diabetes susceptibility gene known so far, TCF7L2, and in 2007 large-scale genome-wide association studies are destined to provide novel insights into the genetic architecture and biology of type 2 diabetes.