Association between IL13 polymorphisms and psoriatic arthritis is modified by smoking

The genetic basis of spondyloarthritis

Modern technological innovations have advanced our understanding of the genetic basis of spondyloarthritis. In ankylosing spondylitis (AS), where the major histocompatibility complex (MHC) accounts for nearly half of the predisposition, most comes from HLA-B27, for which 65 subtypes are now recognised, although other genes are also at work including HLA-B60 (B*40:01). Other genes have been identified, including those involved in peptide editing for loading onto class I MHC molecules (ERAP1) and cytokine genes such as interleukin 1A (IL-1A) and those involved in the Th17 network (IL-23R, an association seen primarily in Caucasians) and others. In acute anterior uveitis, these associations are also seen as well as a region on chromosome 9p and genes whose confirmation is under way. Psoriasis and psoriatic arthritis fall into this disease spectrum, with the largest region of susceptibility coming from the MHC (most likely HLA-C, ie, C*06:02 although additional influences are also being implicated), and most of the other genetic susceptibility coming from genes involved in cytokine production, specifically genes in the Th17 pathway (IL-12B, IL-23A and IL-23R, the latter, like in AS, not seen in Asians), genes in the nuclear factor κB pathway (TNFAIP3 and TNIP1) and genes in the Th2 pathway (IL-4 and IL-13). Given that more than half of patients with AS have evidence on colonoscopy of at least occult inflammatory bowel disease (IBD), it is not surprising that shared genetic influences are operative. In IBD, genes important in the innate immune response (NOD2), autophagy (ATG6L1) and regulation of the IL-23 pathway (IL-23R) play a role in disease susceptibility.

The Genetic Basis of Spondyloarthritis: SPARTAN/IGAS 2009

A joint meeting was held in July 2009 in Houston, Texas, of members of the Spondyloarthritis Research and Therapy Network (SPARTAN), founded in 2003 to promote research, education, and treatment of ankylosing spondylitis (AS) and related forms of spondyloarthritis (SpA), and members of International Genetics of AS (IGAS), founded in 2003 to encourage and coordinate studies internationally in the genetics of AS. The general topic was the genetic basis of SpA, with presentations on the future of human genetic studies; microbes, SpA, and innate immunity; susceptibility of AS to the major histocompatibility complex (MHC) and non-MHC; and individual discussions of the genetics of psoriasis and psoriatic arthritis, uveitis, inflammatory bowel disease, and enteropathic arthritis. Summaries of those discussions are presented.

Genetic variations associated with psoriasis and psoriatic arthritis found by genome-wide association

Psoriasis and psoriatic arthritis are immune disorders with a complex polygenic basis. HLA-Cw6, which lies in the major histocompatibility region on chromosome 6, is considered the major genetic determinant of psoriasis. Recent genome-wide association studies have identified new variants outside of the MHC with relevance to the immunology of psoriasis. Variants in or near genes that encode subunits of cytokines (IL12B, IL23A) or cytokine receptors (IL23R) are interesting given that the gene product of IL12B, p40, is the target of a recently approved monoclonal antibody therapy for psoriasis (ustekinumab). Association with psoriasis and psoriatic arthritis has been found in TNFAIP3 and TNFIP1, ubiquitin ligases in the NF-kappaB pathway, and IL13, a Th2 cytokine. Copy number variation of human beta-defensin and late cornified envelope genes also associate with psoriasis. Many of these genetic variations also associate with immune disorders considered psoriatic co-morbidities, including Crohn's disease and diabetes.

Genetics of psoriasis and psoriatic arthritis

It is well established that psoriasis and psoriatic arthritis (PsA) have a strong genetic component. Recent advances in genetics have confirmed previous associations and new loci have been discovered. However, these loci do not fully account for the high heritability of psoriasis and PsA and therefore many genetic as well as environmental factors remain to be identified. This paper reviews the current status of genetic studies in psoriasis and PsA.

Tumor necrosis factor-alpha-converting enzyme as a potential mediator of the influence of smoking on the response to treatment with narrowband ultraviolet B in psoriasis patients

PURPOSE

The aim of the study was to analyze the relationship between smoking and the treatment with narrowband ultraviolet B (NB-UVB) in psoriasis patients and to examine the role of the soluble tumor necrosis factor-alpha receptor type one (sTNF-R1) in plasma and that of TNF-alpha-converting enzyme (TACE) released from peripheral blood mononuclear cells (PBMC) in this relationship.

METHODS

The study has been conducted among 45 inpatients with plaque-type psoriasis vulgaris and 36 inpatients with other chronic inflammatory skin disorders from similar social background (controls). Taking into account the number of cigarettes smoked daily and the duration of smoking, subjects were classified as mild, moderate and heavy smokers. The severity of psoriasis was assessed using psoriasis area and severity index (PASI) score, concentrations of sTNF-R1 and TACE (expressed in ng/ml)--with quantitative sandwich enzyme immunoassays before (T(0)) and after 20 NB-UVB irradiations (T(20)).

RESULTS

The pretreatment concentration of sTNF-R1 was 2.55+/-0.17 in patients and 1.79+/-0.13 in controls (P<0.05) and that of TACE - 2.62+/-0.34 and 1.29+/-0.25, P<0.05, respectively. PASI score correlated with sTNF-R1 and with TACE concentrations (R=0.40 and R=0.38, P<0.05, respectively). PASI score, sTNF-R1 and TACE concentrations were similar in mild, moderate and in heavy smokers. PASI score and TACE concentration declined significantly after treatment in three groups; the lowest TACE concentration at T(20) was noticed in mild smokers, the highest in heavy smokers (0.86+/-0.26 and 1.91+/-0.20, P<0.05, respectively). The post-treatment PASI score correlated with the intensity of smoking and with TACE concentration (R=0.50 and R=0.47, P<0.05, respectively). The strong correlation between the pretreatment TACE concentration and the treatment outcome was observed in heavy smokers (R=0.63, P<0.05).

CONCLUSIONS

The baseline TACE concentration in PBMC may be of value in predicting the response to the treatment with NB-UVB in smoking psoriasis patients. Smoking may adversely influence this treatment and TACE may be one of mediators in this influence.

Geoepidemiology and environmental factors of psoriasis and psoriatic arthritis

Psoriasis and Psoriatic Arthritis (PsA) are chronic inflammatory diseases that have a major impact on health. The prevalence and incidence estimates of these two closely related diseases show ethnic and geographic variations, being generally more common in the colder north than in the tropics. In Europe the prevalence of psoriasis varies anywhere from 0.6 to 6.5%. In the USA, the estimated prevalence of diagnosed psoriasis is 3.15%. The prevalence in Africa varies depending on geographic location, being lowest in West Africa. Psoriasis is less prevalent in China and Japan than in Europe, and is entirely absent in natives of the Andean region of South America. There are fewer reports on the incidence of psoriasis, but a recent study from Rochester, USA showed an increasing trend over the last 2 decades. The prevalence of PsA also shows similar variation, being highest in people of European descent and lowest in the Japanese. Although, study methodology and case definition may explain some of the variations, genetic and environmental factors are important. Genetic epidemiologic studies have shown that both diseases have a strong genetic component. The strongest association is with HLA-Cw*06. Associations with a number of genes including IL12B and IL23R have recently been confirmed. Environmental risk factors including streptococcal pharyngitis, stressful life events, low humidity, drugs, HIV infection, trauma, smoking and obesity have been associated with psoriasis and PsA. Here we have reviewed the current literature on the epidemiology and genetics of psoriasis and PsA.