Corneodesmosin gene polymorphism demonstrates strong linkage disequilibrium with HLA and association with psoriasis vulgaris

High-Throughput RNA Sequencing Reveals the Effect of NB-UVB Phototherapy on Major Inflammatory Molecules of Lesional Psoriasis

OBJECTIVE

To identify the narrowband ultraviolet B (NB-UVB)-induced molecular mechanisms that may account for their anti-inflammatory efficacy, gene expression and transcriptome profiling, which were performed using advanced molecular techniques.

METHODS

This research was conducted on patients with moderate-to-severe plaque-type psoriasis who received NB-UVB treatment. RNA sequencing (RNA-Seq) was conducted to assay the transcriptomes and identify the differentially expressed transcripts that had been enriched during the major pathway analysis.

RESULTS

Clinical improvement of psoriasis by NB-UVB therapy is linked to the suppression of the "immunological signaling pathways" and "cell cycle regulatory, growth and proliferation pathways" which are critical to the pathogenesis of the disease. In addition, these results were further substantiated by demonstrating that NB-UVB therapy has a significant effect on keratinocyte differentiation and affects the regulation of genes and inflammatory mediators that are related to cell proliferation and apoptosis. Moreover, NB-UVB phototherapy is also involved with the downregulation of toll-like receptors signaling in lesional psoriasis.

CONCLUSION

NB-UVB is an effective treatment for psoriasis. Our study supports the conclusion that the clinical effectiveness of NB-UVB therapy is based on the suppression of a broad range of inflammatory signaling pathways, gene expression of inflammatory cytokines and increased expressions of anti-inflammatory signaling pathways in psoriatic skin. This is the first study that applied advanced molecular techniques to investigate phototherapy as a new key to unlock genetic knowledge and create novel information. Ultimately, the goal is to increase medical knowledge and improve the patient care of psoriasis.

HLA-C*06:02-independent, gender-related association of PSORS1C3 and PSORS1C1/CDSN single-nucleotide polymorphisms with risk and severity of psoriasis

Psoriasis vulgaris (PsV) is a common, chronic skin disease with a complex genetic and environmental etiology. We investigated, in 461 psoriatic patients and 454 healthy controls, the associations with psoriasis of four single-nucleotide polymorphisms (SNPs) from the psoriasis susceptibility 1 (PSORS1) interval: rs1062470 (PSORS1C1/CDSN), rs887466 (PSORS1C3), rs2894207 and rs10484554 (LOC105375015). The minor alleles of three SNPs (rs1062470A, rs2894207C and rs10484554T) strongly increased the disease risk (OR = 2.17, p < 0.0001; OR = 2.33, p < 0.0001 and OR = 2.68, p < 0.0001, respectively), whereas the minor A allele of rs887466 exerted a protective effect (OR = 0.73, p = 0.001). The strength of association for SNPs was the highest in patients with very early onset psoriasis (≤ 20 years), while in late onset psoriasis (> 40 years) the association was the weakest. The haplotype rs1062470A/rs887466G/rs2894207C/rs10484554T highly significantly increased the disease risk (OR = 3.58, p = 8.0e-027), while the haplotypes rs1062470G/rs887466A/rs2894207T/rs10484554C and rs1062470G/rs887466G/rs2894207T/rs10484554C were strongly protective (OR = 0.65, p = 0.002 and OR = 0.55, p = 2.4e-009, respectively). Additionally, we showed a HLA-C*06:02-independent gender-related effect of the rs887466A allele which was protective against psoriasis in males (OR = 0.61, p = 9.2e-005), but not in females (p = 0.66). We also demonstrated a correlation of PASI score value with rs1062470 genotype, and again only in male patients (p = 0.006) and HLA-C*06:02-independent. Our results show, for the first time, the male-only associations of the PSORS1C3 gene with psoriasis risk and of the PSORS1C1/CDSN gene with severity of disease. However, the age dependent associations need to be validated in larger sample sizes as well as in other populations.

Sequencing and annotated analysis of the Holstein cow genome

The aim of our study was to create a high-quality Holstein cow genome reference sequence and describe the different types of variations in this genome compared to the reference Hereford breed. We generated one fragment and three mate-paired libraries from genomic DNA. Raw files were mapped and paired to the reference cow (Bos taurus) genome assemblies bosTau6/UMD_3.1. BioScope (v1.3) software was used for mapping and variant analysis. Initial sequencing resulted in 2,842,744,008 of 50-bp reads. Average mapping efficiency was 78.4 % and altogether 2,168,425,497 reads and 98,022,357,422 bp were successfully mapped, resulting in 36.7X coverage. Tertiary analysis found 5,923,230 SNPs in the bovine genome, of which 3,833,249 were heterozygous and 2,089,981 were homozygous variants. Annotation revealed that 4,241,000 of all discovered SNPs were annotated in the dbSNP database and 1,682,230 SNPs were considered as novel. Large indel variations accounted for 48,537,190 bp of the entire genome and there were 138,504 of them. The largest deletion was 18,594 bp and the largest insertion was 13,498 bp. Another group of variants, small indels (n = 458,061), accounted for the total variation of 1,839,872 nucleotides in the genome. Only 92,115 small indels were listed in the dbSNP and therefore 365,946 small indels were novel. Finally, we identified 1,876 inversions in the bovine genome. In conclusion, this is another description of the Holstein cow genome and, similar to previous studies, we found a large amount of novel variations. Better knowledge of these variations could explain significant phenotypic differences (e.g., health, production, reproduction) between different breeds.

Predictive mutational bioinformatic analysis of variation in the skin and wool associated corneodesmosin (CDSN) gene in sheep

Corneodesmosin (CDSN) is an important component of the desmosome in the epidermal cornified stratum and inner root sheath of hair follicles. DNA from a sheep BAC clone previously identified by us to contain CDSN was PCR amplified using cattle-derived primers and the product sequenced. A region of 4579 bp containing CDSN was shown to contain two exons separated by one intron and spanning 3683 bp. The DNA encodes a predicted protein of 546 amino acids. Phylogenetic analysis shows that sheep CDSN falls within a clade containing cattle and other ruminant-like species. Comparison of sequences generated from 12 unrelated merino sheep and the International Sheep Genome Consortium (ISGC) data identified 58 single nucleotide polymorphisms (SNPs) within the 4579 bp region of which 16 are contained within coding sequences (1 in 80 bp). The SNPs identified in this study will add to the Major Histocompatibility Complex (MHC) SNP panel, which will allow extensive haplotyping of the sheep MHC in future studies.

Targeted deletion of the murine corneodesmosin gene delineates its essential role in skin and hair physiology

Controlled proteolytic degradation of specialized junctional structures, corneodesmosomes, by epidermal proteases is an essential process for physiological desquamation of the skin. Corneodesmosin (CDSN) is an extracellular component of corneodesmosomes and, although considerable debate still exists, genetic studies have suggested that the CDSN gene in the major psoriasis-susceptibility locus (PSORS1) may be responsible for susceptibility to psoriasis, a human skin disorder characterized by excessive growth and aberrant differentiation of keratinocytes. CDSN is also expressed in the inner root sheath of hair follicles, and a heterozygous nonsense mutation of the CDSN gene in humans is associated with scalp-specific hair loss of poorly defined etiology. Here, we have investigated the pathogenetic roles of CDSN loss of function in the development of skin diseases by generating a mouse strain with targeted deletion of the Cdsn gene. Cdsn-deficient mouse skin showed detachment of the stratum corneum from the underlying granular layer and/or detachment within the upper granular layers due to the disrupted integrity of the corneodesmosomes. When grafted onto immunodeficient mice, Cdsn-deficient skin showed rapid hair loss together with epidermal abnormalities resembling psoriasis. These results underscore the essential roles of CDSN in hair physiology and suggest functional relevance of CDSN gene polymorphisms to psoriasis susceptibility.

Fine mapping of the psoriasis susceptibility locus PSORS1 supports HLA-C as the susceptibility gene in the Han Chinese population

PSORS1 (psoriasis susceptibility gene 1) is a major susceptibility locus for psoriasis. Several fine-mapping studies have highlighted a 300-kb candidate region of PSORS1 where multiple biologically plausible candidate genes were suggested. The most recent study has indicated HLA-Cw6 as the primary PSORS1 risk allele within the candidate region in a Caucasian population. In this study, a family-based association analysis of the PSORS1 locus was performed by analyzing 10 polymorphic microsatellite markers from the PSORS1 region as well as HLA-B, HLA-C and CDSN loci in 163 Chinese families of psoriasis. Five marker loci show strong evidence (P<10(-3)), and one marker locus shows weak evidence (P = 0.04) for association. The haplotype cluster analysis showed that all the risk haplotypes are Cw6 positive and share a 369-kb region of homologous marker alleles which carries all the risk alleles, including HLA-Cw6 and CDSN*TTC, identified in this study. The recombinant haplotype analysis of the HLA-Cw6 and CDSN*TTC alleles in 228 Chinese families showed that the HLA-Cw6(-)/CDSN*TTC(+) recombinant haplotype is clearly not associated with risk for psoriasis (TratioNT = 29:57, p = 0.0025) in a Chinese population, suggesting that the CDSN*TTC allele itself does not confer risk without the presence of the HLA-Cw6 allele. The further exclusion analysis of the non-risk HLA-Cw6(-)/CDSN*TTC(+) recombinant haplotypes with common recombination breakpoints has allowed us to refine the location of PSORS1 to a small candidate region. Finally, we performed a conditional linkage analysis and showed that the HLA-Cw6 is a major risk allele but does not explain the full linkage evidence of the PSORS1 locus in a Chinese population. By performing a series of family-based association analyses of haplotypes as well as an exclusion analysis of recombinant haplotypes, we were able to refine the PSORS1 gene to a small critical region where HLA-C is a strong candidate to be the PSORS1 susceptibility gene.

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.

Sequence and haplotype analysis supports HLA-C as the psoriasis susceptibility 1 gene

Previous studies have narrowed the interval containing PSORS1, the psoriasis-susceptibility locus in the major histocompatibility complex (MHC), to an approximately 300-kb region containing HLA-C and at least 10 other genes. In an effort to identify the PSORS1 gene, we cloned and completely sequenced this region from both chromosomes of five individuals. Two of the sequenced haplotypes were associated with psoriasis (risk), and the other eight were clearly unassociated (nonrisk). Comparison of sequence of the two risk haplotypes identified a 298-kb region of homology, extending from just telomeric of HLA-B to the HCG22 gene, which was flanked by clearly nonhomologous regions. Similar haplotypes cloned from unrelated individuals had nearly identical sequence. Combinatorial analysis of exonic variations in the known genes of the candidate interval revealed that HCG27, PSORS1C3, OTF3, TCF19, HCR, STG, and HCG22 bore no alleles unique to risk haplotypes among the 10 sequenced haplotypes. SPR1 and SEEK1 both had messenger RNA alleles specific to risk haplotypes, but only HLA-C and CDSN yielded protein alleles unique to risk. The risk alleles of HLA-C and CDSN (HLA-Cw6 and CDSN*TTC) were genotyped in 678 families with early-onset psoriasis; 620 of these families were also typed for 34 microsatellite markers spanning the PSORS1 interval. Recombinant haplotypes retaining HLA-Cw6 but lacking CDSN*TTC were significantly associated with psoriasis, whereas recombinants retaining CDSN*TTC but lacking HLA-Cw6 were not associated, despite good statistical power. By grouping recombinants with similar breakpoints, the most telomeric quarter of the 298-kb candidate interval could be excluded with high confidence. These results strongly suggest that HLA-Cw6 is the PSORS1 risk allele that confers susceptibility to early-onset psoriasis.

Nested genes in the human genome

Here we studied one special type of gene, i.e., the nested gene, in the human genome. We collected 373 reliably annotated nested genes. Two-thirds of them were on the strand opposite that of their host gene. About 58% coding nested gene pairs were conserved in mouse and some were even maintained in chicken and fish, while nested pseudogenes were poorly conserved. Ka/Ks analysis revealed that nested genes were under strong selection, although they did not demonstrate greater conservation than other genes. With microarray data we observed that two partners of one nested pair seemed to be expressed reciprocally. A significant proportion of nested genes were tissue-specifically expressed. Gene ontology analysis demonstrated that quite a number of nested genes participated in cellular signal transduction. Based on these observations, we think that nested genes are a group of genes with important physiological functions.

Mapping and identifying genes for asthma and psoriasis

Susceptibility genes for complex diseases are characterized by reduced penetrance, caused by the influence of other genes, the environment or stochastic events. Recently, positional cloning efforts have yielded several candidate susceptibility genes in different complex disorders such as Crohn's disease and asthma. Within a genetic locus, however, the identification of the effector gene may pose further challenges and require functional studies. I review two examples of such challenges: the cloning of GPR154 (GPRA) and AAA1 on chromosome 7p14 at a susceptibility locus for atopy and asthma, and the study of HLA-Cw6, CCHCR1 (HCR) and CDSN on chromosome 6p21 at PSORS1, the major susceptibility locus for psoriasis. The susceptibility locus for atopy and asthma contains two genes and only one of them is protein coding. We studied its isoform-specific expression in bronchial biopsies and in a mouse model of ovalbumin-induced inflammation of bronchial epithelia. In the PSORS1 locus, strong linkage disequilibrium between genes has made it difficult to distinguish the effects of the three nearby genes. We engineered transgenic mice with either a HCR non-risk allele or the HCR*WWCC risk allele controlled by the cytokeratin-14 promoter. The results suggested that the overexpression of HCR in mouse skin was insufficient to induce a psoriasiform phenotype, but it appeared to induce allele-specific gene expression changes that were similar to those observed in psoriatic skin.

Distinct HLA-C/KIR genotype profile associates with guttate psoriasis

Psoriasis is a multifactorial disease with a strong genetic background. It associates strongly to HLA-Cw*0602. HLA-C interacts with killer immunoglobulin-like receptors (KIR) on natural killer (NK) and some natural killer-T (NKT) cells. KIR's function is triggered by specific binding to HLA ligands, which depends on the amino acid 80 of the MHC class I alpha-chain. This permits classifying all HLA-C alleles into two functional groups: asparagine (N80) or lysine (K80) carrying alleles. Psoriasis patients recruited at disease onset were categorized as guttate, vulgaris without arthropathy and vulgaris with arthropathy plus skin lesions. Patients and carefully matched controls were genotyped for position 80 of HLA-C and for KIR. Based on possible HLA/KIR combinations, individuals were classified according to expected NK/NKT cell responses: balanced (B), excess inhibition (EI), excess activation (EA), or undetermined (U). HLA-Cw6 and position 80 genotyping associated strongly to disease, whereas KIR2DS1 associated weakly. Individuals of the U and EI classes were more common among guttate psoriasis patients, which related to HLA-Cw*0602 status. These results suggest that different levels for NK/NKT cell activation thresholds, not only reduction, contribute to immune deregulation in psoriasis. In the guttate phenotype, balanced HLA-C/KIR interactions might be altered by the presence of concomitant streptococcal infections.

The Region of 150 kb Telometic to HLA-C Is Associated with Psoriasis in the Jewish Population

The HLA-Cw*0602 has been associated with psoriasis in different ethnic groups. But, it remains unclear whether HLA-C is the PSORS1 gene (the psoriasis gene in the MHC). Thus, several case-control studies have been performed in order to investigate whether HLA-C itself determines the susceptibility to the disease. We studied 59 Jewish patients with type I psoriasis and 79 matched controls. Polymorphic genes and markers from HLA-B (centromeric to HLA-C) to the corneodesmosin (CDSN) gene (telomeric to HLA-C) were genotyped in order to determine their contribution to the susceptibility to psoriasis. Neither HLA-Cw*0602 nor the allele CDSN*TTC were significantly associated with psoriasis with the size of the sample studied. The genes and markers telomeric to HLA-C such as the microsatellite C1_4_4 (OR = 2.6, 95% CI = 1.4-4.7, p(c) = 0.018) the octamer transcription factor (OTF)-3 gene (OR = 2.6, 95% CI = 1.6-4.3, p(c) = 0.0001) and the alpha-helix coiled-coil rod homologue (HCR) gene (OR = 2.5, 95% CI = 1.3-4.5, p(c) = 0.004), however, were associated with the disease. These results suggest that a major psoriasis susceptibility gene is likely to be located within a region of 150 kb telomeric to HLA-C and centromeric to the CDSN gene.

A study of PSORS1C1 gene polymorphisms in Chinese patients with psoriasis

BACKGROUND

Although genetic analyses have identified the HLA-Cw*0602 allele as the major risk allele for chronic plaque psoriasis in various ethnic groups, it has been proposed that the association of Cw*0602 is due to linkage disequilibrium and that other nearby genes are involved in susceptibility to psoriasis. The psoriasis susceptibility 1 candidate 1 (PSORS1C1, formerly SEEK1) gene, located 127 kb telomeric to the HLA-C locus, is considered to be one of the potential candidate genes of psoriasis. Up to the present, no association study of the PSORS1C1 gene has been conducted on Chinese patients with psoriasis.

OBJECTIVES

We aimed to determine whether the genetic polymorphisms of the PSORS1C1 gene were associated with an increased risk of psoriasis in Chinese patients.

METHODS

We investigated the PSORS1C1 gene for disease association by direct sequencing of the PSORS1C1 gene in 143 Chinese patients with chronic plaque psoriasis and 188 control subjects. Genotyping for HLA-Cw*0602 and the alpha-helix coiled-coil rod homologue (C6orf18, formerly HCR) gene was also carried out using a sequence-based typing method.

RESULTS

We identified 10 single nucleotide polymorphisms (SNPs) on the PSORS1C1 gene in our subjects; four of these SNPs cause amino acid change. We also detected poly(C) repeat variants from nucleotide positions 386-392 (poly(C)6-8). The poly(C) repeat polymorphisms cause a frame shift mutation. Another poly(C) repeat variant was also found at nucleotide positions 748-751. No significantly different allelic distributions of the PSORS1C1 SNPs or poly(C) repeat polymorphisms could be found between the patients with chronic plaque psoriasis and controls after correction for multiple testing. However, a significant increase of the Cw*0602 allele and tryptophan-tryptophan allele of the C6orf18 gene (HCR*WW) was found in patients with early onset psoriasis (21.9% vs. 4.8%, P < 10(-7)). Haplotype-based association analysis also showed a susceptibility haplotype carrying Cw*0602 and HCR*WW alleles in early onset Chinese patients.

CONCLUSIONS

Our results indicate that the PSORS1C1 gene might not play an important role in the causation of chronic plaque psoriasis in Chinese people.

Corneodesmosin (CDSN) gene association with psoriasis vulgaris in Caucasian but not in Japanese populations

PSORS1 on chromosome 6p21.3, which contains the MHC, is a major susceptibility locus for psoriasis vulgaris. This region is characterized by strong linkage disequilibrium and contains the corneodesmosin (CSDN) gene, an attractive candidate for psoriasis susceptibility based on its putative biological function in keratinocyte adhesion, and HLA-Cw6, an established marker for psoriasis susceptibility. We compared two genetically independent populations in order to define the major psoriasis susceptibility gene, a British Caucasian population comprising parent-offspring trios analysed by the transmission disequilibrium test (TDT) and a Japanese case-control population. All individuals were investigated for CDSN polymorphism (+619, +1236, +1240 and +1243) and HLA-C association. Our data confirms strong association with HLA-Cw6 and CDSN allele 5 (+619T, +1240G, +1243C) in the Caucasian cohort (TDT, P = 5.4 x 10(-6)) and in addition defines this region further by identifying a high-risk CDSN haplotype (allele 5 and +1236T, P = 8.5 x 10(-8)). In contrast no association was observed in the Japanese cohort for any HLA-C or CDSN alleles. This data supports a role for the CDSN gene in Caucasian populations with psoriasis. However the lack of association with HLA-Cw6 and CDSN alleles in Japanese psoriasis patients may be because Japanese patients exhibit a form of psoriasis similar to late onset or Type II psoriasis vulgaris in contrast to early onset or Type I disease characterizing our Caucasian population.

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

Psoriasis is a chronic inflammatory skin disease with overlapping subphenotypes. It has a strong complex genetic component, but has been problematic to identifying significant loci. We evaluated 1000 patients with chronic plaque psoriasis and documented several subphenotypes. Here we report results of genome-wide linkage scans for psoriasis genes in 238 Icelandic families with 874 patients. MHC linkage was confirmed with LOD score of 10.9. When the entire cohort was analyzed, two other loci with LOD scores of 2.5 and 1.5 were observed on 16q and 4q, respectively. Stratification into subphenotypes revealed additional loci with LOD scores exceeding or approaching significance. A LOD score of 5.7 appeared on 16q in PsA patients with analysis conditioned on parental inheritance. A LOD score of 3.6 on 4q was detected when disease occurred at or older than 17 y, our median cohort age. This locus was defined by a marker near one reportedly displaying significant linkage in a Chinese psoriasis population and near suggestive linkage in a Caucasian population. A LOD of 3.0 was observed on 10q when disease onset occurred in the scalp. Furthermore, clinical stratification either revealed or increased LOD scores when compared to unstratified analysis and some coincided with previous reports.

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.

Genome-wide studies of psoriasis susceptibility loci: a review

Psoriasis is a chronic inflammatory dermatosis affecting approximately 0.3-5% world-wide. Since 1997, nine genome-wide scans have been published in the search for predisposing genes to psoriasis and psoriatic arthritis. These genome-wide scans have provided results that both confirm earlier work, but which also suggest novel regions of interest on the genome. This article reviews the results of these genome-wide scans, in particular two novel regions on chromosomes 3p and 15p, and compares the study types and designs. The results in these two regions were compared in the different studies providing no further suggestive evidence, and we suggest that these results may be false-positives, population-specific susceptibility loci or due to the stratification used in the study design. We suggest stratifying the data into epidemiological subgroups in order to make the genome-wide scans more sensitive to loci specific to these subgroups. This approach could provide a much more powerful technique to study the genetics of a complex disease such as psoriasis.

STG does not associate with psoriasis in the Swedish population

Psoriasis is a chronic inflammatory skin disease that is known to have a strong genetic predisposition. Several psoriasis-susceptibility loci have been previously found through genomic scans. Of these, psoriasis-susceptibility region 1 (PSORS1) on chromosome 6p21 remains the most consistently identified region across populations with the highest association with disease. STG is a gene that was previously isolated from rhesus monkey taste buds, and its ortholog in humans was found to be part of the cluster of genes in PSORS1, which is telomeric to HLA-C. Upon characterization of STG, we identified several sequence variants and investigated their association with psoriasis in cases and controls from the Swedish population. None of these STG single-nucleotide polymorphisms were found to be significantly associated with psoriasis. However, HLA-Cw*0602 status was strongly associated with disease. STG expression was investigated in human tissues and found not to be restricted to taste buds, with signals also being detected in skin and tonsils.

Mapping of the major psoriasis-susceptibility locus (PSORS1) in a 70-Kb interval around the corneodesmosin gene (CDSN)

Numerous putative susceptibility loci have been described for psoriasis. Among the loci confirmed in the literature, PSORS1 (the major histocompatibility complex at 6p21.3) has the strongest effect. Recent studies have highlighted a 200-kb candidate region. However, this region has not been well delimited, mainly because of the strong linkage equilibrium among the associated alleles. To finely map PSORS1, we set up a study using 17 polymorphic markers in a 525-kb interval around the human leucocyte antigen C locus (HLA-C). The results uncovered five loci with alleles strongly associated with psoriasis (Sidak-corrected P [P(c)] values from 1.8 x 10(-7) to .003), all structured in a psoriasis-susceptibility haplotype (PSH). Subsequent analysis of extended haplotypes showed that the PSH was not only present on the traditional psoriasis-susceptibility extended haplotypes (HLA-Cw6-B57, HLA-Cw6-B37, and HLA-Cw6-B13) but also on a haplotype of Sardinian origin (HLA-Cw7-B58) found to be associated with psoriasis (Pc=.0009) because of an ancestral recombination with one of the susceptibility haplotypes carrying the HLA-Cw6 allele. Comparisons of the regions identical by descent among associated and nonassociated haplotypes highlighted a minimum region of 70 kb not recombinant with PSORS1, around the corneodesmosin (CDSN) gene.

An update on the genetics of psoriasis

Psoriasis is a complex inflammatory disorder whose pathogenesis is likely to require the contribution of several genes and environmental triggers. Despite the difficulties posed by the study of multifactorial conditions, significant progress has been achieved in relation to the molecular genetic basis of psoriasis. It has long been recognized that the major histocompatibility complex (MHC) region on chromosome 6p21 harbors the main determinant conferring psoriasis susceptibility. The identification of non-MHC susceptibility regions across the genome has been hindered by the likely occurrence of genetic heterogeneity. Nonetheless, evidence for the assignment of a number of non-MHC loci has been achieved through studies, including the collaborative analysis of large patient cohorts, and also through the observation of overlap between psoriasis and atopic dermatitis susceptibility regions.

[Heredity of psoriasis]

INTRODUCTION

Epidemiological studies of twins show that there is a genetic predisposition to psoriasis. Researches conducted so far show that psoriasis is a multifactorial polygenetic disease with reduced gene penetration. They also show that heredity is more significant than the "trigger" factor whose influence is limited to the exchange of phenotypes. Researches in USA, Canada and Europe identified four most important loci (psoriasis susceptibility--1-4). At least one is in MHC (major histocompatibility complex) due to the connection between psoriasis and alleles of human leukocyte antigen (HLA).

OBJECTIVE

Our study included 117 patients and examined the indicators of genetic predisposition to psoriasis: frequency of psoriasis among relatives of psoriatic probands; frequency of psoriasis among relatives (I and II degree) of psoriatic patients; age of probands and other relatives at the onset of illness.

MATERIAL AND METHODS

We have used a structured questionnaire for collection of data about existence of psoriasis in relatives of I and II degree of psoriatic probands and about the age of probands and relatives at the time of onset.

RESULTS AND DISCUSSION

Twenty six (21.85%) probands have at least one ill relative. The examined patients who have diseased relatives get ill much earlier than those who do not. Probands with two or more diseased relatives get ill much earlier than those who have just one diseased relative. Analysis of our sample shows a significant statistical difference regarding the onset of illness of diseased parents and their children. Children get ill earlier.

CONCLUSIONS

We have concluded that in our sample there is a hereditary component which is related to frequency and onset of psoriasis.

A psoriasis vulgaris protective gene maps close to the HLA-C locus on the EH18.2-extended haplotype

We determined the molecular haplotypes of the HLA-A, HLA-C and HLA-B loci and the MHC class I-B-related (MIB) microsatellite in 179 unrelated psoriatic patients (72 familial cases) and in 120 controls. The HLA-A*3002-Cw*0501-B*1801-MIB1 haplotype showed a strong negative association with psoriasis vulgaris (PV) and in particular with familial PV, revealing the presence of a PV-protective gene. Analysis of association and linkage disequilibrium of the single alleles and the various two-three-four-locus segments of this haplotype indicated the presence of a protective gene telomeric to the HLA-C locus. This finding was confirmed in 13 informative multiplex PV families, in which at least one parent carried the EH18.2 haplotype. In two families, an affected sibling presented HLA-A/C recombination on the EH18.2 haplotype. A study of 12 polymorphic microsatellites in all members of the informative families, 145 PV patients, 120 controls and 32 EH18.2 homozygous healthy individuals demonstrated that the protection conferred by the EH18.2 haplotype lies within a 170 kb interval between the C143 and C244 loci, most probably in a 60 kb segment between the C132 and C244 loci.

Genetic polymorphisms of the HCR gene and a genomic segment in close proximity to HLA-C are associated with patients with psoriasis in Taiwan

BACKGROUND

Although psoriasis vulgaris (PV) is strongly associated with HLA-Cw*0602, it has been proposed that the association of Cw*0602 is due to linkage disequilibrium and that other nearby genes are involved in PV susceptibility. The alpha-helix coiled-coil rod homologue (HCR) gene, located 110 kb telomeric to the HLA-C locus, is presumed to be one of the PV candidate genes. Recently, a 10-kb genomic segment, centromeric to HLA-C, defined by two new single nucleotide polymorphisms (SNPs) n.7*A and n.9*C, was found to have a stronger association with psoriasis than the HCR gene. Until now, no study of the association of the HCR gene, SNPs n.7, and n.9 has been conducted on Chinese patients with psoriasis.

OBJECTIVES

We aimed to determine whether the genetic polymorphisms of the HCR gene, SNPs n.7*A, and n.9*C were associated with an increased risk of psoriasis in Chinese patients.

METHODS

Using direct sequencing of the HCR gene and the genomic region containing SNPs n.7 and n.9, we investigated the HCR gene, SNPs n.7, and n.9 for disease association in 115 Chinese patients with psoriasis and 103 control subjects. The HCR SNPs were confirmed by denaturing high performance liquid chromatography. Genotyping for HLA-Cw*0602 was also carried out using sequence-based typing.

RESULTS

We observed a different allelic distribution between patient and control groups at nucleotide positions 386, 404, 1802 and 2406 of the HCR gene, and SNPs n.7, and n.9. The associations were much stronger in early onset PV patients (for HCR-386*T and HCR-404*T, odds ratio = 5.63, Pc < 0.0001). The HLA-Cw*0602 also displayed a similar association with PV (odds ratio = 5.4, Pc < 0.0001). Moreover, SNP n.7*A, SNP n.9*C, Cw*0602, HCR-386*T, HCR-404*T and HCR-1802*T were in linkage disequilibrium with each other. Haplotype-based association analysis showed SNP n.7*A-SNP n.9*C-Cw*0602-HCR-386*T-HCR-404*T-HCR-1802*T-HCR-2406*G as a major susceptibility haplotype in this Chinese population (for early onset patients, odds ratio = 5.15, Pc < 0.0001).

CONCLUSIONS

Our results indicate that the HCR gene, SNP n.7*A, and SNP n.9*C as well as Cw*0602 are major susceptibility markers for psoriasis in Chinese patients.

Homo-oligomerization of human corneodesmosin is mediated by its N-terminal glycine loop domain

Corneodesmosin (CDSN), a glycoprotein expressed during the late stages of epidermal differentiation, localizes in the extracellular core of upper desmosomes and of corneodesmosomes. Since it displays homophilic adhesive properties, CDSN is thought to reinforce cell-cell cohesion within the upper layers of the epidermis. CDSN presents two serine- and glycine-rich domains in its N- and C-terminus that may fold into highly flexible and adhesive secondary structures called glycine loops. We analyzed the importance of these domains in CDSN homophilic adhesion by producing full-length and truncated recombinant forms of the protein deleted of the N- and/or the C-terminal domain. The adhesive properties of the various proteins were then tested in vitro by overlay binding assays and surface plasmon resonance quantitative analysis. Experiments evidenced the homophilic adhesive properties of the N-terminal glycine loop domain, confirming its involvement in CDSN-CDSN interactions. They further indicated that most of the C-terminal domain is not necessary for the adhesive properties of the protein. The dissociation constant (K(D)) was calculated to be 1.3x10(-5) M. This interaction strength might allow dynamic regulation of the CDSN-CDSN association to occur in vivo. Moreover, molecular filtration analyses demonstrated for the first time that non-glycosylated CDSN is able to spontaneously form large homo-oligomers in vitro and that the N-terminal glycine loop domain is necessary for the formation of these macromolecular complexes.

A 4.2 kb Upstream Region of the Human Corneodesmosin Gene Directs Site-Specific Expression in Hair Follicles and Hyperkeratotic Epidermis of Transgenic Mice

Corneodesmosin (CDSN) is a desmosomal protein expressed in the epidermis during the late stages of differentiation and in the inner root sheath of hair follicles. The homophilic adhesive properties of the protein suggest that it reinforces keratinocyte cohesion in the upper layers of the epidermis (stratum granulosum and stratum corneum). In this study, we analyzed the expression of the CDSN gene in 16 human tissues. We confirmed the closely restricted expression pattern of CSDN. Indeed, apart from the skin, the mRNA was significantly detected only in the placenta and the thymus. As a step in elucidating the mechanisms of tissue-specific expression, transgenic mice bearing a 4.2 kb fragment of the human CSDN gene promoter linked to the LacZ gene were generated. The reporter-gene expression was detected in special areas of the inner root sheath of the hair follicles and the hair medulla but not in the epidermis. Induction of epidermis hyperproliferation however either by pharmacological agents or by wounding led to strong expression of the reporter gene in the keratinocytes of the stratum granulosum and the parakeratotic corneocytes of the stratum corneum. The data suggest that the genomic sequences and/or regulating factors responsible for the cell-specific expression of the human CDSN gene in the normal hair follicle as well as in the hyperproliferative epidermis are different from those necessary for expression in the normal epidermis.

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.

Corneodesmosin gene: no evidence for PSORS 1 gene in North-eastern Thai psoriasis patients

Psoriasis vulgaris, a common inflammatory skin disorder, is known to be associated with the HLA-Cw*06 allele. It has been recently suggested by microsatellite mapping that a real susceptible gene for psoriasis resides in the approximately 100-kb genomic region telomeric of the HLA-C gene. In this respect, the corneodesmosin (CDSN) gene 160-kb telomeric of HLA-C is a strong candidate because of its location and its functional role in corneocyte cohesion and desquamation. In fact, a significant association between CDSN polymorphism and psoriasis was recently recognized in Caucasian populations. However, this association has not been replicated in other studies, being still controversial. In this study, we investigated the genetic polymorphism of the CDSN gene in 139 psoriasis patients and 144 healthy controls in the North-eastern Thai population. By direct sequencing technique, a total of 28 polymorphic sites were found, consisting of 26 single nucleotide polymorphisms (SNPs) and two indels (insertion/deletion). Among them, six SNPs have not been previously reported. Through this analysis, as many as 28 different SNP/indel haplotypes within the CDSN gene were identified. Seven SNPs and one indel, namely 9C, 614 A, 722T, 971T, 1215G, 1243C, 1331G and 1606AAG (deletion), revealed significant deviation in the allelic frequencies of the patients from those of the healthy controls. However, none of them are likely to be responsible for controlling the susceptibility of psoriasis, but these associations can be explained by a linkage disequilibrium to a real pathogenic allele of a nearby gene. Further, the large variations between the CDSN SNP/indel haplotypes and the psoriatic major histocompatibility complex (MHC) haplotypes also make it unlikely that CDSN is a major psoriasis-susceptible gene.

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.

SPR1 gene near HLA-C is unlikely to be a psoriasis susceptibility gene

Although genetics analyses have identified the HLA-Cw6 allele to be the major risk allele for psoriasis vulgaris (PV) in many racial groups, it has been proposed that other putative genes near the HLA-C locus are involved in PV susceptibility and that the association of Cw6 is a result of linkage disequilibrium. The SPR1 gene, a predicted gene located 128 kb telomeric to the HLA-C locus, is considered to be one potential candidate gene of PV. Until now, no association study of the SPR1 gene has been conducted on psoriasis patients. We investigated the SPR1 gene for disease association by direct sequencing of the SPR1 gene in 116 Chinese patients with PV and 116 normal subjects. Genotyping for HLA-Cw6 was also carried out using polymerase chain reaction/restriction fragment length polymorphism. Significant increase of the HLA-Cw6 allele was found in psoriasis patients (32.8% vs. 13.8%, P = 0.001). We found that the SPR1 gene is a highly polymorphic gene containing 13 single nucleotide polymorphisms (SNPs), two of which have not been previously reported, and four SNPs cause amino acid change. No significantly different allelic distribution of 13 SPR1 SNPs could be found between the patients with PV and controls after correction for multiple testing. If the frequencies of SPR1 SNPs were compared between the early onset psoriatics and control subjects, early onset patients were more likely to have G allele at position 988 (60% vs. 35.3%, P = 0.001). However, the significance disappeared upon stratification for the Cw6 status. Haplotype-based association analysis showed two susceptibility haplotypes (types 8 and 19) in early onset psoriasis patients. Nonetheless, the significance also disappeared after stratification of the Cw6 status. Our results suggest that HLA-Cw6 remains the major risk allele in Chinese psoriatics, and that the SPR1 gene might not play an important role in the causation of PV.

Genetic basis of psoriasis vulgaris and its pharmacogenetic potential

Psoriasis vulgaris is one of the most prevalent T cell-mediated inflammatory diseases in humans. It is multifactorial in origin and shows polygenic inheritance. Systemic immunosuppressive therapies play an important role in management of severe disease cases but are associated with variable response and toxicity. Within the last decade there have been significant advances in our understanding of the genetic basis of this complex disease and polymorphic candidate genes have been proposed. Susceptibility gene characterization together with an explosion in knowledge of its primary immune basis will further define disease pathways involved in psoriasis pathogenesis. This holds the promise of rational design of new therapeutic agents and pharmacogenetic testing to predict responders from non-responders and those at risk of toxicity.

Association of TAP and HLA-DM genes with psoriasis in Koreans

To investigate the possible involvement of antigen-processing genes in the pathogenesis of psoriasis, we analyzed the polymorphisms of the TAP1, TAP2, LMP2, LMP7, DMA, and DMB genes in 98 Korean psoriasis patients and compared them with 184 healthy controls. The frequencies of TAP2*B/B [relative risk (RR)=3.6, p<0.0002] and TAP2*B (RR=1.7, p<0.05) were significantly increased, but TAP1*B (RR=0.3, p<0.002) and TAP2*A (RR=0.6, p<0.03) were significantly decreased, in the patients compared to the controls. We performed further analysis on the TAP1 and TAP2 single nucleotide polymorphisms and found significant differences between the patients and controls in TAP1 single nucleotide polymorphism at position 637 and in TAP2 at 665. In HLA-DM, DMA*0102 (RR=2.5, p<0.0003) was significantly increased, but DMA*0101/0101 (RR=0.4, p<0.0004) and DMB*0103/0103 (RR= 0.3, p<0.005) were significantly decreased in the patients compared to the controls. The TAP and HLA-DM alleles were also analyzed according to the age of onset of psoriasis in the patients (types I and II). It was found that the HLA-DM alleles showed a greater association in type I than type II patients. An analysis of the linkage disequilibrium and stratification also indicated that the alleles of TAP and HLA-DM might be independently associated with HLA-Cw*0602 in psoriasis patients. The stratification analysis between DMA*0101/0101 and DMB*0103/0103 showed that a certain factor, controlled by a gene located between DMA and DMB, might provide strong protection against psoriasis, independently of Cw*0602, in our Korean population. In conclusion, our data suggest that the TAP and HLA-DM alleles could lead to genetic susceptibility toward psoriasis in Koreans.

Genetic analysis of PSORS1 distinguishes guttate psoriasis and palmoplantar pustulosis

The PSORS1 locus in the major histocompatibility complex region is the major genetic determinant for psoriasis vulgaris. Within the PSORS1 region reside at least three potential candidate genes for psoriasis susceptibility. Specific allelic variants of the genes HLA-Cw*6, HCR*WWCC, and CDSN*5 are strongly associated with psoriasis vulgaris and are in strong linkage disequilibrium with each other. We have genotyped the three psoriasis vulgaris susceptibility alleles of the PSORS1 locus in two clinical variants of psoriasis (guttate psoriasis and palmoplantar pustulosis) to study whether PSORS1 is also involved in the pathogenesis of these variants. We also asked whether these two clinical subgroups could help us to distinguish the causative gene within the high-risk PSORS1 haplotype. The association of guttate psoriasis with the three PSORS1 susceptibility alleles was similar and even stronger than seen with psoriasis vulgaris. Palmoplantar pustulosis, however, did not show association with any of the three candidate genes at this locus. Finally, no correlation with the age of onset for disease was observed. Our results show conclusively that psoriasis vulgaris and guttate psoriasis have a similar genetic basis for their association to PSORS1, whereas palmoplantar pustulosis appears to be a distinct disorder.

Polymorphisms of tumor necrosis factor (TNF) alpha and beta genes in Korean patients with psoriasis

To evaluate the association of TNF-alpha (TNFA) and TNF-beta (TNFB) polymorphisms with psoriasis in the Korean population, we investigated TNF-alpha -238 and -308 promoter region and TNF-beta NcoI polymorphism using PCR-RFLP in 103 Korean psoriasis patients and 125 normal controls. The carriage and allele frequencies of TNFB*2 were significantly increased in patients with psoriasis compared with normal controls. However, TNFB*1/1 homozygote and TNFB*1 allele were significantly decreased in the patients. There were no significant differences in the polymorphism of TNF-alpha promoter -238 and -308 between the patients and controls. We also analyzed the frequencies of TNFB alleles according to the clinical characteristics of the psoriasis patients, but no significant differences were found. However, female patients with early-onset psoriasis showed an association with the TNFB*2 allele. In conclusion, our results suggest that polymorphisms of the TNFB gene may contribute to a predisposition to psoriasis in the Korean population.

A study of candidate genes for psoriasis near HLA-C in Chinese patients with psoriasis

BACKGROUND

Genetic analyses have identified the HLA-Cw6 allele as the major risk allele for psoriasis in many racial groups. However, by serological typing, HLA-Cw6 is not considered a risk factor in Chinese psoriatics. There are several susceptibility genes for psoriasis residing in chromosome 6p near the HLA-C locus, including the corneodesmosin (CDSN) gene, the octamer transcription factor-3 (POU5F1) gene, the major histocompatibility complex class I chain-related gene A (MICA), and the gene for tumour necrosis factor (TNF)-alpha. However, the information about their role in psoriasis in Chinese patients is limited.

OBJECTIVES

We aimed to determine whether Cw6 and the genetic polymorphism of the CDSN gene, POU5F1 gene, MICA gene and the gene for TNF-alpha promoter region were associated with an increased risk of psoriasis in Chinese patients.

METHODS

We conducted a case-control association study in 105 Chinese patients with psoriasis vulgaris and 160 control subjects of similar ages. Genotypes of Cw6, the CDSN gene, the POU5F1 gene, and the gene for the TNF-alpha promoter region were determined by polymerase chain reaction (PCR) followed by restriction enzyme digestion. Genotyping of MICA was determined by PCR combined with fluorescent-based automated fragment detection technology. Results The allele frequencies showed no differences between patients and controls for the POU5F1 gene, MICA gene and the gene for TNF-alpha promoter region. The frequency of the HLA-Cw6 allele in the psoriasis group was significantly higher than that in the control group (18.6% vs. 6.56%, P < 0.00005). For the CDSN gene, patients were more likely to have C allele at position +619 (P = 0.006) and C allele at position +1243 (P = 0.007), but the significance disappeared after correction for multiple testing (Pc > 0.05).

CONCLUSIONS

HLA-Cw6 remains the most significant susceptibility gene in Chinese patients with psoriasis. However, the role of the CDSN gene in the pathogenesis of psoriasis deserves further scrutiny.

Psoriasis is associated with a SNP haplotype of the corneodesmosin gene (CDSN)

A psoriasis susceptibility locus has been mapped to the HLA region in the proximity of the HLA-C locus. This critical region also contains the CDSN gene coding for the corneodesmosin protein. In a case-control association study of psoriasis in the Sardinian population, we analyzed the allele distribution of eight intragenic SNPs (positions 619, 767, 1215, 1118, 1236, 1243, 1331, 1593) of the CDSN gene and the six haplotypes that are coded by these SNPs. Our study showed that these CDSN haplotypes are very stable and well-conserved in the Sardinian population. The CDSN2 haplotype was found to be associated with susceptibility to psoriasis. The association did not depend upon any one of the intragenic SNPs taken separately. At the HLA-C locus, the Cw6 and Cw7 alleles were dragged along by linkage disequilibrium with the CDSN2 haplotype and only revealed a trend towards association with the disease. Therefore, the intragenic SNPs of the CDSN gene and the HLA-Cw6 and Cw7 alleles are not directly involved in susceptibility to psoriasis. However, the strong association of the CDSN2 haplotype suggests a possible role for the CDSN gene and its chromosome region in susceptibility to psoriasis.

Family-based analysis using a dense single-nucleotide polymorphism-based map defines genetic variation at PSORS1, the major psoriasis-susceptibility locus

Psoriasis is a common skin disorder of multifactorial origin. Genomewide scans for disease susceptibility have repeatedly demonstrated the existence of a major locus, PSORS1 (psoriasis susceptibility 1), contained within the major histocompatibility complex (MHC), on chromosome 6p21. Subsequent refinement studies have highlighted linkage disequilibrium (LD) with psoriasis, along a 150-kb segment that includes at least three candidate genes (encoding human leukocyte antigen-C [HLA-C], alpha-helix-coiled-coil-rod homologue, and corneodesmosin), each of which has been shown to harbor disease-associated alleles. However, the boundaries of the minimal PSORS1 region remain poorly defined. Moreover, interpretations of allelic association with psoriasis are compounded by limited insight of LD conservation within MHC class I interval. To address these issues, we have pursued a high-resolution genetic characterization of the PSORS1 locus. We resequenced genomic segments along a 220-kb region at chromosome 6p21 and identified a total of 119 high-frequency SNPs. Using 59 SNPs (18 coding and 41 noncoding SNPs) whose position was representative of the overall marker distribution, we genotyped a data set of 171 independently ascertained parent-affected offspring trios. Family-based association analysis of this cohort highlighted two SNPs (n.7 and n.9) respectively lying 7 and 4 kb proximal to HLA-C. These markers generated highly significant evidence of disease association (P<10-9), several orders of magnitude greater than the observed significance displayed by any other SNP that has previously been associated with disease susceptibility. This observation was replicated in a Gujarati Indian case/control data set. Haplotype-based analysis detected overtransmission of a cluster of chromosomes, which probably originated by ancestral mutation of a common disease-bearing haplotype. The only markers exclusive to the overtransmitted chromosomes are SNPs n.7 and n.9, which define a 10-kb PSORS1 core risk haplotype. These data demonstrate the power of SNP haplotype-based association analyses and provide high-resolution dissection of genetic variation across the PSORS1 interval, the major susceptibility locus for psoriasis.

Corneodesmosin DNA polymorphisms in MHC haplotypes and Japanese patients with psoriasis

In order to examine the relationship between corneodesmosin (CDSN) and psoriasis we have determined the presence of CDSN polymorphisms by DNA sequencing in (a) nine B-LCL cell lines of major histocompatibility complex ancestral haplotypes known to be associated with psoriasis vulgaris including 13.1AH, 46.1AH, 46.2 and 57.1AH, and in (b) a group of 267 unrelated individuals comprising Japanese psoriasis patients (n = 101) and Japanese subjects without the disease (n = 166). Three novel CDSN gene sequences were identified. In addition, we have classified the 18 alleles into seven main groups based on phylogeny of non-synonymous substitutions. However, we have found no statistically significant differences between the patients and the unaffected individuals in any of these groups. These findings indicate that CDSN is not a major psoriasis susceptibility gene.

Searching for the major histocompatibility complex psoriasis susceptibility gene

Psoriasis, a common skin disorder, is widely regarded to be multifactorial in origin including gene-gene and gene-environment interactions. Genetic and allelic heterogeneity, multifactorial inheritance, and low penetrance of susceptibility alleles substantially complicate both study design and interpretation of results. Notwithstanding these difficulties, genome-wide scans for psoriasis susceptibility have generated robust evidence for a major locus lying within the major histocompatibility complex (PSORS1, Psoriasis Susceptibility 1), on the short arm of chromosome 6. Subsequent studies have sought to refine the PSORS1 boundaries by means of linkage disequilibrium fine mapping. Studies of positional candidate genes have also been undertaken, focusing on HLA-C, corneodesmosin, and alpha-helix coiled-coil rod homolog genes. Methodologic approaches, results, and interpretations of these studies are discussed, as well as future research objectives. In particular, we emphasize the importance of characterizing PSORS1 linkage disequilibrium patterns and developing functional assays for disease-associated alleles.

Corneodesmosin, a component of epidermal corneocyte desmosomes, displays homophilic adhesive properties

Corneodesmosomes, the modified desmosomes of the uppermost layers of the epidermis, play an important role in corneocyte cohesion. Corneodesmosin is a secreted glycoprotein located in the corneodesmosomal core and covalently linked to the cornified envelope of corneocytes. Its glycine- and serine-rich NH(2)-terminal domain may fold to give structural motifs similar to the glycine loops described in epidermal cytokeratins and loricrin and proposed to display adhesive properties. A chimeric protein comprising human corneodesmosin linked to the transmembrane and cytoplasmic domains of mouse E-cadherin was expressed in mouse fibroblasts to test the ability of corneodesmosin to promote cell-cell adhesion. Classic aggregation assays indicated that corneodesmosin mediates homophilic cell aggregation. Moreover, Ca(2+) depletion showed a moderate effect on aggregation. To assess the involvement of the glycine loop domain in adhesion, full-length corneodesmosin, corneodesmosin lacking this domain, or this domain alone were expressed as glutathione S-transferase fusion proteins and tested for protein-protein interactions by overlay binding assays. The results confirmed that corneodesmosin presents homophilic interactions and indicated that its NH(2)-terminal glycine loop domain is sufficient but not strictly necessary to promote binding. Altogether, these results provide the first experimental evidence for the adhesive properties of corneodesmosin and for the involvement of its glycine loop domain in adhesion.

Psoriatic arthritis: clinical aspects, genetics, and the role of T cells

In the last 2 years there has been considerable progress in investigating the genetic and immunologic background of psoriasis and psoriatic arthritis. This review focuses on genetics and the role of T-cells in the immunopathogenesis of the disease, with particular reference to psoriatic arthritis.

Corneodesmosin expression in psoriasis vulgaris differs from normal skin and other inflammatory skin disorders

SUMMARY

Corneodesmosin (Cdsn) is a late differentiation epidermal glycoprotein putatively involved in keratinocyte adhesion. The Cdsn gene lies within the susceptibility region on chromosome 6p21.3 (PSORS1) for psoriasis, a common chronic disfiguring skin disease. A particular allelic variant of Cdsn has a strong association with psoriasis. Therefore, genetically and biologically, Cdsn is a possible candidate gene for psoriasis susceptibility. To investigate a potential role for Cdsn in psoriasis pathogenesis, protein expression studies were performed by quantitative immunohistochemistry on normal skin, psoriatic skin (lesional and nonlesional), and other skin disorders using monoclonal antibodies (G36-19 and F28-27). In normal and nonlesional skin, Cdsn was expressed in stratum corneum and one or two layers of superficial stratum granulosum. In lesional psoriasis, there was a significant increase in Cdsn expression, which was observed in multiple layers of stratum spinosum and in stratum corneum. The expression pattern varied from granular, cytoplasmic immunoreactivity to cell surface labeling with weakly immunoreactive cytoplasm. In chronic atopic dermatitis, lichen planus, mycosis fungoides, and pityriasis rubra pilaris, Cdsn immunoreactivity was confined to stratum corneum and upper stratum granulosum with no stratum spinosum immunoreactivity. Immunoelectron microscopy of normal and lesional psoriatic skin demonstrated Cdsn release concomitant with involucrin incorporation into cell envelopes and completed before mature envelope formation. Extracellular release of Cdsn occurred at a lower level of the epidermis in psoriasis than normal skin. These protein expression studies provide evidence of altered Cdsn expression in psoriasis consistent with a role of Cdsn in disease pathogenesis. Further functional and genetic studies of Cdsn are justified to determine its role as a potential psoriasis-susceptibility factor.

Refined characterization of corneodesmosin proteolysis during terminal differentiation of human epidermis and its relationship to desquamation

Corneodesmosin is a putative adhesion glycoprotein located in the extracellular part of the desmosomes in the upper layers of the epidermis. Synthesized by granular keratinocytes as a 52-56-kDa protein, corneodesmosin is progressively proteolysed during corneocyte maturation. This processing is a prerequisite for desquamation. Two glycine- and serine-rich domains of the protein might take on the conformation of adhesive secondary structures similar to glycine loops. Corneodesmosin proteolysis was further characterized. Deglycosylation experiments and reactivity with lectins demonstrated that the corneodesmosin carbohydrate moiety does not prevent the proteolysis. Immunoblotting, immunohistochemistry, and immunoelectron microscopy experiments using affinity-purified anti-peptide antibodies raised to four of the five structural domains of corneodesmosin and a monoclonal antibody against its fifth central domain showed that the first step in corneodesmosin processing is the cleavage of its extremities and probably occurs before its incorporation into desmosomes. Then the glycine loop-related domains are cleaved, first the N-terminal and then part of the C-terminal domain. At the epidermis surface, the multistep proteolytic cleavage leaves intact only the central domain, which was detected on exfoliated corneocytes and probably lacks adhesive properties. Importantly, corneodesmosin was demonstrated to be a preferred substrate of two serine proteases involved in desquamation, the stratum corneum tryptic and chymotryptic enzymes.

Psoriasis vulgaris--a sterile antibacterial skin reaction mediated by cross-reactive T cells? An immunological view of the pathophysiology of psoriasis

The understanding of the pathogenesis of psoriasis vulgaris has advanced significantly since the therapeutic efficacy of immunosuppressive drugs has drawn attention to the role of immune mechanisms in psoriasis manifestation. Today, the results of many experimental studies provide evidence that psoriasis is largely a T-cell mediated disorder. It may result from antigen-specific activation of T cells in the skin of genetically predisposed individuals. These T cells apparently have a particular functional differentiation and promote the psoriatic skin changes by secreting a certain set of cytokines. Based on the fact that streptococcal throat infections are a trigger of guttate psoriasis, the putative psoriatic antigens are assumed to be in keratinocyte proteins that share structural homologies with streptococcal proteins and thus induce cross-reactive responses of antibacterial T cells against skin components. Together with the particular phenotype of psoriatic skin lesions these findings suggest that psoriasis represents a sterile antibacterial tissue reaction, which is mediated by streptococci-specific T cells that cross-react against epidermal autoantigens.

The HCR Gene on 6p21 is Unlikely to be a Psoriasis Susceptibility Gene

The PSORS1 locus in the human major histocompatibility complex on 6p21 has been consistently associated with psoriasis in populations of diverse ethnicity. The HLA-C allele Cw*0602, located therein, has been found in up to 67% of psoriasis patients but is no longer considered a candidate gene in itself. The alpha-helix coiled-coil rod homolog gene (HCR, previously Pg8) is located 110 kb from the HLA-C gene, positioned between the CDSN and SC1 genes, within a region thought to harbor a psoriasis gene (PSORS1). We investigated the HCR gene for disease association by direct sequencing of nine polymerase chain reaction products amplified from a series of Swedish psoriasis patients and controls. We found that HCR is a very polymorphic gene with 25 polymorphisms in the open reading frame alone, of which 10 demonstrated disease association; however, the relationship between HCR polymorphisms and HLA-Cw*0602 indicates that HCR cannot truly be considered a likely candidate gene. We investigated Cw*0602 association while stratifying for HCR single nucleotide polymorphisms. We also investigated HCR single nucleotide polymorphism association with the disease while stratifying for the presence of Cw*0602. We found that whichever single nucleotide polymorphism that was stratified for, there was still a strongly significant Cw*0602 association with psoriasis; however, when we stratified for Cw*0602 presence, only one silent polymorphism showed significant association. In a recent similar study this polymorphism was actually found to be decreased in psoriasis individuals. Thus we conclude that HCR polymorphisms display association with psoriasis due to linkage disequilibrium with Cw*0602 and is, therefore, unlikely to be directly involved in the development of psoriasis.

Comparative association analysis reveals that corneodesmosin is more closely associated with psoriasis than HLA-Cw*0602-B*5701 in German families

HLA antigens are associated with psoriasis vulgaris across populations with different ethnic background. We have previously shown that in Caucasians this association is primarily based on the class I alleles of the extended HLA haplotype 57.1 (EH57.1/I), HLA-Cw6-HLA-B57. However, it remained unclear whether HLA-Cw6 itself or a closely linked locus predisposes to the disease. An interesting candidate for this presumed locus is corneodesmosin, which is exclusively synthesized in keratinocytes. The corneodesmosin gene locus (CDSN) is only 160 kb telomeric to HLA-C and tightly associated with psoriasis. In order to find out whether EH57.1/I or a corneodesmosin variant are the susceptibility determinants on 6p, HLA class I alleles and single-nucleotide polymorphisms (SNPs) of corneodesmosin were investigated at the sequence level and analyzed by comparative association tests. Transmission disequilibrium tests (TDT) were performed in 52 nuclear families, of which 36 were fully informative for a joint comparison of HLA and CDSN with regard to association to psoriasis. The extended TDT according to Wilson was employed to test for locus interaction. Using the HLA haplotype EH57.1/I and the CDSN haplotype formed by three intragenic variant sites at nt=619 (T), 1236 (T), and 1243 (C), we obtained the best resolution of parental transmission to index cases in the trio families. On direct comparison of the contributions of the HLA and the CDSN haplotypes, there was a markedly stronger association of the corneodesmosin TTC haplotype, which is not apparent in single locus analysis. We show furthermore that there is no higher order interaction between psoriasis, HLA, and CDSN. This lack of three-locus interaction is suggestive of two independent genetic contributions to psoriasis within the major histocompatibility complex (MHC).

Psoriasis: the future

The aetiology of psoriasis is still unclear but our knowledge of the psoriatic process has grown substantially over the last two decades. The future will undoubtedly bring advances in our understanding of the pathogenesis of psoriasis and, as a consequence, new therapies. Defining the molecular genetics of psoriasis will enhance our understanding of the disease process and hopefully facilitate the development of a representative animal model. This in itself will be a key step in the development and testing of new therapies. Precise identification of the immunological events involved in psoriasis will allow specific T-cell- and cytokine-targeted, and perhaps less toxic. immunotherapies. Anti-angiogenic agents that are in development for use in oncology may also be effective in psoriasis. The adaptation of current topical therapies such as retinoids and vitamin D analogues to produce more effective and better-tolerated formulations will also play a significant role in our future first-line management of patients. The increased recognition and better management of environmental trigger factors such as psychological distress will become an important factor in future psoriasis care. The development of physical therapies including photodynamic therapy and excimer lasers has the potential to expand the remit of psoriasis therapy. There is little doubt that the future for our patients with psoriasis is bright. However, this will only be achievable by a concerted research effort to understand all facets of this enigmatic disease ranging from the molecular to the environmental.