Genetics of Psoriasis in Iceland: Evidence for Linkage of Subphenotypes to Distinct Loci

State-of-the-Art Review of Pregnancy-Related Psoriasis

Psoriasis is a chronic immunologic disease involving inflammation that can target internal organs, the skin, and joints. The peak incidence occurs between the age of 30 and 40 years, which overlaps with the typical reproductive period of women. Because of comorbidities that can accompany psoriasis, including metabolic syndrome, cardiovascular involvement, and major depressive disorders, the condition is a complex one. The role of hormones during pregnancy in the lesion dynamics of psoriasis is unclear, and it is important to resolve the implications of this pathology during pregnancy are. Furthermore, treating pregnant women who have psoriasis represents a challenge as most drugs generally prescribed for this pathology are contraindicated in pregnancy because of teratogenic effects. This review covers the state of the art in psoriasis associated with pregnancy. Careful pregnancy monitoring in moderate-to-severe psoriasis vulgaris is required given the high risk of related complications in pregnancy, including pregnancy-induced hypertensive disorders, low birth weight for gestational age, and gestational diabetes. Topical corticosteroids are safe during pregnancy but effective only for localised forms of psoriasis. Monoclonal antibodies targeting cytokines specifically upregulated in psoriasis, such as ustekinumab (IL-12/23 inhibitor), secukinumab (IL-17 inhibitor) can be effective for the severe form of psoriasis during pregnancy. A multidisciplinary team must choose optimal treatment, taking into account fetal and maternal risks and benefits.

Fourteen sequence variants that associate with multiple sclerosis discovered by meta-analysis informed by genetic correlations

A meta-analysis of publicly available summary statistics on multiple sclerosis combined with three Nordic multiple sclerosis cohorts (21,079 cases, 371,198 controls) revealed seven sequence variants associating with multiple sclerosis, not reported previously. Using polygenic risk scores based on public summary statistics of variants outside the major histocompatibility complex region we quantified genetic overlap between common autoimmune diseases in Icelanders and identified disease clusters characterized by autoantibody presence/absence. As multiple sclerosis-polygenic risk scores captures the risk of primary biliary cirrhosis and vice versa (P = 1.6 × 10⁻⁷, 4.3 × 10⁻⁹) we used primary biliary cirrhosis as a proxy-phenotype for multiple sclerosis, the idea being that variants conferring risk of primary biliary cirrhosis have a prior probability of conferring risk of multiple sclerosis. We tested 255 variants forming the primary biliary cirrhosis-polygenic risk score and found seven multiple sclerosis-associating variants not correlated with any previously established multiple sclerosis variants. Most of the variants discovered are close to or within immune-related genes. One is a low-frequency missense variant in TYK2, another is a missense variant in MTHFR that reduces the function of the encoded enzyme affecting methionine metabolism, reported to be dysregulated in multiple sclerosis brain.

Combining studies and comparing across diseases turned up 14 novel gene variants linked to multiple sclerosis (MS). A team led by Kári Stefánsson and Ingileif Jónsdóttir from deCODE genetics in Reykjavík, Iceland, amalgamated data from a large international study of MS with three smaller ones from Sweden, Norway and Iceland. They conducted a meta-analysis on the combined data set — which encompassed around 21,000 MS patients and 372,000 population controls — and uncovered seven new genetic risk variants linked to MS. The researchers then compared the genetic overlap between various autoimmune diseases in the Icelandic cohort, and documented a close relationship between MS and primary biliary cirrhosis (PBC). They looked more closely at variants linked to PBC, and found that seven also increased the risk for MS, bringing the tally of novel gene variants up to fourteen.

Psoriasis

Psoriasis is a chronic, immune-mediated disorder with cutaneous and systemic manifestations and substantial negative effects on patient quality of life. Psoriasis has a strong, albeit polygenic, genetic basis. Whereas approximately half of the accountable genetic effect of psoriasis maps to the major histocompatibility complex, >70 other loci have been identified, many of which implicate nuclear factor-κB, interferon signalling and the IL-23-IL-23 receptor axis. Psoriasis pathophysiology is characterized by abnormal keratinocyte proliferation and immune cell infiltration in the dermis and epidermis involving the innate and adaptive immune systems, with important roles for dendritic cells and T cells, among other cells. Frequent comorbidities are rheumatological and cardiovascular in nature, in particular, psoriatic arthritis. Current treatments for psoriasis include topical agents, photo-based therapies, traditional systemic drugs and biologic agents. Treatments can be used in combination or as monotherapy. Biologic therapies that target specific disease mediators have become a mainstay in the treatment of moderate-to-severe disease, whereas advances in the treatment of mild-to-moderate disease have been limited.

Commonalities in Development of Pure Breeds and Population Isolates Revealed in the Genome of the Sardinian Fonni's Dog

The island inhabitants of Sardinia have long been a focus for studies of complex human traits due to their unique ancestral background and population isolation reflecting geographic and cultural restriction. Population isolates share decreased genomic diversity, increased linkage disequilibrium, and increased inbreeding coefficients. In many regions, dogs and humans have been exposed to the same natural and artificial forces of environment, growth, and migration. Distinct dog breeds have arisen through human-driven selection of characteristics to meet an ideal standard of appearance and function. The Fonni's Dog, an endemic dog population on Sardinia, has not been subjected to an intensive system of artificial selection, but rather has developed alongside the human population of Sardinia, influenced by geographic isolation and unregulated selection based on its environmental adaptation and aptitude for owner-desired behaviors. Through analysis of 28 dog breeds, represented with whole-genome sequences from 13 dogs and ∼170,000 genome-wide single nucleotide variants from 155 dogs, we have produced a genomic illustration of the Fonni's Dog. Genomic patterns confirm within-breed similarity, while population and demographic analyses provide spatial identity of Fonni's Dog to other Mediterranean breeds. Investigation of admixture and fixation indices reveals insights into the involvement of Fonni's Dogs in breed development throughout the Mediterranean. We describe how characteristics of population isolates are reflected in dog breeds that have undergone artificial selection, and are mirrored in the Fonni's Dog through traditional isolating factors that affect human populations. Lastly, we show that the genetic history of Fonni's Dog parallels demographic events in local human populations.

What can the genetics of psoriasis teach us about alopecia areata?

Previous genetic epidemiological studies of psoriasis and alopecia areata demonstrated strong heritability in first-degree relatives and in twins. In recent years, these two conditions have emerged as two skin diseases that are starting to yield their secrets through genome-wide association studies. Both diseases manifest prominent human leukocyte antigen (HLA) associations, psoriasis primarily with major histocompatibility complex (MHC) Class 1, specifically HLA-Cw6, and alopecia areata primarily with MHC Class II. Despite these differences in HLA associations, both diseases have in common a prominent role for CD8+ lymphocytes. The purpose of this brief review is to present the recent developments in the genetics of psoriasis.

Meta-analysis of NOD2/CARD15 polymorphisms with psoriasis and psoriatic arthritis

Psoriasis and psoriatic arthritis (PsA) is a complex autoimmune disease. NOD2/CARD15 gene has been suggested to play an important role in the pathogenesis of psoriasis and PsA. This study aims to assess the association between NOD2/CARD15 polymorphisms and the susceptibility to psoriasis/PsA. A meta-analysis was performed to survey studies on the NOD2/CARD15 polymorphisms and psoriasis/PsA using comprehensive PubMed, Embase, and Web of Science citation search. A total of 9 published studies were involved. Meta-odds ratios (ORs) and 95% confidence intervals (CIs) based on fixed effects models or random effects models were depended on Cochran's Q-statistic. Potential publication bias was evaluated by Egger's linear regression test. As for R702W, the pooled ORs were 1.041 (95% CI 0.854-1.268, P = 0.693; 2,081 patients vs. 2,717 controls) for C allele and 0.886 (95% CI 0.565-1.391. P = 0.600; 1,222 patients vs. 1,818 controls) for genotype. Then for G908R, the pooled ORs were 1.042 (95% CI, 0.761-1.426, P = 0.799; 2,053 patients vs. 2,743 controls) for C allele and 0.942 (95% CI 0.708-1.254, P = 0.683; 1,226 patients vs. 1,824 controls) for the homozygous wild type. Then for Leu1007fsinsC allele polymorphism and genotype, the pooled ORs were 1.160 (95% CI, 0.893-1.507, P = 0.266; 2,279 patients vs. 3,067 controls) and 1.266 (95% CI 0.897-1.789, P = 0.180; 1,979 patients vs. 1,607 controls), respectively. No obvious publication bias was shown in the results. The association between NOD2/CARD15 polymorphisms and psoriasis/PsA was not found. Taken together, our results suggest that NOD2/CARD15 might not be a susceptibility gene for psoriasis and psoriatic arthritis.

Psoriasis--as an autoimmune disease caused by molecular mimicry

Psoriasis is strongly associated with streptococcal throat infection, and patients have increased occurrence of such infections. Psoriatic lesional T cells are oligoclonal, and T cells recognizing determinants common to streptococcal M-protein and keratin have been detected in patients' blood. We propose that CD8(+) T cells in psoriatic epidermis respond mainly to such determinants, whereas CD4(+) T cells in the dermis preferentially recognize determinants on the streptococcal peptidoglycan that might itself act as an adjuvant. The streptococcal association might reflect the concurrence of superantigen production promoting skin-homing of tonsil T cells, M-protein mimicking keratin determinants, and adjuvant effects of the peptidoglycan. Accordingly, improvement of psoriasis after tonsillectomy should be associated with fewer T cells that recognize keratin and streptococcal determinants.

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.

On the heritability of psoriatic arthritis. Disease concordance among monozygotic and dizygotic twins

OBJECTIVE

A nationwide unselected twin population to estimate the relative importance of genetic and environmental effectors in the aetiopathogenesis of psoriatic arthritis (PsA).

METHODS

The study comprised three Danish nationwide twin cohorts. In 1994 and 2002 a total of 37 388 and 46 418 Danish twin individuals respectively were asked by questionnaire if they had PsA. Twins reporting PsA were invited to participate in a clinical examination. Patients were classified according to the Moll and Wright and the CASPAR (ClASsification criteria for Psoriatic ARthritis) criteria. Heritability was estimated by probandwise concordance rates and variance component analysis.

RESULTS

228 twin individuals reported PsA. Following diagnostic validation in 164 (70%), 50 probands were diagnosed with PsA according to the Moll and Wright criteria. Five of their co-twins were either dead, had emigrated, or did not participate in the twin study and nine did not respond, resulting in 36 complete pairs. A total of one of 10 monozygotic pairs and one of 26 dizygotic pairs were concordant for PsA, yielding a 6.2% difference in proportions (95% CI: -11%, 37%). Five of 10 monozygotic pairs and four of 26 dizygotic pairs were concordant for psoriatic skin disease implying a 35% difference (95% CI: 2%, 60%, p<0.05).

CONCLUSIONS

This first twin study on PsA confirms that genes are important in the causation of psoriatic skin disease. Despite the limited statistical power, the almost identical concordance rates for PsA in monozygotic and dizygotic twins stresses the importance of the continued search for non-genetic effectors in PsA.

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.

Combined effects of HLA-Cw6 and cigarette smoking in psoriasis vulgaris: a hospital-based case-control study in China

BACKGROUND

Psoriasis is not only related to genetic factors but also to environmental factors. However, the combined effect of genetic and environmental factors in the development of psoriasis has still been unclear.

OBJECTIVE

The study was to analyze the combined effect of HLA-Cw6 and smoking on psoriasis vulgaris.

METHODS

A hospital-based case-control was conducted study. One hundred seventy-eight cases and 178 controls received this epidemiological investigation and HLA typing by polymerase chain reaction utilizing sequence-specific primers.

RESULTS

The risk of psoriasis was related to smoking, the adjusted odds ratio (OR) being 2.07 (P < 0.01), and there is a graded positive association between the risk of psoriasis and intensity or duration of smoking. Stressful life events increased the risk of psoriasis (OR = 7.87, P < 0.01). We found the waist-hip ratio (WHR) increased the risk of psoriasis vulgaris, and OR was 2.67 (P < 0.01) in China. Individuals harboring the HLA-Cw6 gene obviously increased the risk of psoriasis, OR being 9.93 (P < 0.01) after adjusted for potential confounder factors, while the OR of psoriasis for HLA-B57 was 2.41 (P < 0.05). Significant combined effect between HLA-Cw6 and HLA-B57 for psoriasis was found (OR = 10.51, P < 0.01). A striking finding is that the risk of psoriasis for smokers with HLA-Cw6 increased about 11-fold than non-smokers without HLA-Cw6, and the risk increased some 20-fold in individuals with HLA-Cw6 having stressful life events compared with one without HLA-Cw6 and stressful life events.

CONCLUSION

Our study suggested that the combined effect between HLA-Cw6 and cigarette smoking or stressful life events may play an important role in the development of psoriasis vulgaris in Han Chinese population.

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.

The genetic basis of psoriasis

For a complex genetic disease, psoriasis has a high penetration within families and a concordance rate of up to 70% in identical twins. Despite this and the endeavors of many research groups for more than a decade, no susceptibility allele has so far been unequivocally identified, although about 20 genetic loci associated with psoriasis have been reported from linkage-based studies. Moreover, only 1 of these linkage-based loci, PSORS1, that includes the HLA-C gene on chromosome 6p21, has been universally confirmed. Very recent data strongly indicate that HLA-Cw*0602 is the susceptibility allele in this locus, a finding that is consistent with the notion that the pathogenesis of psoriasis involves autoantigen recognition by epidermal CD8+ T lymphocytes. Several candidate genes in some of the other 7 PSORS designated loci are currently being evaluated. The relative lack of success in elucidating the genetic basis of psoriasis highlights the formidable challenge of dissecting the genetic basis of diseases with a complex mode of inheritance.

Psoriatic arthritis: genetic susceptibility and pharmacogenetics

Psoriatic arthritis (PsA) is an inflammatory arthritis associated with psoriasis. The etiology of PsA is unknown; however, there is mounting evidence for a strong genetic contribution to PsA. A few disease-related genes have already been identified in PsA. Cytokines associated with PsA appear to be the most promising targets for pharmacogenetics. Blockade of TNF-α and IL-12/23 is associated with a marked clinical response to PsA and/or psoriasis, implying a pivotal role of these cytokines in the pathogenesis of these two disease entities. To date, only the -308 variant of the TNF-α promoter gene has been shown to be important in predicting response to TNF-α blockade in inflammatory arthritis.

The sodium-dependent glucose cotransporter SLC5A11 as an autoimmune modifier gene in SLE

Genetic studies in several human autoimmune diseases suggest that the pericentromeric region of chromosome 16 might harbor an autoimmune modifier gene. We hypothesized that the sodium-dependent glucose cotransporter gene SLC5A11 is such a gene, and so might interact with immune-related genes. Herein, this hypothesis was tested in a genetic evaluation of the multiple gene effect in systemic lupus erythematosus (SLE). We used the case-control candidate gene association approach. Eight immune-related genes involved in inflammation and autoantibody generation and clear-up [interleukin 1 receptor antagonist (IL1RN), interleukin 1-beta (IL1-beta), tumor necrosis factor-alpha (TNF-alpha), lymphotoxin-alpha (LTA), tumor necrosis factor ligand superfamily, member 6 (TNFSF6), programmed cell death 1 (PDCD1), C2, and complement component 4 (C4)] were selected for study. Frequency of each candidate's genotype and allele between case and control were compared. Results were stratified by reanalyzing genotype data with relevant symptoms. Finally, improved computational data mining was used to analyze the phenotypes in a large data set. In the frequency analysis, only IL1-beta was significantly associated with SLE. Stratification analysis showed a significant association with SLE symptoms between SLC5A11 and the other immune-related genes, with the exceptions of TNFSF6 and C4. SLC5A11 was significantly associated with low C4 (as was TNF-alpha), anti-Smith antibody (anti-Sm) (as was C2), serositis, and alopecia. Finally, SLC5A11 interacted with PDCD1, TNF-alpha, LTA, and C4. After our study, we concluded that SLC5A11 is involved with some immune effects and interacts with immune-related gene(s), consistent with its function as an autoimmune modifier gene. Furthermore, SLC5A11 might induce apoptosis through the TNF-alpha, PDCD1 pathway. The present genotype-phenotype mapping approach should be applicable to genetic study of other complex 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.

Genetik der Psoriasis

Psoriasis ist eine chronische, entzündliche Hauterkrankung mit einer multifaktoriellen Vererbung. Als wichtigster Risikofaktor gilt derzeit das HLA-CW0602-Allel [bzw. ein Faktor in starkem LD („linkage disequilibrium“)], das insbesondere für die frühere Manifestationsform (< 40. Lebensjahr) prädisponiert und u. a. einen Einfluss auf die Schwere des Verlaufs hat. Durch genomweite Kopplungsanalysen konnten bisher 11 weitere Suszeptibilitätsloci, jedoch nur wenige Kandidatengene identifiziert werden, alle mit vergleichsweise geringem relativem Risiko (Odds-Ratio, OR). Weitere Aspekte der komplexen Ätiopathogenese dieser Erkrankung konnten in immunologischen Ansätzen, aufgrund von Therapieerfolgen mit Antikörpern gegen immunrelevante Moleküle und bei kandidatengenorientierten Assoziationsstudien aufgeklärt werden. Die pathophysiologischen und genetischen Befunde konvergieren zunehmend und zeichnen die Psoriasis als Erkrankung eines fehlgesteuerten immunologischen Regulationsprozesses zwischen Keratinozyten und Zellen des angeborenen und erworbenen Immunsystems aus.

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.

A classification of psoriasis vulgaris according to phenotype

For nearly 200 years it has been appreciated that plaque psoriasis consists of a number of distinct clinical phenotypes. However, a reliable and simple stratification of clinical presentation of psoriasis is lacking. In the era of immunogenetic association studies and an advanced understanding of the pathomechanisms of psoriasis it is important that a classification of the disease according to phenotype is readily available. Such a classification would facilitate clinically relevant interpretation of investigational data. A meeting of the International Psoriasis Council produced a consensus on clinical phenotypes of psoriasis equally relevant to clinical practitioners and psoriasis researchers.

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.

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.

Increase in linkage information by stratification of pedigree data into gold-standard and standard diagnoses: application to the NIMH Alzheimer Disease Genetics Initiative Dataset

Patients diagnosed with a standard clinical method (subject to misclassification error) are often combined with patients diagnosed with a gold-standard method (with zero or very small misclassification error) in family-based studies of complex disease. For example, non-autopsied patients (NAP) are often included along with autopsy-proven (AP) patients in family-based studies of complex diseases, such as Alzheimer's disease (AD). Theoretical and simulation studies suggest that certain misclassification errors can result in severe reduction of power in genetic linkage and association analyses and that phenotype (or diagnostic) error can produce misleading results. Morton's test for heterogeneity can identify genomic regions where error may have led to loss in power. We applied this test to pedigree data from the NIMH Alzheimer's Disease Genetics Initiative Database separated into AP and NAP pedigrees. Morton's test identified one highly significant region of heterogeneity on chromosome 2. The source of the heterogeneity was due to significant indication of linkage in the AP pedigrees at position 109 cM (p value = 6.68 x 10(-5)) with no indication in the NAP pedigrees. Furthermore, Morton's test showed no evidence for heterogeneity on chromosome 19 in early-onset pedigrees that showed highly significant evidence for linkage in other published reports. These results suggest that supplementing linkage analysis with Morton's test can be usefully applied to genetic data sets that have AP and NAP samples, or other sample mixtures that include a 'gold standard' subgroup with reduced error rate, to increase power to detect linkage in the presence of diagnostic misclassification.

Distinct clinical differences between HLA-Cw*0602 positive and negative psoriasis patients--an analysis of 1019 HLA-C- and HLA-B-typed patients

A major susceptibility gene for psoriasis is located in the major histocompatibility complex class I region on chromosome 6 very close to the HLA-Cw6 gene. We collected a cohort of 1,019 patients with chronic plaque psoriasis. The patients were typed for HLA-C and HLA-B. A total of 654 (64.2%) were HLA-Cw*0602 positive but 365 (35.8%) carried other HLA-C alleles. We confirmed that HLA-Cw*0602 positive patients have younger age of onset (17.5 vs 24.3 years, P<10(-10)), higher incidence of guttate and the eruptive type of psoriasis (P<0.0001), more frequent exacerbations with throat infections (P=0.01), higher incidence of the Koebner's phenomenon (P=0.01), and more extensive disease (P=0.03). A striking new finding was a diverging pattern of disease severity in HLA-Cw*0602 positive and negative patients depending on the age of onset of the disease (P=0.0006). HLA-Cw*0602 positive women also had more frequent remissions during pregnancy (P<0.0001). All types of nail changes were, however, more common in the Cw*0602 negative patients (P=0.003) and they more often had multiple types of nail lesions (P<0.0001). The three ancestral haplotypes of Cw*0602 all conferred an increase in odds ratio but showed no difference in any of the clinical features studied. Our findings indicate that the genetic factor on chromosome 6 has a strong influence on the phenotype of the disease, and underline that differences in clinical features of psoriasis may be to a large extent genetically determined.

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.