Stanca A. Birlea

Variant of TYR and Autoimmunity Susceptibility Loci in Generalized Vitiligo

BACKGROUND Generalized vitiligo is an autoimmune disease characterized by melanocyte loss, which results in patchy depigmentation of skin and hair, and is associated with an elevated risk of other autoimmune diseases. METHODS To identify generalized vitiligo susceptibility loci, we conducted a genomewide association study. We genotyped 579,146 single-nucleotide polymorphisms (SNPs) in 1514 patients with generalized vitiligo who were of European-derived white (CEU) ancestry and compared the genotypes with publicly available control genotypes from 2813 CEU persons. We then tested 50 SNPs in two replication sets, one comprising 677 independent CEU patients and 1106 CEU controls and the other comprising 183 CEU simplex trios with generalized vitiligo and 332 CEU multiplex families. RESULTS We detected significant associations between generalized vitiligo and SNPs at several loci previously associated with other autoimmune diseases. These included genes encoding major-histocompatibility-complex class I molecules (P=9.05x10(-23)) and class II molecules (P=4.50x10(-34)), PTPN22 (P=1.31x10(-7)), LPP (P=1.01x10(-11)), IL2RA (P=2.78x10(-9)), UBASH3A (P=1.26x10(-9)), and C1QTNF6 (P=2.21x10(-16)). We also detected associations between generalized vitiligo and SNPs in two additional immune-related loci, RERE (P=7.07x10(-15)) and GZMB (P=3.44x10(-8)), and in a locus containing TYR (P=1.60x10(-18)), encoding tyrosinase. CONCLUSIONS We observed associations between generalized vitiligo and markers implicating multiple genes, some associated with other autoimmune diseases and one (TYR) that may mediate target-cell specificity and indicate a mutually exclusive relationship between susceptibility to vitiligo and susceptibility to melanoma.

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

We previously reported a genome-wide association study (GWAS) identifying 14 susceptibility loci for generalized vitiligo. We report here a second GWAS (450 individuals with vitiligo (cases) and 3,182 controls), an independent replication study (1,440 cases and 1,316 controls) and a meta-analysis (3,187 cases and 6,723 controls) identifying 13 additional vitiligo-associated loci. These include OCA2-HERC2 (combined P = 3.80 × 10−8), MC1R (P = 1.82 × 10−13), a region near TYR (P = 1.57 × 10−13), IFIH1 (P = 4.91 × 10−15), CD80 (P = 3.78 × 10−10), CLNK (P = 1.56 × 10−8), BACH2 (P = 2.53 × 10−8), SLA (P = 1.58 × 10−8), CASP7 (P = 3.56 × 10−8), CD44 (P = 1.78 × 10−9), IKZF4 (P = 2.75 × 10−14), SH2B3 (P = 3.54 × 10−18) and TOB2 (P = 6.81 × 10−10). Most vitiligo susceptibility loci encode immunoregulatory proteins or melanocyte components that likely mediate immune targeting and the relationships among vitiligo, melanoma, and eye, skin and hair coloration.

Common variants in FOXP1 are associated with generalized vitiligo

In a recent genome-wide association study of generalized vitiligo, we identified ten confirmed susceptibility loci. By testing additional loci that showed suggestive association in the genome-wide study, using two replication cohorts of European descent, we observed replicated association of generalized vitiligo with variants at 3p13 encompassing FOXP1 (rs17008723, combined P = 1.04 × 10−8) and with variants at 6q27 encompassing CCR6 (rs6902119, combined P = 3.94 × 10−7).

Comprehensive Association Analysis of Candidate Genes for Generalized Vitiligo Supports XBP1, FOXP3, and TSLP

We previously carried out a genome-wide association study of generalized vitiligo (GV) in non-Hispanic whites, identifying 13 confirmed susceptibility loci. In this study, we re-analyzed the genome-wide data set (comprising 1,392 cases and 2,629 controls) to specifically test association of all 33 GV candidate genes that have previously been suggested for GV, followed by meta-analysis incorporating both current and previously published data. We detected association of three of the candidate genes tested: TSLP (rs764916, P=3.0E-04, odds ratio (OR)=1.60; meta-P for rs3806933=3.1E-03), XBP1 (rs6005863, P=3.6E-04, OR=1.17; meta-P for rs2269577=9.5E-09), and FOXP3 (rs11798415, P=5.8E-04, OR=1.19). Association of GV with CTLA4 (rs12992492, P=5.9E-05, OR=1.20; meta-P for rs231775=1.0E-04) seems to be secondary to epidemiological association with other concomitant autoimmune diseases. Within the major histocompatibility complex (MHC), at 6p21.33, association with TAP1-PSMB8 (rs3819721, P=5.2E-06) seems to derive from linkage disequilibrium with major primary signals in the MHC class I and class II regions.

Genome-wide association study of generalized vitiligo in an isolated European founder population identifies SMOC2, in close proximity to IDDM8.

Generalized vitiligo is a common disorder in which patchy loss of skin and hair pigmentation principally appears to result from autoimmune loss of melanocytes from affected regions. We previously characterized a unique founder population in an isolated Romanian community with elevated prevalence of generalized vitiligo and other autoimmune diseases, including autoimmune thyroid disease, rheumatoid arthritis, and type I diabetes mellitus. Here, we describe a genome-wide association study (GWAS) of generalized vitiligo in 32 distantly related affected patients from this remote village and 50 healthy controls from surrounding villages. Vitiligo was significantly associated with single-nucleotide polymorphisms (SNPs) in a 30-kb LD block on chromosome 6q27, in close vicinity to IDDM8, a linkage and association signal for type I diabetes mellitus and rheumatoid arthritis. The region of association contains only one gene, SMOC2, within which SNP rs13208776 attained genome-wide significance for association with generalized vitiligo (P=8.51x10(-8)) at odds ratio 7.445 (95% confidence interval=3.56-15.53) for the high-risk allele and population attributable risk 28.00. SMOC2 encodes a modular extracellular calcium-binding glycoprotein of unknown function. Our findings indicate that SMOC2 is a risk locus for generalized vitiligo and perhaps other autoimmune diseases.

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.

Epithelial stem cell mutations that promote squamous cell carcinoma metastasis.

Squamous cell carcinomas (SCCs) originate in stratified epithelia, with a small subset becoming metastatic. Epithelial stem cells are targets for driver mutations that give rise to SCCs, but it is unknown whether they contribute to oncogenic multipotency and metastasis. We developed a mouse model of SCC by targeting two frequent genetic mutations in human SCCs, oncogene Kras(G12D) activation and Smad4 deletion, to mouse keratin 15-expressing (K15+) stem cells. We show that transgenic mice developed multilineage tumors, including metastatic SCCs. Among cancer stem cell-enriched (CSC-enriched) populations, those with increased side population (SP) cells correlated with epithelial-mesenchymal transition (EMT) and lung metastasis. We show that microRNA-9 (miR-9) contributed to SP expansion and metastasis, and miR-9 inhibition reduced the number of SP cells and metastasis. Increased miR-9 was detected in metastatic human primary SCCs and SCC metastases, and miR-9-transduced human SCC cells exhibited increased invasion. We identified α-catenin as a predominant miR-9 target. Increased miR-9 in human SCC metastases correlated with α-catenin loss but not E-cadherin loss. Our results demonstrate that stem cells with Kras(G12D) activation and Smad4 depletion can produce tumors that are multipotent and susceptible to EMT and metastasis. Additionally, tumor initiation and metastatic properties of CSCs can be uncoupled, with miR-9 regulating the expansion of metastatic CSCs.

Genome-wide association studies of autoimmune vitiligo identify 23 new risk loci and highlight key pathways and regulatory variants

Vitiligo is an autoimmune disease in which depigmented skin results from the destruction of melanocytes, with epidemiological association with other autoimmune diseases. In previous linkage and genome-wide association studies (GWAS1 and GWAS2), we identified 27 vitiligo susceptibility loci in patients of European ancestry. We carried out a third GWAS (GWAS3) in European-ancestry subjects, with augmented GWAS1 and GWAS2 controls, genome-wide imputation, and meta-analysis of all three GWAS, followed by an independent replication. The combined analyses, with 4,680 cases and 39,586 controls, identified 23 new significantly associated loci and 7 suggestive loci. Most encode immune and apoptotic regulators, with some also associated with other autoimmune diseases, as well as several melanocyte regulators. Bioinformatic analyses indicate a predominance of causal regulatory variation, some of which corresponds to expression quantitative trait loci (eQTLs) at these loci. Together, the identified genes provide a framework for the genetic architecture and pathobiology of vitiligo, highlight relationships with other autoimmune diseases and melanoma, and offer potential targets for treatment.

New insights on therapy with vitamin D analogs targeting the intracellular pathways that control repigmentation in human vitiligo.

Vitiligo is a progressive depigmenting disorder affecting 0.5–2% of the population worldwide in which destruction of functional melanocytes from epidermis is a composite of multiple processes influencing melanocyte function and survival. A number of studies have recently reported that the treatment with vitamin D compounds or their combination with ultraviolet light or corticosteroids enhances repigmentation in vitiligo; however, the causal relationship at the cellular and molecular levels has not so far been investigated. This review details the main intracellular pathways through which vitamin D ligands alone or in different combinations may contribute to pigment restoration in vitiligo, outlines the most recent achievements in vitiligo treatment using vitamin D analogs, and compares their efficacy with other treatment regimens in vitiligo. Based on the reviewed literature and data, we foresee the need for designing new vitamin D compounds to achieve maximal therapeutic efficacy. Such compounds should have high selectivity for melanocytes, stimulatory effects on melanogenesis, and minimal suppressive effects on melanocyte growth. An approach combining clinical investigations and focused research on the cellular and molecular mechanisms of vitiligo repigmentation will lead to finding better treatments for this disease.

CTLA4 and generalized vitiligo: two genetic association studies and a meta-analysis of published data.

Several lines of evidence have implicated the gene encoding cytotoxic T lymphocyte antigen 4 (CTLA4) in susceptibility to various autoimmune diseases. However, published studies of genetic association between CTLA4 polymorphisms and vitiligo have yielded conflicting results. Here, we describe two new genetic association studies of CTLA4 single‐nucleotide polymorphisms (SNPs) and generalized vitiligo in two independent Romanian Caucasian (CEU) case‐control cohorts. The first study, of SNPs rs1863800, rs231806, rs231775, rs3087243, rs11571302, rs11571297, and rs10932037, showed no allelic, genotypic, or haplotypic association with generalized vitiligo. The second study, of SNP rs231775, likewise showed no significant association. To enhance statistical power over that of any individual study, we carried out a meta‐analysis that incorporated these two new studies and all other published genetic association studies of CTLA4 SNPs and vitiligo in CEU populations. While there was no association with vitiligo overall, the meta‐analysis showed significant association of SNP rs231775 in that subgroup of vitiligo patients who also had other concomitant autoimmune diseases. Similarly, there was near‐significant association in this same patient subgroup with several other CTLA4 SNPs that are in linkage disequilibrium with rs231775. Our results indicate that the association of CTLA4 with vitiligo is weak, and indeed may be secondary, driven by primary genetic association of CTLA4 with other autoimmune diseases that are epidemiologically associated with vitiligo.