The effect of HLA‐DR antigens on the susceptibility to, and clinical expression of psoriatic arthritis

Differences between psoriatic arthritis and psoriasis in multi-omics

We aim to systemically review the genomics, transcriptomics, epigenetics, proteomics, metabonomics and microbiota of psoriatic arthritis and psoriasis, illustrating the differences of these two diseases, broadening our understanding of the pathogenesis of them and providing important clues for valuable biomarkers of earlier diagnosis and treatments. To our knowledge, this is the first study that combine all omics studies from genomics to microbiota and may serve as a reference for future studies to identify the key underlying pathways in psoriatic arthritis.

New Insights on Juvenile Psoriatic Arthritis

Juvenile psoriatic arthritis (JPsA) is a relatively rare condition in childhood as it represents approximately 5% of the whole Juvenile Idiopathic Arthritis (JIA) population. According to International League of Associations of Rheumatology (ILAR) classification, JPsA is defined by the association of arthritis and psoriasis or, in the absence of typical psoriatic lesions, with at least two of the following: dactylitis, nail pitting, onycholysis or family history of psoriasis in a first-degree relative. However, recent studies have shown that this classification system could conceal more homogeneous subgroups of patients differing by age of onset, clinical characteristics and prognosis. Little is known about genetic factors and pathogenetic mechanisms which distinguish JPsA from other JIA subtypes or from isolated psoriasis without joint involvement, especially in the pediatric population. Specific clinical trials testing the efficacy of biological agents are lacking for JPsA, while in recent years novel therapeutic agents are emerging in adults. In this review, we summarize the clinical features and the current evidence on pathogenesis and therapeutic options for JPsA in order to provide a comprehensive overview on the clinical management of this complex and overlapping entity in childhood.

Association of HLA Alleles and HLA Haplotypes with Psoriasis, Psoriatic Arthritis and Disease Severity in a Miscegenated Population

Background

The study of HLA classes I and II in Brazilian psoriasis patients may contribute to a better understanding of their association with the disease.

Objective

To describe HLA classes I and II of Brazilian patients with psoriasis, with or without arthritis, compare them to controls and correlate HLA markers with epidemiological and evolutional aspects of psoriasis.

Methods

A total of 55 patients with more than 5 years of psoriasis, with or without arthritis, answered a questionnaire on ethnic background and disease severity. A total of 134 bone marrow donors were controls. HLA class I and II genotyping was determined by PCR-SSP.

Results

Mean age was 42.4 years; 23 women and 32 men. HLA-B*57 was present in 23.6% patients and in 7.5% controls (p=0.00200, OR= 3.8381), and HLA-C*06 in 29.1% patients and in 16.4% controls (p= 0.04832, OR=2.0886). HLA-B*57 and HLA-C*18 were significantly present in patients with arthritis (p=0.00104, OR=6.6769 and p=0.00269, OR=16.50, respectively). HLA-B*57 was significantly present in patients with history of erythroderma (p=0.00548, OR= 5.1059), as was HLA-C*06 (p=0.02158, OR=3.0545). HLA-B*57 was also frequent in patients with history of hospital internment due to psoriasis (p= 0.00094, OR=7.8909) and in the ones with history of systemic treatment for psoriasis (p= 0.00011, OR= 5.3733). Haplotype HLA-A*02 B*57 C*06 DRB1*07DQB1*03 was the most common among the patients (p= 0.00069, OR= 3.528).

Conclusion

HLA-B*57 and HLA-C*06 were significantly increased in the patients indicating risk for psoriasis. HLA-B*57 remained high in patients with history of erythroderma, hospital internment, systemic treatment, and psoriatic arthritis, showing association with disease severity. HLA-C*18 was significantly high only in patients with psoriatic arthritis. HLA-B*57 and HLA-C*06 and haplotype HLA-A*02B*57Cw*06DRB1*07 DQB1*03 seen in this study were already described before, associated with psoriasis. HLA-Cw*18 was not described in other populations in association with psoriasis.

Human leukocyte antigen and demographic characteristics in Chinese patients with active peripheral type psoriatic arthritis who had inadequate response to conventional disease-modifying antirheumatic drugs in a single dermatologic clinic

Background

Correlation between severity of psoriasis and psoriatic arthritis (PsA) is inconsistent. Also, human leukocyte antigen (HLA)-Cw6 was found to be underrepresented in severe psoriasis who failed conventional systemic therapies, but the effect of HLA polymorphism on PsA severity needs to be confirmed.

Objectives

To describe the severity of psoriasis, demographic features and HLA polymorphism among Chinese patients with active peripheral type PsA who had inadequate response to conventional disease-modifying antirheumatic drugs.

Methods

We included all patients with PsA who had at least 3 tender and swollen peripheral joints despite at least two conventional non-biologic treatments in our clinic. Demographic results were compared with global pivotal studies of biologics for PsA. HLA-Cw and HLA-DRB1 genotyping was also analyzed.

Results

We identified 60 patients who met our inclusion criteria. The male to female ratio was 1.31:1. The majority of patients presented with psoriasis first (81.7%). The mean interval between psoriasis and PsA was 7.2 ± 8.1 years (mean ± SD). The baseline number of tender and swollen joints was 14.9 ± 10.7 and 11.3 ±10.2, respectively. In total, 41.7% subjects had more than 3% body surface area involvement of psoriasis. Genotyping of HLA-Cw and HLA-DRB1 was performed in 47 subjects. HLA-Cw*0702 was the most frequent allele (29.8%), followed by HLA-Cw*01 (26.6%). The frequency of HLA-Cw*0602 allele was similar to normal population. The most frequent HLA-DRB1 allele was HLA-DRB1*04 (20.2%), followed by HLA-DRB1*08 (16.0%). No cases carrying HLA-DRB1*13 were detected.

Conclusions

Compared with Western population, our patients had less psoriasis and PsA burden. The frequencies of HLA-Cw*06, HLA-Cw*12, and HLA-DRB1*07 were not increased. In contrast, HLA-Cw*0702 and HLA-DRB1*08 allele frequencies were increased compared with psoriasis patients and normal population in Taiwan. Future studies are still needed to characterize the demographic and genetic features of high need PsA patients.

HLA-Cw6 and psoriasis

Psoriasis is a multifactorial disease with a strong genetic background. HLA-Cw6 is one of the most strongly associated psoriasis susceptibility alleles. It is repeatedly observed to affect disease course, phenotypic features, severity, comorbidities and treatment outcomes. To the best of our knowledge, the roles of HLA-Cw6 in psoriasis have not yet been thoroughly reviewed. The worldwide frequency of the HLA-Cw6 allele varies greatly, with it being generally higher in white people than in Asians. The allele is associated with type I early-onset psoriasis. Stress, obesity and streptococcal pharyngitis are commonly observed in HLA-Cw6-positive patients. Phenotypically, HLA-Cw6 has been found to be associated with guttate psoriasis. In addition, patients carrying the allele are more likely to have arm, leg and trunk involvement, and the Koebner phenomenon. Patients with psoriatic arthritis with HLA-Cw6 more often have early onset and tend to show cutaneous symptoms before musculoskeletal symptoms. HLA-Cw6-positive patients have been shown in several studies to be more responsive to methotrexate and ustekinumab. However, this difference in ustekinumab efficacy was only moderate in a post-hoc analysis of a pivotal phase III study. HLA-Cw6 positivity also tends to be less frequent in high-need patients who fail conventional therapy. Small studies have also investigated the role of HLA-Cw6 in remission of psoriasis during pregnancy, and with the comorbidities of photosensitivity and atherosclerosis. Given the diverse nature of psoriasis pathogenesis, as well as the difference of HLA-Cw6 positivity in different ethnic groups, more studies are needed to confirm the role of HLA-Cw6 in psoriasis.

Prevalence of psoriatic arthritis and costs generated by treatment of psoriatic arthritis patients in the public health system - the case of Poland

Objective

The objective of the study was to analyse the prevalence of psoriatic arthritis (PsA) in Poland and to assess the costs generated by treatment of PsA patients in the system of public healthcare.

Material and methods

The analysis was based on the database of the public payer, the National Health Fund (NFZ). PsA was defined by the diagnostic ICD-10 codes M07 (Enteropathic arthropathies) and L40.5 (Psoriatic arthropathies). The estimate of the costs was based on the reports submitted to the NFZ by health service providers. The prevalence rates were calculated using the NFZ data and the population estimates from the Central Statistical Office of Poland (GUS).

Results

In 2015, the prevalence of PsA (ICD-10: L40.5 and M07) in Poland was 3.2 per 10 000 population (3.7 in women and 2.6 in men). In 2015, nearly 7.3 thousand patients with the diagnosis of M07 and 6.3 thousand patients with the diagnosis of L40.5 received healthcare benefits. Women accounted for 60.6% of those patients. Nearly three fourths of PsA patients were aged 40 to 69 years with the median age of 54 years (56 years in women and 50 years in men). Between 2008 and 2015 the NFZ expenditure on the treatment of PsA increased from 6.6 million Polish zloty (PLN) (1.9 million EUR) to PLN 50.8 million (12.1 million EUR). In the same period, the number of PsA patients increased from 3.4 thousand to 11.9 thousand. In 2015, the mean cost of treatment per PsA patient was PLN 3.8 thousand.

Conclusions

The PsA prevalence rates estimated by the authors from the NFZ database are clearly lower than those derived from studies in other European countries, which may suggest that the actual number of PsA patients in Poland may be underestimated. Still the number of patients treated for PsA increased nearly 3.5-fold during 2008–2015, when the cost of PsA treatment rose more than 7 times.

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.

Concepts of pathogenesis in psoriatic arthritis: genotype determines clinical phenotype

This review focuses on the genetic features of psoriatic arthritis (PsA) and their relationship to phenotypic heterogeneity in the disease, and addresses three questions: what do the recent studies on human leukocyte antigen (HLA) tell us about the genetic relationship between cutaneous psoriasis (PsO) and PsA – that is, is PsO a unitary phenotype; is PsA a genetically heterogeneous or homogeneous entity; and do the genetic factors implicated in determining susceptibility to PsA predict clinical phenotype? We first discuss the results from comparing the HLA typing of two PsO cohorts: one cohort providing the dermatologic perspective, consisting of patients with PsO without evidence of arthritic disease; and the second cohort providing the rheumatologic perspective, consisting of patients with PsA. We show that these two cohorts differ considerably in their predominant HLA alleles, indicating the heterogeneity of the overall PsO phenotype. Moreover, the genotype of patients in the PsA cohort was shown to be heterogeneous with significant elevations in the frequency of haplotypes containing HLA-B*08, HLA-C*06:02, HLA-B*27, HLA-B*38 and HLA-B*39. Because different genetic susceptibility genes imply different disease mechanisms, and possibly different clinical courses and therapeutic responses, we then review the evidence for a phenotypic difference among patients with PsA who have inherited different HLA alleles. We provide evidence that different alleles and, more importantly, different haplotypes implicated in determining PsA susceptibility are associated with different phenotypic characteristics that appear to be subphenotypes. The implication of these findings for the overall pathophysiologic mechanisms involved in PsA is discussed with specific reference to their bearing on the discussion of whether PsA is conceptualised as an autoimmune process or one that is based on entheseal responses.

Certain class I HLA alleles and haplotypes implicated in susceptibility play a role in determining specific features of the psoriatic arthritis phenotype

OBJECTIVES

Psoriatic arthritis (PsA) susceptibility is associated with several different class I alleles, suggesting separate patterns of MHC effect. This exploratory study was based on the hypothesis that heterogeneity of the clinical phenotype of PsA might be explained by differing associations of clinical features with these susceptibility genes.

METHODS

The clinical phenotype of 282 PsA patients in a cohort previously studied for associations with human leukocyte antigen (HLA)-B and HLA-C genotypes was first preliminarily assessed by univariate associations of susceptibility genes with specific clinical characteristics. To explore the potential genotypic effects of pairwise combinations of different HLA-B and C alleles/haplotypes, we created a series of allele/haplotype risk scores combining single alleles/haplotypes separately associated with being in the highest PsA severity propensity tertile based on the features studied by univariate analysis.

RESULTS

In exploratory univariate analyses, B*27:05:02 was positively associated with enthesitis, dactylitis and symmetric sacroiliitis, whereas B*08:01:01-C*07:01:01and its component alleles were positively associated with joint fusion and deformities, asymmetrical sacroiliitis, and dactylitis. HLA-C*06:02:01 was negatively associated with asymmetrical sacroiliitis. The highest propensity score for severe PsA was with B*27:05:02-C*02:02:02, B*08:01:01-C*07:01:01 and B*37:01:01-C*06:02:01, but not the B*27:05:02-C*01:01:01 or B*57:01:01-C*06:02:01 haplotypes. In contrast, B*44 haplotypes were associated with presence of milder disease, and in univariate analysis with a decreased frequency of enthesitis, joint fusion, deformities and dactylitis.

CONCLUSIONS

Different HLA susceptibility genes were associated with particular features that defined the PsA phenotype of a given patient. Additive interactions between different susceptibility HLA alleles defined the propensity for a more severe or milder musculoskeletal phenotype.

The Region Centromeric to HLA-C Is a Key Region for Understanding the Phenotypic Variability of Psoriatic Arthritis

With the aim of clarifying the role of several polymorphisms around the HLA-C locus in the clinical expression of PsA, the distribution of several polymorphic markers and genes located around the HLA-C locus was analyzed in a well-established cohort of 110 patients with PsA, 50 patients with psoriasis alone, and 110 healthy controls. The frequency of these genes was also analyzed by PsA articular models, based on three main subgroups: oligoarthritis, polyarthritis, and spondylitis. Distal interphalangeal joint (DIP) involvement was associated with the presence of MICB-CA20 (OR 6.0, 95% CI: 1.58-22.69, P = 0.005). HLA-DRB∗07 was associated with oligoarticular forms of PsA (OR 4.1, 95% CI: 1.8-9.3, P = 0.0007). The spondylitic forms overexpressed the antigen HLA-B∗27 (OR 5.7, 95% CI: 2.4-13.6, P = 0.0001). MICA-A5.1 showed association with polyarthritis (OR 3.7, 95% CI: 1.5-8.8, P = 0.006). Genes telomeric to HLA-C were overexpressed in psoriasis but not in PsA subphenotypes. This study shows that the region centromeric to HLA-C is a key region that expresses not only disease risk genes but also genes that help explain the phenotypic variability of PsA.

ACPA-negative RA consists of two genetically distinct subsets based on RF positivity in Japanese

HLA-DRB1, especially the shared epitope (SE), is strongly associated with rheumatoid arthritis (RA). However, recent studies have shown that SE is at most weakly associated with RA without anti-citrullinated peptide/protein antibody (ACPA). We have recently reported that ACPA-negative RA is associated with specific HLA-DRB1 alleles and diplotypes. Here, we attempted to detect genetically different subsets of ACPA-negative RA by classifying ACPA-negative RA patients into two groups based on their positivity for rheumatoid factor (RF). HLA-DRB1 genotyping data for totally 954 ACPA-negative RA patients and 2,008 healthy individuals in two independent sets were used. HLA-DRB1 allele and diplotype frequencies were compared among the ACPA-negative RF-positive RA patients, ACPA-negative RF-negative RA patients, and controls in each set. Combined results were also analyzed. A similar analysis was performed in 685 ACPA-positive RA patients classified according to their RF positivity. As a result, HLA-DRB1*04:05 and *09:01 showed strong associations with ACPA-negative RF-positive RA in the combined analysis (p = 8.8×10⁻⁶ and 0.0011, OR: 1.57 (1.28–1.91) and 1.37 (1.13–1.65), respectively). We also found that HLA-DR14 and the HLA-DR8 homozygote were associated with ACPA-negative RF-negative RA (p = 0.00022 and 0.00013, OR: 1.52 (1.21–1.89) and 3.08 (1.68–5.64), respectively). These association tendencies were found in each set. On the contrary, we could not detect any significant differences between ACPA-positive RA subsets. As a conclusion, ACPA-negative RA includes two genetically distinct subsets according to RF positivity in Japan, which display different associations with HLA-DRB1. ACPA-negative RF-positive RA is strongly associated with HLA-DRB1*04:05 and *09:01. ACPA-negative RF-negative RA is associated with DR14 and the HLA-DR8 homozygote.

Frequency of iridocyclitis in patients with early psoriatic arthritis: a prospective, follow up study

OBJECTIVE

The occurrence of iridocyclitis (IC) in early psoriatic arthritis (PsA) has been rarely assessed. The primary end-point of this study was to evaluate the frequency of IC at onset in patients with early PsA.

METHODS

We evaluated the frequency of IC in a clinical series of consecutive, new outpatients with early PsA observed between January 2000 and December 2009. All patients met the Classification Criteria for Psoriatic Arthritis (CASPAR) criteria for PsA and had a disease duration ≤12 months. The following clinical patterns were considered: peripheral PsA (oligoarthritis ≤4 and polyarthritis ≥5 involved joints), axial PsA and mixed. IC diagnosis was made by the ophthalmologist. Follow-up visits were scheduled at baseline and every 4 months with interval shortening in the case of urgent clinical problems.

RESULTS

Two hundred and forty-two patients, 137 (57%) women and 105 (43%) men (mean age 50.33 ± 11.7 years; mean symptom duration 9.38 ± 3.1 months) were studied. One hundred and thirty-two (51%) patients had peripheral PsA, 41 (17%) axial and 69 (28%) mixed. Twenty-six episodes of IC were recorded at diagnosis in 22 (9%) patients, 17 (77.3%) female and five (22.7%) male; 11 (50%) patients had peripheral PsA, two (9.1%) axial, and nine (40.9%) mixed; 5/22 (22.7%) patients were B27-positive. IC recurred in 2/22 (9%) patients over the follow-up period. Mean follow-up duration was 51 ± 23.2 months. Dactylitis was significantly more frequent in patients with IC compared to those without this feature (P = 0.032).

CONCLUSION

IC occurred in 9% of 242 patients with early PsA with no association with the clinical pattern and B27 positivity. This frequency is higher than previously reported.

Psoriatic arthritis: a systematic review

Psoriatic arthritis is an inflammatory rheumatic disorder of unknown etiology occurring in patients with psoriasis. The Classification Criteria for Psoriatic Arthritis study group has recently developed a validated set of classification criteria for psoriatic arthritis with a sensitivity of 91.4% and a specificity of 98.7%. Three main clinical patterns have been identified: oligoarticular (≤ 4 involved joints) or polyarticular (≥ 5 involved joints) peripheral disease and axial disease with or without associated peripheral arthritis. In this context distal interphalangeal arthritis and arthritis mutilans may occur. According to other reports, also in our centre, asymmetric oligoarthritis is the most frequent pattern at onset. Axial disease has been estimated between 5% and 36% of patients. It is characterized by an irregular involvement of the axial skeleton with a predilection for the cervical spine. Recurrent episodes of enthesitis and dactylitis represent a hallmark of psoriatic arthritis. In around 20% of cases distal extremity swelling with pitting edema of the hands or feet is observed. Unilateral acute iridocyclitis, usually recurrent in alternate fashion, is the most frequent extra-articular manifestation, and accelerated atherosclerosis is the prominent comorbidity. The clinical course of peripheral and axial psoriatic arthritis is usually less severe than rheumatoid arthritis and ankylosing spondylitis, respectively. Local corticosteroid injections and non-steroidal anti-inflammatory drugs are recommended in milder forms. Sulphasalazine and methotrexate are effective in peripheral psoriatic arthritis. Recent studies have provided evidence on the efficacy of anti-tumor necrosis factor-α drugs to control symptoms and to slow or arrest radiological disease progression.

Psoriasis and psoriatic arthritis: separate or one and the same?

The presence and severity of skin and joint symptoms in patients with psoriasis and psoriatic arthritis frequently do not correspond, a discrepancy that has raised the question of whether they represent two related but different disease processes. The fact that some agents seem to work preferentially in one state over the other reinforces this idea. However, there are also several agents with combined efficacy against cutaneous and articular inflammation that appear to support the existence of a common aetiology. Here we review the clinical, epidemiological and genetic evidence for and against a common pathogenesis for the two diseases. We then discuss the cellular and molecular targets of their selected therapies and how they potentially implicate effector pathways as a common immunopathogenic mechanism. Finally, we examine a recently proposed model of psoriasis pathogenesis involving type 1 interferon-producing plasmacytoid dendritic cells and how it may provide further clues to the aetiological links between psoriasis and psoriatic arthritis.

Pathogenesis of psoriatic arthritis

PURPOSE OF REVIEW

Heterogeneity in clinical presentation and disease course has hindered understanding of disease mechanisms in psoriatic arthritis, but recent studies have provided insights into pathogenesis. This review examines relevant animal models and genetic factors implicated in disease susceptibility. Also, recent reports on mechanisms related to synovial and entheseal inflammation are discussed.

RECENT FINDINGS

Two transgenic mouse models (amphiregulin, STAT-3) were reported that have features of psoriatic arthritis and psoriasis respectively. Genetic studies did not find associations between psoriatic arthritis and several class I major histocompatibility complex alleles, the caspase-activating recruitment domain 15 domain, or the major histocompatibility complex class I chain-related gene A9 allele, in sharp contrast to previous reports. The striking association of psoriatic arthritis with mutations in the killer immunoglobulin receptors on natural killer cells is particularly exciting but needs further study. Psoriatic arthritis has histopathologic features that are more characteristic of other forms of spondyloarthritis than rheumatoid arthritis. Moreover, several of these features correlate with clinical disease activity. Matrix metalloproteinases are strongly expressed in psoriatic arthritis synovium, and serum matrix metalloproteinases-3 may be a reliable biomarker for monitoring disease response. Finally, the concept of an 'enthesis organ' may explain the magnetic resonance imaging findings and clinical signs of psoriatic enthesitis and dactylitis.

SUMMARY

Recent findings highlight the importance of innate immune mechanisms in disease pathogenesis. Moreover, psoriatic arthritis and rheumatoid arthritis synovium have divergent histopathologic features that indicate distinct disease mechanisms. The generation of appropriate animal models coupled with reliable biomarkers will result in a deeper understanding of disease pathogenesis and will facilitate the identification of new therapeutic targets.