Comprehensive association analysis of candidate genes for generalized vitiligo supports XBP1, FOXP3, and TSLP. J Invest Dermatol. 2011;131:371-381. [PMID: 21085187 DOI: 10.1038/jid.2010.337]

Regulatory T cells in vitiligo: Implications for pathogenesis and therapeutics

Vitiligo is a hypomelanotic autoimmune skin disease arising from a breakdown in immunological self-tolerance, which leads to aberrant immune responses against melanocytes. Regulatory T cells (Tregs) are crucial to the development of self-tolerance and so are major foci in the study of autoimmune pathogenesis of vitiligo. This review will summarise recent findings concerning the role of Tregs in the pathogenesis of vitiligo. In addition, as antigen-specific Tregs are a potential route for the reinstatement of immune tolerance, new strategies that expand or induce de novo generation of Tregs and which are currently being investigated as therapies for other autoimmune diseases, will be discussed. These approaches will highlight the opportunities for Treg cell-based therapeutics in vitiligo.

Accounting for eXentricities: analysis of the X chromosome in GWAS reveals X-linked genes implicated in autoimmune diseases

Many complex human diseases are highly sexually dimorphic, suggesting a potential contribution of the X chromosome to disease risk. However, the X chromosome has been neglected or incorrectly analyzed in most genome-wide association studies (GWAS). We present tailored analytical methods and software that facilitate X-wide association studies (XWAS), which we further applied to reanalyze data from 16 GWAS of different autoimmune and related diseases (AID). We associated several X-linked genes with disease risk, among which (1) ARHGEF6 is associated with Crohn's disease and replicated in a study of ulcerative colitis, another inflammatory bowel disease (IBD). Indeed, ARHGEF6 interacts with a gastric bacterium that has been implicated in IBD. (2) CENPI is associated with three different AID, which is compelling in light of known associations with AID of autosomal genes encoding centromere proteins, as well as established autosomal evidence of pleiotropy between autoimmune diseases. (3) We replicated a previous association of FOXP3, a transcription factor that regulates T-cell development and function, with vitiligo; and (4) we discovered that C1GALT1C1 exhibits sex-specific effect on disease risk in both IBDs. These and other X-linked genes that we associated with AID tend to be highly expressed in tissues related to immune response, participate in major immune pathways, and display differential gene expression between males and females. Combined, the results demonstrate the importance of the X chromosome in autoimmunity, reveal the potential of extensive XWAS, even based on existing data, and provide the tools and incentive to properly include the X chromosome in future studies.

Dissecting the role of the FOXP3 gene in the joint genetic susceptibility to autoimmune thyroiditis and diabetes: a genetic and functional analysis

We have previously shown that a (TC)n microsatellite in intron 5 of the Forkhead Box Protein 3 (FOXP3) gene was associated with a variant of the autoimmune polyglandular syndrome type 3 (APS3v), that is defined as the co-occurrence of type 1 diabetes (T1D) and autoimmune thyroiditis (AITD). Allele 10, containing 25 repeats of the microsatellite (long repeats), is preferentially transmitted to offspring with APS3v, while allele 2, containing 14 repeats of the microsatellite (short repeats), is protective. We hypothesized that the long repeats of the intron 5 microsatellite decrease FOXP3 splicing and function, thereby reducing regulatory T cell activity and promoting the development of APS3v. We cloned genomic DNA from two males hemizygous for the long and short repeats of the microsatellite on their X-chromosomes and transfected them into human embryonic kidney 293 (HEK 293) cells to perform direct splicing analysis. We identified a novel splice variant of FOXP3 lacking exon 6, and showed that it is expressed in human thymus and lymph node. However, the length of the repeats in the microsatellite did not significantly influence the expression of this FOXP3 splice variant in vitro. Interestingly, this splice variant was expressed in human regulatory T cells, suggesting that it may play a role in their function. In conclusion, we identified a novel splice variant FOXP3Δ6. The role of its expression in regulatory T cells in the development of autoimmunity remains to be determined.

Vitiligo--part 1

Vitiligo is a chronic stigmatizing disease, already known for millennia, which mainly affects melanocytes from epidermis basal layer, leading to the development of hypochromic and achromic patches. Its estimated prevalence is 0.5% worldwide. The involvement of genetic factors controlling susceptibility to vitiligo has been studied over the last decades, and results of previous studies present vitiligo as a complex, multifactorial and polygenic disease. In this context, a few genes, including DDR1, XBP1 and NLRP1 have been consistently and functionally associated with the disease. Notwithstanding, environmental factors that precipitate or maintain the disease are yet to be described. The pathogenesis of vitiligo has not been totally clarified until now and many theories have been proposed. Of these, the autoimmune hypothesis is now the most cited and studied among experts. Dysfunction in metabolic pathways, which could lead to production of toxic metabolites causing damage to melanocytes, has also been investigated. Melanocytes adhesion deficit in patients with vitiligo is mainly speculated by the appearance of Köebner phenomenon, recently, new genes and proteins involved in this deficit have been found.

Current aspects of vitiligo genetics

Vitiligo is a common acquired depigmentation disorder of the skin manifested by the presence of white macules. The disease occurs at a frequency of approximately 1–4% of the world population. Currently, the most popular theory of vitiligo development is a multifactorial hypothesis according to which genetic conditions predispose vitiligo macules to occur as a result of specific environmental factors. According to the genetic hypothesis, vitiligo inheritance is multigenic. Genetic studies conducted so far concern patients with non-segmental vitiligo. There are three basic techniques of genetic studies: candidate gene association studies, genomewide linkage studies and genome-wide association studies (GWAS). The GWAS are the “gold standard” for detecting susceptibility genes. Up to now, approximately 36 convincing non-segmental vitiligo susceptibility loci have been identified. Approximately 90% of them encode immunoregulatory proteins, while approximately 10% encode melanocyte proteins. The existence of various associations between vitiligo and other autoimmune diseases may provide new knowledge on the causes of many disorders. Examples include the inverse relationship between vitiligo and melanoma and association of vitiligo with other autoimmune diseases. The main goal of all researches is to find new, optimal therapeutic strategies for vitiligo and other autoimmune diseases.

Analysis of oxidative stress status, catalase and catechol-O-methyltransferase polymorphisms in Egyptian vitiligo patients

Vitiligo is the most common depigmentation disorder of the skin. Oxidative stress is implicated as one of the probable events involved in vitiligo pathogenesis possibly contributing to melanocyte destruction. Evidence indicates that certain genes including those involved in oxidative stress and melanin synthesis are crucial for development of vitiligo. This study evaluates the oxidative stress status, the role of catalase (CAT) and catechol-O-Methyltransferase (COMT) gene polymorphisms in the etiology of generalized vitiligo in Egyptians. Total antioxidant capacity (TAC) and malondialdehyde (MDA) levels as well as CAT exon 9 T/C and COMT 158 G/A polymorphisms were determined in 89 patients and 90 age and sex-matched controls. Our results showed significantly lower TAC along with higher MDA levels in vitiligo patients compared with controls. Meanwhile, genotype and allele distributions of CAT and COMT polymorphisms in cases were not significantly different from those of controls. Moreover, we found no association between both polymorphisms and vitiligo susceptibility. In conclusion, the enhanced oxidative stress with the lack of association between CAT and COMT polymorphisms and susceptibility to vitiligo in our patients suggest that mutations in other genes related to the oxidative pathway might contribute to the etiology of generalized vitiligo in Egyptian population.

Modern vitiligo genetics sheds new light on an ancient disease

Vitiligo is a complex disorder in which autoimmune destruction of melanocytes results in white patches of skin and overlying hair. Over the past several years, extensive genetic studies have outlined a biological framework of vitiligo pathobiology that underscores its relationship to other autoimmune diseases. This biological framework offers insight into both vitiligo pathogenesis and perhaps avenues towards more effective approaches to treatment and even disease prevention.

The angiotensin-converting enzyme gene insertion/deletion polymorphism in Indian patients with vitiligo: a case-control study and meta-analysis

BACKGROUND

Vitiligo is a common, acquired, idiopathic depigmenting skin disorder. Although the exact pathogenesis remains unknown, genetic susceptibility and autoimmune responses play a role in vitiligo development. Previous studies have suggested that the D allele of the insertion/deletion (I/D) polymorphism of the angiotensin-converting enzyme (ACE) gene is associated with vitiligo in Indians and Koreans. Furthermore, significantly higher serum ACE levels have been demonstrated in patients with some autoimmune and autoinflammatory disorders.

OBJECTIVES

The objectives were to investigate any association between the ACE I/D polymorphism and vitiligo susceptibility in an Indian population, and to compare serum ACE levels in patients with vitiligo and healthy subjects.

METHODS

The ACE I/D genotypes of 79 patients with vitiligo and 100 normal individuals were determined by polymerase chain reaction amplification. A meta-analysis was done to compare the distribution of the ACE I/D alleles and genotypes in the current and three previous studies. Serum ACE levels were evaluated by enzyme-linked immunosorbent assay.

RESULTS

A significant increase in the frequency of the ACE I/D D allele was evident in patients with vitiligo in both the case-control study [P=0·005; odds ratio (OR) 1·87; 95% confidence intervals (CI) 1·22-2·85] and the meta-analysis (P=0·044; OR 1·44; 95% CI 1·01-2·06). Serum ACE levels were significantly increased in patients with vitiligo compared with healthy subjects (P<0·0001).

CONCLUSIONS

In agreement with earlier reports, the ACE I/D D allele is associated with vitiligo susceptibility in the Indian population. The significantly elevated serum ACE levels in our cohort of patients with vitiligo concur with those previously found in patients with some other autoimmune diseases.

Concise review of recent studies in vitiligo

Vitiligo is an acquired pigmentry disorder of the skin and mucous membranes which manifests as white macules and patches due to selective loss of melanocytes. Etiological hypotheses of vitiligo include genetic, immunological, neurohormonal, cytotoxic, biochemical, oxidative stress and newer theories of melanocytorrhagy and decreased melanocytes survival. There are several types of vitiligo which are usually diagnosed clinically and by using a Wood's lamp; also vitiligo may be associated with autoimmune diseases, audiological and ophthalmological findings or it can be a part of polyendocrinopathy syndromes. Several interventions are available for the treatment for vitiligo to stop disease progression and/or to attain repigmentation or even depigmentation. In this article, we will present an overall view of current standing of vitiligo research work especially in the etiological factors most notably the genetic components, also, types and associations and various and newer treatment modalities.

Latent class analysis of a series of 717 patients with vitiligo allows the identification of two clinical subtypes

Non-segmental vitiligo (NSV) is an enigmatic disease with various clinical courses. To empirically identify underlying subtypes of NSV, we performed latent class analysis (LCA) of 717 consecutive patients with NSV seen between 2006 and 2012 and were analyzed. Median age was 32 yrs (14-45), median age at NSV onset was 18 yrs (8-32), and median NSV duration 5 yrs (0.75-78.5). A two-class model showed the best fit. Of the 717 patients, 280 (39%) belonged to LC1 and 437 (61%) to LC2. LC1 patients had high probabilities for early disease onset (<12 yrs), halo nevi, family history of premature hair greying, Koebner phenomenon, previous episodes of repigmentation, and family history of vitiligo. By contrast, LC2 patients were characterized by a late disease onset (after or at the age of 12 yrs, median age of 30 yrs) and acrofacial localization without any lesions on trunk or limbs. These two LCA classes (LC1, 'prepubertal onset'; LC2, 'post-pubertal onset') may help refining results from genome-wide association studies (GWAS) and allow a more accurate genotype-phenotype correlation and help defining more directed treatment protocols.

The pathogenesis of vitiligo

BACKGROUND

Vitiligo is a commonly encountered pigmentary disorder. Numerous studies and investigations from all over the world have attempted to determine the mechanisms behind this disease; however, the pathogenesis of vitiligo remains elusive.

OBJECTIVE

n this comprehensive review article, we present the findings behind the five overarching theories of what causes this disfiguring and psychologically debilitating disease.

METHOD

We begin our discussion with the role of genetic predisposition and move onward to the neural theory first proposed in the 1950s. Next we discuss the autoimmune hypothesis, followed by the reactive oxygen species model, and conclude by describing the findings of the more recent melanocytorrhagy hypothesis.

CONCLUSION

Although the exact pathogenesis of vitiligo is uncertain, each of these theories likely plays a role. Understanding each theory would pave the way for therapeutic advances for this disease.

Association of FOXP3 (rs3761548) promoter polymorphism with nondermatomal vitiligo: A study from India

BACKGROUND

The rs3761548 polymorphism (-3279 C>A) of FOXP3 gene is associated with several autoimmune disorders.

OBJECTIVE

We sought to determine whether rs3761548 polymorphism is associated with nondermatomal vitiligo in Indian subjects.

METHODS

Genomic DNA was isolated from blood samples of 303 patients and 305 control subjects and genotyping was done by allele-specific primers. Data analysis was carried out for the entire cohort and separately for male and female participants as FOXP3 is an X-linked marker. Statistics were performed using software.

RESULTS

The genotype frequencies differed significantly from patients to control subjects (P = .002). Further analysis demonstrated female participants with CC genotype were protected (CC vs CA+AA; odds ratio 0.38, 95% confidence interval 0.238-0.615) and those with CA genotype were at higher risk to develop vitiligo (CA vs CC+AA; odds ratio 2.634, 95% confidence interval 1.604-4.325). However, no such statistical difference was observed in male participants.

LIMITATIONS

Our study is, to our knowledge, the first report from India with respect to vitiligo and rs3761548; however, we lack adequate literature assistance.

CONCLUSIONS

The rs3761548 of FOXP3 gene in our population may be associated with susceptibility to vitiligo because of altered expression. CC genotype appears to be protective and CA genotype seems to impart nearly 3-fold risk to develop vitiligo in women and girls.

Pre- vs. post-pubertal onset of vitiligo: multivariate analysis indicates atopic diathesis association in pre-pubertal onset vitiligo

BACKGROUND

Limited epidemiological data exist that compare clinical features of pre- and post-pubertal nonsegmental vitiligo.

OBJECTIVES

To compare factors associated with pre- and post-pubertal onset vitiligo.

PATIENTS AND METHODS

A prospective observational study was conducted of patients with vitiligo attending the clinic between 1 January 2006 and 1 July 2011. The Vitiligo European Task Force questionnaire was completed for each patient and thyroid function and antithyroid antibodies were screened. Other forms of vitiligo (segmental, focal, mucosal, not classifiable) were excluded.

RESULTS

A total of 679 patients were included; 422 had post-pubertal and 257 pre-pubertal onset of vitiligo. Vitiligo universalis was seen only in post-pubertal onset. In univariate analysis, there was no significant statistical difference for sex, Koebner phenomenon or disease activity between both groups; thyroid disease or presence of thyroid antibodies was more frequent in post-pubertal onset [odds ratio (OR) 0·31, P < 0·003] whereas atopic dermatitis was more often associated with or preceding pre-pubertal onset (OR 2·42, P = 0·006). In multivariate analysis, halo naevi, family history of vitiligo, premature hair greying, atopic dermatitis and previous episode of spontaneous repigmentation were independently associated with pre-pubertal onset. In contrast, stress as onset factor, personal history of thyroid disease and acrofacial type were associated with post-pubertal onset.

CONCLUSIONS

Pre-pubertal onset vitiligo is strongly associated with personal and family history of atopy, suggesting that the predisposing immune background in vitiligo is not limited to autoimmunity, as also noted in alopecia areata. This study also suggests reconsidering the epidemiological data on sex ratio in vitiligo.

Possible contribution of GSTP1 and other xenobiotic metabolizing genes to vitiligo susceptibility

Vitiligo is an acquired pigmentary disorder with several proposed pathogenesis mechanisms and complex multifactorial genetic predisposition. We analyzed 65 polymorphisms in genes potentially relevant to vitiligo pathogenesis mechanism to reveal novel and confirm reported genetic risk factors in general Russian population. We found that polymorphism rs1138272 (TC + CC) in GSTP1 gene encoding enzyme involved in xenobiotic metabolism is associated with vitiligo (Bonferroni adjusted P value 0.0015) with extraordinary high odds ratio 13.03, and haplotype analysis confirmed association of GSTP1 gene with vitiligo risk. Moreover, analysis of variations in several genes encoding enzymes of xenobiotic metabolism showed that higher risk of vitiligo is associated with higher number of risk alleles. This finding reveals possible contribution of genetic background to observed imbalance of oxidative stress control in vitiligo through cumulative effect of multiple genetic variations in xenobiotic metabolizing genes, supporting the concept of multigenic nature of vitiligo with multiple low-risk alleles cumulatively contributing to vitiligo risk.

Potential role of neurogenic inflammatory factors in the pathogenesis of vitiligo

BACKGROUND

Vitiligo is a highly complex multifactorial condition of the skin that has an unclear mechanism of pathogenesis.

OBJECTIVE

This review summarizes the role of various neurogenic inflammatory factors significantly upregulated in vitiligo.

METHODS

A literature review was conducted of all pertinent data regarding neuropeptides that are altered in vitiligo and their possible role in the destruction of melanocytes.

RESULTS

The close associations between the skin, immune system, and nervous system, along with specific changes demonstrated in vitiligo patients, support a pathogenic mechanism of vitiligo that involves neuroimmunologic factors, the release of which can be governed by mental stress.

CONCLUSION

Neuropeptides and nerve growth factors are critical regulators of emotional response and may precipitate the onset and development of vitiligo in certain predisposed individuals. More studies are required to investigate whether a direct link exists between genetics, mental stress, and neurogenic factors in vitiligo.

Genetic association of FOXP3 gene polymorphisms with allograft rejection in renal transplant patients

AIM

FOXP3 gene is known to be important for regulatory T cell development and function, and is associated with the rejection of human kidney transplants. The present study was therefore conducted to determine the effect of FOXP3 polymorphisms on allograft rejection in renal transplant recipients.

METHODS

A total of 166 adult patients were categorized into either a Rejection group (65 patients) or a No rejection group (101 patients). Rs3761547, rs3761548 and rs2232365 variant alleles in the FOXP3 gene were genotyped using a TaqMan probe technique, and their relationships with rejection were investigated.

RESULTS

There was no significant difference in the genotype frequencies of rs3761547 and rs2232365 variants between patients with and without rejection history (P > 0.05). Binary logistic regression analysis showed that the rs3761548 AA genotype carriers were associated with about a fourfold greater risk for rejection compared with CC genotype (5 years post-transplant: odds ratio 3.95, 95% confidence interval 1.27-12.29, P = 0.018). Kaplan-Meier analysis revealed a lower mean time to the first rejection in rs3761548 AA compared with CC genotype patients (Log rank = 4.303, P = 0.038). Multivariate Cox regression analysis indicated that rs3761548 AA genotype carriers have up to about a twofold (hazard ratio 2.37, 95% confidence interval 1.17-4.80, P = 0.017) higher risk for rejection than CC carriers.

CONCLUSION

Our study suggests an association between FOXP3 rs3761548 polymorphisms and allograft rejection in renal transplantation. This association should be further proven in large prospective studies because of the small sample size and confounding factors in this retrospective study.

Systemic analyses of immunophenotypes of peripheral T cells in non-segmental vitiligo: implication of defective natural killer T cells

Although it is widely believed that non-segmental vitiligo (NSV) results from the autoimmune destruction of melanocytes, a clear understanding of defects in immune tolerance, which mediate this uncontrolled self-reactivity, is still lacking. In the present study, we systemically evaluated circulating regulatory T (Treg) cells, including CD4(+) CD25(+) FoxP3(+) Treg cells and invariant natural killer T (iNKT) cells, as well as naïve and memory CD4(+) and CD8(+) T cells and their cytokine production, in a cohort of 43 progressive NSV patients with race-, gender-, and age-matched healthy controls. We found that the general immunophenotypes of CD4(+) and CD8(+) T cells and the percentage of CD4(+) CD25(+) FoxP3(+) Tregs were comparable between NSV and healthy controls. However, percentages of peripheral iNKT cells were significantly decreased in NSV patients compared to that in healthy controls. Our data confirm the previous notion that the percentage of peripheral CD4(+) CD25(+) FoxP3(+) Tregs remains unaltered in NSV and suggests the involvement of defective iNKT cells in the pathogenesis of NSV.

Genome-wide association analyses identify 13 new susceptibility loci for generalized vitiligo

In previous linkage and genome-wide association studies we identified 17 susceptibility loci for generalized vitiligo. By a second genome-wide association study, meta-analysis, and independent replication study, we have now identified 13 additional vitiligo-associated loci, including OCA2-HERC2, a region of 16q24.3 containing MC1R, a region of chromosome 11q21 near TYR, several immunoregulatory loci including IFIH1, CD80, CLNK, BACH2, SLA, CASP7, CD44, IKZF4, SH2B3, and a region of 22q13.2 where the causal gene remains uncertain. Functional pathway analysis shows that most vitiligo susceptibility loci encode immunoregulatory proteins or melanocyte components that likely mediate immune targeting and genetic relationships among vitiligo, malignant melanoma, and normal variation of eye, skin, and hair color.

Male gender bias in autism and pediatric autoimmunity

Male bias in both autism and pediatric autoimmune disease is thought to involve hormonal perturbations in pregnancy or early childhood in the context of genetic control. These early molecular events, at a time of rapid development, are intimately linked to concurrent development in the brain and immune system. It is suggested here that these early regulatory events may overlap between autism and autoimmunity in determining male sex bias and may provide evidence of an etiological link among autism, immune dysregulation, and autoimmune disease.

Six decades of vitiligo genetics: genome-wide studies provide insights into autoimmune pathogenesis

Generalized vitiligo (GV) is a complex disease in which patchy depigmentation results from autoimmune loss of melanocytes from affected regions. Genetic analyses of GV span six decades, with the goal of understanding biological mechanisms and elucidating pathways that underlie the disease. The earliest studies attempted to describe the mode of inheritance and genetic epidemiology. Early genetic association studies of biological candidate genes resulted in some successes, principally HLA and PTPN22, but in hindsight many such reports now seem to be false-positives. Later, genome-wide linkage studies of multiplex GV families identified NLRP1 and XBP1, which appear to be valid GV susceptibility genes that control key aspects of immune regulation. Recently, the application of genome-wide association studies to analysis of GV has produced a rich yield of validated GV susceptibility genes that encode components of biological pathways reaching from immune cells to the melanocyte. These genes and pathways provide insights into underlying pathogenetic mechanisms and possible triggers of GV, establish relationships to other autoimmune diseases, and may provide clues to potential new approaches to GV treatment and perhaps even prevention. These results thus validate the hopes and efforts of the early investigators who first attempted to comprehend the genetic basis of vitiligo.

Neuro-Immuno-Endocrine Processes in Vitiligo Pathogenesis

Vitiligo is a cutaneous disorder of depigmentation, clinically characterized by well-demarcated, white macules of varying size and distribution. It can affect up to 2% of the population, especially younger ages. In spite of recent findings implicating genetic, immune and oxidative stress factors, the exact pathogenesis of vitiligo remains obscure. Here, we briefly discuss the prevailing theories, and offer new suggestions that could explain in part the damage of melanocyte in the vitiliginous lesions. Our emerging hypothesis is that neuropeptides released from peripheral nerve endings could synergize with new cytokines to adversely affect melanocyte function and viability. These may include corticotropin-releasing hormone (CRH) and neurotensin (NT), as well as interleukin 33 (IL-33) and thymic stromal lymphopoietin (TSLP). Such interactions could serve the basis for further research, possibly leading to new treatments.

Generalized vitiligo and associated autoimmune diseases in Japanese patients and their families

BACKGROUND

Generalized vitiligo is an acquired disorder in which depigmented macules result from the autoimmune loss of melanocytes from the involved regions of skin. Generalized vitiligo is frequently associated with other autoimmune diseases, particularly autoimmune thyroid diseases (Hashimoto's thyroiditis and Graves' disease), rheumatoid arthritis, adult-onset type 1 diabetes mellitus, psoriasis, pernicious anemia, systemic lupus erythematosus, and Addison's disease.

METHODS

One hundred and thirty-three Japanese patients with generalized vitiligo were enrolled in this study to investigate the occurrence of autoimmune diseases in Japanese patients with generalized vitiligo and their families.

RESULTS

Twenty-seven of the patients with generalized vitiligo (20.3%) had autoimmune diseases, particularly autoimmune thyroid disease (sixteen patients, 12%) and alopecia areata (seven patients, 5.3%). Thirty-five patients (26.3%) had a family history of generalized vitiligo and/or other autoimmune diseases. Familial generalized vitiligo was present in fifteen (11.3%), including four families with members affected by autoimmune disorders. Twenty (15.0%) had one or more family members with only autoimmune disorders.

CONCLUSIONS

Among Japanese vitiligo patients, there is a subgroup with strong evidence of genetically determined susceptibility to not only vitiligo, but also to autoimmune thyroid disease and other autoimmune disorders.

Nonsegmental vitiligo and autoimmune mechanism

Nonsegmental vitiligo is a depigmented skin disorder showing acquired, progressive, and depigmented lesions of the skin, mucosa, and hair. It is believed to be caused mainly by the autoimmune loss of melanocytes from the involved areas. It is frequently associated with other autoimmune diseases, particularly autoimmune thyroid diseases including Hashimoto's thyroiditis and Graves' disease, rheumatoid arthritis, type 1 diabetes, psoriasis, pernicious anemia, systemic lupus erythematosus, Addison's disease, and alopecia areata. This indicates the presence of genetically determined susceptibility to not only vitiligo but also to other autoimmune disorders. Here, we summarize current understanding of autoimmune pathogenesis in non-segmental vitiligo.

Recent progress in the genetics of generalized vitiligo

Vitiligo is an acquired disease characterized principally by patchy depigmentation of skin and overlying hair. Generalized vitiligo (GV), the predominant form of the disorder, results from autoimmune loss of melanocytes from affected regions. GV is a "complex trait", inherited in a non-Mendelian polygenic, multifactorial manner. GV is epidemiologically associated with other autoimmune diseases, both in GV patients and in their close relatives, suggesting that shared genes underlie susceptibility to this group of diseases. Early candidate gene association studies yielded a few successes, such as PTPN22, but most such reports now appear to be false-positives. Subsequent genomewide linkage studies identified NLRP1 and XBP1, apparent true GV susceptibility genes involved in immune regulation, and recent genome-wide association studies (GWAS) of GV in Caucasian and Chinese populations have yielded a large number of additional validated GV susceptibility genes. Together, these genes highlight biological systems and pathways that reach from the immune cells to the melanocyte, and provide insights into both disease pathogenesis and potential new targets for both treatment and even prevention of GV and other autoimmune diseases in genetically susceptible individuals.

Genome-wide analysis identifies a quantitative trait locus in the MHC class II region associated with generalized vitiligo age of onset

Generalized vitiligo is a common autoimmune disease in which acquired patchy depigmentation of skin, hair, and mucous membranes results from loss of melanocytes from involved areas. Previous genetic analyses have focused on vitiligo susceptibility, and have identified a number of genes involved in disease risk. Age of onset of generalized vitiligo also involves a substantial genetic component, but has not previously been studied systematically. In this study, we report a genome-wide association study of vitiligo age of onset in 1,339 generalized vitiligo patients, with replication in an independent cohort of 677 cases. We identified a quantitative trait locus for vitiligo age of onset in the major histocompatibility complex (MHC) class II region, located near c6orf10-BTNL2 (rs7758128; P=8.14 × 10(-11)), a region that is also associated with generalized vitiligo susceptibility. In contrast, there was no association of vitiligo age of onset with any other MHC or non-MHC loci that are associated with vitiligo susceptibility. These findings highlight the differing roles played by genes involved in vitiligo susceptibility versus vitiligo age of onset, and illustrate that genome-wide analyses can be used to identify genes involved in quantitative aspects of disease natural history, as well as disease susceptibility per se.

The genetics of generalized vitiligo: autoimmune pathways and an inverse relationship with malignant melanoma

Generalized vitiligo (GV) is the most common pigmentation disease, in which white spots of skin and overlying hair result from loss of melanocytes from the involved regions. GV is a complex disease involving both genetic predisposition and unknown environmental triggers. Whereas various pathogenetic mechanisms have been suggested, most evidence supports an autoimmune basis for this disease. Recently, three different genome-wide association studies of GV have been reported, identifying a total of 17 confirmed GV susceptibility loci. Almost all of these genes encode immunoregulatory proteins, together highlighting pathways by which melanocytes might be recognized and killed. Moreover, the biological interaction between two of these GV susceptibility genes, HLA-A and TYR (encoding tyrosinase), points to an apparent inverse relationship between susceptibility to GV versus malignant melanoma, suggesting that GV may result, in part, from dysregulation of normal processes of immune surveillance against melanoma.