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Objective Psoriatic arthritis (PsA) is a common inflammatory joint disease distinct from other chronic arthritides and frequently accompanied by psoriasis vulgaris. In a first genome-wide association study (GWAS), we were able to identify several genetic risk factors. However, even combined with previously identified factors, the genetic contribution to disease was not fully explained. Therefore, we undertook this study to investigate further 17 loci from our GWAS that did not reach genome-wide significance levels of association in the initial analysis. Methods Twenty-one of 22 single-nucleotide polymorphisms were successfully genotyped in independent cohorts of 1,398 PsA patients and 6,389 controls and in a group of 964 German patients with psoriasis vulgaris. Results Association with a RUNX3 variant, rs4649038, was replicated in independent patients and controls and resulted in a combined P value of 1.40 x 108 by Cochran-Mantel-Haenszel test and an odds ratio (OR) of 1.24 (95% confidence interval [95% CI] 1.151.33). Further analyses based on linkage disequilibrium (LD) at RUNX3 refined the most significant association to an LD block located in the first intron of one isoform. Weaker evidence for association was detected in German patients with psoriasis vulgaris (P = 5.89 x 102; OR 1.13 [95% CI 1.001.28]), indicating a role in the skin manifestations of psoriasis. Conclusion Our analyses identified variants in RUNX3 as susceptibility factors for PsA. RUNX3 has already been implicated in susceptibility to ankylosing spondylitis, another spondyloarthritis, although its risk allele is independent from the one for PsA. RUNX-3 is involved in CD8+ T lymphocyte differentiation and is therefore a good candidate for involvement in PsA and psoriasis vulgaris as T cellmediated diseases.

Psoriatic Arthritis (PsA) is a heterogonous inflammatory arthritis associated with psoriasis. The disease leads to inflammation of peripheral joints, axial skeleton and/or enthesites, and can result in severe destruction of affected joints. In contrast to rheumatoid arthritis (RA), most individuals with PsA are seronegative for rheumatoid factor (RF) and/or anti-citrullinated protein/peptide antibodies (ACPA) and the distal interphalangeal (DIP) joints are often involved. Dactylitis, a diffuse swelling of an entire digit (finger or toe), is also common. Traditional markers of systemic inflammation, such as erythrocyte sedimentation rate (ESR) and/or C-reactive protein (CRP) are elevated in only 50% of the individuals with PsA.

Underlying genetic factors are considered important for the aetiology, disease expression and prognosis of PsA. To date no specific biomarker for PsA disease or disease activity/severity is available and there is a need for diagnostic and prognostic tools to meet the challenge of early diagnosis and assessment of disease severity.

An increased risk of co-morbidity, particularly cardiovascular disease (CVD), has been demonstrated in patients suffering from different rheumatic diseases, e.g. systemic lupus erythematosus (SLE) and rheumatoid arthritis (RA). Corresponding data for patients with PsA are more limited, but evidence exists for an increased risk of mortality and cardiovascular morbidity. However, published results are conflicting and heterogeneity among studies makes interpretation of data difficult.

The aim of this study was to investigate genetic and serological biomarkers, and also mortality and cardiovascular comorbidity, in different phenotypes of PsA and in comparison with healthy controls. Patients with PsA were included between 1995 and 2015, the majority from the county of Västerbotten, except for two cohorts from Örnsköldsvik (n=55) and Östersund (n=98).

The genetic polymorphism PTPN22+1858C/T, previously found to be associated with several autoimmune diseases, was also found associated with PsA, the results were later confirmed in a genome wide association study (GWAS). Additionally, among PsA patients, the minor allele, T, was associated with the number of deformed joints and dactylitis (Paper I). 

Genetic polymorphisms in genes related to the inflammasome were also investigated, both in comparison with healthy controls and in relation to different phenotypes of PsA (Paper II). An association was identified between patients with PsA and the polymorphism CARD8-C10X in comparison with controls. In addition, associations between various inflammasome polymorphisms and different clinical phenotypes of PsA were detected.

To investigate the relation of serological biomarkers and PsA, individuals with blood samples collected in conjunction with clinical investigation were selected (Paper III).  Associations with different biomarkers and different clinical phenotypes of PsA were identified In addition, associations were found with different biomarkers and patients with moderate/high disease activity at clinical investigation, confirming the inflammatory nature of the disease.

Mortality and incidence of acute cardiovascular disease were investigated with standardized mortality rateratio (SMR) and standardized incidence ratio (SIR) compared with the general population of Västerbotten (Paper IV). An increased SMR for diseases of the circulatory system in PsA compared with controls was found. Among PsA patients, death was associated with a composite disease activity index (DAI) and with a disease phenotype including both axial- and peripheral joint involvement. 

In conclusion, associations were found with different clinical phenotypes of PsA, both with genetic polymorphisms and serological biomarkers that confirm the inflammatory nature of the disease and illustrate the disease heterogeneity. As in many other inflammatory diseases, an increased cardiovascular mortality was found that highlights the importance of considering cardiovascular risk factors in patients with PsA.

INTRODUCTION: The purpose of the present study was to investigate the frequency of the PTPN22 +1858 C/T single nucleotide polymorphism (SNP) (rs 2476601), previously shown to be associated with several autoimmune diseases, in patients with psoriatic arthritis (PsA) in comparison with population based controls.

METHODS: A total of 291 patients (145 male/146 female, mean age (± S.D.) 52.2 (± 13.1) years) with PsA were examined clinically, by standard laboratory tests and their DNA was genotyped for the SNP rs2476601 (PTPN22 +1858 C/T). Allelic frequencies were determined and compared with 725 controls.

RESULTS: Carriage of the risk allele, PTPN22+1858T, showed a significant association with patients with PsA compared with controls (χ2 = 6.56, P = 0.010, odds ratio (OR) 1.49; 95% confidence interval (CI) 1.10 to 2.02). A significantly higher proportion of carriers of the risk allele (T) had significantly more deformed joints (n ± SEM) (5.9 ± 1.2 vs 2.8 ± 0.5; P = 0.005).

CONCLUSIONS: In this study the +1858T allele of the PTPN22 gene, known to be associated with several autoimmune diseases, was associated with PsA. The finding of significantly more joints with deformities among carriers of the T variant could indicate a more aggressive phenotype of disease.

Objective: Psoriatic arthritis (PsA) is a heterogeneous inflammatory disease associated with psoriasis. Underlying genetic factors are considered important for disease expression and prognosis of PsA. Interleukin-1 beta-regulating protein complexes called inflammasomes are associated with several inflammatory diseases, e.g. rheumatoid arthritis and psoriasis. The aim was to determine whether inflammasome-related genetic variation is associated with PsA susceptibility or different disease phenotypes.

Method: DNA from 724 patients with PsA and 587 population-based controls from northern Sweden was analysed for single-nucleotide polymorphisms in NLRP3-Q750K (rs35829419), NLRP3 (rs10733113), CARD8-C10X (rs2043211), NLRP1 (rs8079034), and NLRP1 (rs878329).

Results: Significant associations were found with the genotype AA (vs AT+TT) of rs2043211 for PsA patients compared with controls [odds ratio (OR), 95% confidence interval (CI) 1.32 (1.05-1.65), p = 0.016]; and between the C-allele of rs878329 and axial involvement of PsA [OR (95% CI) 1.37 (1.02-1.84), p = 0.035], the T-allele of rs8079034 with prescription of conventional synthetic disease-modifying anti-rheumatic drugs [OR (95% CI) 1.76 (1.23-2.53), p = 0.0020], the G-allele of rs10733113 and patients with a skin disease with early onset [OR (95% CI) 1.58 (1.13-2.21), p = 0.007], and the C-allele of rs35829419 and a destructive/deforming disease [OR (95% CI) 1.63 (1.04-2.55), p = 0.030].

Conclusions: This study is the first to show an association with a genetic polymorphism in an inflammasome-related gene, CARD8-C10X (rs2043211), in patients with PsA. Associations between different phenotypes of PsA and different polymorphisms of the inflammasome genes were also found. Our results indicate the involvement of inflammasome genes in the pathogenesis and disease expression of PsA.

Objective: Recent studies indicate increased cardiovascular (CV) morbidity and mortality in patients with psoriatic arthritis (PsA), but results are inconsistent. This prompted our investigation of the mortality rate, cause of death, and incidence of acute CV events in patients from northern Sweden with PsA.

Methods: Patients with established PsA (464) were included. To calculate standardized mortality ratio (SMR) and standardized incidence ratio (SIR) for CV events, data were extracted from the National Causes of Death Register and the National Inpatient Care Register in Sweden, and compared with the general population. The study period was 1995-2011. To study the effect of inflammatory activity, a composite disease activity index (DAI) was used.

Results: The SMR (95% CI) for overall mortality and diseases of the circulatory system (International Classification of Diseases, 10th edition; I00-I99) was 1.22 (0.89-1.63) and 1.64 (1.02-2.52), respectively. In regression analysis, DAI was significantly associated with death (OR 1.99, 95% CI 1.41-2.80) when adjusted for age and sex (p < 0.001), and remained significant after stratifying patients into the 2 major causes of death: diseases of the circulatory system and malignant neoplasms. Peripheral and axial disease was associated with death (OR 4.02, 95% CI 1.84-8.84, p < 0.001) compared with peripheral disease only. The SIR (95% CI) for a CV event (myocardial infarction or stroke) was 0.597 (0.40-0.86); this association was only significant in men.

Conclusion: Patients with PsA had a small but significant increase in SMR for death due to diseases of the circulatory system compared with the general population. Among patients, death was associated with DAI, as well as axial involvement in combination with peripheral disease, indicating more aggressive disease phenotypes.