A genome-wide search for genes predisposing to familial psoriasis by using a stratification approach

Proteomic Studies of Psoriasis

In this review paper, we discuss the contribution of proteomic studies to the discovery of disease-specific biomarkers to monitor the disease and evaluate available treatment options for psoriasis. Psoriasis is one of the most prevalent skin disorders driven by a Th17-specific immune response. Although potential patients have a genetic predisposition to psoriasis, the etiology of the disease remains unknown. During the last two decades, proteomics became deeply integrated with psoriatic research. The data obtained in proteomic studies facilitated the discovery of novel mechanisms and the verification of many experimental hypotheses of the disease pathogenesis. The detailed data analysis revealed multiple differentially expressed proteins and significant changes in proteome associated with the disease and drug efficacy. In this respect, there is a need for proteomic studies to characterize the role of the disease-specific biomarkers in the pathogenesis of psoriasis, develop clinical applications to choose the most efficient treatment options and monitor the therapeutic response.

The Model of PPARγ-Downregulated Signaling in Psoriasis

Interactions of genes in intersecting signaling pathways, as well as environmental influences, are required for the development of psoriasis. Peroxisome proliferator-activated receptor gamma (PPARγ) is a nuclear receptor and transcription factor which inhibits the expression of many proinflammatory genes. We tested the hypothesis that low levels of PPARγ expression promote the development of psoriatic lesions. We combined experimental results and network functional analysis to reconstruct the model of PPARγ-downregulated signaling in psoriasis. We hypothesize that the expression of IL17, STAT3, FOXP3, and RORC and FOSL1 genes in psoriatic skin is correlated with the level of PPARγ expression, and they belong to the same signaling pathway that regulates the development of psoriasis lesion.

A Case of Familial Psoriasis with Predominant Hand Involvement

Psoriasis has been recognized as a familial disease with a polygenic inheritance. A case is reported of a father and four of his seven children with plaque psoriasis localized to the hands. The other three children are not afflicted by psoriasis. All patients developed psoriasis at 5 years of age. Only one member of this family has involvement in an area other than the hands. This case illustrates some of the complexities of the genetics of psoriasis.

HLA-C*12:02 is a susceptibility factor in late-onset type of psoriasis in Japanese

Psoriasis is thought to be a multifactorial disease triggered by both genetic and environmental factors. The HLA-C locus on chromosome 6p21.33 remains the strongest susceptibility candidate locus in psoriasis. The strong association between psoriasis and the HLA-Cw6 allele has been well documented in various races. It is known that psoriatic patients with early onset are more likely to be familial and associated with HLA-Cw6. Familial occurrence of Japanese psoriasis is smaller than other populations. Furthermore, males are predominant over females in Japanese psoriasis. We investigated the relation between HLA-C alleles and age of onset, and in each gender for Japanese psoriasis, and discuss male predominance in the incidence of psoriasis in Japan. Four hundred forty six unrelated Japanese patients with psoriasis vulgaris and 557 sex- and age-matched unrelated Japanese healthy controls were investigated by genotyping. We confirmed the association between early-onset type of psoriasis with HLA-C*06:02 allele in Japanese. In addition, we detected the association between the late-onset type of psoriasis and the HLA-C*12:02 allele in Japanese. No significant differences in allele frequency were observed between females and males. Our results suggest that there is no genetic factor effect on male predominance in Japanese. In contract, the effect of environmental risk factors on the onset of Japanese psoriatic patients is stronger in males than in females. As a result, male predominant in psoriasis may occur in Japan.

Genetic Epidemiology of Psoriasis

Psoriasis is a chronic, inflammatory, immune-mediated skin condition with a prevalence of 0-11.8% across the world. It is associated with a number of cardiovascular, metabolic, and autoimmune disease co-morbidities. Psoriasis is a multifactorial disorder, influenced by both genetic and environmental factors. Its genetic basis has long been established through twin studies and familial clustering. The association of psoriasis with the HLA-Cw6 allele has been shown in many studies. Recent genome-wide association studies have identified a large number of other genes associated with psoriasis. Many of these genes regulate the innate and adaptive immune system. These findings indicate that a dysregulated immune system may play a major role in the pathogenesis of psoriasis. In this article, we review the clinical and genetic epidemiology of psoriasis with a brief description of the pathogenesis of disease.

Global transcriptional analysis of psoriatic skin and blood confirms known disease-associated pathways and highlights novel genomic "hot spots" for differentially expressed genes

There are major gaps in our knowledge regarding the exact mechanisms and genetic basis of psoriasis. To investigate the pathogenesis of psoriasis, gene expression in 10 skin (5 lesional, 5 nonlesional) and 11 blood (6 psoriatic, 5 nonpsoriatic) samples were examined using Affymetrix HG-U95A microarrays. We detected 535 (425 upregulated, 110 downregulated) DEGs in lesional skin at 1% false discovery rate (FDR). Combining nine microarray studies comparing lesional and nonlesional psoriatic skin, 34.5% of dysregulated genes were overlapped in multiple studies. We further identified 20 skin and 2 blood associated transcriptional "hot spots" at specified genomic locations. At 5% FDR, 11.8% skin and 10.4% blood DEGs in our study mapped to one of the 12 PSORS loci. DEGs that overlap with PSORS loci may offer prioritized targets for downstream genetic fine mapping studies. Novel DEG "hot spots" may provide new targets for defining susceptibility loci in future studies.

Fine mapping of a linkage peak with integration of lipid traits identifies novel coronary artery disease genes on chromosome 5

Background

Coronary artery disease (CAD), and one of its intermediate risk factors, dyslipidemia, possess a demonstrable genetic component, although the genetic architecture is incompletely defined. We previously reported a linkage peak on chromosome 5q31-33 for early-onset CAD where the strength of evidence for linkage was increased in families with higher mean low density lipoprotein-cholesterol (LDL-C). Therefore, we sought to fine-map the peak using association mapping of LDL-C as an intermediate disease-related trait to further define the etiology of this linkage peak. The study populations consisted of 1908 individuals from the CATHGEN biorepository of patients undergoing cardiac catheterization; 254 families (N = 827 individuals) from the GENECARD familial study of early-onset CAD; and 162 aorta samples harvested from deceased donors. Linkage disequilibrium-tagged SNPs were selected with an average of one SNP per 20 kb for 126.6-160.2 MB (region of highest linkage) and less dense spacing (one SNP per 50 kb) for the flanking regions (117.7-126.6 and 160.2-167.5 MB) and genotyped on all samples using a custom Illumina array. Association analysis of each SNP with LDL-C was performed using multivariable linear regression (CATHGEN) and the quantitative trait transmission disequilibrium test (QTDT; GENECARD). SNPs associated with the intermediate quantitative trait, LDL-C, were then assessed for association with CAD (i.e., a qualitative phenotype) using linkage and association in the presence of linkage (APL; GENECARD) and logistic regression (CATHGEN and aortas).

Results

We identified four genes with SNPs that showed the strongest and most consistent associations with LDL-C and CAD: EBF1, PPP2R2B, SPOCK1, and PRELID2. The most significant results for association of SNPs with LDL-C were: EBF1, rs6865969, p = 0.01; PPP2R2B, rs2125443, p = 0.005; SPOCK1, rs17600115, p = 0.003; and PRELID2, rs10074645, p = 0.0002). The most significant results for CAD were EBF1, rs6865969, p = 0.007; PPP2R2B, rs7736604, p = 0.0003; SPOCK1, rs17170899, p = 0.004; and PRELID2, rs7713855, p = 0.003.

Conclusion

Using an intermediate disease-related quantitative trait of LDL-C we have identified four novel CAD genes, EBF1, PRELID2, SPOCK1, and PPP2R2B. These four genes should be further examined in future functional studies as candidate susceptibility loci for cardiovascular disease mediated through LDL-cholesterol pathways.

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.

Current concepts in the pathogenesis of psoriasis

Psoriasis is a multi-factorial skin disease with a complex pathogenesis. Various factors which have been suggested to play a key role in the pathogenesis are T cells, antigen presenting cells (APC's), keratinocytes, Langerhans' cells, macrophages, natural killer cells, an array of Th1 type cytokines, certain growth factors like vascular endothelial growth factor (VEGF), keratinocyte growth factor (KGF), and others. It has been hypothesized that the disease starts with the activation of T cell by an unknown antigen, which leads to secretion of an array of cytokines by activated T cells, inflammatory cells, and keratinocytes. The characteristic lesion of psoriasis is due to the hyper-proliferation of the keratinocyte. Activated Langerhans' cells migrate from skin to lymph nodes presenting the antigen to nodal naïve T cells (cells that have not been activated by antigen previously). The T cells activated by non-antigen-dependent mechanism may, however, become antigen-specific memory cells that react with a cross-reactive auto-antigen such as keratin (molecular mimicry). The genetic background of the disease may be suggested from the fact that concordance rate is 63–73% in monozygotic twins, as compared to 17–20% in dizygotic twins. Several disease susceptibility loci have been suggested as predisposing factors, PSORS1-PSORS9.

Fine mapping of the CELIAC2 locus on chromosome 5q31-q33 in the Finnish and Hungarian populations

Celiac disease is a chronic inflammation of the small intestine, arising in genetically predisposed individuals as a result of ingestion of dietary gluten. The only confirmed and functionally characterised genetic risk factors for celiac disease are the DQ2 or DQ8 heterodimers at the major histocompatibility complex (MHC) class II locus (CELIAC1). These genes are necessary but alone not sufficient for disease onset. Genome-wide linkage scans have suggested chromosome 5q31-q33 (CELIAC2) as an important risk locus for celiac disease. This region has also been associated to other inflammatory disorders, although as yet, no clear gene associations have been found. In the current study, 11 celiac disease candidate loci were screened for genetic linkage in the Hungarian population. As the CELIAC2 locus showed the strongest evidence for linkage, this locus was selected for follow-up. Seventeen candidate genes were selected from the CELIAC2 locus, and genotyped using 48 haplotype tagging single nucleotide polymorphisms (SNPs) in large Finnish and Hungarian family materials. A subset of these, 40 tagging SNPs in 15 genes, were genotyped in an independent set of Finnish and Hungarian cases and controls. We confirmed linkage of this region with celiac disease and report strong linkage in both the Finnish and Hungarian populations. The association analysis showed modest associations throughout the whole region. These association findings were not replicated in the case-control datasets. Our study strongly supports the role of the CELIAC2 locus in celiac disease, but it also highlights the need for a more powerful study design in the region, to locate the true disease risk variants.

Molecular dissection of psoriasis: integrating genetics and biology

Psoriasis is a common and debilitating disease of the skin, nails, and joints, with an acknowledged but complex genetic basis. Early genome-wide linkage studies of psoriasis focused on segregation of microsatellite markers in families; however, the only locus consistently identified resided in the major histocompatibility complex. Subsequently, several groups mapped this locus to the vicinity of HLA-C, and two groups have reported HLA-Cw6 itself to be the major susceptibility allele. More recently, the development of millions of single-nucleotide polymorphisms, coupled with the development of high-throughput genotyping platforms and a comprehensive map of human haplotypes, has made possible a genome-wide association approach using cases and controls rather than families. Taking advantage of these developments, we participated in a collaborative genome-wide association study of psoriasis involving thousands of cases and controls. Initial analysis of these data revealed and/or confirmed association between psoriasis and seven genetic loci-HLA-C, IL12B, IL23R, IL23A, IL4/IL13, TNFAIP3, and TNIP1-and ongoing studies are revealing additional loci. Here, we review the epidemiology, immunopathology, and genetics of psoriasis, and present a disease model integrating its genetics and immunology.

Genetic susceptibility to psoriasis: an emerging picture

Psoriasis is recognized as a complex disease for which multiple genetic and non-genetic factors influence susceptibility. The major susceptibility locus resides in the MHC class I region and, until relatively recently, evidence for non-MHC loci was inconsistent. Like many common diseases, knowledge of the genetic basis of this condition has been advanced dramatically in recent times with the advent of genome-wide association studies using single nucleotide polymorphisms. Here, we give an overview of current knowledge of genetic risk factors for psoriasis and consider emerging studies that may further add to our understanding of the genetic basis of the disease.

Meta-analysis of genome-wide linkage studies across autoimmune diseases

Autoimmune diseases are chronic disorders initiated by a loss of immunologic tolerance to self-antigens. They cluster within families, and patients may be diagnosed with more than one disease, suggesting pleiotropic genes are involved in the aetiology of different diseases. To identify potential loci, which confer susceptibility to autoimmunity independent of disease phenotype, we pooled results from genome-wide linkage studies, using the genome scan meta-analysis method (GSMA). The meta-analysis included 42 independent studies for 11 autoimmune diseases, using 7350 families with 18 291 affected individuals. In addition to the HLA region, which showed highly significant genome-wide evidence for linkage, we obtained suggestive evidence for linkage on chromosome 16, with peak evidence at 10.0-19.8 Mb. This region may harbour a pleiotropic gene (or genes) conferring risk for several diseases, although no such gene has been identified through association studies. We did not identify evidence for linkage at several genes known to confer increased risk to different autoimmune diseases (PTPN22, CTLA4), even in subgroups of diseases consistently found to be associated with these genes. The relative risks conferred by variants in these genes are modest (<1.5 in most cases), and even a large study like this meta-analysis lacks power to detect linkage. This study illustrates the concept that linkage and association studies have power to identify very different types of disease-predisposing variants.

The 5q31 variants associated with psoriasis and Crohn's disease are distinct

Predisposition to psoriasis is known to be affected by genetic variation in HLA-C, IL12B and IL23R, but other genetic risk factors also exist. We recently reported three psoriasis-associated single nucleotide polymorphisms (SNPs) in the 5q31 locus, a region of high linkage disequilibrium laden with inflammatory pathway genes. The aim of this study was to assess whether other variants in the 5q31 region are causal to these SNPs or make independent contributions to psoriasis risk by genotyping a comprehensive set of tagging SNPs in a 725 kb region bounded by IL3 and IL4 and testing for disease association. Ninety SNPs, capturing 86.4% of the genetic diversity, were tested in one case–control sample set (467 cases/460 controls) and significant markers (P_allelic < 0.05) (n = 9) were then tested in two other sample sets (981 cases/925 controls). All nine SNPs were significant in a meta-analysis of the combined sample sets. Pair-wise conditional association tests showed rs1800925, an intergenic SNP located just upstream of IL13 (Mantel–Haenszel P_combined = 1.5 × 10⁻⁴, OR = 0.77 [0.67–0.88]), could account for observed significant association of all but one other SNP, rs11568506 in SLC22A4 [Mantel–Haenszel P_combined = 0.043, OR = 0.68 (0.47–0.99)]. Haplotype analysis of these two SNPs showed increased significance for the two common haplotypes (rs11568506–rs1800925: GC, P_combined = 5.67 × 10⁻⁶, OR = 1.37; GT, P_combined = 6.01 × 10⁻⁵, OR = 0.75; global haplotype P = 8.93 × 10⁻⁵). Several 5q31-region SNPs strongly associated with Crohn's disease (CD) in the recent WTCCC study were not significant in the psoriasis sample sets tested here. These results identify the most significant 5q31 risk variants for psoriasis and suggest that distinct 5q31 variants contribute to CD and psoriasis risk.

Genes and structure of selected cytokines involved in pathogenesis of psoriasis

Psoriasis is a common skin disease involving 1-4% of human population worldwide, of strong genetic background. The following cytokines are directly involved in psoriasis: TNF, IL-1, IL-2, IL-6, IL-7, IL-8, IL-15, IL-18, IL-19, IL-20, IL-23 whereas IL-4, IL-10, IL-12 as well as IL-11, IL-17 and IFN-gamma are rather indirectly engaged. This work is a review of some genetic factors and structure of selected cytokines and receptors and their genes location.

Polymorphisms in the PTPN22 region are associated with psoriasis of early onset

Background

Psoriasis, a chronic inflammatory skin disease, affects approximately 2% of the population worldwide. Although the aetiology of psoriasis is poorly understood, patients with disease of early onset (Type I, age of onset ≤ 40 years) usually have a strong genetic component to the disease.

Objectives

The purpose of this study was to investigate the role of the protein tyrosine phosphatase nonreceptor type 22 (PTPN22) gene region in susceptibility to Type I psoriasis.

Patients and methods

Thirteen single nucleotide polymorphisms (SNPs) mapping to the PTPN22 region were genotyped in 647 patients with Type I psoriasis and 566 normal controls.

Results

The rs2476601 (R620W) SNP, widely associated with other inflammatory autoimmune diseases, showed no evidence of association with susceptibility to Type I psoriasis. Two SNPs (rs1217414 and rs3789604) demonstrated significant association with Type I psoriasis and were subsequently genotyped in a further 253 unrelated patients and 2024 normal controls. rs1217414 and rs3789604 were also significantly associated with Type I psoriasis in the combined datasets (P = 0·003 and P = 0·0002, respectively); furthermore carriage of both risk alleles was also significantly associated (P = 0·002).

Conclusions

This study demonstrates evidence of association of two SNPs (rs1217414 and rs3789604) in the PTPN22 region with Type I psoriasis, providing evidence for a role of this gene in Type I psoriasis that is not conferred by the R620W variant previously associated with a number of inflammatory diseases.

Polymorphisms in Interleukin-15 Gene on Chromosome 4q31.2 Are Associated with Psoriasis Vulgaris in Chinese Population

Through a series of linkage analyses in a large Chinese family cohort of psoriasis, we previously identified and confirmed a non-HLA psoriasis linkage locus PSORS9 within a small region at 4q31.2-32.1. Within the critical region of the PSORS9 locus, IL-15 has been long recognized as a strong candidate gene for psoriasis. In this study, we investigated the association between IL-15 genetic polymorphisms and psoriasis in a large Chinese sample. Highly significant evidence for association was identified at a single-nucleotide polymorphism (SNP) (g.96516A --> T) within the 3'-untranslated region (UTR) of the IL-15 gene (P=0.00006, after correction for multiple testing). Haplotype analysis using the SNPs within the 3'UTR region also provided strong supporting evidence for association (P=0.00005), where we identified a haplotype of the 3'UTR region of IL-15 associated with increased risk to psoriasis (odds ratio=1.65). This association was also supported by the results of our expression activity analyses, where we demonstrated that the identified risk haplotype is associated with an increased activity of IL-15. Therefore, we provided early evidence for the important role of IL-15 genetic variants in the pathogenesis of psoriasis, probably by increasing interleukin production and inflammation in the lesions of psoriasis.

ADAM33, a new candidate for psoriasis susceptibility

Psoriasis is a chronic skin disorder with multifactorial etiology. In a recent study, we reported results of a genome-wide scan on 46 French extended families presenting with plaque psoriasis. In addition to unambiguous linkage to the major susceptibility locus PSORS1 on Chromosome 6p21, we provided evidence for a susceptibility locus on Chromosome 20p13. To follow up this novel psoriasis susceptibility locus we used a family-based association test (FBAT) for an association scan over the 17 Mb candidate region. A total of 85 uncorrelated SNP markers located in 65 genes of the region were initially investigated in the same set of large families used for the genome wide search, which consisted of 295 nuclear families. When positive association was obtained for a SNP, candidate genes nearby were explored more in detail using a denser set of SNPs. Thus, the gene ADAM33 was found to be significantly associated with psoriasis in this family set (The best association was on a 3-SNP haplotype P = 0.00004, based on 1,000,000 permutations). This association was independent of PSORS1. ADAM33 has been previously associated with asthma, which demonstrates that immune system diseases may be controlled by common susceptibility genes with general effects on dermal inflammation and immunity. The identification of ADAM33 as a psoriasis susceptibility gene identified by positional cloning in an outbred population should provide insights into the pathogenesis and natural history of this common disease.

Investigating the role of the HLA-Cw*06 and HLA-DRB1 genes in susceptibility to psoriatic arthritis: comparison with psoriasis and undifferentiated inflammatory arthritis

Objective:

Psoriasis of early onset (type I; age of onset ⩽40 years) is associated with HLA-Cw*06 while the shared epitope (SE) is associated with rheumatoid arthritis susceptibility. Our aim was to investigate the role of HLA-Cw*06 and HLA-DRB1 genes (including SE) with psoriatic arthritis (PsA) susceptibility.

Methods:

In a case–control association study, HLA-Cw*06 phenotype frequencies were compared between patients with PsA (n = 480), psoriasis alone (n = 611) and healthy controls (n = 166). Similarly, at the HLA-DRB1 locus, phenotype and SE frequencies were compared in patients with PsA (n = 480), early undifferentiated inflammatory arthritis alone (n = 1621) and healthy controls (n = 537).

Results:

The HLA-Cw*06 phenotype was associated with type I psoriasis (OR 6.9, 95% CI 4.4, 11.1, p = 2.2×10⁻²¹) and with patients with PsA having type I psoriasis (OR 5.0, 95% CI 3.2, 7.9, p = 4.39×10⁻¹³), but not with patients with PsA having type II psoriasis (age of onset >40 years). HLA-DRB1*07, in linkage disequilibrium with HLA-Cw*06, was also associated with patients with PsA having type I psoriasis (OR 2.7, 95% CI 2.1, 3.7, p<0.00001). HLA-DRB1*04 alleles and the SE were associated with undifferentiated inflammatory arthritis but not with PsA.

Conclusions:

The SE is not a PsA susceptibility locus. HLA-Cw*06 and HLA-DRB1*07 are associated with patients with PsA having type I psoriasis, suggesting that the primary association is with age of onset of psoriasis. Patients with PsA having type I psoriasis, therefore, have a genetic background different to those with type II psoriasis, and adjustment for this is necessary in future studies that investigate the genetic susceptibility of PsA.

Contribution of genetic studies in rodent models of autoimmune arthritis to understanding and treatment of rheumatoid arthritis

Rheumatoid arthritis (RA) is a chronic and potentially debilitating autoimmune disease. While novel therapies have emerged in recent years, disease remission is rarely achieved. RA is a complex trait, and the identifying of its susceptibility and severity genes has been anticipated to generate new targets for therapeutic intervention. However, finding those genes and understanding their function has been a challenging task. Studies in rodent intercrosses and congenics generated from inbred strains have been an important complementary strategy to identify arthritis genes, and understand how they operate to regulate disease. Furthermore, these new rodent arthritis genes will be new targets for therapeutic interventions, and will identify new candidate genes or candidate pathways for association studies in RA. In this review-opinion article I discuss RA genetics, difficulties involved in gene identification, and how rodent models can facilitate (1) the discovery of both arthritis susceptibility and severity genes, (2) studies of gene-environment interactions, (3) studies of gene-gender interactions, (4) epistasis, (5) functional characterization of the specific genes, (6) development of novel therapies and (7) how the information generated from rodent studies will be useful to understanding and potentially treating RA.

Evidence for a Novel Psoriasis Susceptibility Locus at 9q33–9q34 in Chinese Hans

Psoriasis is a heterogeneous disease for which nine linkage loci (PSORS loci 1-5 and PSORS7-10) have been accepted by the Human Genome Nomenclature Committee and an additional 16 potential susceptibility loci have been reported so far. Our previous genome-wide scan in 61 Chinese Han psoriasis vulgaris families found two susceptibility loci at 6p21.3 and 4q31 and additional suggestive linkage evidence at other regions, including 9q33. In this follow-up study, the linkage evidence at 9q33 was further investigated using an expanded sample of 160 families and improved marker coverage. Our follow-up linkage analysis of the 160 families demonstrated strong linkage evidence (P < or = 0.000022) throughout a region between 133.38 and 146.23 cM with a maximum nonparametric linkage (NPL) score of 4.64 (P = 0.00000023) and a heterogeneity LOD (HLOD) score of 5.03 (alpha = 46%) at 142.39 cM near the marker D9S290. By stratifying the 160 families into the subtypes of 130 early-onset and 30 late-onset families, we revealed stronger linkage evidence in the early-onset psoriasis families with a maximum multipoint HLOD score of 6.48 (alpha = 58%) and a maximum NPL score of 4.69 (P = 0.00000012) near marker D9S290. Our follow-up study has confirmed a novel susceptibility locus at 9q33-34 for early-onset psoriasis in the Chinese population.

Confirmation of psoriasis susceptibility loci on chromosome 6p21 and 20p13 in French families

Plaque psoriasis is a chronic inflammatory disorder of the skin. It is inherited as a multifactorial trait, with a strong genetic component. Linkage studies have identified a large number of disease loci, but very few could be replicated in independent family sets. In this study, we present the results of a genome-wide scan carried out in 14 French extended families. Candidate regions were then tested in a second set of 32 families. Analysis of the pooled samples confirmed linkage to chromosomes 6p21 (Z(MLB) score=3.5, P=0.0002) and 20p13 (Z(MLB) score=2.9, P=0.002), although there was little contribution of the second family set to the 20p13 linkage signal. Moreover, we identified four additional loci potentially linked to psoriasis. The major histocompatibility complex region on 6p21 is a major susceptibility locus, referred to as PSORS1, which has been found in most of the studies published to date. The 20p13 locus segregates independently of PSORS1 in psoriasis families. It has previously been thought to be involved in the predisposition to psoriasis and other inflammatory disorders such as atopic dermatitis (AD) and asthma. Although psoriasis and AD rarely occur together, this reinforces the hypothesis that psoriasis is influenced by genes with general effects on inflammation and immunity.

Follow-Up Analysis of PSORS9 in 151 Chinese Families Confirmed the Linkage to 4q31–32 and Refined the Evidence to the Families of Early-Onset Psoriasis

Psoriasis linkage to 4q28-32 (PSORS9) was initially identified by our genome-wide scan in 61 Chinese families and subsequently supported by a meta-analysis of five genome-wide linkage scans of European populations. In this study, we performed a follow-up analysis of PSORS9 using an additional 90 families and improved marker coverage. Joint analysis of all 151 families obtained significant linkage evidence (HLOD=4.53, nonparametric linkage (NPL)=4.03 (P=0.000003)) at the marker interval D4S2997-D4S3033, and the same was obtained for the analysis of the independent new families (HLOD=4.33, NPL=3.15 (P=0.00004)). The linkage evidences from the whole families and the new families exceeded the genome-wide criteria for significant linkage. Furthermore, by performing an ordered subset analysis using mean age at onset as a covariate, we demonstrated that evidence for linkage to PSORS9 is concentrated in the early-onset families and suggested that further study of PSORS9 should focus on early-onset patients. This finding is contradictory to what was found in the Icelandic population and, together with other linkage results, suggests that Chinese and European populations are genetically different for linkage to PSORS9, which may partially explain the influence of ethnic factors on the varying prevalence of psoriasis.

Psoriatic arthritis as a distinct disease entity

Psoriatic arthritis (PsA) is a chronic systemic inflammatory disease characterized by joint inflammation associated with cutaneous psoriasis. For many years, the amount of attention directed to PsA had been less than that for various other arthropathies. With the advances in understanding its pathogensis, it is now recognized as a distinct disease entity with characteristic features. Psoriatic arthritis has a greater tendency towards asymmetric oligoarticular involvement, distal interphalangeal involvement and spondylitis. Associated features such as enthesitis and dactylitis are more common. Specific radiological features include ankylosis and bone resorption. With the availability of potent new therapeutic agents for psoriasis and PsA, interest in research and clinical care for these conditions has been reinvigorated. Anti-TNF therapy has achieved encouraging efficacy in both the joints and skin disease, improving function and quality of life and inhibiting radiological progression measured in patients with PsA and psoriasis. Biologic agents may have the potential in addressing the unmet medical need in patients with PsA.

The CX3CL1-CX3CR1 system and psoriasis

CX3CL1 is a chemoattractant and adhesion molecule that induces the redistribution of CX3CR1-positive inflammatory leucocytes to sites of inflammation. As a consequence of their increased expression in plaques of psoriasis, and location within genomic regions previously linked to this disease, CX3CL1, and its receptor CX3CR1, represent attractive positional and functional 'psoriasis susceptibility genes'. To investigate the CX3CL1-CX3CR1 system in psoriasis, eight single nucleotide polymorphisms (SNPs) in CX3CL1 and two SNPs in CX3CR1 were genotyped in 281 psoriasis patients and 184 unrelated controls. Allele, genotype and estimated haplotype frequencies were then compared between experimental groups. Allele frequency differences between healthy volunteers and psoriasis patients revealed associations with two CX3CR1 SNPs (hCV11578468, P = 0.03 and c_5687_1, P = 0.04). No associations were observed between CX3CL1 SNPs and psoriasis. These results support a role for the CX3CL1-CX3CR1 system in the pathogenesis of psoriasis and identify SNPs within the chemokine receptors that are associated with the disease.

Observations of Psoriasis in the Absence of Therapeutic Intervention Identifies Two Unappreciated Morphologic Variants, Thin-Plaque and Thick-Plaque Psoriasis, and their Associated Phenotypes

Psoriatic plaque thickness is a clinical measure of psoriasis severity. We have observed that patients tend to revert to a baseline thickness of psoriatic plaques when in an untreated state, and hypothesized that other features of psoriasis could associate with this trait. Data prospectively collected on 500 participants in the Utah Psoriasis Initiative were used for the study. In response to a question assessing plaque thickness when disease was at its worst, 144 (28.8%) reported thick plaques, 123 (24.6%) reported thin plaques, and 233 (46.6%) reported intermediate thickness. For patients with "worst-ever" disease at enrollment (n=122), there was significant correlation of thickness between assessment by the patient and the physician (r=0.448, P-value 0.01). Thick plaques associated with male gender, increased body mass index, nail disease, psoriatic arthritis, larger plaques, more body sites, and greater total body surface area affected. Thin plaques associated with eczema, guttate psoriasis, and skin cancer. We suggest that this is preliminary evidence that plaque thickness is an easily measured trait that associates with other clinical features of psoriasis, and that stratification on this phenotype may be useful in further defining the genetic basis of this disease.

Familial aggregation and linkage analysis of autoantibody traits in pedigrees multiplex for systemic lupus erythematosus

Autoantibodies are clinically relevant biomarkers for numerous autoimmune disorders. The genetic basis of autoantibody production in systemic lupus erythematosus (SLE) and other autoimmune diseases is poorly understood. In this study, we characterized autoantibody profiles in 1,506 individuals from 229 multiplex SLE pedigrees. There was strong familial aggregation of antinuclear antibodies (ANAs), anti-double-stranded DNA (dsDNA), anti-La/SSB, anti-Ro/SSA, anti-Sm, anti-nRNP (nuclear ribonucleoprotein), IgM antiphospholipid (aPL) antibodies (Abs) and rheumatoid factor (RF) across these families enriched for lupus. We performed genome-wide linkage analyses in an effort to map genes that contribute to the production of the following autoantibodies: Ro/SSA, La/SSB, nRNP, Sm, dsDNA, RF, nuclear and phospholipids. Using an approach to minimize false positives and adjust for multiple comparisons, evidence for linkage was found to anti-La/SSB Abs on chromosome 3q21 (adjusted P=1.9 x 10(-6)), to anti-nRNP and/or anti-Sm Abs on chromosome 3q27 (adjusted P=3.5 x 10(-6)), to anti-Ro/SSA and/or anti-La/SSB Abs on chromosome 4q34-q35 (adjusted P=3.4 x 10(-4)) and to anti-IgM aPL Abs on chromosome 13q14 (adjusted P=2.3 x 10(-4)). These results support the hypothesis that autoantibody production is a genetically complex trait. Identification of the causative alleles will advance our understanding of critical molecular mechanisms that underlie SLE and perhaps other autoimmune diseases.

Systematic evaluation of association between the microsomal glutathione S-transferase 2 common variation and psoriasis vulgaris in Chinese population

Several recent studies have demonstrated the possible involvement of the microsomal glutathione S-transferase 2 (MGST2) gene in the pathogenesis of psoriasis. The objectives of this work are to determine whether the genetic polymorphisms of the MGST2 gene were associated with an increased risk of psoriasis in Chinese patients. We first characterized the linkage disequilibrium pattern within MGST2 and identified single-nucleotide polymorphisms (SNPs) for tagging common genetic variants. Genotype- and haplotype-based analyses were then performed by genotyping the Tag SNPs in a large-scale sample of cases and controls. We characterized the linkage disequilibrium pattern within MGST2 using 12 densely distributed SNPs and identified 6 SNPs for tagging common genetic variants. We then performed an association analysis by genotyping the six SNPs in 552 cases and 384 controls, but none of the genotype- and haplotype-based analyses revealed significant evidence for association. We also performed family-based association analysis by genotyping the six SNPs in 95 trios; no evidence for association was identified. Our comprehensive genetic analysis of MGST2 common variants in a large Chinese sample of psoriasis did not provide any supporting evidence for MGST2 to be the susceptibility gene within the PSORS9 locus.

Analysis of Chromosome 5q31–32 and Psoriasis: Confirmation of a Susceptibility Locus but no Association with SNPs within SLC22A4 and SLC22A5

We have previously reported a region on chromosome 5q as a possible susceptibility region for psoriasis. This cytokine cluster-rich region has also been suggested as a susceptibility locus in other autoimmune or inflammatory diseases including Crohn's disease (CD) and rheumatoid arthritis (RA). Three specific single-nucleotide polymorphisms (SNPs) have been reported to associate with RA and CD and to change the functional activity of two organic cation transporters, solute carrier family 22 member 4/5 (SLC22A4) and (SLC22A5). In this study, we have analyzed these SNPs for an association with psoriasis. We have also performed a denser linkage analysis of this region with an additional 31 microsatellite markers. We were not able to detect any association with any of the three SNPs analyzed. However, our linkage result supports the involvement of this region in the etiology of psoriasis. We obtained a peak non-parametric linkage value of 3.1 for marker D5S436 in a subgroup of patients with joint complaints. This result supports the findings in another study of psoriasis patients originating from Iceland in which the authors obtained a peak logarithm of the odds score of 2.6 for marker D5S2090, only 2 Mb from D5S436. This suggests a psoriasis susceptibility locus on chromosome 5q32 that is involved in the arthritic phenotype of the disease.

Single-point haplotype scores telomeric to human leukocyte antigen-C give a high susceptibility major histocompatibility complex haplotype for psoriasis in a Caucasian population

Psoriasis is a chronic inflammatory skin disease that affects 0.1%-5% depending on the population. PSORS1 is the major susceptibility locus, accounting for approximately 33%-50% of the genetic component of psoriasis among Caucasians. PSORS1 is located within the major histocompatibility complex (MHC) locus on 6p21.3. Its position has been refined to hundreds of kilobase and the region located at approximately 100-200 kb telomeric to human leukocyte antigen (HLA)-C is a very strong candidate. To determine the MHC psoriasis risk haplotype, we screened the whole 46 kb interval for single-nucleotide polymorphisms (SNP) and identified 138 SNP. We genotyped 29 SNP throughout this region in psoriatic nuclear families. We calculated the frequency of haplotypes generated by the 29 SNP using all genotyped founder individuals and found four common haplotype with frequency >0.10. We then used SNPtagger to derive the best six SNP and fed these into Transmit using 148 nuclear families. We found that CTGGAC haplotype is a single-point score haplotypes telomeric to HLA-C and gives a 1 df, chi2 of 50.27 (p<0.0001). Most importantly the six selected SNP accurately tagged the most common haplotype found in this region. Moreover, using the same program (Transmit) we show that the association with CTGGAC is higher than the one with HLA-Cw6 (chi2=10.53; p=0.0051). Our results give scores as high as the highest single-point scores suggesting that it is unlikely to be able to discriminate the origin of the association on this analysis on strength of association.

Psoriasis pathophysiology: current concepts of pathogenesis

Psoriasis vulgaris is a common skin disorder characterised by focal formation of inflamed, raised plaques that constantly shed scales derived from excessive growth of skin epithelial cells. The disease is defined by a series of linked cellular changes in the skin: hyperplasia of epidermal keratinocytes, vascular hyperplasia and ectasia, and infiltration of T lymphocytes, neutrophils, and other types of leucocyte in affected skin. In a relatively short period, psoriasis vulgaris has been conceptualised as a T lymphocyte mediated autoimmune disease and new biological therapies that target T cells have just entered routine clinical practice. Similarly, rapid progress has been made towards dissecting cellular and molecular pathways of inflammation that contribute to disease pathogenesis. This short review presents current pathogenic concepts that have emerged from genetic, genomic, and cellular information obtained in basic studies and from clinical studies of selective immune targeting drugs.

hRDH-E2 gene polymorphisms, variable transcriptional start sites, and psoriasis

hRDH-E2 is a member of the short-chain alcohol dehydrogenase/reductase (SDR) family that converts retinol to retinaldehyde as the first and rate-limiting step in the retinoic acid synthetic pathway. This pathway is critical for the maintenance of epidermal homeostasis in vivo. Previously, we reported that the mRNA levels of hRDH-E2 in psoriatic skin were elevated significantly compared with that in healthy individual skin and psoriatic unaffected skin. The gene encoding hRDH-E2 is located on Chromosome 8 close to a candidate region for psoriasis and therefore is a functional and positional candidate for this disorder. In the present study, the transcription start sites for hRDH-E2 gene transcription in the lung were found to be more upstream of those that were identified previously in keratinocytes. Consequently, differences in the nucleotide sequence were determined for all of the coding exons, untranslated regions, and at least 2850 bp of 5'-noncoding sequence of hRDH-E2 by direct sequencing of polymerase chain reaction (PCR)-amplified DNA samples obtained from 8 psoriatic patients and 8 healthy controls. One polymorphic microsatellite marker at the noncoding 3' end of the gene and six single nucleotide polymorphisms (SNPs) (three in the 5' flanking sequence, two in the coding sequence, and one in the intronic sequence) were identified. One of the SNPs was nonsynonymous in the second exon with an allelic variation between the amino acid sequences Arg and Trp. The microsatellite marker and the six SNPs were all genotyped in 100 Japanese psoriatic patients and 120 controls. However, there were no statistically significant differences in the genotype or allele frequency distributions between the cases and controls. On this basis, we conclude that the polymorphisms that we detected for the hRDH-E2 gene do not contribute to the etiology of psoriasis but may be important in diseases of other tissues.

A candidate region on 11p13 for systemic lupus erythematosus: a linkage identified in African-American families

Systemic Lupus Erythematosus (SLE), a chronic, complex disease, is the prototype for systemic human autoimmune diseases. Although environmental factors are crucial in triggering the condition, twin and family studies, as well as genetic linkage and association studies, have established its strong genetic predisposition. During the past few years, there has been considerable interest in identifying genomic segments linked to SLE through either a whole genome scan or a candidate gene approach. The discoid lupus erythematosus (DLE) skin lesion is one of the major, and discriminating, manifestations in SLE, especially in African American patients. In this study we have identified 58 multiplex families--27 African American, 26 European American, and 5 others--where at least one SLE patient is also reported to be afflicted with DLE. These families were chosen from the collection of families that are part of our ongoing linkage study for SLE. A genome-wide parametric and nonparametric linkage analysis was conducted with 320 markers. Significant evidence of linkage was identified in only one chromosomal location, 11p13, in the African American families. The maximum 2-point linkage was 5.6 in these pedigrees, obtained at a marker located 47 CM away from the pterminal end of chromosome 11. The peak multipoint LOD score of 4.6 was obtained very nearby. The segregation of this gene suggests dominant inheritance. These results reveal an important genetic effect related to discoid rash at 11p13 in African Americans with SLE, and demonstrate, through increasing genetic homogeneity, the power of pedigree stratification to detect linkage in complex diseases.

Identification and characterization of a novel component of the cornified envelope, cornifelin

Psoriasis is recognized as a chronic inflammatory disease characterized by epidermal hyperproliferation. To identify psoriasis-related genes, we compared the mRNA populations of normal and psoriatic skin. We identified one gene, designated as cornifelin, which showed increased expression in psoriatic skin. Human cornifelin contains 112 amino acids and is expressed in the uterus, cervix, and skin. In situ hybridization analysis demonstrated the presence of human cornifelin in the granular cell layer of the epidermis. To investigate the function of cornifelin, we established a transgenic mouse line overexpressing human cornifelin. Using these mice, we have shown that cornifelin is directly or indirectly cross-linked to at least two other cornified envelope proteins, loricrin and involucrin, in vivo. Overexpression of human cornifelin correlated with decreased loricrin expression and increased involucrin expression in the transgenic mouse. However, abnormality of epidermal differentiation was not observed in the transgenic mouse.

Association Analysis of Cystatin A and Zinc Finger Protein 148, Two Genes Located at the Psoriasis Susceptibility Locus PSORS5

Psoriasis is a multifactorial hereditary skin disease. The searches for causative DNA variations have generated several susceptibility loci, but at present, the gene(s) involved has not been identified. In this article, we investigated whether cystatin A, an upregulated gene in psoriatic plaques and located at chromosome 3q21, is the disease-causing gene at the psoriasis susceptibility locus PSORS5. We also investigated association to a second gene located in this region, zinc finger protein 148. The two genes have been sequenced in a small case/control set in search for SNP markers, followed by family-based association analysis using the transmission disequilibrium test. We did not detect association with either of the genes.

Meta-Analysis of Genome-Wide Studies of Psoriasis Susceptibility Reveals Linkage to Chromosomes 6p21 and 4q28–q31 in Caucasian and Chinese Hans Population

Ten genome-wide scans have been conducted over the past few years in the search for psoriasis susceptibility genes, but only one potential susceptibility region has been consistently replicated. A meta-analysis using the genome-search meta-analysis method was undertaken combining the results of six of these psoriasis genome-wide studies. The results of this analysis revealed linkage to the major histocompatibility complex on chromosome 6p21 that includes the PSORS1 locus. In addition, linkage was also recorded to a region on chromosome 4q28-q31 previously identified only in a Chinese Hans population. Both these regions were statistically significant even after correction for multiple testing. A possible reason for the erratic replication of findings could be the large effect of the PSORS1 locus (6p21) masking the effect of other loci involved in psoriasis. To overcome this problem, we suggest that future studies condition on the effect of the PSORS1 locus.

Psoriasis Susceptibility Locus on 18p Revealed by Genome Scan in Finnish Families Not Associated with PSORS1

The major susceptibility locus for psoriasis, PSORS1, resides on chromosome 6p and includes the candidate genes HLA-C, HCR, and CDSN. Based on a nationwide collection of psoriasis patients and genotyping for the PSORS1 susceptibility haplotype, we selected for a genome scan nine families who do not show association with PSORS1 to more easily detect minor loci for psoriasis susceptibility. In the genome scan, five loci gave initial evidence of linkage and were studied with a denser marker map. After fine mapping, only one locus on 18p11.23 showed suggestive evidence of linkage (nonparametric multipoint linkage analysis score, 3.58; p = 0.0038). The bootstrapping analysis showed that one large family contributed the majority of the linkage (p = 0.0039), but was supported by other families. Haplotype sharing between the linked families and haplotype association analysis gave additional support for the locus. Further, the 18p locus has shown nominal evidence of linkage with psoriasis in the British population. Taken together, these findings confirm the presence of a minor susceptibility locus for psoriasis on 18p11.

Polymorphisms in the SEEK1 and SPR1 genes on 6p21.3 associate with psoriasis in the Swedish population

Psoriasis is a chronic skin disease that results in red and scaly lesions. Several psoriasis susceptibility loci have been identified across the genome, of which PSORS1 on 6p21.3 is predominant. There is an ongoing debate regarding whether the HLA-C allele, Cw*0602, can be considered the major predisposing factor in this region. Investigation of other genes in the PSORS1 region with regard to psoriasis may provide alternate candidates to HLA-C. We have characterized two overlapping genes, SEEK1 and SPR1. SEEK1 encodes two putative protein isoforms: the first being one of 152 amino acids from the full-length splice-isoform (exon 1-6), and the second being one of 100 amino acids from an alternate splice-isoform (exon 1 and 6). SPR1 encodes a highly conserved protein of 134 amino acids, and in addition to characterization of human SPR1 we report the cloning of its orthologs in mouse and pig. Both SEEK1 and SPR1 are expressed in normal and psoriasis skin. In a case-control study, five of the nine single nucleotide polymorphisms (SNPs) found in SEEK1 were associated with psoriasis, while one of the four SNPs found in SPR1 showed association. Testing the Cw*0602 confounding status revealed that two of the SEEK1 SNPs showed Cw*0602-independent association, while the SPR1 SNP showed Cw*0602-dependent association. The second exon of SEEK1, containing the two Cw*0602-independent SNPs, showed the highest concentration of the psoriasis-associating SNPs, but did not appear to be translated.

The International Psoriasis Genetics Study: assessing linkage to 14 candidate susceptibility loci in a cohort of 942 affected sib pairs

In an effort to confirm previously reported linkages to psoriasis, we analyzed 942 affected sibling pairs (ASPs) from 710 pedigrees for 53 polymorphic microsatellites spanning 14 psoriasis candidate regions at an intermarker spacing of approximately 5 cM. Maximum LOD score (MLS) analysis of ASPs yielded allele sharing of 60% for markers within the major histocompatibility complex (MHC) (P=2 x 10(-14)), which yielded a gene-specific lambda(s) of 1.6. Across the remainder of the genome, the strongest evidence of allele sharing was obtained on chromosomes 16q (D16S3032; MLS=1.3; P=.007) and 10q22-q23 (D10S2327; MLS=1.1; P=.012). None of the remaining loci exceeded MLS=0.9, the value expected to occur by chance once in this study. In agreement with previous studies, strong linkage disequilibrium was also observed between psoriasis and the MHC (pedigree disequilibrium test P=3.9 x 10(-8) for D6S1014). Two psoriasis-associated MHC haplotypes were identified with the haplotype-based transmission/disequilibrium test. Analysis of only those families carrying either of these haplotypes significantly increased the chromosome 16q LOD score from 1.3 to 2.4 (P=.045). These results underscore the importance of the MHC in psoriasis and provide a rationale for more-detailed examination of candidate regions on chromosomes 16q and 10q.

Psoriasiform dermatitis susceptibility in Itgb2(tm1Bay) PL/J mice requires low-level CD18 expression and at least two additional loci for progression to severe disease

Itgb2(tm1Bay) PL/J mice express low levels of the beta(2) integrins and, unlike Itgb2(tm1Bay) C57BL/6J mice, spontaneously develop psoriasiform dermatitis with several similarities to human psoriasis. To define the genetic requirements for skin disease susceptibility we analyzed more than 500 F2 progeny from an Itgb2(tm1Bay) (PL/J x C57BL/6J) intercross. We found that 23.5% developed chronic inflammatory skin disease, although significant differences in severity were observed. Another CD18 mutation, Itgb2(tm2Bay), has now been generated that completely eliminates CD18 expression. Surprisingly, of 10 Itgb2(tm2Bay) homozygote PL/J N4 mice generated, none showed clinical or histopathological evidence of disease. However, Itgb2(tm1Bay)/Itgb2(tm2Bay) PL/J mice developed dermatitis indistinguishable from Itgb2(tm1Bay) PL/J mice. In addition, approximately half of Itgb2(tm1Bay)/Itgb2(tm2Bay) (C57BL/6J x PL/J)F1 mice were found to develop mild psoriasiform dermatitis identical to the early stages of disease seen in Itgb2(tm1Bay) PL/J mice. Collectively, these results suggest a complex inheritance pattern of psoriasiform dermatitis in this model that involves lowered, but not absent, CD18 expression and at least two additional PL/J loci for the development of severe disease. The susceptibility allele can act in either a heterozygous or homozygous state, dependent on the level of CD18 expression.