TNFa microsatellite polymorphism modulates the risk of type 1 diabetes in the Belgian population, independent of HLA-DQ

Tumor necrosis factor haplotype diversity in Mestizo and native populations of Mexico

The so-called tumor necrosis factor (TNF) block includes the TNFA, lymphotoxin alpha and beta (LTA and LTB) genes with single-nucleotide polymorphisms (SNP) and microsatellites with an allele frequency that exhibits interpopulation variability. To date, no reports have included both SNPs and microsatellites at the TNF block to study Mestizo or Amerindian populations from Mexico. In this study, samples of five Mexican Mestizo populations (Durango, Guadalajara, Monterrey, Puebla, and Tierra Blanca) and four native-Mexican populations (North Lacandonians, South Lacandonians, Tepehuanos, and Yaquis) were genotyped for two SNPs (LTA+252A>G and TNFA-308G>A) and four microsatellites (TNFa, d, e, and f), to analyze the genetic substructure of the Mexican population. Allele and haplotype frequencies, linkage disequilibrium (LD), and interpopulation genetic relationships were calculated. There was significant LD along almost all of the TNF block but the lowest D' values were observed for the TNFf-TNFd pair. Mestizos showed higher allele and haplotype diversity than did natives. The genetic differentiation level was reduced among Mestizos; however, a slightly, but significant genetic substructure was observed between northern and southern Mexican Mestizos. Among the Amerindian populations, the genetic differentiation level was significantly elevated, particularly in both North and South Lacandonians. Furthermore, among Southern Lacandonians, inhabitants of Lacanja town were the most differentiated from all the Mexicans analyzed. The data presented here will serve as a reference for further population and epidemiological studies including these TNF polymorphisms in the Mexican population.

Tumor necrosis factor-associated susceptibility to type 1 diabetes is caused by linkage disequilibrium with HLA-DR3 haplotypes

Tumor necrosis factor-α (TNF-α) is an important proinflammatory cytokine involved in the pathogenesis of autoimmune type 1 diabetes (T1D). The TNF gene locus is located in the major histocompatibility complex (MHC) class III region and its genetic polymorphisms have been reported to be associated with T1D. However, it is not clear whether these associations are primary or caused by their linkage disequilibrium with other predisposing genes within the MHC. We have tested 2 TNF-α single nucleotide polymorphisms at positions -308G/A and -238G/A in the 5' untranslated region and a (GT)n microsatellite TNFa in the North Indian healthy population and T1D patients with known HLA-A-B-DR-DQ haplotypes. The allele frequencies of TNFa5, -308A, and -238G were determined to be significantly increased among patients compared with controls. Although the observed positive association of -238G was caused by its presence on all 3 DR3(+) groups, namely, B8-DR3-DQ2, B50-DR3-DQ2, and B58-DR3-DQ2 haplotypes associated with T1D in this population, the increase of the -308A allele was caused by its association with the latter 2 haplotypes. On the other hand, TNF -308G occurred on B8-DR3 haplotypes along with -238G and TNFa5 alleles, particularly in T1D patients with late disease onset (at >20 years of age). These results indicate that TNF associations with T1D are caused by their linkage disequilibrium with specific HLA-DR3-DQ2 haplotypes in the Indian population. Because polymorphisms in the promoter region regulate TNF expression levels (e.g., -308A), they retain crucial immunological significance in the development of T1D and its management.

Meta-analysis of TNF 308 G/A polymorphism and type 2 diabetes mellitus

Background and Objectives

Many investigations have focused the association between TNF 308 G/A polymorphism and risk for type 2 diabetes mellitus (T2DM). However, the sample sizes of most of the studies were small. The aim of this study is to evaluate the precise association between this variant and risk for T2DM in a large-scale meta-analysis.

Methods

All publications were searched on the association between TNF 308 G/A polymorphism and T2DM. The key words were as follows: diabetes, tumor necrosis factor and polymorphism/variant/genotype. This meta-analysis was assessed by Review manager 5.0.

Results

There were 18 studies identified. The odd ritos (ORs) and 95% confidence intervals (CI) for GA+AA versus GG genotype of TNF 308 G/A polymorphism were 1.03 (0.95–1.12), 1.03 (0.94–1.13) and 1.03 (0.78–1.36) in overall, Caucasian and Asian populations, respectively. The sensitivity analysis further strengthened the validity of this association. No publication bias or heterogeneity was observed in this study.

Conclusion

In summary, there was no significant association detected between the TNF 308 G/A polymorphism and risk for T2DM.

Lack of association between TNF 238 G/A polymorphism and type 2 diabetes: a meta-analysis

The aim of this meta-analysis was to determine the nature of the association between TNF 238 G/A polymorphism and the risk for T2D. We searched databases updated on January 2009 for all publications on the association between this variation and T2D. Data on genotypes and the numbers of cases and controls were assessed using Review Manager 4.2. Meta-analysis of the overall and specific populations was conducted, and odds ratios (OR) and 95% confidence intervals (95% CI) were calculated in the fixed-effect model. I(2) statistic was calculated to examine heterogeneity, and publication bias was evaluated by Egger test. The overall OR (95% CI) for AA and GA genotypes versus GG genotype for TNF-alpha-238 was 1.15 (0.92-1.44), which in European and Asian populations were 1.18 (0.92-1.51) and 1.13 (0.62-2.04), respectively. This first meta-analysis of data from the current and published studies did not detect any association between the polymorphism of TNF 238 G/A and risk for T2D.

Joint genetic susceptibility to type 1 diabetes and autoimmune thyroiditis: from epidemiology to mechanisms

Type 1 diabetes (T1D) and autoimmune thyroid diseases (AITD) frequently occur together within families and in the same individual. The co-occurrence of T1D and AITD in the same patient is one of the variants of the autoimmune polyglandular syndrome type 3 [APS3 variant (APS3v)]. Epidemiological data point to a strong genetic influence on the shared susceptibility to T1D and AITD. Recently, significant progress has been made in our understanding of the genetic association between T1D and AITD. At least three genes have been confirmed as major joint susceptibility genes for T1D and AITD: human leukocyte antigen class II, cytotoxic T-lymphocyte antigen 4 (CTLA-4), and protein tyrosine phosphatase non-receptor type 22. Moreover, the first whole genome linkage study has been recently completed, and additional genes will soon be identified. Not unexpectedly, all the joint genes for T1D and AITD identified so far are involved in immune regulation, specifically in the presentation of antigenic peptides to T cells. One of the lessons learned from the analysis of the joint susceptibility genes for T1D and AITD is that subset analysis is a key to dissecting the etiology of complex diseases. One of the best demonstrations of the power of subset analysis is the CTLA-4 gene in T1D. Although CTLA-4 showed very weak association with T1D, when analyzed in the subset of patients with both T1D and AITD, the genetic effect of CTLA-4 was significantly stronger. Gene-gene and genetic-epigenetic interactions most likely play a role in the shared genetic susceptibility to T1D and AITD. Dissecting these mechanisms will lead to a better understanding of the etiology of T1D and AITD, as well as autoimmunity in general.