Association of PTPN22 1858C/T polymorphism with vitiligo susceptibility in Gujarat population

Whole Exome Sequencing Reveals Clustering of Variants of Known Vitiligo Genes in Multiplex Consanguineous Pakistani Families

Vitiligo is an autoimmune complex pigmentation disease characterized by non-pigmented patches on the surface of the skin that affect approximately 0.5-2% population worldwide. The exact etiology is still unknown; however, vitiligo is hypothesized to be a multifactorial and genetically heterogeneous condition. Therefore, the current study is designed to investigate the anthropometric presentation and genetic spectrum of vitiligo in fifteen consanguineous Pakistani families. The clinical evaluation of participating individuals revealed varying degrees of disease severity, with 23 years as the average age of disease onset. The majority of the affected individuals had non-segmental vitiligo (NSV). Whole exome sequencing analysis revealed clustering of rare variants of known vitiligo-associated genes. For instance, in the affected individuals of family VF-12, we identified three novel rare variants of PTPN22 (c.1108C>A), NRROS (c.197C>T) and HERC2 (c.10969G>A) genes. All three variants replaced evolutionarily conserved amino acid residues in encoded proteins, which are predicted to impact the ionic interactions in the secondary structure. Although various in silico algorithms predicted low effect sizes for these variants individually, the clustering of them in affected individuals increases the polygenic burden of risk alleles. To our knowledge, this is the first study that highlights the complex etiology of vitiligo and genetic heterogeneity in multiplex consanguineous Pakistani families.

Genetic Polymorphism of PTPN22 in Autoimmune Diseases: A Comprehensive Review

It is known that the etiology and clinical outcomes of autoimmune diseases are associated with a combination of genetic and environmental factors. In the case of the genetic factor, the SNPs of the PTPN22 gene have shown strong associations with several diseases. The recent exploding numbers of genetic studies have made it possible to find these associations rapidly, and a variety of autoimmune diseases were found to be associated with PTPN22 polymorphisms. Proteins encoded by PTPN22 play a key role in the adaptative and immune systems by regulating both T and B cells. Gene variants, particularly SNPs, have been shown to significantly disrupt several immune functions. In this review, we summarize the mechanism of how PTPN22 and its genetic variants are involved in the pathophysiology of autoimmune diseases. In addition, we sum up the findings of studies reporting the genetic association of PTPN22 with different types of diseases, including type 1 diabetes mellitus, systemic lupus erythematosus, juvenile idiopathic arthritis, and several other diseases. By understanding these findings comprehensively, we can explain the complex etiology of autoimmunity and help to determine the criteria of disease diagnosis and prognosis, as well as medication developments.

Patho-immunological mechanisms of vitiligo: the role of the innate and adaptive immunities and environmental stress factors

Epidermal melanocyte loss in vitiligo, triggered by stresses ranging from trauma to emotional stress, chemical exposure or metabolite imbalance, to the unknown, can stimulate oxidative stress in pigment cells, which secrete damage-associated molecular patterns that then initiate innate immune responses. Antigen presentation to melanocytes leads to stimulation of autoreactive T-cell responses, with further targeting of pigment cells. Studies show a pathogenic basis for cellular stress, innate immune responses and adaptive immunity in vitiligo. Improved understanding of the aetiological mechanisms in vitiligo has already resulted in successful use of the Jak inhibitors in vitiligo. In this review, we outline the current understanding of the pathological mechanisms in vitiligo and locate loci to which therapeutic attack might be directed.

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.

A Concise Review on the Role of Endoplasmic Reticulum Stress in the Development of Autoimmunity in Vitiligo Pathogenesis

Vitiligo is characterized by circumscribed depigmented macules in the skin resulting due to the autoimmune destruction of melanocytes from the epidermis. Both humoral as well as cell-mediated autoimmune responses are involved in melanocyte destruction. Several studies including ours have established that oxidative stress is involved in vitiligo onset, while autoimmunity contributes to the disease progression. However, the underlying mechanism involved in programing the onset and progression of the disease remains a conundrum. Based on several direct and indirect evidences, we suggested that endoplasmic reticulum (ER) stress might act as a connecting link between oxidative stress and autoimmunity in vitiligo pathogenesis. Oxidative stress disrupts cellular redox potential that extends to the ER causing the accumulation of misfolded proteins, which activates the unfolded protein response (UPR). The primary aim of UPR is to resolve the stress and restore cellular homeostasis for cell survival. Growing evidences suggest a vital role of UPR in immune regulation. Moreover, defective UPR has been implicated in the development of autoimmunity in several autoimmune disorders. ER stress-activated UPR plays an essential role in the regulation and maintenance of innate as well as adaptive immunity, and a defective UPR may result in systemic/tissue level/organ-specific autoimmunity. This review emphasizes on understanding the role of ER stress-induced UPR in the development of systemic and tissue level autoimmunity in vitiligo pathogenesis and its therapeutics.

Association of Functional Polymorphism in Protein Tyrosine Phosphatase Nonreceptor 22 (PTPN22) Gene with Vitiligo

The protein tyrosine phosphatase nonreceptor 22 (PTPN22) is associated with susceptibility to autoimmune diseases. The functional polymorphism in PTPN22 at 1857 is a strong risk factor for vitiligo susceptibility in Europeans; however, controversy exits in other populations. Present study was aimed to determine whether the PTPN22 C1857T polymorphism confers susceptibility to vitiligo in Saudi Arabians. Genomic DNA was extracted and amplified using tetra primer amplification-refractory mutation system polymerase chain reaction (ARMS-PCR) method. The frequencies of allele T and genotype CT of PTPN22 C1858T polymorphism were significantly higher, whereas those of allele C and genotype CC were lower in patients as compared with controls (P < 0.0001). The genotype TT was absent in both the patients and controls. It is concluded that PTPN22 C1858T polymorphism is strongly associated with vitiligo susceptibility. However, additional studies are warranted using large number of samples from different ethnicities and geographical areas.

The role of human leukocyte antigen DRB1-DQB1 haplotypes in the susceptibility to acquired idiopathic thrombotic thrombocytopenic purpura

The acquired form of idiopathic thrombotic thrombocytopenic purpura (TTP) is an autoimmune disease, in which the underlying ADAMTS13-deficiency is caused by inhibitory autoantibodies against the protease. Human leukocyte antigens (HLA), responsible for antigen presentation, play an important role in the development of antibodies. The loci coding HLA DR and DQ molecules are inherited in linkage as haplotypes. The c.1858C>T polymorphism of the PTPN22 gene, which codes a protein tyrosine phosphatase important in lymphocyte activation, predisposes to a number of autoimmune diseases. We determined the HLA-DRB1-DQB1 haplotypes and the PTPN22 c.1858C>T genotypes in 75 patients with acquired idiopathic TTP and in healthy controls, in order to assess the role of these genetic factors and their interactions in the susceptibility to TTP. We found that the carrier frequencies of the DRB1^∗11-DQB1^∗03 and DRB1^∗15-DQB1^∗06 haplotypes were higher, while those of the DRB1^∗07-DQB1^∗02 and DRB1^∗13-DQB1^∗06 haplotypes were lower in TTP patients. There was no difference in the overall frequency of the PTPN22 c.1858T allele between TTP patients and controls. In conclusion, we identified four HLA-DRB1-DQB1 haplotypes associated with an increased (DRB1^∗11-DQB1^∗03 and DRB1^∗15-DQB1^∗06) or a decreased (DRB1^∗07-DQB1^∗02 and DRB1^∗13-DQB1^∗06) susceptibility to acquired idiopathic TTP.

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.

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.

Lack of Association between PTPN22 Gene +1858 C>T Polymorphism and Susceptibility to Generalized Vitiligo in a Turkish Population

BACKGROUND

Vitiligo is an autoimmune polygenic disorder characterized by loss of pigmentation due to melanocyte destruction. The PTPN22 gene +1858 C>T single nucleotide polymorphism (rs2476601) has been shown to be associated with various autoimmune disorders.

OBJECTIVE

The aim of this study was to investigate whether the PTPN22 gene +1858 C>T single nucleotide polymorphism is associated with susceptibility to generalized vitiligo in a Turkish population.

METHODS

One hundred and seven patients with generalized vitiligo, and one hundred and twelve gender-, age-, and ethnic-matched controls were enrolled in the study. Genotyping was done by polymerase chain reaction-restriction fragment length polymorphism.

RESULTS

The PTPN22 +1858 C>T genotype and allele frequencies of the generalized vitiligo patients did not differ significantly from those of healthy controls.

CONCLUSION

We found no association between the PTPN22 +1858 C>T gene polymorphism and vitiligo susceptibility in Turkish generalized-vitiligo patients.

Association of glutathione S-transferase M1/T1 polymorphisms with susceptibility to vitiligo

BACKGROUND

Some studies suggested that Glutathione S-transferases M1/T1(GSTM1/T1) null polymorphisms may be associated with the risk of vitiligo.

AIMS

The purpose of this study is to further evaluate the association between GSTM1/T1 null polymorphisms and the susceptibility to vitiligo.

METHODS

We carried out a retrieval of studies in the databases. Odds ratios (OR) and 95% confidence intervals (95% CIs) were used to assess the strength of this association. We analyzed the data using Stata 11.0.

RESULTS

Six case-control studies including 1358 cases and 1673 controls were included in this meta-analysis. Our overall results showed the GSTM1 or GSTT1 null polymorphism was associated with vitiligo (GSTM1:OR=1.59, 95% CI: 1.21-2.08, P=0.001; GSTT1: OR=1.30, 95% CI: 1.12-1.51, P=0.001). In the subgroup analysis, the GSTM1 null polymorphism might be a genetic risk factor to vitiligo in East Asian (OR=1.71, 95% CI: 1.12-2.63, P=0.014) but not in the Mediterranean, however individuals with the GSTT1 null polymorphism in the Mediterranean (OR=1.76, 95% CI: 1.15-2.71, P=0.010) but not in East Asian have a greater predisposition to vitiligo. In addition there was also a significant trend toward an association with the combination of the GSTM1 null and GSTT1 null in either East Asians or Mediterraneans.

CONCLUSION

The GSTM1/T1 null polymorphisms may be associated with vitiligo. More studies are needed to confirm this conclusion.

Tumor necrosis factor B (TNFB) genetic variants and its increased expression are associated with vitiligo susceptibility

Genetic polymorphisms in TNFB are involved in the regulation of its expression and are found to be associated with various autoimmune diseases. The aim of the present study was to determine whether TNFB +252A/G (rs909253) and exon 3 C/A (rs1041981) polymorphisms are associated with vitiligo susceptibility, and expression of TNFB and ICAM1 affects the disease onset and progression. We have earlier reported the role of TNFA in autoimmune pathogenesis of vitiligo, and we now show the involvement of TNFB in vitiligo pathogenesis. The two polymorphisms investigated in the TNFB were in strong linkage disequilibrium and significantly associated with vitiligo. TNFB and ICAM1 transcripts were significantly increased in patients compared to controls. Active vitiligo patients showed significant increase in TNFB transcripts compared to stable vitiligo. The genotype-phenotype analysis revealed that TNFB expression levels were higher in patients with GG and AA genotypes as compared to controls. Patients with the early age of onset and female patients showed higher TNFB and ICAM1 expression. Overall, our findings suggest that the increased TNFB transcript levels in vitiligo patients could result, at least in part, from variations at the genetic level which in turn leads to increased ICAM1 expression. For the first time, we show that TNFB +252A/G and exon 3 C/A polymorphisms are associated with vitiligo susceptibility and influence the TNFB and ICAM1 expression. Moreover, the study also emphasizes influence of TNFB and ICAM1 on the disease progression, onset and gender bias for developing vitiligo.

Involvement of interferon-gamma genetic variants and intercellular adhesion molecule-1 in onset and progression of generalized vitiligo

Interferon-gamma (IFN-γ) is a paracrine inhibitor of melanocytes and genetic variability due to intron 1 polymorphisms in IFNG has been reported to be associated with increased risk for several autoimmune diseases. The aim of present study was to determine whether intron 1 +874A/T (rs2430561) and CA microsatellite (rs3138557) polymorphisms in IFNG are associated with generalized vitiligo (GV) susceptibility and expression of IFNG and intercellular adhesion molecule-1 (ICAM1) affects the disease onset and progression. Here we report that IFNG CA microsatellite but not +874A/T may be a genetic risk factor for GV; however, +874T allele plays a crucial role in increased expression of IFNG mRNA and protein levels which could affect the onset and progression of the disease. Active GV patients showed increased IFNG levels compared to stable GV patients. The genotype-phenotype analysis revealed that IFNG expression levels were higher in patients with +874 TT genotypes and 12 CA repeats. Patients with the early age of onset showed higher IFNG expression and female GV patients showed higher IFNG and ICAM1 expression implicating gender biasness and involvement of IFN-γ in early onset of the disease. Moreover, the increased IFN-γ levels in patients lead to increased ICAM1 expression, which could be a probable link between cytokines and T-cell involvement in pathogenesis of GV.

Association of NLRP1 genetic variants and mRNA overexpression with generalized vitiligo and disease activity in a Gujarat population

BACKGROUND

It has been suggested that NLRP1 is involved in susceptibility to a wide range of autoimmune diseases including generalized vitiligo (GV). Genetic polymorphisms in the gene encoding NLRP1 (previously known as NALP1) have previously been shown to be associated with GV and there is speculation about their involvement in the regulation of NLRP1 expression.

OBJECTIVES

To explore NLRP1 polymorphisms and investigate their association with NLRP1 mRNA expression and disease activity in patients with GV.

METHODS

Polymerase chain reaction (PCR)-restriction fragment length polymorphism and TaqMan single nucleotide polymorphism (SNP) genotyping techniques were used to genotype NLRP1 A/G (rs2670660), T/C (rs6502867) and A/T (rs12150220) polymorphisms in 537 patients with GV and 645 controls in Gujarat. NLRP1 mRNA levels were measured in the whole blood of 122 patients with GV and 175 controls using real-time PCR.

RESULTS

The NLRP1 rs2670660 and rs6502867 polymorphisms were found to be in significant association with GV, minor alleles of these SNPs being prevalent in active cases of GV. The rs12150220 polymorphism was found have a marginal association with GV. The frequency of susceptible haplotype 'GCT' was significantly higher in patients with GV and increased the risk of vitiligo twofold. A significant increase in NLRP1 mRNA expression was observed in patients with GV and patients with active GV. NLRP1 mRNA expression was increased in patients with GV with the susceptible GG (rs2670660) and CC (rs6502867) genotypes. Patients with the susceptible GG (rs2670660) and CC (rs6502867) genotypes had early age of onset of GV. Moreover, patients in the age at onset group of 1-20 years showed increased expression of NLRP1 mRNA compared with the older age groups. Female patients showed a significant increase in NLRP1 mRNA and early age at onset of GV compared with male patients.

CONCLUSIONS

Our results suggest that NLRP1 rs2670660 and rs6502867 polymorphisms may be genetic risk factors for susceptibility to and progression of GV. The upregulation of NLRP1 mRNA in patients with susceptible genotypes advocates the crucial role of NLRP1 in GV.

Correlation of increased MYG1 expression and its promoter polymorphism with disease progression and higher susceptibility in vitiligo patients

BACKGROUND

MYG1 (Melanocyte proliferating gene 1 or C12orf10) -119C/G promoter and Arg4Gln structural polymorphisms have a functional impact on its regulation. The promoter polymorphism was shown to be associated with vitiligo in Caucasian population.

OBJECTIVE

The present study explores MYG1 polymorphisms and correlates them with MYG1 mRNA expression, disease onset and progression in vitiligo patients.

METHODS

Polymerase chain reaction-restriction fragment length polymorphism (PCR-RFLP) technique was used for genotyping of MYG1 -119C/G promoter (rs1465073) and 11-12AA/GC structural polymorphisms (rs1534284-rs1534283; Arg4Gln) in 846 vitiligo patients and 726 age-matched unaffected controls. MYG1 mRNA levels were assessed in whole blood of 166 patients and 175 controls by Real-time PCR.

RESULTS

The MYG1 -119C/G promoter polymorphism was found to be in significant association with vitiligo being 'G' allele prevalent in patients. However, 11-12AA/GC structural polymorphism was prevalently monogenic in patients and controls with only MYG1 GC (4Arg) allele being present. Significant increase in MYG1 mRNA expression was observed in vitiligo patients compared to controls. The MYG1 mRNA expression was increased in patients with active and generalized vitiligo as compared to stable and localized vitiligo. MYG1 mRNA expression was increased in patients with susceptible -119 GG genotype compared to controls. Also, patients with susceptible -119 GG genotype had early age of onset of vitiligo. Moreover, patients with age groups 1-20 years and 21-40 years showed increased expression of MYG1 mRNA compared to those of controls. Female patients showed significant increase in MYG1 mRNA and early age of onset of vitiligo compared to male patients.

CONCLUSION

The present study suggests that MYG1 -119C/G promoter polymorphism may be a genetic risk factor for susceptibility and progression of vitiligo. The up-regulation of MYG1 transcript in patients with susceptible -119GG genotype advocates the crucial role of MYG1 in autoimmune pathogenesis of vitiligo.

Vitiligo: interplay between oxidative stress and immune system

Vitiligo is a multifactorial polygenic disorder with a complex pathogenesis, linked with both genetic and non-genetic factors. The precise modus operandi for vitiligo pathogenesis has remained elusive. Theories regarding loss of melanocytes are based on autoimmune, cytotoxic, oxidant-antioxidant and neural mechanisms. Reactive oxygen species (ROS) in excess have been documented in active vitiligo skin. Numerous proteins in addition to tyrosinase are affected. It is possible that oxidative stress is one among the main principal causes of vitiligo. However, there also exists ample evidence for altered immunological processes in vitiligo, particularly in chronic and progressive conditions. Both innate and adaptive arms of the immune system appear to be involved as a primary event or as a secondary promotive consequence. There is speculation on the interplay, if any, between ROS and the immune system in the pathogenesis of vitiligo. The article focuses on the scientific evidences linking oxidative stress and immune system to vitiligo pathogenesis giving credence to a convergent terminal pathway of oxidative stress-autoimmunity-mediated melanocyte loss.

Increased Tumor Necrosis Factor (TNF)-α and its promoter polymorphisms correlate with disease progression and higher susceptibility towards vitiligo

Tumor Necrosis Factor (TNF)-α, is a paracrine inhibitor of melanocytes, which plays a critical role in the pathogenesis of several autoimmune diseases including vitiligo, as abnormal immune responses have frequently been observed in vitiligo patients. Moreover, vitiligo patients show higher lesion levels of TNF-α. Genetic polymorphisms in the promoter region of TNF-α are involved in the regulation of its expression. The present study explores TNF-α promoter polymorphisms and correlates them with TNF-α transcript and protein levels in vitiligo patients and controls of Gujarat along with its effect on disease onset and progression. PCR-RFLP technique was used for genotyping of these polymorphisms in 977 vitiligo patients and 990 controls. TNF-α transcript and protein levels were measured by Real time PCR and ELISA respectively. The genotype and allele frequencies for the investigated polymorphisms were significantly associated with vitiligo patients. The study revealed significant increase in TNF-α transcript and protein levels in vitiligo patients compared to controls. In particular, haplotypes: AATCC, AACCT, AGTCT, GATCT, GATCC and AGCCT were found to increase the TNF-α levels in vitiligo patients. Analysis of TNF-α levels based on the gender and disease progression suggests that female patients and patients with active vitiligo had higher levels of TNF-α. Also, the TNF-α levels were high in patients with generalized vitiligo as compared to localized vitiligo. Age of onset analysis of the disease suggests that the haplotypes: AACAT, AACCT, AATCC and AATCT had a profound effect in the early onset of the disease. Moreover, the analysis suggests that female patients had an early onset of vitiligo. Overall, our results suggest that TNF-α promoter polymorphisms may be genetic risk factors for susceptibility and progression of the disease. The up-regulation of TNF-α transcript and protein levels in individuals with susceptible haplotypes advocates the crucial role of TNF-α in autoimmune pathogenesis of vitiligo.

Interleukin-4 genetic variants correlate with its transcript and protein levels in patients with vitiligo

BACKGROUND

Vitiligo is an acquired pigmentary disorder resulting from loss of melanocytes. Interleukin (IL)-4 has been shown to stimulate B-cell proliferation, to regulate immunoglobulin class switching (IgG1 and IgE) and to promote T-cell development. Polymorphisms in the IL4 gene are known to increase its expression, thereby implicating its role in vitiligo susceptibility.

OBJECTIVES

To explore intron 3 VNTR (IVS3) and -590 C/T (rs2243250) promoter polymorphisms in the IL4 gene and to correlate them with the IL4 transcript, serum IL-4 and IgE levels to achieve genotype-phenotype correlation in patients with vitiligo from Gujarat. A replication study was done in a North Indian population.

METHODS

The case-control study was performed to investigate these polymorphisms in 505 patients and 744 controls in Gujarat, and 596 patients and 397 controls in North India by polymerase chain reaction (PCR) and PCR-restriction fragment length polymorphism analysis. IL4 transcript levels were monitored by real-time PCR. Serum IL-4 and IgE levels were measured by enzyme-linked immunosorbent assay and electrochemiluminescence immunoassay, respectively.

RESULTS

The genotype frequencies differed significantly between patients with generalized vitiligo and controls for both the polymorphisms in both populations. Allele frequencies significantly differed between patients with generalized vitiligo and controls for both the polymorphisms in the population from Gujarat. Interestingly, genotype and allele frequencies for -590 C/T single nucleotide polymorphism were significantly different between patients with localized vitiligo and controls in both the populations. The study revealed significantly increased IL4 mRNA, serum IL-4 and IgE levels in patients from Gujarat. Age of onset analysis of disease in patients suggested that the TTR2R2, TTR1R2 and CTR2R2 haplotypes had a profound effect in the early onset of the disease.

CONCLUSIONS

Our results suggest that these polymorphisms of the IL4 gene may be genetic risk factors for susceptibility towards vitiligo and the upregulation of the IL4 transcript, protein and IgE levels in individuals with susceptible haplotypes reveal the crucial role of IL-4 in the pathogenesis of 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.

Why is PTPN22 a good candidate susceptibility gene for autoimmune disease?

The PTPN22 locus is one of the strongest risk factors outside of the major histocompatability complex that associates with autoimmune diseases. PTPN22 encodes lymphoid protein tyrosine phosphatase (Lyp) which is expressed exclusively in immune cells. A single base change in the coding region of this gene resulting in an arginine to tryptophan amino acid substitution within a polyproline binding motif associates with type 1 diabetes, rheumatoid arthritis, systemic lupus erythematosis, Hashimotos thyroiditis, Graves disease, Addison's disease, Myasthenia Gravis, vitiligo, systemic sclerosis juvenile idiopathic arthritis and psoriatic arthritis. Here, we review the current understanding of the PTPN22 locus from a genetic, geographical, biochemical and functional perspective.

Shared genetic relationships underlying generalized vitiligo and autoimmune thyroid disease

BACKGROUND

Generalized vitiligo is an autoimmune disease of skin pigmentation that is associated with increased prevalence of other autoimmune diseases, particularly autoimmune thyroid disease (AITD; principally Hashimoto's disease and Graves' disease), both in vitiligo patients and their close relatives, suggesting a heritable predisposition involving, in part, shared susceptibility genes.

SUMMARY

This review summarizes current knowledge of vitiligo epidemiology and genetics, highlighting recent findings from genome-wide approaches to disease gene identification, emphasizing susceptibility loci shared with other autoimmune diseases, particularly AITD, as well as some important differences.

CONCLUSIONS

Inherited susceptibility to generalized vitiligo involves a number of specific genes, many of which are shared with other autoimmune diseases that are epidemiologically associated with vitiligo, including AITD, confirming a longstanding hypothesis about the genetic basis of these disorders. These genes provide potential therapeutic targets for novel approaches to treatment as well as for approaches to presymptomatic diagnosis and disease prevention in individuals with inherited susceptibility to this group of autoimmune diseases.

Lack of genetic association of promoter and structural variants of mannan-binding lectin (MBL2) gene with susceptibility to generalized vitiligo

BACKGROUND

Vitiligo is a common depigmenting disorder resulting from the loss of functional melanocytes in the skin. It is hypothesized to be of autoimmune origin. Mannan-binding lectin (MBL) plays an important role in innate immunity. It helps in the clearance of apoptotic cells and in complement activation. Genetic variability due to structural and promoter polymorphisms in the MBL2 gene has been reported to be associated with increased risk for several autoimmune diseases including vitiligo.

OBJECTIVES

The aim of this study was to explore whether MBL2 structural and promoter polymorphisms are associated with generalized vitiligo in Gujarat where the prevalence of vitiligo is alarmingly high.

MATERIALS AND METHODS

We undertook a case-control study to investigate the association of MBL2 gene exon 1 polymorphisms - codon 52, codon 54 and codon 57 as well as promoter -221 polymorphism in 92 patients with generalized vitiligo and 94 unaffected age-matched controls by polymerase chain reaction-heteroduplex analysis.

RESULTS

The genotype and allele frequencies of MBL2 structural and promoter polymorphisms did not differ significantly between the control and patient population (P-values: P < 0.019 for codon 52, P < 0.373 for codon 54, P < 0.855 for codon 57 and P < 0.889 for -221 promoter polymorphisms) after Bonferroni's correction for multiple testing, which suggests that there is no association of MBL2 structural and promoter polymorphisms with generalized vitiligo.

CONCLUSIONS

Our results suggest that the well-documented structural and promoter polymorphisms of the MBL2 gene may not be associated with generalized vitiligo in the Gujarat population.