An update on the genetics of psoriasis

Functional Genomics in Psoriasis

Psoriasis is an autoimmune cutaneous condition that significantly impacts quality of life and represents a burden on society due to its prevalence. Genome-wide association studies (GWASs) have pinpointed several psoriasis-related risk loci, underlining the disease's complexity. Functional genomics is paramount to unveiling the role of such loci in psoriasis and disentangling its complex nature. In this review, we aim to elucidate the main findings in this field and integrate our discussion with gold-standard techniques in molecular biology-i.e., Clustered Regularly Interspaced Short Palindromic Repeats (CRISPR)-and high-throughput technologies. These tools are vital to understanding how disease risk loci affect gene expression in psoriasis, which is crucial in identifying new targets for personalized treatments in advanced precision medicine.

Disentangling the complexity of psoriasis in the post-genome-wide association era

In recent years, genome-wide association studies (GWAS) have been instrumental in unraveling the genetic architecture of complex diseases, including psoriasis. The application of large-scale GWA studies in psoriasis has illustrated several associated loci that participate in the cutaneous inflammation, however explaining a fraction of the disease heritability. With the advent of high-throughput sequencing technologies and functional genomics approaches, the post-GWAS era aims to unravel the functional mechanisms underlying the inter-individual variability in psoriasis patients. In this review, we present the key advances of psoriasis GWAS in under-represented populations, rare, non-coding and structural variants and epistatic phenomena that orchestrate the interplay between different cell types. We further review the gene-gene and gene-environment interactions contributing to the disease predisposition and development of comorbidities through Mendelian randomization studies and pleiotropic effects of psoriasis-associated loci. We finally examine the holistic approaches conducted in psoriasis through system genetics and state-of-the-art transcriptomic analyses, discussing their potential implication in the expanding field of precision medicine and characterization of comorbidities.

The Role of Inflammation in the Pathogenesis of Psoriasis

"Psoriasis is a chronic inflammatory skin condition with genetic determinism characterized by the presence of welldefined, erythematous plaques, covered by white, pearly, stratified scales, located on the extension areas, the skin of the scalp, intertriginous regions. The origin of psoriasis is multifactorial, involving hereditary and environmental pathogenic mechanisms. It is triggered by various risk factors involving a variety of processes, such as inflammation, antigen presentation, cell signaling, and transcriptional regulation. "

Biological Treatments for Pediatric Psoriasis: State of the Art and Future Perspectives

Psoriasis is a chronic systemic inflammatory disease that primarily affects the skin and is associated with multiple comorbidities with a considerable reduction in quality of life of affected patients. One-third of psoriasis cases begin in childhood and are associated with significant medical comorbidities such as obesity, metabolic syndrome, arthritis, and psychiatric disorders. In addition, because of its chronic nature and frequent relapses, psoriasis tends to require long-term treatment. Treatment of pediatric psoriasis usually involves the same methods used for adults. However, most treatments for pediatric psoriasis are used off-label, and research in this regard is still lacking. Targeted therapies involving the use of newly developed biologic drugs are also increasingly being applied to childhood psoriasis. This review summarizes the clinical features of pediatric psoriasis and focuses mainly on the updated concepts of pathogenesis and biological treatments of pediatric psoriasis.

Gene interaction analysis of psoriasis in Chinese Han population

Background/aims

Psoriasis is a chronic immune‐mediated inflammatory skin disease characterized by excessive proliferation of keratinocytes. It has a strong genetic predisposition; gene‐gene interactions are important genetic models for common diseases. In this study, we explore pair‐wise interactions among SNPs contributing to psoriasis susceptibility.

Methods

We first performed gene interactions with exome‐sequencing, next, we analyzed gene interactions combining the exome sequencing data with the targeted sequencing data. After we sequenced HLA region, we analyzed gene interactions including HLA regions and non‐HLA regions.

Results

We found interactions between HLA regions were significant. We observed significant interactions between HLA‐C*06:02 and rs118179173 (snp31443520; p = 8.21 × 10⁻²⁰, OR = 0.22) and between HLA‐C*06:02 and HLA‐B:AA67 (p = 1.22 × 10⁻¹², OR = 0.45).

Conclusion

This study provides evidence that HLA is the most important susceptibility region on the risk of psoriasis and interactions that occur in this region are still significant.

Successful Treatment of Plaque Psoriasis with Allogeneic Gingival Mesenchymal Stem Cells: A Case Study

Plaque psoriasis is the most common type of psoriasis that manifests as red scaly patches with white scales affecting body areas including scalp, elbows, knees, trunk, and buttocks. Although many treatment options are available including novel biologics, no cure is available. Mesenchymal stem cells (MSCs) have been safely used to treat a variety of human diseases. Allogeneic MSCs possess unique characteristics including hypoimmunogenicity, immunomodulatory, and anti-inflammatory properties, and they are currently being explored for potential therapeutic use for many systemic inflammatory diseases. The human gingival tissue is an easily accessible and obtainable source for the isolation of MSCs. MSCs from adult human gingiva are of fetal-like phenotype, multipotent, and easy to isolate and expand in vitro. Herein, we report a case of a 19-year-old man with a 5-year history of severe plaque psoriasis refractory to multiple topical and systemic therapies who was treated with allogeneic human gingival MSCs. Complete regression was achieved after 5 infusions with no adverse reaction occurred. The patient has been followed for three years and has remained disease free.

Anti-Atopic Dermatitis Effect of Seaweed Fulvescens Extract via Inhibiting the STAT1 Pathway

Seaweed fulvescens (SF) is a green alga rich in chlorophyll with unique flavor and taste. It is also called Maesaengi which has antioxidant and other physiological activities. In the present study, we evaluated the therapeutic effects of SF in a mouse model of Dermatophagoides farinae body-induced atopic dermatitis (AD) and in tumor necrosis factor-α and interferon-γ-stimulated HaCaT keratinocytes. SF treatment (200 mg/mouse) inhibited the development of AD symptoms, compared to that in the control group, as evidenced from the improved dorsal skin lesion, reduced thickness and infiltration of inflammatory cells and smaller lymph nodes, and reduced levels of proinflammatory cytokines. In HaCaT keratinocytes, SF (10, 25, and 50 μg/mL) suppressed the production of proinflammatory cytokines in a dose-dependent manner. In addition, SF reduced the phosphorylation of signal transducer and activator of transcription 1, which is one of the major signaling molecules involved in cellular inflammation. These results suggested that SF could be a potential therapeutic alternative for the treatment of AD.

Pediatric psoriasis: Evolving perspectives

BACKGROUND/OBJECTIVES

Childhood-onset psoriasis is a common skin disorder that has recently received increasing attention, particularly because of its significant medical, social, financial, and psychological burdens and its associated comorbidities. With limited data available and lack of standardized management guidelines for pediatric psoriasis, an expert panel desired to provide an updated critical overview and practical guidance for management of the affected population.

METHODS

A panel of pediatric dermatologists with extensive experience in pediatric psoriasis defined and prioritized a core set of topics, performed an English-language literature review, prepared critical evaluations and presentations of topic areas, and carried out a consensus meeting and follow-up consensus manuscript.

RESULTS

The summation of evolving perspectives in pediatric psoriasis includes epidemiology and natural history of the disease, precipitating factors and comorbidities, quality of life and burden of disease, clinical features and disease presentation, differential diagnosis, pathogenesis and treatment, including topical, photo, and systemic therapies.

CONCLUSION

Pediatric psoriasis is an important immune-mediated inflammatory skin disease with potential for significant impact on affected individuals and their caregivers. Current state-of-the-art care is based primarily on experience and expert consensus, but pediatric data are accumulating and therapeutic options are rapidly evolving.

Seasonality and BDNF polymorphism influences depression outcome in patients with atopic dermatitis and psoriasis

OBJECTIVES

To examine the effect of seasonality and rs6265 genotype on depression outcome and brain-derived neurotrophic factor (BDNF) level with dermatitis patients from onset through remission.

METHODS

Atopic dermatitis (AD, 56) and psoriasis (PS, 33) patients and healthy controls (HC, 49) were recruited over the 2014 calendar year. Patients were subdivided by immunoglobulin E (IgE) sensitivity (AD only), season and rs6265 genotype. Assessments were performed at onset and week 10 (Hamilton Depression Rating Scale [HAM-D], SCORAD/PASI, IgE, BDNF). Patients received standard corticosteroid and antihistamine interventions.

RESULTS

All patients responded to corticosteroid treatment. Seasonally differential outcomes were observed in all groups. HAM-D was elevated at onset and improved over 10 weeks: AD cohort 1 (autumn/winter, AD-1) patients improved and AD cohort 2 (spring/summer, AD-2) patients remained elevated. BDNF levels were elevated in AD and seasonal differential: AD-2 declined at 10 weeks, whereas AD-1 remained high (intrinsic AD) or elevated further (extrinsic AD). PS cohort 2 declined to below control at 10 weeks. AD Val/Val had persistently elevated HAM-D and AD Val/Met were either normal (AD-1) or persistently elevated (AD-2).

CONCLUSIONS

Findings presented here suggest a strong influence of seasonality on depression outcome and BDNF expression in AD and PS and likely reflect separate patient populations which differentially respond to environment-based stressors.

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.

Identification of single nucleotide polymorphisms in Toll-like receptor candidate genes associated with tuberculosis infection in water buffalo (Bubalus bubalis)

Background

Toll-like receptors play a key role in innate immunity by recognizing pathogens and activating appropriate responses. Pathogens express several signal molecules (pathogen-associated molecular patterns, PAMPs) essential for survival and pathogenicity. Recognition of PAMPs triggers an array of anti-microbial immune responses through the induction of various inflammatory cytokines. The objective of this work was to perform a case-control study to characterize the distribution of polymorphisms in three candidate genes (toll-like receptor 2, toll-like receptor 4, toll-like receptor 9) and to test their role as potential risk factors for tuberculosis infection in water buffalo (Bubalus bubalis).

Results

The case-control study included 184 subjects, 59 of which resulted positive to both intradermal TB test and Mycobacterium bovis isolation (cases) and 125 resulted negative to at least three consecutive intradermal TB tests. The statistical analysis indicated that two polymorphisms exhibited significant differences in allelic frequencies between cases and controls. Indeed, the TT genotype at TLR9 2340 C > T locus resulted significantly associated with susceptibility to bovine tuberculosis (P = 0.030, OR = 3.31, 95% CI = 1.05-10.40). One polymorphism resulted significantly associated with resistance to the disease, and included the CC genotype, at the TLR4 672 A > C locus (P = 0.01, OR = 0.26, 95% CI = 0.08-0.80). Haplotype reconstruction of the TLR2 gene revealed one haplotype (CTTACCAGCGGCCAGTCCC) associated with disease resistance (P = 0.04, OR = 0.51, 95% CI = 0.27–0.96), including the allelic variant associated with disease resistance.

Conclusions

The work describes novel mutations in bubaline TLR2, TLR4 and TLR9 genes and presents their association with M. bovis infection. These results will enhance our ability to determine the risk of developing the disease by improving the knowledge of the immune mechanisms involved in host response to mycobacterial infection, and will allow the creation of multiple layers of disease resistance in herds by selective breeding.

What can the genetics of psoriasis teach us about alopecia areata?

Previous genetic epidemiological studies of psoriasis and alopecia areata demonstrated strong heritability in first-degree relatives and in twins. In recent years, these two conditions have emerged as two skin diseases that are starting to yield their secrets through genome-wide association studies. Both diseases manifest prominent human leukocyte antigen (HLA) associations, psoriasis primarily with major histocompatibility complex (MHC) Class 1, specifically HLA-Cw6, and alopecia areata primarily with MHC Class II. Despite these differences in HLA associations, both diseases have in common a prominent role for CD8+ lymphocytes. The purpose of this brief review is to present the recent developments in the genetics of psoriasis.

Lifting the silver flakes: the pathogenesis and management of chronic plaque psoriasis

Psoriasis is a common chronic inflammatory skin condition in which patients suffer from mild to chronic plaque skin plaques. The disease manifests through an excessive inflammatory response in the skin due to complex interactions between different genetic and environmental factors. Psoriasis can affect the physical, emotional, and psychosocial well-being of patients, and currently there is no cure with treatments focusing primarily on the use of anti-inflammatory agents to control disease symptoms. Traditional anti-inflammatory agents can cause immunosuppression and adverse systemic effects. Further understanding of the disease has led to current areas of research aiming at the development of selective molecular targets to suppress the pathogenic immune responses.

Analysis of genetic variants of class II cytokine and their receptor genes in psoriasis patients of two ethnic groups from the Volga-Ural region of Russia

BACKGROUND

The molecular basis of pathogenesis of psoriasis remains unclear, but one unifying hypothesis of disease aetiology is the cytokine network model. The class II cytokines (CF2) and their receptors (CRF2) are all involved in the inflammatory processes and single nucleotide polymorphisms (SNPs) in respective genes have been associated with psoriasis in a previous study of the Estonian population.

OBJECTIVE

We performed a replication study of 47 SNPs in CF2 and CRF2 genes in independent cohorts of psoriasis patients of two ethnic groups (Russians and Bashkirs) from the Volga-Ural region of Russia.

METHODS

DNA was obtained from 395 psoriasis patients of two ethnic groups from the Volga-Ural region of Russia and 476 ethnically matched controls. 47 SNPs in the loci of the genes encoding Class II cytokines and their receptors were selected by SNPbrowser version 3.5. Genotyping was performed using the SNPlex™ (Applied Biosystems) platform.

RESULTS

The genetic variant rs30461 previously associated in original case-control study in Estonians, was also associated in Russians (corrected P-value (Pc=0.008, OR=0.44), but did not reach statistical significance in the Bashkir population. Additionally, the haplotype analysis provided that CC haplotype formed by the SNPs rs30461 and rs955155 had a protective effect in Russians (Pc=0.0024, OR=0.44), supporting the involvement of this locus in the protection against psoriasis. Combined meta-analysis of three populations, including 943 psoriasis patients and 812 healthy controls, showed that the IL29 rs30461 C-allele was not associated with decreased risk of psoriasis (P=0.165, OR=0.68). Moreover, stratification of studies by ethnicity revealed a significant association in the European cohort (P=9.506E-006, OR=0.53).

CONCLUSION

Therefore, there is no overall evidence of association between psoriasis and SNP rs30461 of the IL29 gene, but there is some evidence to suggest that an association exists in Europeans. However, this current concept should be considered as preliminary and the results need to be confirmed in future independent studies.

Genetics of psoriasis and psoriatic arthritis: a report from the GRAPPA 2010 annual meeting

Psoriasis vulgaris (PsV) and psoriatic arthritis (PsA) are interrelated disorders, PsA representing a disease within a disease. From an epidemiological perspective, the genetic contributions of PsV and PsA are now well documented. HLA-C is firmly established as a PsV/PsA gene, with HLA-Cw*0602 as a major risk allele. Fine-mapping studies within the MHC region in PsV and PsA have identified novel loci that are independent of the HLA-Cw6 allele. Recent genome-wide association scans have led to a substantial increase in the number of candidate genes reaching genome-wide significance in PsV and PsA cohorts. Most of these genes can be grouped into an integrated pathogenic model of PsV/psoriatic disease comprising distinct signaling networks affecting skin barrier function (LCE3, DEFB4, GJB2), innate immune responses involving nuclear factor-κB and interferon signaling (TNFAIP3, TNIP1, NFKBIA, REL, FBXL19, TYK2, NOS2), and adaptive immune responses involving CD8 T lymphocytes and interleukin 23 (IL-23)/IL-17-mediated lymphocyte signaling (HLA-C, IL12B, IL23R, IL23A, TRAF3IP2, ERAP1). Further development of a global genetic risk score and inclusion of potential gene/gene and gene/environment interactions will likely enhance the predictive value of recently identified genetic variants.

Psoriasis and other complex trait dermatoses: from Loci to functional pathways

Driven by advances in molecular genetic technologies and statistical analysis methodologies, there have been huge strides taken in dissecting the complex genetic basis of many inflammatory dermatoses. One example is psoriasis, for which application of classical linkage analysis and genome-wide association investigation has identified genetic loci of major and minor effect. Although most loci independently have modest genetic effects, they identify important biological pathways potentially relevant to disease pathogenesis and therapeutic intervention. In the case of psoriasis, these appear to involve the epidermal barrier, NF-κB mechanisms, and T helper type 17 adaptive immune responses. The advent of next-generation sequencing methods will permit a more detailed and complete map of disease genetic architecture, a key step in developing personalized medicine strategies in the clinical management of the complex inflammatory dermatoses.

Psoriasis regression analysis of MHC loci identifies shared genetic variants with vitiligo

Psoriasis is a common inflammatory skin disease with genetic components of both immune system and the epidermis. PSOR1 locus (6q21) has been strongly associated with psoriasis; however, it is difficult to identify additional independent association due to strong linkage disequilibrium in the MHC region. We performed stepwise regression analyses of more than 3,000 SNPs in the MHC region genotyped using Human 610-Quad (Illumina) in 1,139 cases with psoriasis and 1,132 controls of Han Chinese population to search for additional independent association. With four regression models obtained, two SNPs rs9468925 in HLA-C/HLA-B and rs2858881 in HLA-DQA2 were repeatedly selected in all models, suggesting that multiple loci outside PSOR1 locus were associated with psoriasis. More importantly we find that rs9468925 in HLA-C/HLA-B is associated with both psoriasis and vitiligo, providing first important evidence that two major skin diseases share a common genetic locus in the MHC, and a basis for elucidating the molecular mechanism of skin disorders.

Psoriasis: from pathogenesis to novel therapeutic approaches

Psoriasis is one of the commonest chronic inflammatory disorders. Its cause is unknown, but a wealth of studies indicate that the disease results from a complex and dynamic interplay between genetic and environmental factors that trigger an excessive inflammatory response in the skin. Dendritic cells and effector T-cells are central in the development of the psoriastic lesion, and cytokines produced by these cells stimulate keratinocytes to proliferate and increase the migration of inflammatory cells into the skin, promoting epidermal hyperplasia and inflammation. Understanding the immunology of the psoriatic plaque has led to new therapeutic options and novel candidates for immunomodulation, and has changed the ways psoriatic patients are managed.

Psoriasis: what we have learned from mouse models

Psoriasis is a common inflammatory skin disease of unknown etiology, for which there is no cure. This heterogeneous, cutaneous, inflammatory disorder is clinically characterized by prominent epidermal hyperplasia and a distinct inflammatory infiltrate. Crosstalk between immunocytes and keratinocytes, which results in the production of cytokines, chemokines and growth factors, is thought to mediate the disease. Given that psoriasis is only observed in humans, numerous genetic approaches to model the disease in mice have been undertaken. In this Review, we describe and critically assess the mouse models and transplantation experiments that have contributed to the discovery of novel disease-relevant pathways in psoriasis. Research performed using improved mouse models, combined with studies employing human cells, xenografts and patient material, will be key to our understanding of why such distinctive patterns of inflammation develop in patients with psoriasis. Indeed, a combination of genetic and immunological investigations will be necessary to develop both improved drugs for the treatment of psoriasis and novel curative strategies.

Progress in understanding the immunopathogenesis of psoriasis

This review emphasizes how translation from bench research to clinical knowledge and vice versa has resulted in considerable progress in understanding the immunopathogenesis of psoriasis. First, the journey in understanding the pathogenic mechanisms behind psoriasis is described. The roles of different components of the adaptive and innate immune systems involved in driving the inflammatory response are explained. Discovery of new immune pathways i.e. the IL23/Th17 axis and its subsequent impact on the development of novel biological therapies is highlighted. Identification of potential targets warranting further research for future therapeutic development are also discussed.

Down-regulation of IL-6, IL-8, TNF-α and IL-1β by glucosamine in HaCaT cells, but not in the presence of TNF-α

There is considerable evidence that glucosamine exerts an inhibitory effect on inflammatory cytokine expression in cells. Glucosamine has been recommended as a promising anti-inflammatory modulator, which has been applied in clinical trials for attenuation of the inflammatory process. However, it is unknown whether glucosamine reduces the expression of TNF-α-induced inflammatory cytokines in HaCaT cells. The anti-inflammatory effects of curcumin in HaCaT cells have been extensively investigated in several studies. Thus, in this study we investigated the expression of IL-6, IL-8, TNF-α and IL-1β in glucosamine-treated HaCaT cells, and the effects of glucosamine were compared to those of curcumin-treated HaCaT cells. Our data showed that the expression of IL-6, IL-8, TNF-α and IL-1β was decreased by glucosamine treatment in the HaCaT cells. In contrast, the expression of IL-6, IL-8, TNF-α and IL-1β was not attenuated by glucosamine treatment in the TNF-α-treated HaCaT cells. Notably, curcumin induced an increased expression of IL-8 and IL-1β in the HaCaT cells, but not that of IL-6 and TNF-α. On the other hand, curcumin attenuated the expression of IL-6 and IL-8 in the TNF-α-treated HaCaT cells. Our data indicated that glucosamine induced the down-regulation of IL-6, IL-8, TNF-α and IL-1β expression in the HaCaT cells. However, the stimulation of TNF-α abolished the inhibitory effects of glucosamine on the expression of inflammatory cytokines in the HaCaT cells. Thus, even though glucosamine induces the down-regulation of inflammatory cytokines in HaCaT cells, the anti-inflammatory role of glucosamine in TNF-α-mediated inflammatory skin diseases should be investigated.

Studying of relationship of Histocompatibility antigens and N-acetylation phenotype in patients of Uzbek populations with psoriasis

There studied the distribution of Histocompatibility antigens and N-acetylation phenotype in patients of Uzbek populations with psoriasis and it has been revealed, that HLA antigenes A11, A28, В5, В13 and Cw3 are antigenes of predisposition to presented disease and the individuals with slow N-acetylation phenotype prevail among them. The relationship of more frequent associated Histocompatibility antigens and N-acetylation phenotype marked by the prevalence of patients with a slow phenotype in the dermatosis has been revealed in patients of Uzbek populations with psoriasis.

Molecular dissection of psoriasis: integrating genetics and biology

Psoriasis is a common and debilitating disease of the skin, nails, and joints, with an acknowledged but complex genetic basis. Early genome-wide linkage studies of psoriasis focused on segregation of microsatellite markers in families; however, the only locus consistently identified resided in the major histocompatibility complex. Subsequently, several groups mapped this locus to the vicinity of HLA-C, and two groups have reported HLA-Cw6 itself to be the major susceptibility allele. More recently, the development of millions of single-nucleotide polymorphisms, coupled with the development of high-throughput genotyping platforms and a comprehensive map of human haplotypes, has made possible a genome-wide association approach using cases and controls rather than families. Taking advantage of these developments, we participated in a collaborative genome-wide association study of psoriasis involving thousands of cases and controls. Initial analysis of these data revealed and/or confirmed association between psoriasis and seven genetic loci-HLA-C, IL12B, IL23R, IL23A, IL4/IL13, TNFAIP3, and TNIP1-and ongoing studies are revealing additional loci. Here, we review the epidemiology, immunopathology, and genetics of psoriasis, and present a disease model integrating its genetics and immunology.

Multiple Loci within the major histocompatibility complex confer risk of psoriasis

Psoriasis is a common inflammatory skin disease characterized by thickened scaly red plaques. Previously we have performed a genome-wide association study (GWAS) on psoriasis with 1,359 cases and 1,400 controls, which were genotyped for 447,249 SNPs. The most significant finding was for SNP rs12191877, which is in tight linkage disequilibrium with HLA-Cw*0602, the consensus risk allele for psoriasis. However, it is not known whether there are other psoriasis loci within the MHC in addition to HLA-C. In the present study, we searched for additional susceptibility loci within the human leukocyte antigen (HLA) region through in-depth analyses of the GWAS data; then, we followed up our findings in an independent Han Chinese 1,139 psoriasis cases and 1,132 controls. Using the phased CEPH dataset as a reference, we imputed the HLA-Cw*0602 in all samples with high accuracy. The association of the imputed HLA-Cw*0602 dosage with disease was much stronger than that of the most significantly associated SNP, rs12191877. Adjusting for HLA-Cw*0602, there were two remaining association signals: one demonstrated by rs2073048 (p = 2×10⁻⁶, OR = 0.66), located within c6orf10, a potential downstream effecter of TNF-alpha, and one indicated by rs13437088 (p = 9×10⁻⁶, OR = 1.3), located 30 kb centromeric of HLA-B and 16 kb telomeric of MICA. When HLA-Cw*0602, rs2073048, and rs13437088 were all included in a logistic regression model, each of them was significantly associated with disease (p = 3×10⁻⁴⁷, 6×10⁻⁸, and 3×10⁻⁷, respectively). Both putative loci were also significantly associated in the Han Chinese samples after controlling for the imputed HLA-Cw*0602. A detailed analysis of HLA-B in both populations demonstrated that HLA-B*57 was associated with an increased risk of psoriasis and HLA-B*40 a decreased risk, independently of HLA-Cw*0602 and the C6orf10 locus, suggesting the potential pathogenic involvement of HLA-B. These results demonstrate that there are at least two additional loci within the MHC conferring risk of psoriasis.

Psoriasis (Ps) is a chronic inflammatory disease of the skin, affecting approximately 2% of Europeans. The HLA-C gene, located within the major histocompatibility complex (MHC) region on chromosome 6, is the major genetic determinant of psoriasis. However, multiple susceptibility genes within MHC are also hypothesized. Recently, we carried out a genome-wide association scan (GWAS) on psoriasis with 1,359 patients and 1,400 healthy controls, which identified seven psoriasis loci in the human genome and confirmed the effect of HLA-C. This dataset contains densely distributed genetic variations, single nucleotide polymorphisms (SNPs), which were then further analyzed in search for additional susceptibility genes within the MHC region. Using the SNP data, we imputed in all samples the HLA-C risk allele with high accuracy. Adjusting for the HLA-C, two additional loci, one near C6orf10 and one near HLA-B/MICA, have significant associations with psoriasis, which were also observed in an independent Han Chinese dataset, suggesting that within the MHC there are at least three genes moderating susceptibility to psoriasis.

Association of skin barrier genes within the PSORS4 locus is enriched in Singaporean Chinese with early-onset psoriasis

Psoriasis (OMIM#177900) is a common polygenic skin disorder affecting approximately 2% of the northern European population and 0.1% of the Han Chinese. Psoriasis patients suffer from chronic skin inflammation, manifested by erythematous scaly lesions. PSORS1-PSORS9 have been confirmed as psoriasis susceptibility loci in independent genetic studies on predominantly Caucasian populations, with psoriasis susceptibility loci (PSORS1, PSORS9) and additional loci at 9q33-34 and 2p22.3-11.2 reported in Han Chinese patients. In this study, we show the association of PSORS4 with psoriasis in Singaporean Chinese. Dense genotyping of single-nucleotide polymorphism-tagging candidate genes within the epidermal differentiation complex revealed significant association in the proximity of the involucrin gene (IVL); the strongest association was seen in early-onset psoriasis patients (P=0.0014). A follow-up genome-wide association screen localized the psoriasis susceptibility region to approximately 360 kb along chromosome 1 in the vicinity of IVL, small proline-rich region (SPRR) and proline-rich region 9 (PRR9) genes. The study of interactions between the causative variant(s) in this locus will provide insights into a possible role for epidermal barrier formation in the pathogenesis of psoriasis.

Combined effects of HLA-Cw6 and cigarette smoking in psoriasis vulgaris: a hospital-based case-control study in China

BACKGROUND

Psoriasis is not only related to genetic factors but also to environmental factors. However, the combined effect of genetic and environmental factors in the development of psoriasis has still been unclear.

OBJECTIVE

The study was to analyze the combined effect of HLA-Cw6 and smoking on psoriasis vulgaris.

METHODS

A hospital-based case-control was conducted study. One hundred seventy-eight cases and 178 controls received this epidemiological investigation and HLA typing by polymerase chain reaction utilizing sequence-specific primers.

RESULTS

The risk of psoriasis was related to smoking, the adjusted odds ratio (OR) being 2.07 (P < 0.01), and there is a graded positive association between the risk of psoriasis and intensity or duration of smoking. Stressful life events increased the risk of psoriasis (OR = 7.87, P < 0.01). We found the waist-hip ratio (WHR) increased the risk of psoriasis vulgaris, and OR was 2.67 (P < 0.01) in China. Individuals harboring the HLA-Cw6 gene obviously increased the risk of psoriasis, OR being 9.93 (P < 0.01) after adjusted for potential confounder factors, while the OR of psoriasis for HLA-B57 was 2.41 (P < 0.05). Significant combined effect between HLA-Cw6 and HLA-B57 for psoriasis was found (OR = 10.51, P < 0.01). A striking finding is that the risk of psoriasis for smokers with HLA-Cw6 increased about 11-fold than non-smokers without HLA-Cw6, and the risk increased some 20-fold in individuals with HLA-Cw6 having stressful life events compared with one without HLA-Cw6 and stressful life events.

CONCLUSION

Our study suggested that the combined effect between HLA-Cw6 and cigarette smoking or stressful life events may play an important role in the development of psoriasis vulgaris in Han Chinese population.

The 5q31 variants associated with psoriasis and Crohn's disease are distinct

Predisposition to psoriasis is known to be affected by genetic variation in HLA-C, IL12B and IL23R, but other genetic risk factors also exist. We recently reported three psoriasis-associated single nucleotide polymorphisms (SNPs) in the 5q31 locus, a region of high linkage disequilibrium laden with inflammatory pathway genes. The aim of this study was to assess whether other variants in the 5q31 region are causal to these SNPs or make independent contributions to psoriasis risk by genotyping a comprehensive set of tagging SNPs in a 725 kb region bounded by IL3 and IL4 and testing for disease association. Ninety SNPs, capturing 86.4% of the genetic diversity, were tested in one case–control sample set (467 cases/460 controls) and significant markers (P_allelic < 0.05) (n = 9) were then tested in two other sample sets (981 cases/925 controls). All nine SNPs were significant in a meta-analysis of the combined sample sets. Pair-wise conditional association tests showed rs1800925, an intergenic SNP located just upstream of IL13 (Mantel–Haenszel P_combined = 1.5 × 10⁻⁴, OR = 0.77 [0.67–0.88]), could account for observed significant association of all but one other SNP, rs11568506 in SLC22A4 [Mantel–Haenszel P_combined = 0.043, OR = 0.68 (0.47–0.99)]. Haplotype analysis of these two SNPs showed increased significance for the two common haplotypes (rs11568506–rs1800925: GC, P_combined = 5.67 × 10⁻⁶, OR = 1.37; GT, P_combined = 6.01 × 10⁻⁵, OR = 0.75; global haplotype P = 8.93 × 10⁻⁵). Several 5q31-region SNPs strongly associated with Crohn's disease (CD) in the recent WTCCC study were not significant in the psoriasis sample sets tested here. These results identify the most significant 5q31 risk variants for psoriasis and suggest that distinct 5q31 variants contribute to CD and psoriasis risk.

Identification of ZNF313/RNF114 as a novel psoriasis susceptibility gene

Psoriasis is an immune-mediated skin disorder that is inherited as a multifactorial trait. Linkage studies have clearly identified a primary disease susceptibility locus lying within the major histocompatibility complex (MHC), but have generated conflicting results for other genomic regions. To overcome this difficulty, we have carried out a genome-wide association scan, where we analyzed more than 408,000 SNPs in an initial sample of 318 cases and 288 controls. Outside of the MHC, we observed a single cluster of disease-associated markers, spanning 47 kb on chromosome 20q13. The analysis of two replication data sets confirmed this association, with SNP rs495337 yielding a combined P-value of 1.4 x 10(-8) in an overall sample of 2679 cases and 2215 controls. Rs495337 maps to the SPATA2 transcript and is in absolute linkage disequilibrium with five SNPs lying in the adjacent ZNF313 gene (also known as RNF114). Real-time PCR experiments showed that, unlike SPATA2, ZNF313 is abundantly expressed in skin, T-lymphocytes and dendritic cells. Furthermore, an analysis of the expression data available from the Genevar database indicated that rs495337 is associated with increased ZNF313 transcripts levels (P = 0.003), suggesting that the disease susceptibility allele may be a ZNF313 regulatory variant tagged by rs495337. Homology searches indicated that ZNF313 is a paralogue of TRAC-1, an ubiquitin ligase regulating T-cell activation. We performed cell-free assays and confirmed that like TRAC-1, ZNF313 binds ubiquitin via an ubiquitin-interaction motif (UIM). These findings collectively identify a novel psoriasis susceptibility gene, with a putative role in the regulation of immune responses.

Psoriasis: the epidermal component

Besides the infiltrate of immune cells in psoriatic lesions, the principal characteristic changes in the skin are changes of the epidermal architecture and alterations of keratinocyte differentiation, which are distinct from other inflammatory skin diseases clinically and histologically. Several lines of evidence suggest that 3 of the 9 psoriasis susceptibility loci identified today might play a role in the keratinocyte differentiation program. Therefore, besides the dysregulation of the immune system, intrinsic epidermal components are also likely to play a role in triggering and/or sustaining the disease process and contribute to the chronicity of psoriasis and its frequent relapses.

Psoriasis: epidemiology

Psoriasis is a chronic, inflammatory and hyperproliferative skin disease with a genetic basis. While epidermal hyperplasia and altered keratinocyte differentiation are prominent features, considerable evidence indicates that psoriasis is immunologically mediated. Recently, the identification of HLA-Cw6 as the disease allele conferring susceptibility to psoriasis has provided a focus for elucidation of these events. In this article, we will focus on the epidemiology of psoriasis and its associated arthritis.

Altered claudin expression is a feature of chronic plaque psoriasis

Epithelial tight junctions play a central role in cell-cell adhesion and are necessary for the selective paracellular movement of ions. Claudins are key components of tight junctions and their expression is altered in gut epithelia in a variety of inflammatory enteropathies, including ulcerative colitis and Crohn's disease. Psoriasis is a chronic inflammatory skin disease affecting approximately 2% of the western population, with significantly increased occurrence in individuals with Crohn's disease. Initial studies investigated the expression of claudins in skin of healthy volunteers and patients with chronic plaque psoriasis. We report here that claudins-1 and -3 are the major protein species present in the epidermis of healthy skin; they are expressed on the surface of epidermal keratinocytes, consistent with their localization to tight junctions. In plaques of psoriasis, claudin-1 was not identifiable in the epidermis, although typical staining patterns were observed in clinically normal, uninvolved skin of patients with psoriasis. Claudin-3 was present in the epidermal granular cell layer in normal skin, but was only identified within the cytosol of epidermal keratinocytes in both involved and uninvolved skin of psoriasis patients. We examined further whether exposure of keratinocytes in vitro to pro-inflammatory cytokines mimicked the observed changes in claudin expression seen in chronic plaque psoriasis; lipopolysaccharide, interferon-gamma and tumour necrosis factor-alpha had no effect on claudin protein expression or distribution. Addition of interleukin-1beta, however, resulted in down-regulation of claudins-1 and -3. Tumour necrosis factor-alpha and interleukin-1beta were further used in an in vivo model of skin inflammation; interleukin-1beta alone modulated claudin protein expression in this system. These data demonstrate that epidermal claudin expression is altered in chronic plaque psoriasis and that expression is in part modulated by interleukin-1beta.

Pathogenesis and clinical features of psoriasis

Psoriasis, a papulosquamous skin disease, was originally thought of as a disorder primarily of epidermal keratinocytes, but is now recognised as one of the commonest immune-mediated disorders. Tumour necrosis factor alpha, dendritic cells, and T-cells all contribute substantially to its pathogenesis. In early-onset psoriasis (beginning before age 40 years), carriage of HLA-Cw6 and environmental triggers, such as beta-haemolytic streptococcal infections, are major determinants of disease expression. Moreover, at least nine chromosomal psoriasis susceptibility loci have been identified. Several clinical phenotypes of psoriasis are recognised, with chronic plaque (psoriasis vulgaris) accounting for 90% of cases. Comorbidities of psoriasis are attracting interest, and include impairment of quality of life and associated depressive illness, cardiovascular disease, and a seronegative arthritis known as psoriatic arthritis. A more complete understanding of underlying pathomechanisms is leading to new treatments, which will be discussed in the second part of this Series.

Psoriasis vulgaris and human leukocyte antigens

BACKGROUND

Psoriasis vulgaris is a skin disease with a complex immunological and genetic background, triggered by environmental factors. The association of human leukocyte antigens (HLA) and psoriasis has long been reported on population and familial studies.

OBJECTIVES

To review and discuss studies on psoriasis vulgaris and HLA, in Caucasian and non-Caucasian populations.

METHODS

The major population studies on psoriasis vulgaris and the associated HLA antigens and alleles are described and discussed based on a review of the current literature.

RESULTS

Population studies demonstrate the presence of different HLA specificities as well as extended haplotypes in patients with psoriasis, when compared to controls. Some alleles occur in a lower frequency in patients with psoriasis, indicating they could be protection alleles. In all studies which HLA class I was typed, Cw6 or Cw*0602 was present in a significant frequency in patients with psoriasis, mainly when early onset and positive family history were considered. HLA-DRB1*0701 was also present in a higher frequency in patients in different populations.

CONCLUSIONS

Different antigens and alleles from both HLA classes I and II were seen in a significantly higher frequency in patients with psoriasis vulgaris. HLA Cw*0602 and DRB1*0701 were represented in different reports, and the former was related mainly to psoriasis type I.

Sequence variants in the genes for the interleukin-23 receptor (IL23R) and its ligand (IL12B) confer protection against psoriasis

Psoriasis is an inflammatory skin disorder that is inherited as a multifactorial trait. Genetic analyses have repeatedly identified a primary disease susceptibility locus lying within the major histocompatibility complex (MHC), on chromosome 6p21. A small number of non-MHC susceptibility loci have also been identified. These regions tend to overlap with susceptibility intervals for Crohn's disease and atopic dermatitis, suggesting the possibility that genetic variants affecting inflammatory pathways may contribute to the pathogenesis of multiple disorders. Here, we report a genetic analysis of the interleukin 23 receptor gene (IL23R), which was recently identified as a susceptibility determinant for Crohn's disease. We initially examined the results of a whole-genome association scan, carried out on 318 cases and 288 controls. We observed a significant increase of a non-synonymous substitution (p.Arg381Gln) among controls (P = 0.00036). We validated this finding by extending our cohort to include a further 519 cases and 528 controls. In the overall sample, the frequency of the 381Gln allele was 3.6% in cases and 7% in controls, yielding a P value of 0.00014. Next, we examined genetic variation at the IL12RB1, IL23A and IL12B genes, respectively, encoding the second subunit of the IL23R receptor and the two subunits of its ligand. This analysis identified independent associations for IL12B SNPs rs10045431 (P value for the extended dataset = 0.0001) and rs3212227 (P = 0.036). Altogether, these findings indicate that genes participating in IL23 signalling play a significant role in the pathogenesis of chronic epithelial inflammation.

Filaggrin null alleles are not associated with psoriasis

Psoriasis is a common skin disease with an etiology consistent with a multifactorial trait. Several psoriasis susceptibility loci are known, a number of which are also implicated in a predisposition to atopic dermatitis (AD), including the epidermal differentiation complex on chromosome 1q21. It has recently been shown in several replicate studies that prevalent null alleles for the filaggrin gene (FLG) on 1q21 are an important genetic factor in AD. Here, we examined the role of these FLG variants in psoriasis using case:control association studies comparing Irish and UK psoriasis cohorts (combined n=691) to ethnically matched populations (combined n=2117). No association was present for the two common European FLG mutations R501X and 2282del4 (combined chi2 P=0.989). In addition, the 3' end of the FLG open-reading frame was sequenced in a number of patients with differing types of psoriasis (plaque, guttate, palmoplantar, and late-onset), which excluded the possibility of a gain-of-function frameshift mutation such as those found in loricrin or certain keratin genes. These data suggest that FLG mutations are unlikely to be involved in genetic susceptibility to psoriasis and implies that there may be within-locus heterogeneity in chromosomal regions involved in both AD and psoriasis.