Genetics of susceptibility and treatment response in psoriatic arthritis

Recent Advances in Biosensors for Diagnosis of Autoimmune Diseases

Over the last decade, autoimmune diseases (ADs) have undergone a significant increase because of genetic and/or environmental factors; therefore, their simple and fast diagnosis is of high importance. The conventional diagnostic techniques for ADs require tedious sample preparation, sophisticated instruments, a dedicated laboratory, and qualified personnel. For these reasons, biosensors could represent a useful alternative to these methods. Biosensors are considered to be promising tools that can be used in clinical analysis for an early diagnosis due to their high sensitivity, simplicity, low cost, possible miniaturization (POCT), and potential ability for real-time analysis. In this review, recently developed biosensors for the detection of autoimmune disease biomarkers are discussed. In the first part, we focus on the main AD biomarkers and the current methods of their detection. Then, we discuss the principles and different types of biosensors. Finally, we overview the characteristics of biosensors based on different bioreceptors reported in the literature.

Phenotypic heterogeneity in psoriatic arthritis: towards tissue pathology-based therapy

Psoriatic arthritis (PsA) is a heterogeneous disease involving multiple potential tissue domains. Most outcome measures used so far in randomized clinical trials do not sufficiently reflect this domain heterogeneity. The concept that pathogenetic mechanisms might vary across tissues within a single disease, underpinning such phenotype diversity, could explain tissue-distinct levels of response to different therapies. In this Review, we discuss the tissue, cellular and molecular mechanisms that drive clinical heterogeneity in PsA phenotypes, and detail existing tissue-based research, including data generated using sophisticated interrogative technologies with single-cell precision. Finally, we discuss how these elements support the need for tissue-based therapy in PsA in the context of existing and new therapeutic modes of action, and the implications for future PsA trial outcomes and design.

Etiopathogenesis of Psoriasis from Genetic Perspective: An updated Review

Psoriasis is an organ-specific autoimmune disease characterized by the aberrant proliferation and differentiation of keratinocytes, leading to skin lesions. Abnormal immune responses mediated by T cells and dendritic cells and increased production of inflammatory cytokines have been suggested as underlying mechanisms in the pathogenesis of psoriasis. Emerging evidence suggests that there is a heritable basis for psoriatic disorders. Moreover, numerous gene variations have been associated with the disease risk, particularly those in innate and adaptive immune responses and antigen presentation pathways. Herein, this article discusses the genetic implications of psoriatic diseases' etiopathogenesis to develop novel investigative and management options.

Using functional genomics to advance the understanding of psoriatic arthritis

Psoriatic arthritis (PsA) is a complex disease where susceptibility is determined by genetic and environmental risk factors. Clinically, PsA involves inflammation of the joints and the skin, and, if left untreated, results in irreversible joint damage. There is currently no cure and the few treatments available to alleviate symptoms do not work in all patients. Over the past decade, genome-wide association studies (GWAS) have uncovered a large number of disease-associated loci but translating these findings into functional mechanisms and novel targets for therapeutic use is not straightforward. Most variants have been predicted to affect primarily long-range regulatory regions such as enhancers. There is now compelling evidence to support the use of chromatin conformation analysis methods to discover novel genes that can be affected by disease-associated variants. Here, we will review the studies published in the field that have given us a novel understanding of gene regulation in the context of functional genomics and how this relates to the study of PsA and its underlying disease mechanism.

Genetics of psoriasis: a basis for precision medicine

Psoriasis is an inflammatory skin disease with a background of polygenic inheritance. Both environmental and genetic factors are involved in the etiology of the disease. In the last two decades, numerous studies have been conducted through linkage analysis, genome-wide association study (GWAS), and direct sequencing to explore the role of genetic variation in disease pathogenesis and progression. To date, >80 psoriasis susceptibility genes have been identified, including HLA-Cw6, IL12B, IL23R, and LCE3B/3C. Some genetic markers have been applied in disease prediction, clinical diagnosis, treatment, and new drug development, which could further explain the pathogenesis of psoriasis and promote the development of precision medicine. This review summarizes related research on genetic variation in psoriasis and explores implications of the findings in clinical application and the promotion of a personalized medicine project.

A review of ustekinumab in the treatment of psoriatic arthritis

Psoriatic arthritis is an inflammatory arthritis associated with psoriasis. The IL-23/IL-17 axis is an important pathway in the development of psoriatic disease. Ustekinumab is a fully human monoclonal IgG1 antibody that binds to the p40 subunit of IL-12 and IL-23, which, in turn, inhibits downstream signaling pathways. PSUMMIT-1 and PSUMMIT-2 are two pivotal Phase III trials demonstrating global improvement in primary and secondary outcomes including inhibition of radiographic progression. Therapeutic benefit of ustekinumab for synovitis appears independent of previous disease modifying antirheumatic disease or anti-TNF exposure. At present, the data support the use of ustekinumab in the treatment of psoriatic arthritis after the failure of NSAIDs and conventional disease modifying antirheumatic diseases as an alternative to, or after failure of an anti-TNF agent.

Targeting IL-17 in psoriatic arthritis

Psoriatic arthritis (PsA) is a chronic and progressive inflammatory arthritis intimately associated with psoriasis, and can be an impairing disease that leads to reduced quality of life and significant morbidity. Treatment often requires TNF antagonists, yet many patients with PsA are not responsive to the standard anti-TNF therapies. The interleukin-17 (IL-17)/IL-17 receptor (IL-17R) family has recently been implicated in the pathogenesis of PsA and psoriasis. Much enthusiasm has been generated for the development of biologics that target the IL-17 signaling pathway directly or indirectly, many of which have produced striking results in the setting of psoriasis and PsA. Herein, we review the role of IL-17 and the IL-17 receptor (IL-17R) in the pathogenesis of PsA, as well as the clinical evidence for IL-17 and IL-17R targeted therapeutics.

KIF3A and IL-4 are disease-specific biomarkers for psoriatic arthritis susceptibility

To date, the genes associated with Psoriatic Arthritis (PsA) are principally involved in inflammation, immune response and epidermal differentiation, without any information about the relationship between disease and bone metabolism genes. Our work was focused on 5q31 locus, which contains several genetic variants significantly associated with PsA. The study involved 1526 subjects (500 PsA, 426 PsV, 600 controls). The region was evaluated by selecting and genotyping the SNPs of interest by Real Time PCR and direct sequencing. The results were subjected to biostatistic and bioinformatic analysis.

The case-control study highlighted a significant association between KIF3A/IL-4 and PsA, but not with PsV (Psoriasis Vulgaris) patients. In addition, the haplotype analysis revealed two haplotypes significantly associated with PsA susceptibility. The Linkage Disequilibrium (LD) study showed the presence of a specific block in high LD within 132,692,628-132,737,638 bp of 5q31, giving additional evidence of specific association of the 5q31 region in PsA patients. Moreover, KIF3A expression was assessed by immunohistochemistry assays which showed a marked and significant difference of KIF3A expression between pathological and normal tissues. Our analysis described KIF3A and IL-4 as novel susceptibility genes for PsA, suggesting a clear implication of bone metabolism genes in the disease etiopathogenesis.

Psoriasis and Atopic Dermatitis

Psoriasis and atopic dermatitis are common, chronic inflammatory skin diseases. We discuss several aspects of these disorders, including: risk factors; incidence and prevalence; the complex disease burden; and the comorbidities that increase the clinical significance of each disorder. We also focus on treatment management strategies and outline why individualized, patient-centered treatment regimens should be part of the care plans for patients with either psoriasis or atopic dermatitis. Finally, we conclude that, while our theoretical knowledge of the optimum care plans for these patients is increasingly sophisticated, this understanding is, unfortunately, not always reflected in daily clinical practice.

Pharmacogenetics and pharmacogenomics in psoriasis treatment: current challenges and future prospects

INTRODUCTION

Topical, systemic, oral disease modifying, and biologic agents are part of the armamentarium to manage psoriatic disease. The choice of therapy depends upon disease severity, relevant co-morbidities and patient preference. There is great variability in patient response with these agents, and there is still no clear method of selecting the preferred therapeutic agent for efficacy or lack of adverse events.

AREAS COVERED

This article will review the pharmacogenetic and pharmacogenomic targets that are currently known with respect to psoriasis vulgaris, and the most frequent co-morbidity of psoriasis, psoriatic arthritis.

EXPERT OPINION

Presently, no clinically actionable biomarker exists for any therapeutic agent used to treat psoriasis or psoriatic arthritis. The lack of validated outcome measures and conflicting results of open-label studies conducted may be attributed to a multitude of issues that confound discovery. Consequently, studies have been underpowered to identify genes or genetic variants worth translating to clinical practice. In order to achieve a pharmacogenetic/pharmacogenomic signature, improvements in study design of future investigations are required, including carefully designed prospective studies. It is imperative to combine known clinical, serological, and molecular markers with consistent outcomes and an adequate health economic evaluation before they can be adopted widely in clinical practice.

Psoriasis, psoriatic arthritis, and rheumatoid arthritis: Is all inflammation the same?

OBJECTIVES

To review the pathophysiology, co-morbidities, and therapeutic options for psoriasis, psoriatic arthritis and rheumatoid arthritis in order to further understand the similarities and differences in treatment paradigms in the management of each disease. New targets for individualized therapeutic decisions are also identified with the aim of improving therapeutic outcome and reducing toxicity.

SEARCH STRATEGY

Using the PubMed database, we searched literature published from 2000 to 2015 using combinations of the key words "psoriasis," "psoriatic arthritis," "rheumatoid arthritis," "pathogenesis," "immunomodulation," and "treatment."

INCLUSION AND EXCLUSION CRITERIA

This was a non-systematic review and there were no formal inclusion and exclusion criteria.

DATA EXTRACTION

Abstracts identified in the search were screened for relevance and articles considered appropriate evaluated further. References within these selected articles were also screened. Information was extracted from 198 articles for inclusion in this report.

DATA SYNTHESIS

There was no formal data synthesis. Articles were reviewed and summarized according to disease area (psoriasis, psoriatic arthritis, and rheumatoid arthritis).

HEADLINE RESULTS

The pathophysiology of psoriasis, psoriatic arthritis, and rheumatoid arthritis involves chronic inflammation mediated by pro-inflammatory cytokines. Dysfunction in integrated signaling pathways affecting different constituents of the immune system result in varying clinical features in the three diseases. Co-morbidities, including cardiovascular disease, malignancies, and non-alcoholic fatty liver disease are increased. Increased understanding of the immunopathogenesis allowed development of targeted treatments; however, despite a variety of potentially predictive genetic, protein and cellular biomarkers, there is still significant unmet need in these three inflammatory disorders.

Pharmacogenomics of multifactorial diseases: a focus on psoriatic arthritis

This review will outline the current pharmacogenomics knowledge about psoriatic arthritis with a special attention to the perspectives and the challenges for its implementation in the clinical practice. To date, different drugs have been developed to contrast the symptoms and the progression of psoriatic arthritis. However, patients have shown high variability of drug response in relation to their genetic makeup. In this context, the advances made in the knowledge and the potentialities of genome-drugs associations paved the path for the development of a precision medicine. In fact, these associations may be successfully combined with the environment information to provide new strategies able to prevent and improve the disease management as well as to enhance the patients quality of life.

Pharmacogenetics of treatment response in psoriatic arthritis

TNF-blocking agents, non-biological disease-modifying anti-rheumatic drugs (nbDMARDs) and non-steroidal anti-inflammatory drugs (NSAIDs) are commonly prescribed treatments in psoriatic arthritis. A large proportion of patients do not respond to these medications, although unfortunately clinically useful biomarkers that predict future response are currently lacking. Several candidate gene polymorphisms have been associated with responses to biologic therapies and nbDMARDs; however, replication and validation of these variants in large prospective psoriatic arthritis cohorts are required before translating these to clinical practice. In this review, we discuss the advances made in pharmacogenetics of treatment response in psoriatic arthritis to date, with focus on biologic therapies approved for use, nbDMARDs and NSAIDs, as well as outline emerging methodologies to obtain data that will help inform a future precision medicine approach in this condition.

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.

Ustekinumab in the Treatment of Psoriasis and Psoriatic Arthritis

Biologics have revolutionized the therapy of the psoriatic disease spectrum. These new classes of drugs also allow deeper insight into the pathogenesis of the disease and highlight the existence of distinct "molecular" disease subgroups as evidenced by the spectrum of clinical response seen. Molecules associated with both the interleukin (IL)-17 and interferon (IFN)γ pathways have important functions in psoriatic inflammation, and both are targeted by drugs acting on the p40 subunit shared by IL-12 and IL-23. These IL-12 family members are upstream of pathways characterized by the production of IFNγ and IL-17 related molecules, including IL-17, IL-22, and CCL20. We here summarize the mode of action and clinical studies of the p40 inhibitor ustekinumab with focus on both psoriasis and psoriatic arthritis.

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.

PDE3A-SLCO1C1 locus is associated with response to anti-tumor necrosis factor therapy in psoriatic arthritis

Aim: Variation at PDE3A-SLCO1C1 locus has been recently associated with the response to anti-TNF therapy in rheumatoid arthritis. We undertook the present study to determine whether PDE3A-SLCO1C1 is also associated with the response to anti-TNF therapy in psoriatic arthritis. Patients & methods: Genomic DNA was obtained from 81 psoriatic arthritis patients that had been treated with anti-TNF therapy. PDE3A-SLCO1C1 SNP rs3794271 was genotyped using Taqman realt-time PCR. The clinical response to anti-TNF therapy was measured as the change from baseline in the level of disease activity according to the DAS28 score. Results: A significant association between rs3794271 and anti-TNF response in psoriatic arthritis was found (beta = -0.71; p = 0.0036). Conclusion: PDE3A-SLCO1C1 locus is also associated with response to anti-TNF therapy in psoriatic arthritis.

Original submitted 12 May 2014; Revision submitted 18 August 2014

Reactive arthritis

Reactive arthritis (ReA) is an immune-mediated seronegative arthritis that belongs to the group of spondyloarthropathies and develops after a gastrointestinal or genitourinary system infection. The condition is considered to be characterized by a triad of symptoms (conjunctivitis, arthritis and urethritis) although a constellation of other manifestations may also be present. ReA is characterized by psoriasiform dermatological manifestations that may resemble those of pustular psoriasis and, similar to guttate psoriasis, is a post-infectious entity. Also, the articular manifestations of the disorder are similar to those of psoriatic arthritis and both conditions show a correlation with HLA-B27. These facts have led several authors to suggest that there is a connection between ReA and psoriasis, listing ReA among the disorders related to psoriasis. However, the pathogenetic mechanism behind the condition is complex and poorly understood. Bacterial antigenicity, the type of host response (i.e. Th1/Th2 imbalance) and various genetic factors (i.e. HLA-B27 etc.) play an important role in the development of the disorder. It is unknown whether all the aforementioned factors are part of a mechanism that could be similar to, or share basic aspects with known psoriasis pathogenesis mechanisms.

Therapeutic options after treatment failure in rheumatoid arthritis or spondyloarthritides

The prognosis for patients with rheumatoid arthritis or spondyloarthritides has improved dramatically due to earlier diagnosis, recognition of the need to treat early with conventional synthetic disease-modifying antirheumatic drugs (csDMARDs), alone or in combinations, the establishment of treatment targets, and the development of biological DMARDs (bDMARDs). Many patients are now able to achieve clinical remission or low disease activity with therapy, and reduce or eliminate systemic corticosteroid use. Guidelines recommend methotrexate as a first-line agent for the initial treatment of rheumatoid arthritis; however, a majority of patients will require a change of csDMARD or step up to combination therapy with the addition of another csDMARD or a bDMARD. However, treatment failure is common and switching to a different therapy may be required. The large number of available treatment options, combined with a lack of comparative data, makes the choice of a new therapy complex and often not evidence based. We summarize and discuss evidence to inform treatment decisions in patients who require a change in therapy, including baseline factors that may predict response to therapy.

Clinical potential of apremilast in the treatment of psoriatic arthritis

Psoriatic arthritis (PsA) is a frequent chronic inflammatory disease characterized by joint and skin involvement, and by typical extra-articular manifestations. Although the pathogenesis of PsA is still under investigation, the available evidence suggests the importance of the patient’s genetic background, microbial or environmental triggers, and an imbalance in the adaptive and acquired immune system, resulting in the production of inflammatory mediators. New therapeutic approaches have been proposed, among them the use of modulators of intracellular signals and gene transcription such as PDE4-inhibiting compounds, which are able to modulate the activity of transcription factors such as CREB and NF-κB and therefore the synthesis of inflammatory mediators, resulting in immunoregulation. This paper summarizes the mechanism of action of apremilast, a PDE4 inhibitor, and the clinical data available on its clinical efficacy and safety profile in the treatment of PsA patients.

Psoriatic arthritis and nail changes: exploring the relationship

OBJECTIVE

Psoriatic arthritis (PsA) has a diverse range of clinical manifestations, both articular and extra-articular. Although the association of PsA with skin changes is well established, the relationship of PsA with psoriatic nail changes remains relatively unexplored.

METHODS

This report reviews the current literature surrounding the association of PsA with nail changes. A review of the literature was completed using PubMed, MEDLINE, and EMBASE in September 2013, encompassing years 1964-2012.

RESULTS

A total of 21 articles were reviewed. On average, 66% [standard deviation (SD) 17.7] of PsA patients had nail changes. The type of nail changes and their associations varied widely between studies.

CONCLUSIONS

Studies of nail changes in PsA are highly variable with a wide range of results. Given the variability of results that were observed in this review, our recommendations are that further large studies on nail changes in patients with PsA should be conducted.

Advances in the genetics of spondyloarthritis and clinical implications

Spondyloarthritis (SpA) is a group of inflammatory rheumatic diseases whose main clinical feature is inflammation of the axial spine. Articular, periarticular, and extra-articular manifestations can also occur, depending on the type of spondyloarthritis. The most common clinical subsets of SpA are ankylosing spondylitis (AS) and psoriatic arthritis (PsA). SpA is a major health challenge given the propensity to affect young adults and the potential requirement for lifelong treatment. Although the precise etiology of SpA is unknown, there is mounting evidence that these diseases are a result of complex interplay of genetic, environmental, and immunological factors. In this review on SpA, we will discuss genetic variants with genome-wide significance, highlight potential clinical application of genetic variants, and discuss challenges in further elucidating the genetic basis of SpA.

TRAF5 and TRAF3IP2 gene polymorphisms are associated with Behçet's disease and Vogt-Koyanagi-Harada syndrome: a case-control study

Background

TRAF5 and TRAF3IP2 have been reported to be associated with several autoimmune diseases. Behçet's disease (BD) and Vogt-Koyanagi-Harada (VKH) syndrome are two autoimmune uveitis entities whereby both genetic and environmental factors are thought to be involved.

Objective

The role of TRAF5 and TRAF3IP2 in BD and VKH has not yet been reported and was therefore the subject of this study.

Methods

The study included 789 BD patients, 940 VKH patients and 1601 healthy unrelated individuals. Genotyping was performed by polymerase chain reaction-restriction fragment length polymorphism (PCR-RFLP) or TaqMan® SNP Genotyping Assay. Real-Time PCR was used to detect mRNA expression from PBMCs obtained from healthy controls with (n = 22) or without (n = 79) stimulation. Levels of TNF-α, IL-6 and IL-8 in culture supernatants were measured by ELISA (n = 22).

Results

Three SNPs (rs6540679, rs12569232, rs10863888) of TRAF5 and rs13210247 of TRAF3IP2 were significantly associated with Behçet's disease and VKH syndrome (corrected P values ranging from 9.45×10⁻¹² to 0.027). TRAF3IP2 rs33980500 and rs13190932 were not polymorphic in Han Chinese. Following stimulation by lipopolysaccharide (LPS), carriers of the GG genotype of rs6540679/TRAF5 had a higher TRAF5 mRNA expression (p = 0.004) and an increased TNF-α (p = 0.0052) and IL-6 (p = 0.0014) level compared with AA and AG genotype carriers.

Conclusion

This study provides evidence that TRAF5 and TRAF3IP2 genes are involved in the development of BD and VKH syndrome. Functional research suggested that TRAF5 gene polymorphisms may regulate TRAF5 expression and downstream inflammatory cytokines such as TNF-α and IL-6.

The bacterial skin microbiome in psoriatic arthritis, an unexplored link in pathogenesis: challenges and opportunities offered by recent technological advances

The resident microbial community, harboured by humans in sites such as the skin and gastrointestinal tract, is enormous, representing a candidate environmental factor affecting susceptibility to complex diseases, where both genetic and environmental risk factors are important. The potential of microorganisms to influence the human immune system is considerable, given their ubiquity. The impact of the host-gene-microbe interaction on the maintenance of health and the development of disease has not yet been assessed robustly in chronic inflammatory conditions. PsA represents a model inflammatory disease to explore the role of the microbiome because skin involvement and overlap with IBD implicates both the skin and gastrointestinal tract as sources of microbial triggers for PsA. In parallel with genetic studies, characterization of the host microbiota may benefit our understanding of the microbial contribution to disease pathogenesis-knowledge that may eventually inform the development of novel therapeutics.

SNP rs11652075 in the CARD14 gene as a risk factor for psoriasis (PSORS2) in a Spanish cohort

A recent genomic survey identified the association between a common single nucleotide polymorphism (SNP) at the CARD14 gene (SNP rs11652075; p.Arg820Trp) and psoriasis (Psor). Our aim was to replicate the association between this polymorphism and to determine whether other CARD14 variants could explain the association. A total of 400 Psor patients (mean age 47±15; 55% male) and 420 healthy controls (mean age 51±16; 56% male) all Caucasian were genotyped for rs11652075. The rs11652075 CC genotype was significantly associated with Psor in our population (p=0.003; odds ratios=1.59; 95% confidence intervals=1.16-2.19; statistical power >80). The sequencing of the whole CARD14 coding exons in a total of 15 patients did not identify other DNA variants that could explain this association. We did not find significant differences (allele/genotype frequencies) between the patients according to disease severity, presence of arthritis, onset of age, and family history of Psor. We confirmed the association between SNP rs11652075 at the CARD14 gene and Psor. The absence of other coding variants among our patients supported a direct role for this missense polymorphism on Psor risk.

New developments in our understanding of psoriatic arthritis and their impact on the diagnosis and clinical management of the disease

Psoriatic arthritis (PsA) is a spondyloarthritis with a comorbid association with psoriasis. Without appropriate treatment it can be progressive, severe, deforming and destructive. It has long been recognized that subsets of PsA patients exist, characterized by different patterns of joint involvement. Associations between development of PsA and certain human leukocyte antigens (HLA) have been established. Evidence now suggests that progression of PsA is also genetically determined. The presence of one allele (HLA-B*27) has been associated with a distinct phenotype characterized by early joint involvement, whereas development of musculoskeletal symptoms is much slower in patients with another allele, C*06. Dermatologists need to consider what these differences in genotypes and phenotypes mean for clinical practice. Delay in the diagnosis of PsA is a significant contributor to poor patient outcomes, but there is evidence that PsA is underdiagnosed among psoriasis patients attending dermatology clinics. Dermatologists need to identify PsA symptoms among their psoriasis patients and refer for rheumatological assessment where appropriate. Treatment should address all aspects of the disease, including skin, nail and joint symptoms as well as physical functioning and quality of life. The existence of distinct phenotypic and genetic PsA subsets means dermatologists need to consider which drugs are likely to be most efficacious in which patient populations. Stratification of PsA according to susceptibility genes may in future help identify patients requiring more aggressive treatment to prevent progression. Biologic therapies show efficacy in PsA, but the patient populations of clinical trials are not always representative of patients treated with biologics in clinical practice.

Steps in the management of psoriatic arthritis: a guide for clinicians

Psoriatic arthritis is a common systemic inflammatory disorder, which in addition to skin and nail involvement may be associated with peripheral and axial joint involvement, enthesitis, dactylitis, and important comorbidities - especially cardiovascular morbidity. Better insights into the involved pathogenic mechanisms have resulted in an improved therapeutic armamentarium, which targets key pathways in its pathogenesis. This has resulted in significant clinical responses to newer therapeutic agents, especially those directed at inhibition of tumor necrosis factor α. Biological therapy leads to significant levels of remission, improved quality of life, and retards or improves structural radiological damage.

Is psoriatic arthritis a result of abnormalities in acquired or innate immunity?

Psoriatic arthritis is a common chronic inflammatory joint disease in which both inflammation and tissue damage contribute to the patient's outcome. Abnormal activation of the innate and the adaptive immune system contributes to the chronic disease process. Novel insights into these immune pathways are further corroborated by genetic evidence. In this review, we compare the current paradigm of psoriasis to mechanisms that likely play a role in psoriatic arthritis and provide an overview of the role of immune mechanisms in the different features of the disease.

Psoriatic arthritis: an update

Psoriatic arthritis is a debilitating condition, which affects approximately one-quarter of psoriasis patients. Recent findings have furthered our understanding of the complex pathophysiology of PsA. There have been major advances in the identification of genes associated with joint involvement but not with cutaneous disease alone. The elucidation of key immunologic pathways has allowed the development of novel targeted therapies that are in the research pipeline. Currently, good screening tests and biomarkers to diagnose early PsA and to guide therapy are limited. In this paper, we present recent findings with regard to the immunopathogenesis and genetics of PsA, biomarkers, and screening tools and review the targeted therapies currently in clinical trials.

Pathological role of interleukin-6 in psoriatic arthritis

Psoriatic arthritis (PsA) is a clinical manifestation of psoriatic disease. Although the pathogenesis of PsA remains unknown, PsA can be managed by treatments similar to those used for rheumatoid arthritis (RA). Because interleukin-(IL-) 6 has been suggested to have a pathogenic role in PsA, a humanized anti-IL-6 receptor antibody tocilizumab treatment for PsA was recently tried. However, the efficacy of tocilizumab for PsA was not favorable. This suggests that the pathogenic roles of IL-6 in PsA and RA are different. In RA, tumor necrosis factor (TNF) primarily contributes to the arthritis effector phase and IL-6 contributes to the arthritis priming phase. In PsA, the TNF-related effector phase is similar to that in RA, but the IL-6-related priming phase might not be critical. This paper discusses the role of IL-6 in PsA.

The Th17/IL-23 Axis and Natural Immunity in Psoriatic Arthritis

Psoriatic arthritis (PsA) is a chronic inflammatory skin disease that causes enthesitis and destructive arthritis and significantly lowers patient quality of life. Recognition of the two target organs (the skin and joints) involved in the immunopathophysiology of PsA helped in elucidating the pathology of various systemic autoimmune diseases targeting multiple organs. Recent advances in immunology and genetics have made it clear that acquired immunity, especially that mediated by the Th17/IL-23 axis, plays an important role in the inflammatory pathology observed in psoriasis and PsA. Additionally, involvement of natural immunity has also been suggested. Microbial infection has been known to trigger psoriasis and PsA. Recent clinical studies using biopharmaceuticals, such as tumor-necrosis-factor- (TNF-) α inhibitors and IL-12/23 p40 antibodies, indicate that studies need not be based only on the immunological phenomena observed in PsA pathology since disease pathology can now be verified using human-based science. Considering this aspect, this paper discusses the immunopathology of PsA compared to psoriasis (cutaneous) and rheumatoid arthritis in humans and immunopathology of PsA with respect to the Th17/IL-23 axis and microbial infection.