Tumor necrosis factor-α -308G/A polymorphism is associated with active vitiligo vulgaris in a northeastern Mexican population

Identification of TNF-α as Major Susceptible Risk Locus for Vitiligo: A Systematic Review and Meta-Analysis Study in the Asian Population

INTRODUCTION

Vitiligo is a common depigmentation disorder characterized by defined white patches on the skin and affecting around 0.5% to 2% of the general population. Genetic association studies have identified several pre-disposing genes and single nucleotide polymorphisms (SNPs) for vitiligo pathogenesis; nonetheless, the reports are often conflicting and rarely conclusive. This comprehensive meta-analysis study was designed to evaluate the effect of the risk variants on vitiligo aetiology and covariate stratified vitiligo risk in the Asian population, considering all the studies published so far.

METHODS

We followed a systematic and comprehensive search to identify the relevant vitiligo-related candidate gene association studies in PubMed using specific keywords. After data extraction, we calculated, for the variants involved, the study-level unadjusted odds ratio, standard errors, and 95% confidence intervals by using logistic regression with additive, dominant effect, and recessive models using R software package (R, 3.4.2) "metafor." Subgroup analysis was performed using logistic regression (generalized linear model; "glm") of disease status on subgroup-specific genotype counts. For a better understanding of the likely biological function of vitiligo-associated variant obtained through the meta-analysis, in silico functional analyses, through standard publicly available web tools, were also conducted.

RESULTS

Thirty-one vitiligo-associated case-control studies on eleven SNPs were analysed in our study. In the fixed-effect meta-analysis, one variant upstream of TNF-α gene: rs1800629 was found to be associated with vitiligo risk in the additive (p = 4.26E-06), dominant (p = 1.65E-7), and recessive (p = 0.000453) models. After Benjamini-Hochberg false discovery rate (FDR) correction, rs1800629/TNF-α was found to be significant at 5% FDR in the dominant (padj = 1.82E-6) and recessive models (padj = 0.0049). In silico characterization revealed the prioritized variant to be regulatory in nature and thus having potential to contribute towards vitiligo pathogenesis.

CONCLUSION

Our study constitutes the first comprehensive meta-analysis of candidate gene-based association studies reported in the whole of the Asian population, followed by an in silico analysis of the vitiligo-associated variant. According to the findings of our study, TNF-α single nucleotide variant rs1800629G>A has a risk association, potentially contributing to vitiligo pathogenesis in the Asian population.

The role of cytokines and vitamin D in vitiligo pathogenesis

Vitiligo is a pigment-related disease with a global prevalence of 0.2% to 1.8% associated with considerable burden on quality of life. The treatment is still a challenge because of relapses and/or incomplete re-pigmentation. Although the exact cause is still unclear, its pathogenesis seems to be justifiable with the autoimmune theory, supported by the results of clinical research. In this narrative review, we aimed to summarize the evidence related to cytokines and vitiligo development. This review is consisted of English articles published in PubMed and Google Scholar concerning levels of inflammatory mediators, especially interleukins, in vitiligo patients over the last 20 years. References of relevant articles were also considered for review. Crucial role of dysregulated levels of interleukins and their synergistic function to each other, in the onset or progression of the disease is evident. The theory of autoimmune vitiligo is reinforced by the results of the studies in the literature, due to the association of pathogenesis with increased secretion of pro-inflammatory mediators and reduction of anti-inflammatory mediators. Decreased vitamin D levels may have a considerable role in vitiligo development by affecting Th1- and Th17-related immune responses. Cytokines play an important role in the pathogenesis or progression of the disease. Moreover, we believe that decreased vitamin D level has a considerable role in vitiligo development by affecting Th1- and Th17-related immune responses.

Association between the CTLA4 +49A/G (rs231775) and CT60 (rs3087243) gene variants with vitiligo: Study on a Mexican population

Background

Vitiligo is characterized by an autoimmune response targeting melanocytes, thus resulting in skin depigmentation. There are several genetic components involved in the development of vitiligo, of which various gene polymorphisms are currently considered as risk factors. For example, the CTLA4 (T-lymphocyte antigen 4) +49A/G (rs231775) and CT60 (rs3087243) gene variants have been associated with a predisposition for autoimmune diseases in different populations; however, their involvement in the development of vitiligo remains controversial.

Objective

We evaluated the association between vitiligo and the CTLA4 +49A/G (rs231775) and CT60 (rs3087243) gene variants in a Mexican population.

Methods

A total of 116 vitiligo patients and 117 control subjects from northeast Mexico were included in the study and analyzed through PCR-RFLP to determine whether there is an association between vitiligo and CTLA4 +49A/G (rs231775) and CT60 (rs3087243) gene variants.

Results

No statistical difference was observed for both gene polymorphisms between vitiligo patients and controls (p > 0.05). Otherwise, vitiligo activity, family history of vitiligo, personal history of autoimmune diseases, or sex did not show any difference (p > 0.05).

Conclusion

As suggested by the analysis of a northeastern Mexican population, the CTLA4 +49A/G (rs231775) and CT60 (rs3087243) gene variants do not constitute a risk factor in the development of vitiligo.

Meta-analysis for association of TNFA-308(G > A) SNP with vitiligo susceptibility

Vitiligo is an autoimmune progressive skin depigmenting disease. Tumor necrosis factor alpha (TNF-α) is a pro-inflammatory cytokine and plays a crucial role in vitiligo development. Since there are conflicting results and consensus is lacking for the association of the TNFA gene -308 G > A polymorphism with vitiligo susceptibility; we performed a meta-analysis of all the available studies to investigate the association of TNFA -308 G > A polymorphism with vitiligo risk. 11 studies involving 2199 vitiligo patients and 3083 controls were included in the meta-analysis. The meta-analysis revealed an increased vitiligo risk with "AA", "GA" and "AA" + "GA" genotypes and 'A' allele in the overall (p = 0.006, p = 0.003, p = 0.001 & p = 0.003) and Egyptian populations (p = 0.001, p < 0.00001, p < 0.00001 & p = 0.002). Moreover, we found association for "GA" and "AA" + "GA" genotypes in Asian population (p = 0.0009 & p = 0.005) and for 'A' allele in Asian and middle eastern populations (p = 0.04 & p = 0.0002). Interestingly the disease activity based analysis revealed significant association for "GA", "AA" + "GA" genotypes and 'A' allele with active vitiligo patients in the North American population (p = 0.02). Moreover, we found significant association for "GA", "AA" + "GA" genotypes and 'A' allele with localized vitiligo in overall (p = 0.02, p = 0.02 & p = 0.04) and Asian (p = 0.004, p = 0.003 & p = 0.01) populations. Overall, our meta-analysis suggests the involvement of susceptible 'A' allele with: i) vitiligo susceptibility in overall population and specifically with Asian, Middle Eastern and Egyptian populations; ii) vitiligo disease activity in North American population and iii) localized vitiligo in overall population and specifically in Asian population.

The Immunogenetics of Vitiligo: An Approach Toward Revealing the Secret of Depigmentation

Vitiligo is a hypomelanotic skin disease and considered to be of autoimmune origin due to breaching of immunological self-tolerance, resulting in inappropriate immune responses against melanocytes. The development of vitiligo includes a strong heritable component. Different strategies ranging from linkage studies to genome-wide association studies are used to explore the genetic factors responsible for the disease. Several vitiligo loci containing the respective genes have been identified which contribute to vitiligo and genetic variants for some of the genes are still unknown. These genes include mainly the proteins that play a role in immune regulation and a few other genes important for apoptosis and regulation of melanocyte functions. Despite the available data on genetic variants and risk alleles which influence the biological processes, only few immunological pathways have been found responsible for all ranges of severity and clinical manifestations of vitiligo. However, studies have concluded that vitiligo is of autoimmune origin and manifests due to complex interactions in immune components and their inappropriate response toward melanocytes. The genes involved in the immune regulation and processing the melanocytes antigen and its presentation can serve as effective immune-therapeutics that can target specific immunological pathways involved in vitiligo. This chapter highlights those immune-regulatory genes involved in vitiligo susceptibility and loci identified to date and their implications in vitiligo pathogenesis.

Novel immunological and genetic factors associated with vitiligo: A review

Vitiligo is a skin disorder characterized by depigmentation of the skin due to a lack of melanin. This condition affects men and woman of all ages and its incidence is not restricted by ethnicity or region. Vitiligo is a multifactorial disease, in which melanocytes, which serve important functions in skin pigmentation and immune processes, are impaired. There is sufficient evidence that immunological and genetic factors are primarily responsible for the destruction and dysfunction of melanocytes. Therefore, genetic DNA sequence variants that participate in skin homeostasis, pigmentation and immune response regulation, as well as altered expression patterns, may contribute to the risk of developing vitiligo. The current review presented an overview of the mechanism of pigmentation and of currently known factors involved in depigmentation, as well as the classification, epidemiology, associated comorbidities, risk factors, immunopathogenesis and several genetic and molecular changes associated with vitiligo.

Association Analysis of Tumor Necrosis Factor Alpha Promoter Polymorphisms and Vitiligo Susceptibility in South Indian Tamils

Tumor necrosis factor alpha (TNF-α) has been associated with the pathogenesis of several autoimmune diseases. Also, various studies in different ethnics showed an association between TNF-α gene polymorphisms and susceptibility to vitiligo. The paucity of genetic data led us to undertake this study to evaluate the association of five TNF-α SNPs (rs1799964, rs1800630, rs1799724, rs1800629, and rs361525) with the development of vitiligo in South Indian Tamils. A total of 264 vitiligo patients and 264 healthy controls were recruited and TNF-α genotyping was performed using amplification-refractory mutation system polymerase chain reaction and TaqMan allele discrimination assay. Circulatory TNF-α levels were measured by enzyme-linked immunosorbent assay. We observed that a single polymorphic allele A in the promoter region -308 (rs1800629) conferred significant risk to develop vitiligo (p = 0.0002, OR = 1.70, 95% CI = 1.28-2.25), whereas the other polymorphisms failed to contribute to disease risk (p > 0.05). From the constructed haplotypes, TCCAG was found to be a significant risk factor for vitiligo (p < 0.05). Also, a strong linkage disequilibrium was observed between the following SNPs: (1) rs1799964 and rs1800629 (2) rs1800630 and rs1799724 (D' = 0.90). Analysis of the influence of genotype on phenotypes revealed that the A allele of rs361525 was a risk factor for vitiligo in females (p = 0.04, OR = 0.45, 95% CI = 0.21-0.95), whilst the rs1800629 allele conferred protection against early disease onset (p < 0.05). A statistically significant difference in plasma TNF-α levels was found between cases and controls (p < 0.05). The TNF-α -308A allele and TCCAG haplotype were identified as genetic risk factors for vitiligo susceptibility in South Indian Tamils.

TNF-α G-308A genetic variants, serum CRP-hs concentration and DNA damage in obese women

Obesity is associated with inflammation, which can disturb genome stability. Tumor necrosis factor (TNF-α) polymorphism was found to affect TNF-α protein production and inflammation. Therefore, the present study illustrates the relationship between TNF-α polymorphism, the degree of inflammation assessed by serum high sensitivity C-reactive protein concentration (CRP-hs) and basal DNA damage in patients with obesity (BMI 30–34.9 kg/m²) and control subjects with proper body mass (BMI < 25 kg/m²). A total of 115 participants (75 obese premenopausal women; and 40 age-, and gender-matched controls) were included. Biochemical parameters (serum concentrations of total-cholesterol, HDL-cholesterol, LDL- cholesterol, triglycerides, glucose, apolipoprotein AI, CRP-hs) and endogenous DNA damage (determined by comet assay) were measured. TNF-α G-308A polymorphism (rs1800629) was analyzed by PCR-RFLP (PCR-restriction fragments length polymorphism). An effect of TNF-α genotype on serum CRP-hs concentration was noted (p = 0.031). In general, carriers of the rare A allele of the TNF-α G-308A polymorphism had significantly lower endogenous DNA damage and serum CRP-hs concentrations than GG homozygotes, however, the protective effect of the A allele was especially visible in non-obese women. Serum CRP-hs concentrations and levels of DNA damage (% DNA in tail) were significantly higher in obese than in controls (p = 0.001 and p < 0.0001, respectively). The adjusted multiple linear regression analyses revealed a significant, independent impact of obesity on DNA damage (p = 0.00000) and no effect of other covariates i.e. age, TNF-α genotype and serum CRP-hs concentration. Our study showed that obesity has a significant impact on the levels of endogenous DNA damage. Obesity abolished the protective effect of A allele of the TNF-α G-308A polymorphism on DNA damage and on inflammation development observed in non-obese A allele carriers.

Assessment of biochemical parameters and characterization of TNFα -308G/A and PTPN22 +1858C/T gene polymorphisms in the risk of obesity in adolescents

Obesity is currently considered an inflammatory condition associated with autoimmune diseases, suggesting a common origin. Among other factors, candidate genes may explain the development of this disease. Polymorphisms in the tumor necrosis factor α (TNFα) and lymphoid protein tyrosine phosphatase (PTPN22) genes lead to an increased risk to development of immune and inflammatory diseases. The aim of the present study was to analyze the biochemical parameters and the effect of the TNFα -308G/A and PTPN22 +1858C/T polymorphisms in the susceptibility of adolescents to obesity. A group of 253 adolescent subjects were recruited and classified as obese, overweight or normal weight according to their nutritional status. Anthropometric measurements, clinical and biochemical data were analyzed. DNA was extracted from peripheral blood samples by the phenol-chloroform method, and TNFα -308G/A and PTPN22 1858C/T polymorphisms were determined by polymerase chain reaction-restriction fragment length polymorphism assays. Clinical, genetic and biochemical parameters were analyzed to determine the existence of a possible association with the development of obesity. Statistically significant differences in body mass index, insulin, triglyceride levels and homeostatic model assessment for insulin resistance (HOMA-IR) index were observed among the three groups analyzed (P≤0.05). The studied polymorphisms did not confer a risk for developing obesity in the analyzed population (P>0.05); however, significantly low levels of insulin and decreased rates of HOMA-IR were observed in the 1858 CT genotype carriers of the PTPN22 gene. In conclusion, no association between the TNFα -308G/A and PTPN22 +1858C/T polymorphisms and the risk to development of obesity in the adolescent population analyzed was observed. However, the 1858 CT genotype of the PTPN22 gene was associated with variations of certain biochemical parameters analyzed.

The association between tumor necrosis factor-α-308 G/A polymorphism and risk for vitiligo: a meta-analysis

BACKGROUND

The contribution of tumor necrosis factor-α (TNF-α)-308 G/A gene polymorphism (rs1800629) to risk for vitiligo is subject to controversy.

OBJECTIVES

The fundamental purpose of the present meta-analysis was to investigate large-scale evidence to determine the overall association between TNF-α-308 G/A polymorphism and susceptibility to vitiligo.

METHODS

A literature search of the PubMed, EMBASE, Web of Science, and China National Knowledge Infrastructure (CNKI) databases was conducted to identify all studies referring to an association between TNF-α-308 G/A polymorphism and vitiligo published to June 1, 2014. The principal outcome measure for evaluating the strength of the association was the crude odds ratio (OR) along with the corresponding 95% confidence interval (CI). Data were extracted, and statistical analyses were implemented using stata Version 12.0.

RESULTS

Data for a total of 1505 vitiligo cases and 2253 controls from five case-control studies concentrating on the association between TNF-α-308 G/A polymorphism and vitiligo were included in this meta-analysis. Combined analysis revealed there to be no association between this polymorphism and susceptibility to vitiligo in five genetic models under random-effects models. A subgroup analysis by clinical type also demonstrated the absence of any association between TNF-α-308 G/A polymorphism and generalized vitiligo. However, a significant association was detected in the miscellaneous subgroup under the dominant model (fixed-effects model: OR 5.69, 95% CI 4.70-6.88; P = 0.000) and overdominant model (random-effects model: OR 5.24, 95% CI 2.26-12.17; P = 0.000).

CONCLUSIONS

This meta-analysis indicates that TNF-α-308 G/A polymorphism is not a genetic risk factor for vitiligo.

Evaluation of the Efficacy of Topical Tetracycline in Enhancing the Effect of Narrow Band UVB against Vitiligo: A Double-Blind, Randomized, Placebo-Controlled Clinical Trial

Background. Vitiligo is a pigmentary disorder characterized by depigmented macules due to absence of melanocytes. Increased levels of tumor necrosis factor alpha and interleukin-1 in the epidermis of lesions may play a role in keratinocyte apoptosis and less production of melanogenic cytokines. Tetracyclines reduce production of tumor necrosis factor alpha and interleukin-1. Objective. To evaluate the effect of topical tetracycline on vitiligo patients on phototherapy. Methods. Thirty cases of generalized stable vitiligo were chosen randomly and pigmentation of two assigned lesions on right and left sides (same size and location) was determined by vitiligo area severity index, and medication and placebo were randomly assigned to be applied twice daily on either right or left side, respectively. Images were taken of the lesions at the end of the 4th, 8th, and 12th weeks and pigmentations were compared to baseline using aforementioned index. The patients also took narrow band ultraviolet B two to three times a week. Results. Mean pigmentation, based on vitiligo area severity index, changed significantly from 90.1667 to 86.6667 (P = 0.026) and on placebo side from 89.6667 to 86.8333 (P = 0.026). There was no significant difference between medication and placebo sides in terms of pigmentation (P = 0.566). Conclusions. No significant difference in improving repigmentation between medication and placebo sides was seen.

The role of tumor necrosis factor-α in the pathogenesis of vitiligo

Vitiligo is an acquired immune disorder of the skin characterized by the presence of white depigmented macules. Its immunopathogenesis is not completely understood, but inflammatory alterations in the skin microenvironment, and particularly increased expression of the cytokine tumor necrosis factor-α (TNFα), are thought to be essential regulators of melanocyte dysfunction and death. In this article we review the evidence that implicates TNFα in the pathogenesis of vitiligo, including studies on serum and tissue levels of TNFα, TNFα gene polymorphisms, in vitro studies, and therapeutic trials using TNFα inhibitors. TNFα emerges as a complex mediator with apparently conflicting roles in vitiligo.