Managing psoriatic arthritis in different clinical scenarios.

INTRODUCTION: Psoriatic arthritis (PsA) is a chronic, immune-mediated disease characterized by synovio-entheseal inflammation. It is estimated to affect around 30% of patients with psoriasis and significantly reduces patients' physical function and quality of life. There is a growing number of treatment options for PsA, but due to the heterogeneous clinical features of the disease and prevalence of comorbidities, managing PsA can be challenging. AREAS COVERED: In this article, we review current understanding of the disease and available pharmacological options. Based on published treatment guidelines, emerging evidence and clinical experience, we provide our expert opinion on treatment strategies, taking into consideration the predominant disease domain and the presence of comorbidities, which can impact treatment decisions and clinical outcomes. EXPERT OPINION: Biological and targeted synthetic disease-modifying agents are dramatically improving the lives of patients with PsA. Biosimilar TNF inhibitors offer a particularly versatile and cost-effective option, whilst newer biologics and targeted synthetic molecules that can be used to treat most domains of psoriatic disease are an attractive alternative to TNF inhibitors. Despite a lack of consensus on treatment sequencing and tapering, it is important that PsA patients, especially those with comorbidities, are looked after by a multidisciplinary team to optimize their care.

Are Patients with Axial Spondyloarthritis Who Were Breastfed Protected against the Development of Severe Disease?

BACKGROUND AND AIMS: Breastfeeding is recognized as one of the most influential drivers of the gut microbiome. In turn, alterations in the gut microbiome may play a role in the development and severity of spondyloarthritis (SpA). We aimed to analyze different disease outcomes in patients with axial SpA (axSpA) based on the history of breastfeeding. PATIENTS AND METHODS: A random sample was selected from a large database of axSpA patients. Patients were divided based on history of breastfeeding and several disease outcomes were compared. Both groups were also compared based on disease severity. Adjusted linear and logistic regression statistical methods were used. RESULTS: The study included 105 patients (46 women and 59 men), and the median age was 45 years (IQR: 16-72), and the mean age at diagnosis was 34.3 ± 10.9 years. Sixty-one patients (58.1%) were breastfed, with a median duration of 4 (IQR: 1-24) months. After the fully adjusted model, BASDAI [-1.13 (95%CI: -2.04, -0.23), p = 0.015] and ASDAS [-0.38 (95%CI: -0.72, -0.04), p = 0.030] scores were significantly lower in breastfed patients. Forty-two percent had severe disease. In the adjusted logistic model for age, sex, disease duration, family history, HLA-B27, biologic therapy, smoking, and obesity, breastfeeding had a protective effect against the development of severe disease (OR 0.22, 95%CI: 0.08-0.57, p = 0.003). The selected sample size was sufficient to detect this difference with a statistical power of 87% and a confidence level of 95%. CONCLUSION: Breastfeeding might exert a protective effect against severe disease in patients with axSpA. These data need further confirmation.

Treatment Retention and Safety of Ixekizumab in Psoriatic Arthritis: A Real Life Single-Center Experience.

Background and objectives: Information on the performance of ixekizumab (IXE) in patients with psoriatic arthritis (PsA) in clinical practice is scarce. We aimed to analyze the retention rate and safety of IXE in patients with PsA in routine clinical practice. Methods: A retrospective longitudinal observational single-center study of all patients with PsA who had received at least one dose of IXE. Adverse events (AEs) and drug retention rate were the main study focus. Survival was analyzed using Kaplan−Meier curves and predictive factors using multivariate Cox regression analysis. The hazard ratio (HR) was used as a measure of the association. Results: Seventy-two patients were included (52 women and 20 men). Median disease duration was 5 years (IQR 3−9). More than 90% received ≥2 biologic and/or targeted synthetic disease-modifying anti-rheumatic drugs (DMARDs) prior to IXE. Ixekizumab showed a 1-year retention rate of 65% and a 2-year retention rate of 57%. Regarding discontinuation due to AEs, 0.18 AEs per person-year were identified. The number of previous biologics did not influence drug survival but prior use of methotrexate (HR 2.31 (95% CI 1.05−5.10), p < 0.05) and depression (HR 2.40 (95% CI 1.07−5.41), p < 0.05) increased the risk of IXE discontinuation. Conclusions: Ixekizumab showed a good retention rate in a PsA population mostly refractory to biologic and targeted synthetic DMARDs. Drug survival was consistently good regardless of age, gender, metabolic comorbidities, smoking status, or prior number of biologic therapies. This information may be of interest to better position this drug in the PsA treatment algorithms.

Non-Physical Disease Facets in Spondyloarthritis: An ASAS Health Index-Based Analysis between Psoriatic Arthritis and Axial Spondyloarthritis.

Background: Psychosocial health is a key driver of quality of life (QoL) in axial spondyloarthritis (axSpA) and psoriatic arthritis (PsA), but it is often overlooked in clinical practice. We aimed to analyze this aspect of QoL by using the Assessment of SpA International Society−Health Index (ASAS HI) in both SpA phenotypes. Patients and methods: One hundred and eleven patients with axSpA and 90 with PsA were consecutively recruited from two rheumatology centers. In both populations, the categories of stress handling (ASAS HI items #11 and 17) and emotional functions (ASAS HI item #13) were analyzed based on the International Classification of Functioning, Disability, and Health (ICF). A multivariate regression model was used to analyze the explanatory factors associated with positive responses to these items. Results: Thirty-four of the 90 PsA patients (37.8%) and 37/111 of the patients (33.3%) with axSpA reported a positive response to at least one of the stress-handling items. Compared to the patients with PsA, patients with axSpA were less likely to report stress-handling issues (OR 0.48, p < 0.05). Thirty-one of the 90 PsA patients (34.4%) and 44/111 of the patients (39.6%) with axSpA reported positive responses to item #13. In both groups of SpA patients, disease activity and severity (OR 6.6, p < 0.001) were independently associated with alterations in psychosocial health. Compared with those in the axSpA group, the psychosocial health items were better correlated with each other and with the ASAS HI sum score in the PsA group. Conclusions: Psychosocial health is frequently altered in SpA. Both disease activity and severity are associated with this issue. However, psychosocial factors seem to have a greater impact on QoL in PsA than in axSpA.

Interactions between rheumatoid arthritis antibodies are associated with the response to anti-tumor necrosis factor therapy.

BACKGROUND: Blocking of the Tumor Necrosis Factor (TNF) activity is a successful therapeutic approach for 50-60% of rheumatoid arthritis (RA) patients. However, there are yet no biomarkers to stratify patients for anti-TNF therapy. Rheumatoid factor (RF) and anti-cyclic-citrullinated antibodies (anti-CCP) have been evaluated as biomarkers of response but the results have shown limited consistency. Anti-carbamylated protein (anti-CarP) and anti-peptidylarginine deiminase type 4 (anti-PAD4) antibodies have been much less studied. Despite being linked to common immune processes, the interaction between these markers has not been evaluated yet. Our aim was to analyze the interaction between these four antibodies in relation to the response to anti-TNF therapy. METHODS: For this objective, a prospective cohort of n = 80 RA patients starting anti-TNF therapy was recruited. Serum determinations at baseline were performed for RF, anti-CCP, anti-CarP and anti-PAD4 antibodies using enzyme-linked immunosorbent assays (ELISA). The clinical response to anti-TNF therapy was determined at week 12 using the change in DAS28 score. Association was performed using multivariate linear regression adjusting for baseline DAS28, sex and age. RESULTS: The interaction between pairs of antibodies was tested by the addition of an interaction term. We found two highly significant antibody interactions associated with treatment response: anti-CarP with anti-PAD4 (p = 0.0062), and anti-CCP with RF (p = 0.00068). The latter antibody interaction was replicated in an independent retrospective cohort of RA patients (n = 199, p = 0.04). CONCLUSIONS: The results of this study suggest that antibody interaction effects are important factors in the response to anti-TNF therapy in RA.

Food groups associated with immune-mediated inflammatory diseases: a Mendelian randomization and disease severity study.

BACKGROUND/OBJECTIVES: Immune-mediated inflammatory diseases (IMIDs) are prevalent diseases. There is, however, a lack of understanding of the link between diet and IMIDs, how much dietary patterns vary between them and if there are food groups associated with a worsening of the disease. SUBJECTS/METHODS: To answer these questions we analyzed a nation-wide cohort of n = 11,308 patients from six prevalent IMIDs and 2050 healthy controls. We compared their weekly intake of the major food categories, and used a Mendelian randomization approach to determine which dietary changes are caused by disease. Within each IMID, we analyzed the association between food frequency and disease severity. RESULTS: After quality control, n = 11,230 recruited individuals were used in this study. We found that diet is profoundly altered in all IMIDs: at least three food categories are significantly altered in each disease (P < 0.05). Inflammatory bowel diseases showed the largest differences compared to controls (n ≥ 8 categories, P < 0.05). Mendelian randomization analysis supported that some of these dietary changes, like vegetable reduction in Crohn's Disease (P = 2.5 × 10-10, OR(95% CI) = 0.73(0.65, 0.80)), are caused by the disease. Except for Psoriatic Arthritis and Systemic Lupus Erythematosus, we have found ≥2 food groups significantly associated with disease severity in the other IMIDs (P < 0.05). CONCLUSIONS: This cross-disease study demonstrates that prevalent IMIDs are associated to a significant change in the normal dietary patterns. This variation is highly disease-specific and, in some cases, it is caused by the disease itself. Severity in IMIDs is also associated with specific food groups. The results of this study underscore the importance of studying diet in IMIDs.

Disease Activity in Psoriatic Arthritis Index and Psoriatic Arthritis Impact of Disease Questionnaire: correlation and sensitivity to change in a real clinical setting.

OBJECTIVES: The performance of many outcome measures for psoriatic arthritis (PsA) is almost unknown in real clinical practice. Our objective was to study the correlation and sensitivity to change of the Disease Activity in Psoriatic Arthritis (DAPSA) index and the Psoriatic Arthritis Impact of Disease (PsAID) questionnaire in a real practice setting. METHODS: This was a prospective, open, non-controlled study that included 60 consecutive patients with PsA treated with ustekinumab. Most had been previously treated with one or more biologic therapeutic agents. The correlation (Spearman's rho coefficient) and the sensitivity to change [Standardized Mean Response (SMR)] of DAPSA and PsAID were studied. Effect size values of 0.20, 0.50 and 0.80 corresponded to low, moderate and high sensitivity to change, respectively. RESULTS: More than 70% of patients achieved therapeutic goals (21.7% were in remission and 50% in low disease activity according to DAPSA categories). Two out of three patients reached an acceptable symptomatic state (PsAID <4). The correlation between final values of both instruments was substantial (Spearman's rho: 0.62, p<0.0001). The SMR for the PsAID was 1.08 (0.95-1.21) and for DAPSA was 1.5 (1.37-1.63), both values corresponding to instruments with a high sensitivity to change (>0.80). The best PsAID cut-off value for identifying DAPSA remission was 3.32 with an area under the ROC curve of 0.82. CONCLUSIONS: DAPSA and PsAID seem to be useful instruments for a more comprehensive assessment of PsA in daily practice. Our results can help to disseminate the use of these instruments in the clinical practice of many rheumatologists.

Pyle's Disease: A human model of differentiated cortical and trabecular homeostasis. / Enfermedad de Pyle: un modelo humano de homeostasis corticotrabecular diferenciada.

Pyle's disease (OMIN number 265900) is a metaphyseal dysplasia of benign course, inherited with an autosomal recessive pattern. Some 30 genuine cases have been described so far. The cause of this process has been known since 2016, when its relationship to mutations in the gene encoding the sFRP protein, a known inhibitor of the Wnt pathway, was discovered. We report the case of a 58-year-old man, diagnosed with Pyle's disease based on his clinical and radiographic characteristics, whose phenotype suggested a differential control of cortical and trabecular bone homeostasis.

Analysis by Age Group of Disease Outcomes in Patients with Psoriatic Arthritis: A Cross-Sectional Multicentre Study.

OBJECTIVES: Elderly psoriatic arthritis (PsA) patients may show greater inflammatory activity and worse prognoses than patients of other ages. However, these patients may be at risk of receiving fewer systemic treatments. In this report, we have analysed disease outcomes in PsA by age groups. METHODS: This cross-sectional, multicentre study included 227 PsA patients under biological and non-biological systemic therapies. The study population was divided into four categories by age: < 40, 40‒49, 50‒65 and > 65 years. Physical functioning, disease activity, remission rates and disease impact were compared. RESULTS: Thirty-one patients (13.7%) were under 40 years, 26.9% (n = 61) were 40-49 years, 26.4% (n = 60) were 50-65 years and 33.0% (n = 75) were patients > 65 years. Compared with the other age groups, disease duration was significantly higher in subjects older than 65 years (p < 0.001). Only 8% of patients older than 65 years received corticosteroids compared with 29% of patients aged < 40 years, 13.1% of patients aged 40-49 years and 26.7% of patients aged 50-65 years (p = 0.007). Similarly, only 36% of patients over 65 years of age received a biological therapy compared with between 51.6 and 59% for the other age groups (p = 0.036). However, remission rates were not statistically different between groups. Disease-associated physical disability was similar among groups. Compared with patients aged < 40 years, more patients > 65 years achieved low disease impact (10.7% vs 37.7%, respectively; p < 0.05). CONCLUSIONS: Fewer older patients received corticosteroids and biological therapy. However, disease outcomes were similar or even better compared with those observed in younger patients. Therefore, treatment strategies for older patients with PsA should be similar to those offered to younger individuals.

Minimal Disease Activity and Patient-Acceptable Symptom State in Psoriatic Arthritis: A Real-World Evidence Study With Ustekinumab.

BACKGROUND/AIMS: Ustekinumab (UST) is a fully human immunoglobulin G1 monoclonal antibody approved for treating moderate to severe psoriasis and, more recently, psoriatic arthritis (PsA) as well. However, information regarding its clinical usefulness in a real-world setting is scarce. We aimed to evaluate the effectiveness and safety of UST in a real-world clinical setting. METHODS: This single-center observational study included PsA outpatients (n = 50) treated with UST from March 2015 to March 2017. Only patients who used at least 3 doses of UST were analyzed. The percentage of patients who achieved a minimal disease activity (MDA) response was collected. The impact of the disease was also evaluated according to the recently developed Psoriatic Arthritis Impact of Disease (PsAID) questionnaire. A binary logistic regression multivariate model was performed to look for variables predicting MDA. RESULTS: Twenty-seven patients (54%) reached an MDA state. Mean PsAID in MDA group was 3.5 ± 2.9 versus 6.8 ± 5.1 in non-MDA patients (p < 0.001). Among the patients who achieved MDA, 19 (70.4%) had a patient-acceptable symptom state according to the PsAID, whereas only 5 (21.7%) of the 23 patients who did not reach an MDA achieved a patient-acceptable symptom state (p < 0.001). Higher basal Psoriasis Area and Severity Index decreased the odds of achieving MDA (odds ratio [OR], 0.80; 95% CI, 0.65-0.99; p = 0.038), whereas a longer use of UST (OR, 1.52; 95% CI, 1.13-2.06; p = 0.015) and a previous failure to 1 anti-tumor necrosis factor α (OR, 18; 95% CI, 2.52-128.63; p = 0.004) increased this odds. We found no major safety problems. CONCLUSIONS: Ustekinumab was effective and safe in this PsA population. Minimal disease activity and PsAID may be useful tools in the evaluation of PsA therapeutic interventions in routine clinical practice.

Age at disease onset may help to further characterize the disease phenotype in psoriatic arthritis.

OBJECTIVE: To evaluate whether the age of disease presentation helps to better characterize the disease phenotype in PsA. METHODS: Retrospective cohort study that included 205 consecutive patients fulfilling the CASPAR criteria for PsA. Study outcomes were assessed using univariate and multivariate analyses according to the age of onset of both skin and joint disease (cut off at 40years). RESULTS: Early onset psoriasis (EOP) showed more extensive skin involvement (OR 2.3, P=0.011), axial pattern as disease onset (OR 4.6, P=0.009) and mixed pattern during evolution (OR 2.4, P=0.019), family history of both psoriasis (OR 3.1, P=0.003) and PsA (OR 4.0, P=0.021), higher prevalence of HLA-C*06 (OR 2.03, P=0.03) and HLA-B*27 (OR 2.7, P=0.02). Early onset arthritis (EOA) had more family history of PsA (OR 2.9, P=0.007), and HLA-B*27 positivity (OR 5.9, P<0.0001). Patients with late onset arthritis (LOA) were more likely to have DM (OR 4.0, P=0.009), hypertension (OR 2.5, P=0.004), dyslipidemia (OR 2.3, P=0.011), and obesity (OR 1.7, P=0.012). Late onset psoriasis (LOP) tended to have more obesity (OR 1.9, P=0.035), DM (OR 9.4, P<0.0001), hypertension (OR 4.1, P<0.0001), and ischemic heart disease during follow-up (OR 5.9, P=0.021). In multivariate analysis, LOP predicted DM development (OR 12.1, P=0.006). LOA was shown to be an independent risk factor for hypertension (OR 5.2, P=0.039). CONCLUSION: Age at disease onset exerts a strong influence on several domains of disease phenotype in PsA. Therefore, this descriptor should be considered a good stratification option for epidemiological and genetic studies in PsA.

Clinical differences between men and women with psoriatic arthritis: relevance of the analysis of genes and polymorphisms in the major histocompatibility complex region and of the age at onset of psoriasis.

It has been shown that males with spondyloarthritis tend to suffer from more severe spinal disease while females are more likely to have peripheral joint involvement. Nevertheless, gender-related differences have not been thoroughly explored in psoriatic arthritis (PsA). In PsA, males accumulate more peripheral and axial joint damage compared to women. However, it is not clear whether these findings are secondary to differences in occupational physical activity, hormonal changes, or other factors. The present study analyzed the differences in clinical expression of PsA between men and women. We have also evaluated the possible existence of gender-linked differences in the distribution of genes and polymorphisms within the major histocompatibility complex and whether patients' age at the onset of psoriasis established any differences in these aspects. Women suffered more polyarthritis, greater functional impairment, and a larger number of swollen joints during followup. We appreciated a differential expression of certain MHC genes according to gender and age at onset of psoriasis. Our results point to the need to include patient's age at the onset of psoriasis and gender as key stratification elements in future studies of genetic associations in PsA.

Patients with psoriatic arthritis may show differences in their clinical and genetic profiles depending on their age at psoriasis onset.

OBJECTIVES: The age of psoriasis onset has an important impact on the clinical expression and heritability of psoriasis. Psoriasis characteristics according to the age at disease onset have been extensively studied. However, the impact of the age of psoriasis onset on psoriatic arthritis (PsA) features has not been analysed in depth. The aim of the present paper is to analyse whether the age of psoriasis onset may have an impact on the clinical and genetic characteristics in a cohort of PsA patients. METHODS: The study included 110 PsA patients classified in accordance with the CASPAR criteria. Patients were divided into early (onset age <30 years) and late (onset age >30 years) onset psoriasis, and clinical features were studied in accordance to this stratification. Distribution of several genes within the MHC region were analysed in accordance with the prior stratification, and their frequencies compared to that of 110 healthy matched blood donors. RESULTS: Compared to patients with late-onset disease, PsA patients with early-onset psoriasis showed more frequently: a longer psoriasis-arthritis latency period (9.9±6 years vs. 3.8±4 years, p=0.0001), a positive family history of disease (60.3% vs. 20.5%, OR 6.1, 95% CI: 2.5-15.0, p=0.0001), severe psoriasis (PASI 8.2±4 vs. 3.6±2.2, p=0.0001), clinical enthesitis (37.7% vs. 22.4%, OR 2.09, 95% CI: 0.9-4.9, p=0.08), and oligoarthritis (47.5% vs. 28.6%, OR 2.26, 95% CI: 1.02-5.02, p=0.04). MICA-A9 was associated with susceptibility in both early-onset (60.7% vs. 30%, p=0.0002) and late-onset patients (59.2% vs. 30%, p=0.0008). However, HLA-Cw*0602 was significantly increased in patients with early-onset psoriasis (73.8% vs. 17%, p<0.0001), whereas the allele 384 of the microsatellite C1_4_4, located 34 kb telomeric to HLA-C locus, was increased only in late-onset cases (49% vs. 21%, p=0.001). CONCLUSIONS: Clinical and genetic features of PsA may differ depending on the age at psoriasis onset. This type of stratification should be considered in future genetic and epidemiological studies of PsA.

Psoriasis and psoriasiform lesions induced by TNFα antagonists: the experience of a tertiary care hospital from northern Spain.

The aim of this study was to investigate the cumulated incidence and clinical characteristics of the psoriasiform lesions seen in a wide cohort of rheumatic patients exposed to anti-TNFα drugs in a tertiary care hospital from northern Spain. The study population included 450 patients exposed to anti-TNFα agents from 2001 to 2007 and treated in a university hospital in northern Spain. Two hundred patients were exposed to infliximab (44%), 129 (29%) to etanercept, and 121 (27%) to adalimumab. The cumulated incidence (CI) of this skin reaction was calculated for each of the three agents studied. Psoriasis and psoriasiform lesions were documented in 7 patients diagnosed with different rheumatic inflammatory conditions (1.56%). Cases of this adverse effect were identified with all three anti-TNFα agents available at that time, but less frequently with infliximab (CI: 0.5%) compared with etanercept (CI: 2.3%) or adalimumab (CI: 2.5%). The most common lesion was palmoplantar pustulosis (71.3% of the cases), and the latency period to the development of the lesions ranged from 4 to 38 months (mean 9 months). In four of the 7 patients, treatment was suspended, while in the remaining three patients treatment was continued. The CI of this skin reaction in our setting is similar to that published by others. Infliximab was found to be less frequently associated with this adverse event. In our experience, it is not always necessary to stop anti-TNFα therapy for the skin lesions to improve.

[Adverse effects of bisphosphonates]. / Efectos adversos de los bisfosfonatos.

Aminobisphosphonates are drugs that have been used successfully in the treatment of osteoporosis for more than 20 years. Although main registry studies found a scarcity of relevant adverse events, in recent years and as a result of pharmacovigilance, different complications have been reported, some potentially serious. This has raised questions on the safety of these drugs, especially in high doses, like those used in oncology and long-term treatment, as needed in patients with osteoporosis. In this review, based on the analysis of relevant scientific evidence from clinical trials, case series, cohort studies and databases published to date, we summarize the clinical and epidemiological characteristics of the adverse effects of these drugs.

Stratification by age of onset with 30 years as age limit is an effective means of identifying PSORS1-associated psoriasis in patients with psoriatic arthritis.

OBJECTIVES: To determine which of the following is the best method to identify PSORS1-associated psoriasis in patients with psoriatic arthritis (PsA): age at disease onset or positive family history of disease. METHODS: A total of 71 patients with PsA who met the CASPAR criteria were recruited on a randomized basis. The patients were stratified according to age at disease onset, with cutoff points at 25, 30, 35 and 40years of age. The alleles of locus Cw were analyzed by PCR-based methods, and their distribution was compared to that of 177 healthy blood donors. RESULTS: HLA-Cw*0602-PSORS1- was associated with disease risk (56% vs. 18%) OR 5.8, 95%CI: 3.2-10.7, P=0.00001. A close relationship was established between this allele and onset of psoriasis under 30years of age (68% vs. 24%) OR 6.4, 95%CI: 2.3-18.2, P=0.0003. The relationship in turn lost significance above this age limit. An association was found between a family history of psoriasis and disease risk, though there was no specific cutoff point according to age at onset of the disease. Sixty-four percent of the subjects with positive family history were HLA-Cw*06 (+) compared to 44% of those without a family history, OR 2.3, 95% CI: 0.82-6.36, P=0.08. CONCLUSIONS: In patients with PsA, the susceptibility effect of HLA-Cw*06 declines with increasing age of onset. Disease onset under or above 30years of age may contribute to differentiate type I vs. type II psoriasis in PsA populations, while the family history have a lesser contribution to such stratification.

HLA-C locus alleles may modulate the clinical expression of psoriatic arthritis.

The aim of the present study was to evaluate the relative contribution of human leukocyte antigen (HLA)-C locus alleles in determining the risk and the clinical expression of psoriatic arthritis (PsA). One hundred PsA patients were randomly selected and grouped into three disease subsets: oligoarthritis (n = 40), polyarthritis (n = 25) and spondylitis (n = 35). The HLA-C locus profile of this cohort was studied by methods based on molecular biology and was compared with that of 45 patients with psoriasis vulgaris and 177 healthy blood donors from the same ethnic origin. HLA-Cw*0602 was found associated with both psoriasis (odds ratio (OR) 6.2; 95% confidence interval (CI) 3.1 to 12.5; p < 0.0001) and PsA (OR 6.2; 95% CI 3.6 to 10.8; p < 0.0001); however, this allele was equally found among the PsA subsets. HLA-Cw6-positive patients showed a longer psoriasis-arthritis latency period (p = 0.012). HLA-Cw*0701 was found under-represented in PsA in comparison with controls (OR 0.5; 95% CI 0.3 to 0.9; p = 0.04), as was HLA-Cw*0802 (OR 0.3; 95% CI 0.08 to 1; p = 0.05). A positive association was found between psoriatic spondylitis and HLA-Cw*0702 (OR 5.0; 95% CI 1.4 to 25; p = 0.01). HLA-Cw*0602 seems to confer a general risk for psoriasis, but the presence of other HLA-C locus alleles may explain an additional arthritogenic risk. HLA-C alleles may modulate some aspects of the clinical expression of PsA, but these findings need confirmation.