Sequence and haplotype analysis supports HLA-C as the psoriasis susceptibility 1 gene

Psoriasis

Psoriasis is a chronic, immune-mediated disorder with cutaneous and systemic manifestations and substantial negative effects on patient quality of life. Psoriasis has a strong, albeit polygenic, genetic basis. Whereas approximately half of the accountable genetic effect of psoriasis maps to the major histocompatibility complex, >70 other loci have been identified, many of which implicate nuclear factor-κB, interferon signalling and the IL-23-IL-23 receptor axis. Psoriasis pathophysiology is characterized by abnormal keratinocyte proliferation and immune cell infiltration in the dermis and epidermis involving the innate and adaptive immune systems, with important roles for dendritic cells and T cells, among other cells. Frequent comorbidities are rheumatological and cardiovascular in nature, in particular, psoriatic arthritis. Current treatments for psoriasis include topical agents, photo-based therapies, traditional systemic drugs and biologic agents. Treatments can be used in combination or as monotherapy. Biologic therapies that target specific disease mediators have become a mainstay in the treatment of moderate-to-severe disease, whereas advances in the treatment of mild-to-moderate disease have been limited.

Association of IL12B risk haplotype and lack of interaction with HLA-Cw6 among the psoriasis patients in India

Psoriasis is a complex multifactorial chronic inflammatory skin disorder involving both genetic and environmental susceptibility factors. It is strongly associated with HLA-Cw6, but several studies suggested that further genetic factors may confer additional risk. We investigated the association of two single-nucleotide polymorphisms (SNPs), rs3212227 at the 3'-untranslated region and rs7709212 located at ~6.7 kb upstream from the transcription start site of IL12B gene in a case-control study comprising 1702 individuals from India. We found both SNPs were significantly associated with psoriasis (rs7709212: odds ratio (OR)=1.37, P-value=1.09 × 10^-5; rs3212227: OR=1.38, P-value=8.88 × 10^-6). IL12B gene was significantly upregulated in involved skin of psoriasis patients with risk genotype carriers (rs7709212_TT and rs3212227_TT) compared with non-risk genotype carriers (rs7709212_CC and rs3212227_GG). Significantly higher serum protein concentration of IL12 was also observed among risk allele carriers compared with non-risk allele carriers irrespective of the presence of HLA-Cw6 allele. Haplotype analysis suggested significant increased risk (OR=1.50, P-value=5.01 × 10^-8) to the disease when both risk alleles of IL12B were present. IL12 serum protein concentration of risk haplotype (TT-TT) carriers showed significant upregulation compared with the non-risk carriers independent of HLA-Cw6 alleles. Our data suggested the association of IL12B with the psoriasis, however no evidence was observed for the epistatic effect of IL12B with HLA-Cw6 among the psoriasis patients in India.

IL17RA gene variants and anti-TNF response among psoriasis patients

Polymorphisms at genes encoding proteins involved in the pathogenesis of psoriasis (Psor) or in the mechanism of action of biological drugs could influence the treatment response. Because the interleukin (IL)-17 family has a central role in the pathogenesis of Psor, we hypothesized that IL17RA variants could influence the response to anti-TNF drugs among Psor patients. To address this issue we performed a cross-sectional study of Psor patients who received the biological treatments for the first time, with a follow-up of at least 6 months. All of the patients were Caucasian, older than 18 years old, with chronic plaque Psor, and had completed at least 24 weeks of anti-TNF therapy (adalimumab, etanercept or infliximab). The treatment response to anti-TNF agents was evaluated according to the achievement of PASI50 and PASI75 at weeks 12 and 24. Those who achieved PASI75 at week 24 were considered good responders. All patients were genotyped for the selected single-nucleotide polymorphisms (SNPs) at IL17RA gene. A total of 238 patients were included (57% male, mean age 46 years). One hundred and five patients received adalimumab, 91 patients etanercept and 42 infliximab. The rs4819554 promoter SNP allele A was significantly more common among responders at weeks 12 (P=0.01) and 24 (P=0.04). We found a higher frequency of AA versus AG+GG among responders, but the difference was only significant at week 12 (P=0.03, odd ratio=1.86, 95% confidence of interval=1.05-3.27). Thus, in the study population, the SNP rs4819554 in the promoter region of IL17RA significantly influences the response to anti-TNF drugs at week 12.

Evaluation of Psoriasis Genetic Risk Based on Five Susceptibility Markers in a Population from Northern Poland

Psoriasis genetic background depends on polygenic and multifactorial mode of inheritance. As in other complex disorders, the estimation of the disease risk based on individual genetic variants is impossible. For this reason, recent investigations have been focused on combinations of known psoriasis susceptibility markers in order to improve the disease risk evaluation. Our aim was to compare psoriasis genetic risk score (GRS) for five susceptibility loci involved in the immunological response (HLA-C, ERAP1, ZAP70) and in the skin barrier function (LCE3, CSTA) between patients with chronic plaque psoriasis (n = 148) and the control group (n = 146). A significantly higher number of predisposing alleles was observed in patients with psoriasis in comparison to healthy individuals (6.1 vs. 5.2, respectively; P = 8.8×10⁻⁷). The statistical significance was even more profound when GRS weighted by logarithm odds ratios was evaluated (P = 9.9×10⁻¹⁴). Our results demonstrate the developed panel of five susceptibility loci to be more efficient in predicting psoriasis risk in the Polish population and to possess higher sensitivity and specificity for the disease than any of the markers analyzed separately, including the most informative HLA-C*06 allele.

Throat Infections are Associated with Exacerbation in a Substantial Proportion of Patients with Chronic Plaque Psoriasis

Streptococcal throat infections are known to trigger or exacerbate psoriasis, and several studies support the benefit of tonsillectomy. To evaluate the potential of tonsillectomy as a treatment, we used a retrospective study-specific questionnaire to assess the proportion of psoriasis patients with sore throat-associated psoriasis exacerbations. Our survey sampled 275 psoriasis patients. Of patients with plaque psoriasis, 42% reported sore throat-associated psoriasis exacerbations, and of patients with confirmed streptococcal infections, 72% reported aggravation. Notably, women and patients with early onset psoriasis were more likely to report psoriasis exacerbation after a sore throat (p < 0.001, p = 0.046, respectively). Other psoriasis aggravation factors were more common in patients with sore throat-associated exacerbations (p < 0.01). Of tonsillectomized patients, 49% reported subsequent improvement and had more frequent sore throat-associated aggravation of psoriasis than patients who did not improve after tonsillectomy (p = 0.015). These findings suggest a closer association between sore throats, streptococcal throat infections and plaque psoriasis than reported previously.

Tissue-engineered human psoriatic skin supplemented with cytokines as an in vitro model to study plaque psoriasis

AIM

Psoriasis is a chronic inflammatory skin disease. To study its complex etiology, a psoriatic skin substitute model supplemented with a cytokine cocktail has been used.

MATERIALS & METHODS

Reconstructed psoriatic skin substitutes were supplemented with a cocktail of four cytokines: TNF-α, IL-1α, IL-6 and IL-17A, to monitor their impact on gene expression by DNA microarray.

RESULTS

Gene profiling analyses identified several deregulated genes reported as being also deregulated in psoriasis skin in vivo (S100A12, IL-8, DEFB4A and KYNU). The expression of those genes was dramatically increased compared with basal levels of controls (p < 0.005 to < 0.05).

CONCLUSION

Psoriatic substitutes supplemented with a cocktail of TNF-α, IL-1α, IL-6 and IL-17A showed similar transcriptome alterations to those found in psoriasis.

HLA-Cw6 homozygosity in plaque psoriasis is associated with streptococcal throat infections and pronounced improvement after tonsillectomy: A prospective case series

BACKGROUND

Carriage of the HLA-Cw*0602 allele is associated with a particular set of clinical features and treatment responses in psoriasis. Tonsillectomy can improve psoriasis.

OBJECTIVES

We sought to evaluate whether HLA-Cw*0602 predicts a favorable outcome after tonsillectomy of patients with psoriasis.

METHODS

This prospective case series followed up 28 tonsillectomized patients with plaque psoriasis for 24 months. The Psoriasis Area and Severity Index, Psoriasis Disability Index, and Psoriasis Life Stress Inventory were used for assessment. Tonsils were swabbed for bacteria and patients genotyped for HLA-Cw*0602.

RESULTS

After tonsillectomy, HLA-Cw*0602 homozygotes showed significantly more improvement, compared with heterozygous and HLA-Cw*0602-negative patients. Thus, Psoriasis Area and Severity Index score was reduced by 82% in the homozygous patients compared with 42% and 31%, respectively (P < .001), Psoriasis Disability Index score improved by 87% compared with 38% and 41%, respectively (P < .001), and Psoriasis Life Stress Inventory score was 82% reduced compared with 60% and 54%, respectively (P < .001). The homozygotes more often had psoriasis onset associated with a throat infection (P = .007) and an increased frequency of streptococcal throat infections per lifetime (P = .038).

LIMITATIONS

Few patients were included and some data were retrospective.

CONCLUSIONS

Homozygous HLA-Cw*0602 carriage in plaque psoriasis may predict a favorable outcome after tonsillectomy.

Palmoplantar Psoriasis and Palmoplantar Pustulosis: Current Treatment and Future Prospects

Palmoplantar psoriasis and palmoplantar pustulosis are chronic skin diseases with a large impact on patient quality of life. They are frequently refractory to treatment, being generally described as a therapeutic challenge. This article aims to review the definitions of palmoplantar psoriasis and palmoplantar pustulosis, highlighting the similarities and differences in terms of epidemiology, clinical presentation, genetics, histopathology, and pathogenesis, as well as treatment options for both entities. Classical management of mild to moderate palmoplantar pustulosis and palmoplantar psoriasis relies on use of potent topical corticosteroids, phototherapy, and/or acitretin. Nevertheless, these drugs have proven to be insufficient in long-term control of extensive disease. Biologic therapy-namely, anti-interleukin-17 agents and phosphodiesterase type 4 inhibitors-has recently shown promising results in the treatment of palmoplantar psoriasis. Knowledge of the pathophysiologic pathways of both entities is of utmost importance and may, in the future, allow development of molecularly targeted therapeutics.

Random Bits Forest: a Strong Classifier/Regressor for Big Data

Efficiency, memory consumption, and robustness are common problems with many popular methods for data analysis. As a solution, we present Random Bits Forest (RBF), a classification and regression algorithm that integrates neural networks (for depth), boosting (for width), and random forests (for prediction accuracy). Through a gradient boosting scheme, it first generates and selects ~10,000 small, 3-layer random neural networks. These networks are then fed into a modified random forest algorithm to obtain predictions. Testing with datasets from the UCI (University of California, Irvine) Machine Learning Repository shows that RBF outperforms other popular methods in both accuracy and robustness, especially with large datasets (N > 1000). The algorithm also performed highly in testing with an independent data set, a real psoriasis genome-wide association study (GWAS).

The Gut Microbiota in Immune-Mediated Inflammatory Diseases

The collection of microbes and their genes that exist within and on the human body, collectively known as the microbiome has emerged as a principal factor in human health and disease. Humans and microbes have established a symbiotic association over time, and perturbations in this association have been linked to several immune-mediated inflammatory diseases (IMID) including inflammatory bowel disease, rheumatoid arthritis, and multiple sclerosis. IMID is a term used to describe a group of chronic, highly disabling diseases that affect different organ systems. Though a cornerstone commonality between IMID is the idiopathic nature of disease, a considerable portion of their pathobiology overlaps including epidemiological co-occurrence, genetic susceptibility loci and environmental risk factors. At present, it is clear that persons with an IMID are at an increased risk for developing comorbidities, including additional IMID. Advancements in sequencing technologies and a parallel explosion of 16S rDNA and metagenomics community profiling studies have allowed for the characterization of microbiomes throughout the human body including the gut, in a myriad of human diseases and in health. The main challenge now is to determine if alterations of gut flora are common between IMID or, if particular changes in the gut community are in fact specific to a single disease. Herein, we review and discuss the relationships between the gut microbiota and IMID.

[Autoimmune reactions in psoriasis : Spotlight]

BACKGROUND

Psoriasis is a human leukocyte antigen (HLA)-associated T‑cell-mediated disorder.

OBJECTIVES

The role of the main psoriasis risk allele HLA-C*06:02 in disease manifestation and the mechanisms which activate the pathogenic T‑cell response in the skin of psoriasis patients remained elusive.

MATERIALS AND METHODS

Key to the immune pathogenesis of psoriasis was the analysis of the specificity of the infiltrating lesional psoriatic CD8(+) T cells

RESULTS AND CONCLUSION

Analyses of the lesional psoriatic T‑cell reactivity demonstrate that psoriasis is an autoimmune disease. It is based on an autoimmune response against melanocytes which is preferentially mediated by HLA-C*06:02 through autoantigen presentation. Here we discuss the mechanisms of this autoimmune response in the context of the polygenic psoriatic predisposition.

Increased Risk of Psoriasis due to combined effect of HLA-Cw6 and LCE3 risk alleles in Indian population

HLA-Cw6 is one of the most associated alleles in psoriasis. Recently, Late Cornified Envelop 3 (LCE3) genes were identified as a susceptibility factor for psoriasis. Some population showed epistatic interaction of LCE3 risk variants with HLA-Cw6, while some population failed to show any association. We determined the associations of a 32.2 kb deletion comprising LCE3C-3B genes and three SNPs (rs1886734, rs4112788; rs7516108) at the LCE3 gene cluster among the psoriasis patients in India. All three SNPs at the LCE3 gene cluster failed to show any association. In contrary, for patients with HLA-Cw6 allele, all three SNPs and the LCE3C-3B deletion showed significant associations. While, all five LCE3 genes were upregulated in psoriatic skin, only LCE3A showed significant overexpression with homozygous risk genotype compared to the non-risk genotype. LCE3B also showed significant overexpression in patients with HLA-Cw6 allele. Moreover, LCE3A showed significantly higher expression in patients bearing homozygous risk genotype in presence of HLA-Cw6 allele but not in those having non-risk genotype, demonstrating the combined effect of HLA-Cw6 allele and risk associated genotype near LCE3A gene. Integration of genetic and gene expression data thus allowed us to identify the actual disease variants at the LCE3 cluster among the psoriasis patients in India.

Contribution of the IL-17 Pathway to Psoriasis and Psoriatic Arthritis

Investigators have accrued compelling evidence that the IL-17 pathway is central to the pathogenesis of psoriasis and psoriatic arthritis. The evidence comprises genome-wide association studies (GWAS), data from experimental murine models and findings from in vitro studies on patients' cells or tissue biopsies. More recently, the success of drugs blocking the IL-17 pathway in treating both psoriasis (PsO) and psoriatic arthritis (PsA) confirms that IL-17 is a clinically relevant therapeutic target. However, there remain many unanswered questions: is PsA simply an extension of PsO from the skin to the synovial tissue or are there differences in the underlying pathogenesis of these diseases? Which cell type represents the primary source of IL-17 in PsO and PsA? And how are these cells regulated? This review outlines the IL-17 pathway, summarises the evidence supporting its role in PsO and PsA and discusses recent data that may help to address these yet unresolved questions.

The HLA-C*06 allele as a possible genetic predisposing factor to psoriasis in South Indian Tamils

Psoriasis is a multi-factorial heritable prototypical immune-mediated inflammatory disease, characterized by hyperproliferation of keratinocytes in the affected skin. There are no studies till date, to the best of our knowledge, about the association of HLA-C*06, the risk variant in the PSORS 1 susceptibility locus that confers the greatest risk for early onset of psoriasis, with the disease in South Indian Tamil patients with psoriasis. The present study was performed to determine the association of HLA-C*06 with psoriasis in the South Indian Tamil ethnic population. Three hundred and fifty-five cases of psoriasis and 360 healthy controls were included in this case-control study. Severity grading according to psoriasis area severity index (PASI) scoring was done in patients with psoriasis. PCR assays with sequence-specific primers (PCR-SSP) were used for specific detection of HLA-C*06. PCR with analysis of restriction fragment length polymorphism was used to distinguish between patients homozygous and heterozygous for HLA-C*06. We observed that those with the HLA-C*06-positive allele had a 3.5 times higher odds of having psoriasis compared to those without, [p < 0.0001, OR 3.5, 95 % CI (2.59-4.79)]. Among cases of psoriasis, it was noted that there was a significant association of HLA-C*06 positivity with female psoriatics [p = 0.006; OR 2.49 (1.28-4.87)] and early age of onset of psoriasis [p = 0.002; OR 2.04 (1.29-3.20)]. Our results suggest that the HLA-C*06 allele is positively associated with susceptibility to psoriasis, female gender and early onset of psoriasis in South Indian Tamils.

Genome-Wide Pathway Analysis Identifies Genetic Pathways Associated with Psoriasis

Psoriasis is a chronic inflammatory disease with a complex genetic architecture. To date, the psoriasis heritability is only partially explained. However, there is increasing evidence that the missing heritability in psoriasis could be explained by multiple genetic variants of low effect size from common genetic pathways. The objective of this study was to identify new genetic variation associated with psoriasis risk at the pathway level. We genotyped 598,258 single nucleotide polymorphisms in a discovery cohort of 2,281 case-control individuals from Spain. We performed a genome-wide pathway analysis using 1,053 reference biological pathways. A total of 14 genetic pathways (PFDR ≤ 2.55 × 10(-2)) were found to be significantly associated with psoriasis risk. Using an independent validation cohort of 7,353 individuals from the UK, a total of 6 genetic pathways were significantly replicated (PFDR ≤ 3.46 × 10(-2)). We found genetic pathways that had not been previously associated with psoriasis risk such as retinol metabolism (Pcombined = 1.84 × 10(-4)), the transport of inorganic ions and amino acids (Pcombined = 1.57 × 10(-7)), and post-translational protein modification (Pcombined = 1.57 × 10(-7)). In the latter pathway, MGAT5 showed a strong network centrality, and its association with psoriasis risk was further validated in an additional case-control cohort of 3,429 individuals (P < 0.05). These findings provide insights into the biological mechanisms associated with psoriasis susceptibility.

Melanocyte antigen triggers autoimmunity in human psoriasis

Psoriasis vulgaris is a common T cell-mediated inflammatory skin disease with a suspected autoimmune pathogenesis. The human leukocyte antigen (HLA) class I allele, HLA-C*06:02, is the main psoriasis risk gene. Epidermal CD8(+) T cells are essential for psoriasis development. Functional implications of HLA-C*06:02 and mechanisms of lesional T cell activation in psoriasis, however, remained elusive. Here we identify melanocytes as skin-specific target cells of an HLA-C*06:02-restricted psoriatic T cell response. We found that a Vα3S1/Vβ13S1 T cell receptor (TCR), which we had reconstituted from an epidermal CD8(+) T cell clone of an HLA-C*06:02-positive psoriasis patient specifically recognizes HLA-C*06:02-positive melanocytes. Through peptide library screening, we identified ADAMTS-like protein 5 (ADAMTSL5) as an HLA-C*06:02-presented melanocytic autoantigen of the Vα3S1/Vβ13S1 TCR. Consistent with the Vα3S1/Vβ13S1-TCR reactivity, we observed numerous CD8(+) T cells in psoriasis lesions attacking melanocytes, the only epidermal cells expressing ADAMTSL5. Furthermore, ADAMTSL5 stimulation induced the psoriasis signature cytokine, IL-17A, in CD8(+) T cells from psoriasis patients only, supporting a role as psoriatic autoantigen. This unbiased analysis of a TCR obtained directly from tissue-infiltrating CD8(+) T cells reveals that in psoriasis HLA-C*06:02 directs an autoimmune response against melanocytes through autoantigen presentation. We propose that HLA-C*06:02 may predispose to psoriasis via this newly identified autoimmune pathway.

Emerging biomarkers in psoriatic arthritis

Psoriasis is an immune-mediated skin disease which affects 2-4% of the worldwide population. Approximately 20-30% of patients with psoriasis develop psoriatic arthritis (PsA), a frequently destructive and disabling condition. As skin manifestations precede joint symptoms in nearly all patients with PsA, identification of biomarkers for early prediction of joint damage is an important clinical need. Because not all patients with PsA respond to treatment in the same fashion, identification of biomarkers capable of predicting therapeutic response is also imperative. Here, we review existing literature and discuss current investigations to identify potential biomarkers for PsA disease activity, with particular emphasis on microRNAs as novel markers of interest. Serum (soluble) biomarkers, peripheral osteoclast precursor as cellular biomarkers, and genetic loci associated with skin and joint disease are also reviewed.

Update on psoriasis immunopathogenesis and targeted immunotherapy

Over recent years, significant progress has been made in characterisation of the underlying pathogenic mechanisms in psoriasis, a common cutaneous disease that is associated with major systemic co-morbidity and reduced life expectancy. Basic science discoveries have informed the design of novel therapeutic approaches, many of which are now under evaluation in late-stage clinical trials. Here we describe the complex interplay between immune cell types and cytokine networks that acts within self-perpetuating feedback loops to drive cutaneous inflammation in psoriasis. Genetic studies have been pivotal in the construction of the disease model and more recently have uncovered a distinct aetiology for rare, pustular variants of psoriasis. The translation of mechanistic insights into potential advancements in clinical care will also be described, including several treatments that target the interleukin-23 (IL-23)/T17 immune axis.

The genetics of human autoimmune disease: A perspective on progress in the field and future directions

Progress in defining the genetics of autoimmune disease has been dramatically enhanced by large scale genetic studies. Genome-wide approaches, examining hundreds or for some diseases thousands of cases and controls, have been implemented using high throughput genotyping and appropriate algorithms to provide a wealth of data over the last decade. These studies have identified hundreds of non-HLA loci as well as further defining HLA variations that predispose to different autoimmune diseases. These studies to identify genetic risk loci are also complemented by progress in gene expression studies including definition of expression quantitative trait loci (eQTL), various alterations in chromatin structure including histone marks, DNase I sensitivity, repressed chromatin regions as well as transcript factor binding sites. Integration of this information can partially explain why particular variations can alter proclivity to autoimmune phenotypes. Despite our incomplete knowledge base with only partial definition of hereditary factors and possible functional connections, this progress has and will continue to facilitate a better understanding of critical pathways and critical changes in immunoregulation. Advances in defining and understanding functional variants potentially can lead to both novel therapeutics and personalized medicine in which therapeutic approaches are chosen based on particular molecular phenotypes and genomic alterations.

Investigation of association of the IL-12B and IL-23R genetic variations with psoriatic risk in a South Indian Tamil cohort

BACKGROUND

Psoriasis is a T-cell mediated chronic systemic inflammatory skin disease. Emerging evidences suggest the interleukin (IL)-12B and IL-23R genes encoding the common p40 subunit of IL-12 and IL-23 are the key cytokines in T-helper (Th)1 and Th17 differentiation and function. Certain allelic variants of these genes significantly influence the risk of psoriasis. Hence we undertook to study the association of IL-12B and IL-23R gene polymorphisms with disease susceptibility in South Indian Tamil patients with psoriasis.

METHODS

360 psoriatics and 360 healthy controls were included in this case control study. IL-12B gene (rs3212227) and IL-23R gene (rs2201841, rs10889677 and rs11805303) polymorphisms were typed by using TaqMan 5'allele discrimination assay and cytokine levels were assayed by ELISA.

RESULTS

We observed that the patients carrying the risk genotypes of IL-12B (rs3212227) and IL-23R (rs2201841) conferred an increased susceptibility to psoriasis. We did not find any significant association between IL-23R (rs10889677 and rs11805303) gene polymorphisms and psoriasis risk in South Indian Tamil population. We did not observe any significant difference in haplotypes between the psoriasis cases and controls. We observed a significant increase in the mean IL-23 levels in psoriatics and the higher levels of IL-23 were found in the minor variant genotype CC when compared with that of heterozygous CT and major variant TT genotypes of rs2201841. Individual genotypes of rs10889677 and rs11805303 and IL-12 (rs3212227) were not significantly associated with their plasma levels.

CONCLUSION

Our results suggest that IL-12B (rs3212227) and IL-23R (rs2201841) polymorphisms confer increased risk of psoriasis in our ethnic South Indian Tamils.

Natural killer cells from psoriasis vulgaris patients have reduced levels of cytotoxicity associated degranulation and cytokine production

Psoriasis vulgaris is a chronic inflammatory disease of the skin with a strong genetic component and immune system involvement. Although some evidence suggests that Natural Killer (NK) cells may play a part in psoriasis, their role is relatively unstudied and results are controversial. In this current study, NK cells from psoriasis patients exhibited reduced degranulation and produced lower levels of the pro-inflammatory cytokines IFN-γ and TNF-α. Further investigation found that NK cells from psoriasis patients and healthy controls expressed similar levels of activation markers, NK cell receptors and apoptosis-inducing molecules. In addition, comparable levels of several cytokines important in NK cell biology were found in the serum of psoriasis patients and healthy controls. Genotyping analysis revealed that HLA-C2, which provides a ligand for killer-cell immunoglobulin-like receptors (KIR) expressed by NK cells, was strongly associated with psoriasis susceptibility. However, no link between the KIR genes themselves and disease was found.

Psoriasis

Psoriasis is an immune-mediated, genetic disease manifesting in the skin or joints or both. A diverse team of clinicians with a range of expertise is often needed to treat the disease. Psoriasis provides many challenges including high prevalence, chronicity, disfiguration, disability, and associated comorbidity. Understanding the role of immune function in psoriasis and the interplay between the innate and adaptive immune system has helped to manage this complex disease, which affects patients far beyond the skin. In this Seminar, we highlight the clinical diversity of psoriasis and associated comorbid diseases. We describe recent developments in psoriasis epidemiology, pathogenesis, and genetics to better understand present trends in psoriasis management. Our key objective is to raise awareness of the complexity of this multifaceted disease, the potential of state-of-the-art therapeutic approaches, and the need for early diagnosis and comprehensive management of patients with psoriasis.

Genetic, Epigenetic and Pharmacogenetic Aspects of Psoriasis and Psoriatic Arthritis

There is a strong familial component to psoriatic disease as well as a complex array of genetic, immunologic, and environmental factors. The dominant genetic effect is located on chromosome 6p21.3 within the major histocompatibility complex region, accounting for one-third of genetic contribution. Genome-wide association studies (GWAS) identified additional genes, including skin barrier function, innate immune response, and adaptive immune response genes. To better understand disease susceptibility and progression requires replication in larger cohorts, fine-mapping efforts, new technologies, and functional studies of genetic variants, gene-gene interactions and gene-environmental interactions. New technologies available include next-generation sequencing, copy number variation analysis, and epigenetics.

HLA-B27 and psoriatic disease: a modern view of an old relationship

Psoriasis and PsA are the main phenotypes of psoriatic disease. Both conditions are highly polygenic diseases in which stochastic and environmental factors are crucial in the pathogenic process. Although the MHC region is a highly dense genetic area, most of the genetic basis of psoriatic disease within it resides in the HLA region. For decades, HLA-C*06 has been accepted as the main descriptor of the two main phenotypes of skin psoriasis. There is now compelling evidence to suggest that HLA-C*06 is only a genetic biomarker for skin involvement and not for joint involvement in psoriatic disease. The role of HLA-B*27 in the genetic aetiology of PsA has been recognized since the 1970s. Recent population case-control studies with adequate patient groups and replication cohorts, as well as confirmation studies in family pedigrees through the use of modern molecular typing methods, have reinforced the aetiological role of this allele in PsA. These studies have offered a new vision of the role of this allele in disease expression. This review contextualizes the latest findings on the role of HLA-B27 in psoriatic disease, emphasizing those aspects of particular interest for clinical practice.

Genetics of psoriasis

Psoriasis is a common and debilitating immune-mediated skin disease with a complex genetic basis. Genetic studies have provided critical insights into the pathogenesis of disease. This article focuses on the results of genetic association studies, which provide evidence that psoriasis susceptibility genes are involved in innate and adaptive immunity and skin barrier functions. The potential for disease stratification and the development of more effective treatments with fewer side effects using genetic data are highlighted.

Common Variants for Heart Failure

Heart failure (HF) is a common disease with high morbidity and mortality; however, none of the drugs available are now entirely optimal for the treatment of HF. In addition to various clinical diseases and environment influences, genetic factors also contribute to the development and progression of HF. Identifying the common variants for HF by genome-wide association studies will facilitate the understanding of pathophysiological mechanisms underlying HF. This review summarizes the recently identified common variants for HF risk and outcome and discusses their implications for the clinic therapy.

Human Enhancers Are Fragile and Prone to Deactivating Mutations

To explore the underlying mechanisms whereby noncoding variants affect transcriptional regulation, we identified nucleotides capable of disrupting binding of transcription factors and deactivating enhancers if mutated (dubbed candidate killer mutations or KMs) in HepG2 enhancers. On average, approximately 11% of enhancer positions are prone to KMs. A comparable number of enhancer positions are capable of creating de novo binding sites via a single-nucleotide mutation (dubbed candidate restoration mutations or RSs). Both KM and RS positions are evolutionarily conserved and tend to form clusters within an enhancer. We observed that KMs have the most deleterious effect on enhancer activity. In contrast, RSs have a smaller effect in increasing enhancer activity. Additionally, the KMs are strongly associated with liver-related Genome Wide Association Study traits compared with other HepG2 enhancer regions. By applying our framework to lymphoblastoid cell lines, we found that KMs underlie differential binding of transcription factors and differential local chromatin accessibility. The gene expression quantitative trait loci associated with the tissue-specific genes are strongly enriched in KM positions. In summary, we conclude that the KMs have the greatest impact on the level of gene expression and are likely to be the causal variants of tissue-specific gene expression and disease predisposition.

Identification of a Novel Mucin Gene HCG22 Associated With Steroid-Induced Ocular Hypertension

PURPOSE

The pathophysiology of ocular hypertension (OH) leading to primary open-angle glaucoma shares many features with a secondary form of OH caused by treatment with glucocorticoids, but also exhibits distinct differences. In this study, a pharmacogenomics approach was taken to discover candidate genes for this disorder.

METHODS

A genome-wide association study was performed, followed by an independent candidate gene study, using a cohort enrolled from patients treated with off-label intravitreal triamcinolone, and handling change in IOP as a quantitative trait.

RESULTS

An intergenic quantitative trait locus (QTL) was identified at chromosome 6p21.33 near the 5' end of HCG22 that attained the accepted statistical threshold for genome-level significance. The HCG22 transcript, encoding a novel mucin protein, was expressed in trabecular meshwork cells, and expression was stimulated by IL-1, and inhibited by triamcinolone acetate and TGF-β. Bioinformatic analysis defined the QTL as an approximately 4 kilobase (kb) linkage disequilibrium block containing 10 common single nucleotide polymorphisms (SNPs). Four of these SNPs were identified in the National Center for Biotechnology Information (NCBI) GTEx eQTL browser as modifiers of HCG22 expression. Most are predicted to disrupt or improve motifs for transcription factor binding, the most relevant being disruption of the glucocorticoid receptor binding motif. A second QTL was identified within the predicted signal peptide of the HCG22 encoded protein that could affect its secretion. Translation, O-glycosylation, and secretion of the predicted HCG22 protein was verified in cultured trabecular meshwork cells.

CONCLUSIONS

Identification of two independent QTLs that could affect expression of the HCG22 mucin gene product via two different mechanisms (transcription or secretion) is highly suggestive of a role in steroid-induced OH.

Genetic background of skin barrier dysfunction in the pathogenesis of psoriasis vulgaris

Psoriasis is a common inflammatory skin disease. It is known to be a complex condition with multifactorial mode of inheritance, however the associations between particular pathogenic pathways remain unclear. A novel report on the pathogenesis of psoriasis has recently included the genetic determination of the skin barrier dysfunction. In this paper, we focus on specific genetic variants associated with formation of the epidermal barrier and their role in the complex pathogenesis of the disease.

Reactive oxygen species in psoriasis and psoriasis arthritis: relevance to human disease

Psoriasis (Ps) is a chronic, immune-mediated, skin inflammatory disease affecting up to 3% of the population worldwide. Different environmental triggers initiate this complex multifactorial syndrome. Many individuals affected by Ps (6-26%) develop inflammatory disease in other organs, often in the joints as in psoriasis arthritis (PsA). Animal models that reflect the typical Ps syndrome, including both skin and joint pathology as in Ps and PsA, are valuable tools for dissecting disease pathways leading to clinical manifestations. In this context, we developed a new acute Ps and PsA-like disease model that appears after exposure to Saccharomyces cerevisiae mannan in certain mouse strains. The disease was found to be triggered by mannan-activated macrophages, leading to the activation of a pathogenic interleukin-17 pathway involving innate lymphocytes. Interestingly, the production of reactive oxygen species protected the mice from the triggering of this pathway and ameliorated Ps and PsA development.

Psoriasis and the MAITing game: a role for IL-17A+ invariant TCR CD8+ T cells in psoriasis?

Recent findings have indicated that the majority of IL-17A+CD8+ T-cells in the blood belong to a subset of innate T-cells named mucosa-associated invariant T-cells (MAIT). In this issue, Teunissen and colleagues (Teunissen et al., 2014) demonstrate that while MAIT cells are found in psoriatic skin, they are not increased in abundance and that the majority of IL-17A+CD8+ T-cells in plaques of psoriasis are devoid of MAIT cell characteristics.

Genetic and epigenetic basis of psoriasis pathogenesis

Psoriasis is a chronic inflammatory skin disease whose prevalence varies among different populations worldwide. It is a complex multi-factorial disease and the exact etiology is largely unknown. Family based studies have indicated a genetic predisposition; however they cannot fully explain the disease pathogenesis. In addition to genetic susceptibility, environmental as well as gender and age related factors were also been found to be associated. Recently, imbalances in epigenetic networks are indicated to be causative elements in psoriasis. The present knowledge of epigenetic involvement, mainly the DNA methylation, chromatin modifications and miRNA deregulation is surveyed here. An integrated approach considering genetic and epigenetic anomalies in the light of immunological network may explore the pathogenesis of psoriasis.

The TNFRSF1B rs1061622 polymorphism (p.M196R) is associated with biological drug outcome in Psoriasis patients

Genetic factors are involved not only in the overall risk of suffering psoriasis, but also in their clinical characteristics and eventually in drug outcome. Biological therapies have dramatically improved the prognosis of Psoriasis. However, these treatments are very expensive and patients often exhibit a heterogeneous response that could be partially attributed to their genetic background. Thus, the research for genetic markers in psoriatic patients that could predict a poor response to biological therapies is an important issue. Our aim was to evaluate the effect of DNA variants at the "TNFα pathway" that could affect the risk of developing Psoriasis or the response to biological therapies among these patients. The genetic association study included a total of 518 Psoriatic patients and 480 healthy controls. Ninety of these patients received biological treatment and based on the change in the PASI score after 24 weeks were classified as good (PASI score ≥75%), intermediate (PASI 50-75), and non-responders (PASI <50). Next generation sequencing (NGS) with semiconductor-array technology was used to identify the nucleotide variants in the TNF α, TNFRSF1A and TNFRSF1B, and we only found three missense amino acid changes, all in TNFRSF1B. Interestingly, we found a significantly higher frequency of rs1061622 G carriers among CW6-positive patients (p = 0.004; OR = 1.69, 95% CI = 1.18-2.41). Allele G (p.196R) carriers were significantly more frequent in the non-responder group (56%) (p = 0.05). In conclusion, we report a significant association between the TNFRSF1B p.M196R variant and the risk for psoriasis and the response to treatment with anti-TNF or anti-Il-12/Il-23. The genotyping of this polymorphism could help to optimize the treatment by identifying patients with a likely poor response to biological drugs.

The antimicrobial peptide LL37 is a T-cell autoantigen in psoriasis

Psoriasis is a common T-cell-mediated skin disease with 2-3% prevalence worldwide. Psoriasis is considered to be an autoimmune disease, but the precise nature of the autoantigens triggering T-cell activation remains poorly understood. Here we find that two-thirds of patients with moderate-to-severe plaque psoriasis harbour CD4(+) and/or CD8(+) T cells specific for LL37, an antimicrobial peptide (AMP) overexpressed in psoriatic skin and reported to trigger activation of innate immune cells. LL37-specific T cells produce IFN-γ, and CD4(+) T cells also produce Th17 cytokines. LL37-specific T cells can infiltrate lesional skin and may be tracked in patients blood by tetramers staining. Presence of circulating LL37-specific T cells correlates significantly with disease activity, suggesting a contribution to disease pathogenesis. Thus, we uncover a role of LL37 as a T-cell autoantigen in psoriasis and provide evidence for a role of AMPs in both innate and adaptive immune cell activation.

The IL-17A-producing CD8+ T-cell population in psoriatic lesional skin comprises mucosa-associated invariant T cells and conventional T cells

IL-17A is pivotal in the etiology of psoriasis, and CD8(+) T cells with the ability to produce this cytokine (Tc17 cells) are over-represented in psoriatic lesions. Here we demonstrate that the frequency of Tc17 cells in peripheral blood of psoriasis patients correlated with the clinical severity of the disease. Analysis of cutaneous-associated lymphocyte antigen expression showed that the blood Tc17 population contains a significantly higher proportion of cells with skin-homing potential compared with the CD8(+) T-cell population lacking IL-17A/IL-22 expression. IL-17A-producing CD8(+) T cells in blood have previously been reported to belong mainly to the mucosa-associated invariant T-cell (MAIT cell) lineage characterized by TCR Vα7.2 chain, CD161, IL-18Rα, and multidrug transporter ABCB1 expression. We demonstrate the presence of CD8(+) MAIT cells in the dermis and epidermis of psoriatic plaques, as well as healthy skin; however, IL-17A-producing CD8(+) MAIT cells were predominantly found in psoriatic skin. Notably, we observed IL-17A production in a large proportion of psoriatic plaque-derived CD8(+) T cells devoid of MAIT cell characteristics, likely representing conventional CD8(+) T cells. In conclusion, we provide supporting evidence that implicates Tc17 cells in the pathogenesis of psoriasis and describe the presence of innate CD8(+) MAIT cells in psoriatic lesions as an alternative source of IL-17A.

Significance of association of HLA-C and HLA-E with psoriatic arthritis

Psoriatic arthritis (PsA) is a complex genetic disorder that results from an interplay between multiple genetic and environmental factors. The aim of the study was to assess the significance of the association between the HLA-C and HLA-E allelic groups and PsA. Our results confirm the association between HLA-C(∗)06 and PsA (OR=5.16, p<0.0001). Furthermore, HLA-C(∗)06-positive patients develop more severe disease (p<0.01) and more frequently present with polyarticular pattern of PsA (p=0.08). Additionally our study revealed that the HLA-C(∗)02 allele was more frequently observed in PsA patients (OR=5.40, p<0.0005) and also that the HLA-E(∗)01:01 allele was significantly over-represented among HLA-C(∗)02-negative patients in comparison to healthy individuals (OR=6.44, p=0.045). Therefore these results suggest that the HLA-E and HLA-C(∗)02 molecules may also play an important role in determination immune response contributing to the PsA development.

Lack of association of ALOX12 and ALOX15B polymorphisms with psoriasis despite altered urinary excretion of 12(S)-hydroxyeicosatetraenoic acid

BACKGROUND

Pro- and anti-inflammatory metabolites of arachidonic acid - eicosanoids - participate in skin homeostasis, affecting the growth and differentiation of keratinocytes. Alterations of 12-lipoxygenase (LOX) and 15-LOX and their metabolites have been described in the epidermis of patients with psoriasis, but systemic production of 12-LOX and 15-LOX eicosanoids has not been studied in the disease.

OBJECTIVES

To ascertain the frequencies of the genetic variants ALOX12 rs1126667 and ALOX15 rs11568070 in cases and controls, and to compare urinary metabolites of 12(S)-hydroxyeicosatetraenoic acid (HETE) between patients with psoriasis and healthy controls.

METHODS

Patients with psoriasis (n = 200) were stratified depending on the severity of their dermal lesions. Genotyping was performed using a 5'-nuclease real-time assay. The concentrations of 12(S)-HETE, its metabolites and 15(S)-HETE were determined in urine samples using high-performance liquid chromatography-tandem mass spectrometry.

RESULTS

Tetranor-12(S)-HETE metabolite excretion was significantly higher in urine of patients with psoriasis, while excretion of 12(S)-HETE was decreased. Neither 12(S)-HETE nor tetranor-12(S)-HETE correlated with the type of disease or severity score. No difference in urinary 15(S)-HETE was found between the study groups. Genotype distribution of the ALOX12 rs1126667 or ALOX15 rs11568070 polymorphisms did not discriminate for the disease or its severity.

CONCLUSIONS

Systemic metabolism of 12(S)-HETE is accelerated in psoriasis because excretion of the tetranor-12(S)-HETE inactivation product is elevated. No correlation with the severity or extent of psoriasis is detectable. We propose that in patients with psoriasis, 12(S)-HETE to tetranor-12(S)-HETE conversion could be at least a marker for this disease, in which inflammation of the skin can induce microsomal beta-oxidation of this eicosanoid.

Systemic Sclerosis is a Complex Disease Associated Mainly with Immune Regulatory and Inflammatory Genes

Systemic sclerosis (SSc) is a fibrotic and autoimmune disease characterized clinically by skin and internal organ fibrosis and vascular damage, and serologically by the presence of circulating autoantibodies. Although etiopathogenesis is not yet well understood, the results of numerous genetic association studies support genetic contributions as an important factor to SSc. In this paper, the major genes of SSc are reviewed. The most recent genome-wide association studies (GWAS) are taken into account along with robust candidate gene studies. The literature search was performed on genetic association studies of SSc in PubMed between January 2000 and March 2014 while eligible studies generally had over 600 total participants with replication. A few genetic association studies with related functional changes in SSc patients were also included. A total of forty seven genes or specific genetic regions were reported to be associated with SSc, although some are controversial. These genes include HLA genes, STAT4, CD247, TBX21, PTPN22, TNFSF4, IL23R, IL2RA, IL-21, SCHIP1/IL12A, CD226, BANK1, C8orf13-BLK, PLD4, TLR-2, NLRP1, ATG5, IRF5, IRF8, TNFAIP3, IRAK1, NFKB1, TNIP1, FAS, MIF, HGF, OPN, IL-6, CXCL8, CCR6, CTGF, ITGAM, CAV1, MECP2, SOX5, JAZF1, DNASEIL3, XRCC1, XRCC4, PXK, CSK, GRB10, NOTCH4, RHOB, KIAA0319, PSD3 and PSOR1C1. These genes encode proteins mainly involved in immune regulation and inflammation, and some of them function in transcription, kinase activity, DNA cleavage and repair. The discovery of various SSc-associated genes is important in understanding the genetics of SSc and potential pathogenesis that contribute to the development of this disease.

Allele-specific network reveals combinatorial interaction that transcends small effects in psoriasis GWAS

Hundreds of genetic markers have shown associations with various complex diseases, yet the “missing heritability” remains alarmingly elusive. Combinatorial interactions may account for a substantial portion of this missing heritability, but their discoveries have been impeded by computational complexity and genetic heterogeneity. We present BlocBuster, a novel systems-level approach that efficiently constructs genome-wide, allele-specific networks that accurately segregate homogenous combinations of genetic factors, tests the associations of these combinations with the given phenotype, and rigorously validates the results using a series of unbiased validation methods. BlocBuster employs a correlation measure that is customized for single nucleotide polymorphisms and returns a multi-faceted collection of values that captures genetic heterogeneity. We applied BlocBuster to analyze psoriasis, discovering a combinatorial pattern with an odds ratio of 3.64 and Bonferroni-corrected p-value of 5.01×10⁻¹⁶. This pattern was replicated in independent data, reflecting robustness of the method. In addition to improving prediction of disease susceptibility and broadening our understanding of the pathogenesis underlying psoriasis, these results demonstrate BlocBuster's potential for discovering combinatorial genetic associations within heterogeneous genome-wide data, thereby transcending the limiting “small effects” produced by individual markers examined in isolation.

Most complex diseases arise due to combinations of genetic factors, yet current genome-wide association studies (GWAS) typically examine individual genetic markers in isolation because of the complexity of considering a prohibitively large number of marker combinations. Another complication for GWAS stems from genetic heterogeneity, in which different subsets of individuals develop a given disease due to different sets of genetic factors. We present BlocBuster, a network-based method that addresses these challenges and extracts inter-correlated genetic markers that manifest significant associations with complex diseases. Our analysis of psoriasis GWAS data revealed a significant combinatorial genetic pattern, which was validated using stringent computational tests and replication in independent data. This pattern is more significant than other previously identified markers. We also compared Pearson's correlation coefficient and observed that it introduced more type I errors and produced a less structured network than BlocBuster; the former also broke the combinatorial pattern into pieces. In addition to improving prediction of disease susceptibility and broadening our understanding of the pathogenesis underlying psoriasis, these results demonstrate BlocBuster's effectiveness for discovering combinatorial genetic associations within heterogeneous backgrounds, thereby transcending the limiting “small effects” produced by individual markers examined in isolation.