Genetic Susceptibility to Vitiligo: GWAS Approaches for Identifying Vitiligo Susceptibility Genes and Loci

Association of rs2111485 and rs1990760 Polymorphisms of Interferon Induced with Helicase C Domain 1 Gene with Hepatitis C Virus Clearance in Chinese Han Population

Interferon induced with helicase C domain 1 (IFIH1), which is a type of cytological RNA helicase protein and an important initiator of innate immune response to RNA virus infection, may play an important role in hepatitis C virus (HCV) infection outcomes. This study was conducted to investigate the association of IFIH1 gene polymorphisms with HCV clearance in Chinese Han population. A total of 1,527 subjects positive for anti-HCV and 357 chronic hepatitis C (CHC) patients were enrolled in this study. Two single nucleotide polymorphisms in IFIH1 gene (rs2111485 and rs1990760) were selected and genotyped by TaqMan real-time polymerase chain reaction. Haplotypes analysis was further performed by HaploView software and PHASE software. Our results demonstrated that the mutant alleles of rs2111485 (dominant model: odds ratio [OR] = 1.41, 95% confidence interval [CI] = 1.11-1.79) and rs1990760 (dominant model: OR = 1.63, 95% CI = 1.30-2.06) decreased the possibility of spontaneous HCV clearance, but it had no association with HCV clearance induced by interferon-alfa (IFN-α). And, CHC risk increased with the increasing number of unfavorable alleles (p_trend < 0.001). In addition, haplotype analysis also showed that the A-C protective haplotype (rs2111485-rs1997060) promoted spontaneous HCV clearance (p < 0.001). Variants of rs2111485 and rs1990760 at IFIH1 may be associated with spontaneous HCV clearance in Chinese Han population, but have no effect on HCV clearance induced by IFN-α.

VitiVar: A locus specific database of vitiligo associated genes and variations

Vitiligo is the most common skin pigmentation disorder which affects around 1% of the population worldwide. The disease has complex pathogenesis and is of multifactorial etiology, that finally culminates in patchy depigmentation of skin. Genetic contribution to the disease is well studied, however the information about multiple associated genes and contributing variations are scattered across the literature. To address this complex disorder affecting the skin, we systematically cataloged the genes and variations by creating a Locus Specific Database for vitiligo called, “VitiVar”. This comprehensive resource houses manually curated 322 genes and 254 variations, from 202 articles indexed in PubMed. We applied an integrative approach to stratify genes and variations to facilitate dissection of vitiligo pathogenesis by layering it with expression status in specific constituent cell types of skin and in-house vitiligo expression data. Finally, we were able to demonstrate the utility of VitiVar by generating a vitiligo interactome using GeneMANIA and overlaying the vitiligo and cell type specific information. This interaction network yielded 20 new genes (apart from 322 VitiVar genes) of which we were able to prioritize IFI27 and IFI6 for further validation. This, thereby makes VitiVar a comprehensive integrative platform in unravelling disease biology by providing meaningful leads for functional interrogation. VitiVar is freely accessible to the research community for prioritizing and validating the candidate genes and variations (http://vitivar.igib.res.in/).

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We developed a Vitiligo centric web resource cataloguing the associated genes and variations

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Overlaid the information of cell type specificity and expression status in Vitiliginous skin

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Utilizing the network approach, we prioritized IFI6 & IFI27 which could be functionally interrogated in disease pathology

Evaluation of skin expression profiles of patients with vitiligo treated with narrow-band UVB therapy by targeted RNA-seq

BACKGROUND

Vitiligo is characterized by a lack of pigmentation in the skin. To date, there are no studies that analyze the changes in gene expression in the skin of vitiligo patients in response to narrow-band ultraviolet B (nb-UVB) phototherapy treatment.

OBJECTIVE

Explore the usefulness of new generation RNA sequencing in the identification of gene expression changes in the skin of vitiligo patients treated with nb-UVB phototherapy.

METHODS

Four skin biopsies (4mm in diameter) were collected from 45 Mexican vitiligo vulgaris patients, 2 specimens before and 2 after treatment with nb-UVB phototherapy, obtained from pigmented and non-pigmented tissue. RNA extracted from the biopsies was analyzed using the Illumina TruSeq Targeted RNA Expression protocol to study the expression of genes that participate in pathways of skin homeostasis. The 2 groups were compared using Student's t-test and the Mann-Whitney U-test.

RESULTS

The expression analysis identified differences in 12 genes included in this study after comparing the samples obtained before and after treatment: 5 genes involved in skin pigmentation, 2 genes involved in apoptosis, 2 genes involved in cell survival, 2 genes involved in oxidative stress responses and 1 gene involved in signal transduction mechanisms (p<0.05).

STUDY LIMITATIONS

The small size of skin biopsies limits the amount of RNA obtained, the number of genes to be analyzed and the use of conventional techniques such as RT-qPCR.

CONCLUSION

We demonstrated usefulness of new generation RNA sequencing in the identification of gene expression changes, in addition to identifying new targets in the study of vitiligo.

Therapeutic management of vitiligo

Affecting 0.5 % of the world's population, vitiligo is an acquired skin disorder that poses major challenges in terms of dermatological care. Characterized by patchy depigmentation, the disease is frequently associated with cosmetic disfigurement and considerable psychological distress. The primary pathophysiological causes for the loss of functional melanocytes are thought to include genetic predisposition, autoimmune mechanisms, and oxidative stress. The present article highlights treatment recommendations contained in the European guidelines as well as those provided by recent reviews on vitiligo. Current therapeutic options are based on three approaches: (1) Regulation of the autoimmune response using topical and systemic immunomodulatory agents (corticosteroids and calcineurin inhibitors); (2) decrease in oxidative stress in melanocytes by means of topical and systemic antioxidants; and (3) activation of melanocyte regeneration using phototherapy (UVB in particular) and transplantation of pigment cells. In addition, patients should be educated in techniques for cosmetic camouflage. Following successful repigmentation, application of calcineurin inhibitors is recommended to prevent recurrences. Combination therapies of the aforementioned approaches are generally considered to be more successful than monotherapies. Early initiation of treatment is associated with a more favorable prognosis. Using the above treatment options, it may be possible to halt disease progression, stabilize depigmented lesions, and achieve repigmentation. Only in exceptional cases should permanent depigmentation be considered as a possible option. New insights into the pathogenesis of vitiligo will likely give rise to novel therapeutic approaches.

Genetic polymorphisms of GZMB and vitiligo: A genetic association study based on Chinese Han population

Vitiligo is a skin disease that affects 1% of the population worldwide. Both environmental and genetic factors contribute to the risk of vitiligo. GZMB encodes the enzyme Granzyme B, which plays an important role in cytotoxic T cell-induced apoptosis, and it has been considered one of the candidate genes for vitiligo because of its connections with human immune system. Overall, 3,120 study subjects with Chinese Han ancestry were recruited, and 15 pre-selected SNPs of GZMB were genotyped. Genetic association analyses were performed to evaluate the genetic risk of these SNPs to vitiligo. Further bioinformatic analyses were conducted to examine the potential biological function of targeted SNPs. The SNP rs8192917, a non-synonymous coding SNP, was identified to be significantly associated with the disease status of vitiligo, with OR = 1.39 and P = 1.92 × 10-8. Differences in the association signal can be observed in the stratification analyses of multiple clinical variables. Our positive results provide additional supportive evidence that GZMB gene is an important locus for vitiligo in Han Chinese population.

Vitiligo: An Update on Pathophysiology and Treatment Options

The pathophysiology of vitiligo is becoming increasingly clarified. In non-segmental vitiligo, early factors include activation of innate immunity, inflammasome activation, oxidative stress, and loss of melanocyte adhesion. Nonetheless, the main mechanism leading to non-segmental vitiligo involves an immune-mediated destruction of melanocytes. Anti-melanocyte-specific cytotoxic T cells exert a central role in the final effector stage. Genetic research revealed a multi-genetic inheritance displaying an overlap with other autoimmune disorders. However, some melanocyte-specific genes were also affected. Segmental vitiligo carries a different pathogenesis with most evidence indicating a mosaic skin disorder. Current management includes topical corticosteroids and immunomodulators. Narrow-band ultraviolet B can be used in patients not responding to topical treatment or in patients with extensive disease. Pigment cell transplantation offers an alternative for the treatment of segmental vitiligo or stable non-segmental lesions. Recent findings have revealed new targets for treatment that could lead to more efficient therapies. Targeted immunotherapy may halt the active immune pathways, although combination therapy may still be required to induce satisfying repigmentation. A recently established core set of outcome measures, new measurement instruments, and biomarker research pave the way for future standardized clinical trials.

Vitiligo Pathogenesis and Emerging Treatments

The pathogenesis of vitiligo involves interplay between intrinsic and extrinsic melanocyte defects, innate immune inflammation, and T-cell-mediated melanocyte destruction. The goal of treatment is to not only halt disease progression but also promote repigmentation through melanocyte regeneration, proliferation, and migration. Treatment strategies that address all aspects of disease pathogenesis and repigmentation are likely to have greatest efficacy, a strategy that may require combination therapies. Current treatments generally involve nontargeted suppression of autoimmunity, whereas emerging treatments are likely to use a more targeted approach based on in-depth understanding of disease pathogenesis, which may provide higher efficacy with a good safety profile.

Large Intragenic Deletion in DSTYK Underlies Autosomal-Recessive Complicated Spastic Paraparesis, SPG23

SPG23 is an autosomal-recessive neurodegenerative subtype of lower limb spastic paraparesis with additional diffuse skin and hair dyspigmentation at birth followed by further patchy pigment loss during childhood. Previously, genome-wide linkage in an Arab-Israeli pedigree mapped the gene to an approximately 25 cM locus on chromosome 1q24-q32. By using whole-exome sequencing in a further Palestinian-Jordanian SPG23 pedigree, we identified a complex homozygous 4-kb deletion/20-bp insertion in DSTYK (dual serine-threonine and tyrosine protein kinase) in all four affected family members. DSTYK is located within the established linkage region and we also found the same mutation in the previously reported pedigree and another Israeli pedigree (total of ten affected individuals from three different families). The mutation removes the last two exons and part of the 3' UTR of DSTYK. Skin biopsies revealed reduced DSTYK protein levels along with focal loss of melanocytes. Ultrastructurally, swollen mitochondria and cytoplasmic vacuoles were also noted in remaining melanocytes and some keratinocytes and fibroblasts. Cultured keratinocytes and fibroblasts from an affected individual, as well as knockdown of Dstyk in mouse melanocytes, keratinocytes, and fibroblasts, were associated with increased cell death after ultraviolet irradiation. Keratinocytes from an affected individual showed loss of kinase activity upon stimulation with fibroblast growth factor. Previously, dominant mutations in DSTYK were implicated in congenital urological developmental disorders, but our study identifies different phenotypic consequences for a recurrent autosomal-recessive deletion mutation in revealing the genetic basis of SPG23.