Psoriatic arthritis (PsA) is a chronic inflammatory musculoskeletal disease affecting up to 30% of psoriasis vulgaris (PsV) cases and approximately 0.25% to 1% of the general population. To identify common susceptibility loci, we performed a meta-analysis of three imputed genome-wide association studies (GWAS) on psoriasis, stratified for PsA. A total of 1,160,703 SNPs were analyzed in the discovery set consisting of 535 PsA cases and 3,432 controls from Germany, the United States and Canada. We followed up two SNPs in 1,931 PsA cases and 6,785 controls comprising six independent replication panels from Germany, Estonia, the United States and Canada. In the combined analysis, a genome-wide significant association was detected at 2p16 near the REL locus encoding c-Rel (rs13017599, P=1.18×10−8, OR=1.27, 95% CI=1.18–1.35). The rs13017599 polymorphism is known to associate with rheumatoid arthritis (RA), and another SNP near REL (rs702873) was recently implicated in PsV susceptibility. However, conditional analysis indicated that rs13017599, rather than rs702873, accounts for the PsA association at REL. We hypothesize that c-Rel, as a member of the Rel/NF-κB family, is associated with PsA in the context of disease pathways that involve other identified PsA and PsV susceptibility genes including TNIP1, TNFAIP3 and NFκBIA.

The TNFAIP3 gene has been associated with psoriasis, rheumatoid arthritis, type 1 diabetes mellitus, systemic lupus erythematosus and celiac disease. TNFAIP3 encodes A20, a TNF-α-inducible zinc finger protein thought to limit NF-κB mediated immune responses. In this study we report association of response of psoriasis to TNF blockers with two TNFAIP3 SNPs (rs2230926 in exon 3 and rs610604 in intron 6) and their haplotypes. Treatment response was self-evaluated using a 0–5 visual analog scale in 433 psoriasis patients who received TNF blockers. Confirmation was sought in 199 psoriasis and psoriatic arthritis patients from Toronto who were followed prospectively. Response variables were dichotomized separately in the two cohorts, yielding similar proportions of good responses. While significant associations were observed only for the Michigan cohort, fixed-effects meta-analysis retained significant association between dosage of the G allele of rs610604 and good combined response to all TNF blockers (OR = 1.50, pcorr = 0.050) and etanercept (OR = 1.64, pcorr = 0.016). The rs2230926 T–rs610604 G haplotype was similarly associated. By demonstrating an association with therapeutic response, these results provide a clinically relevant functional correlate to the recently described genetic association between psoriasis and TNFAIP3.

A multicenter meta-analysis including data from 9389 psoriasis patients and 9477 control subjects was performed to investigate the contribution of the deletion of genes LCE3C and LCE3B, involved in skin barrier defense, to psoriasis susceptibility in different populations. The study confirms that the deletion of LCE3C and LCE3B is a common genetic factor for susceptibility to psoriasis in European populations [OROverall = 1.21 (1.15–1.27)], and for the first time directly demonstrated the deletion's association with psoriasis in [Chinese OR = 1.27 (1.16–1.34); Mongolian OR = 2.08 (1.44–2.99)] populations. The analysis of the HLA-Cw6 locus showed significant differences in the epistatic interaction with the LCE3C and LCE3B deletion in at least some European populations, indicating epistatic effects between these two major genetic contributors to psoriasis. The study highlights the value of examining genetic risk factors in multiple populations to identify genetic interactions, and indicates the need of further studies to understand the interaction of the skin barrier and the immune system in susceptibility to psoriasis.

The clinical features of psoriasis, characterized by sharply demarcated scaly erythematous plaques, are typically so distinctive that a diagnosis can easily be made on these grounds alone. However, there is great variability in treatment response between individual patients, and this may reflect heterogeneity of inflammatory networks driving the disease. In this study, whole-genome transcriptional profiling was used to characterize inflammatory and cytokine networks in 62 lesional skin samples obtained from patients with stable chronic plaque psoriasis. We were able to stratify lesions according to their inflammatory gene expression signatures, identifying those associated with strong (37% of patients), moderate (39%) and weak inflammatory infiltrates (24%). Additionally, we identified differences in cytokine signatures with heightened cytokine-response patterns in one sub-group of lesions (IL-13-strong; 50%) and attenuation of these patterns in a second sub-group (IL-13-weak; 50%). These sub-groups correlated with the composition of the inflammatory infiltrate, but were only weakly associated with increased risk allele frequency at some psoriasis susceptibility loci (e.g., REL, TRAF3IP2 and NOS2). Our findings highlight variable points in the inflammatory and cytokine networks known to drive chronic plaque psoriasis. Such heterogeneous aspects may shape clinical course and treatment responses, and can provide avenues for development of personalized treatments.

Earlier studies have shown that psoriasis in Japan and Thailand is associated with two different MHC haplotypes—those bearing HLA-Cw6 and those bearing HLA-Cw1 and HLA-B46. In an independent case-control sample from Thailand, we confirmed association of psoriasis with both haplotypes. No association was seen in Thai HLA-Cw1 haplotypes lacking HLA-B46, nor was HLA-Cw1 associated with psoriasis in a large Caucasian sample. To assess whether these risk haplotypes share a common origin, we sequenced genomic DNA from a Thai HLA-Cw1-B46 homozygote across the ~300 kb MHC risk interval, and compared it to sequence of a HLA-Cw6-B57 risk haplotype. Three small regions of homology were found, but these regions share equivalent sequence similarity with one or more clearly non-risk haplotypes, and they contain no polymorphism alleles unique to all risk haplotypes. Differences in psoriasis phenotype were also observed, including lower risk of disease, greater nail involvement, and later age at onset in HLA-Cw1-B46 carriers compared to HLA-Cw6 carriers. These findings suggest locus heterogeneity at PSORS1, the major psoriasis susceptibility locus in the MHC, with HLA-Cw6 imparting risk in both Caucasians and Asians, and an allele other than HLA-Cw1 on the HLA-Cw1-B46 haplotype acting as an additional risk variant in East Asians.

Psoriasis is a multifactorial skin disease characterized by epidermal hyperproliferation and chronic inflammation, the most common form of which is psoriasis vulgaris (PsV). We present a genome-wide association analysis of 2,339,118 SNPs in 472 psoriasis patients and 1,146 controls from Germany, with follow-up of the 147 most significant SNPs in 2,746 PsV cases and 4,140 controls from three independent replication panels. We identified an association at TRAF3IP2 on 6q21 and genotyped two SNPs at this locus in two additional replication panels (the combined discovery and replication panels consisted of 6,487 cases and 8,037 controls; combinded P = 2.36×10−10 for rs13210247 and combined P = 1.24×10−16 for rs33980500). About 15% of psoriasis cases develope psoriatic arthritis (PsA). A stratified analysis of our datasets including only PsA cases (1,922 cases compared to 8,037 controls, P=4.57×10−12 for rs33980500) suggested that TRAF3IP2 represents a shared susceptibility for PsV and PsA. TRAF3IP2 encodes a protein involved in IL-17 signaling and which interacts with memebers of the Rel/NF-κB transcription factor family.

Psoriasis is a common inflammatory skin disease with a prevalence of 2% to 3% in Caucasians1. In a genome-wide search for copy number variants (CNV) using a sample pooling approach we have identified a deletion comprising LCE3B and LCE3C, members of the late cornified envelope (LCE) gene cluster2. The absence of LCE3B and LCE3C (LCE3C-LCE3B-del) is significantly associated (p=1.38E-08) with risk of psoriasis in 2,831 samples from Spain, The Netherlands, Italy and the USA, and in a family-based study (p=5.4E-04). LCE3C-LCE3B-del is tagged by rs4112788 (r2=0.93), which is also strongly associated with psoriasis (p<6.6E-09). LCE3C-LCE3B-del shows epistatic effects with the HLA-Cw6 allele on the development of psoriasis in Dutch samples, and multiplicative effects in the other samples. LCE expression can be induced in normal epidermis by skin barrier disruption and is strongly expressed in psoriatic lesions, suggesting that compromised skin barrier function plays a role in psoriasis susceptibility.

To identify novel psoriasis susceptibility loci, we carried out a meta-analysis of two recent genome-wide association studies 1,2, yielding a discovery sample of 1,831 cases and 2,546 controls. 102 of the most promising loci in the discovery analysis were followed up in a three-stage replication study using 4,064 cases and 4,685 controls from Michigan, Toronto, Newfoundland, and Germany. Association at a genome-wide level of significance for the combined discovery and replication samples was found for three genomic regions. One contains NOS2 (rs4795067, p = 4 × 10−11), another contains FBXL19 (rs10782001, p = 9 × 10−10), and a third contains PSMA6 and NFKBIA (rs12586317, p = 2 × 10−8). All three loci were also strongly associated with the subphenotypes of psoriatic arthritis and purely cutaneous psoriasis. Finally, we confirmed a recently identified3 association signal near RNF114.

A recent genome-wide association analysis of psoriasis identified IL12B and IL23R as significantly associated with psoriasis. Here we report association test results of a Thai cohort consisting of 206 psoriasis cases and 114 controls. The IL23R SNPs rs7530511 and rs11209026, and IL12B SNPs rs3212227 and rs6887695 were genotyped using Taqman assays. Data were analyzed using a logistic regression model for linear trend of association. One of the IL23R markers, rs7530511, was marginally significant (p=0.017). The other IL23R marker, rs11209026, was not polymorphic. One of the IL12B markers, rs3212227, showed significant association with psoriasis (OR = 1.64, p = 0.0058) while the other, rs6887695, did not (OR = 1.29, p = 0.12). Haplotype analysis of the two IL12B SNPs yielded highly significant association (p=0.00081, OR=1.73). These results show that IL12B is an important genetic factor in psoriasis pathogenesis in the Thai population, with an association strong enough to yield significant confirmatory evidence using a modest sample size. Together with previously reported evidence for IL12B association in Caucasian, Japanese and Chinese psoriatics, our results support the hypothesis that genes encoding components of the IL23-mediated inflammatory pathway are important determinants of psoriasis pathogenesis across multiple racial groups.

Psoriasis is a common immune mediated disorder that affects the skin, nails, and joints. To identify psoriasis susceptibility loci, we genotyped 438,670 SNPs in 1,409 European ancestry psoriasis cases and 1,436 controls. Twenty-one promising SNPs were followed-up in 5,048 psoriasis cases and 5,041 controls. Our results provide strong support for the association of at least seven genetic loci and psoriasis (each with p < 5×10−8 overall). Loci with confirmed association encode HLA-C, three genes involved in IL-23 signaling (IL23A, IL23R, IL12B), two genes that act downstream of TNF-α and regulate NF-κB signaling (TNIP1, TNFAIP3), and two genes involved in the modulation of Th2 immune responses (IL4, IL13). Although the proteins encoded in these loci are known to interact biologically, we found no evidence for epistasis between associated SNPs. Our results expand the catalog of genetic loci implicated in psoriasis susceptibility and suggest priority targets for study in other auto-immune disorders.

Psoriasis is a common inflammatory and hyperproliferative skin disease with a multifactorial genetic basis. A recent study reported that psoriasis was associated with the IL12B haplotype rs3212227 (3' UTR) - rs6887695 (60 kb 5’) and the IL23R haplotype rs7530511 (L310P) -rs11209026 (Q381R). We examined these four SNPs for association with psoriasis in two groups of North American and German Caucasians: (1) 1,810 cases and 2,522 controls and (2) 509 pedigrees. Both IL12B markers showed highly significant association with psoriasis in the case-control (rs3212227, OR = 1.62, p = 1.7 × 10−15; rs6887695, OR = 1.49, p = 2.7 × 10−15) and in the family-based analysis (rs3212227, p = 2.2 × 10−3; rs6887695, p = 1.7 × 10−3). The IL23R SNPs also showed significant association in the cases and controls (rs7530511, OR = 1.22, p = 3.9 × 10−3; rs11209026, OR = 1.40, p = 3.8 × 10−4). For both genes, common risk haplotypes were identified whose statistical significance approached (IL23R) or exceeded (IL12B) genome-wide criteria. We found no statistical evidence for interactions of these haplotypes with HLA-Cw6. Our results confirm associations between IL12B and IL23R and psoriasis in Caucasians, and provide a genetic basis for the clinical association between psoriasis and Crohn disease.

Systemic lupus erythematosus (SLE) is a chronic autoimmune disease characterized by the production of autoantibodies to a wide range of self-antigens. Recent genome screens have implicated numerous chromosomal regions as potential SLE susceptibility loci. Among these, the 1q41 locus is of particular interest, because evidence for linkage has been found in several independent SLE family collections. Additionally, the 1q41 locus appears to be syntenic with a susceptibility interval identified in the NZM2410 mouse model for SLE. Here, we report the results of genotyping of 11 microsatellite markers within the 1q41 region in 210 SLE sibpair and 122 SLE trio families. These data confirm the modest evidence for linkage at 1q41 in our family collection (LOD = 1.21 at marker D1S2616). Evidence for significant linkage disequilibrium in this interval was also found. Multiple markers in the region exhibit transmission disequilibrium, with the peak single marker multiallelic linkage disequilibrium noted at D1S490 (pedigree disequilibrium test [PDT] global P value = 0.0091). Two- and three-marker haplotypes from the 1q41 region similarly showed strong transmission distortion in the collection of 332 SLE families. The finding of linkage together with significant transmission disequilibrium provides strong evidence for a susceptibility locus at 1q41 in human SLE.

We extended our previous GWAS for psoriasis with a a multistage replication study including 8,312 cases and 12,919 controls from China as well as 3,293 cases, 4,188 controls from Germany and the USA, and 254 nuclear families from the USA. We identified 6 new susceptibility loci associated to psoriasis in Chinese, containing candidate genes ERAP1, PTTG1, CSMD1, GJB2, SERPINB8, ZNF816A (PCombined<5×10−8) and replicated one locus 5q33.1 (TNIP1/ANXA6) previously reported (PCombined=3.8×10−21) in European studies. Two of these loci showed evidence for association evidence in the German study, at ZNF816A and GJB2 with P=3.6×10−3 and P=7.9×10−3, respectively. ERAP1 and ZNF816A were preferentially associated with Type I (early onset) psoriasis in Chinese Han population (test for heterogeneity P=6.5×10−3 and P=1.5×10−3, respectively). Comparisons with previous GWAS of psoriasis highlight the heterogeneity of disease susceptibility between Chinese and European populations. Our study identifies new genetic susceptibility factors and suggests new biological pathways in psoriasis.