Genetic polymorphisms in the cell growth regulated gene, SC1 telomeric of the HLA-C gene and lack of association of psoriasis vulgaris

Search for new molecular targets for anticytokine therapy of patients, suffering from the immune dependent skin disease — psoriasis

The authors describe the results of a study aimed at searching for new molecular targets for anticytokine therapy of patients with psoriasis. The authors examined 26 patients with psoriasis who were treated with such immune biologic substances as infliximab, ustekinumab, adalimumab and 10 healthy volunteers. They performed a quality and quantity analysis of the spectrum of protein molecules of cytokines (L-4, IL-6, IL-17, TNF-α and IL-20, IL-22, IL-31, IL-12, IL-11, IL-18) аs well as VEGF and ICAM-1 molecules in patients receiving the therapy with immune biologic substances before and after treatment using the methodology of the immune enzyme analysis and xMAP multiplex technology. The authors studied the correlation between the level of cytokine expression, on the one hand, and the occurrence and limitation of the disease, on the other hand. The obtained data are sufficient to conclude that the spectrum of molecules of IL6, IL20, IL22 anti-inflammatory cytokines аs well as VEGF and ICAM-1 molecules, for which pathogenic importance in case of psoriasis was revealed as a result of the study , may serve as a potential (new, additional) molecular target for anticytokine therapy of patients suffering with such an immune-dependent skin disease as psoriasis.

A whole-genome association study of major determinants for allopurinol-related Stevens-Johnson syndrome and toxic epidermal necrolysis in Japanese patients

Stevens-Johnson syndrome and toxic epidermal necrolysis (SJS/TEN) are severe, cutaneous adverse drug reactions that are rare but life threatening. Genetic biomarkers for allopurinol-related SJS/TEN in Japanese were examined in a genome-wide association study in which Japanese patients (n=14) were compared with ethnically matched healthy controls (n=991). Associations between 890 321 single nucleotide polymorphisms and allopurinol-related SJS/TEN were analyzed by the Fisher's exact test (dominant genotype mode). A total of 21 polymorphisms on chromosome 6 were significantly associated with allopurinol-related SJS/TEN. The strongest association was found at rs2734583 in BAT1, rs3094011 in HCP5 and GA005234 in MICC (P=2.44 × 10(-8); odds ratio=66.8; 95% confidence interval, 19.8-225.0). rs9263726 in PSORS1C1, also significantly associated with allopurinol-related SJS/TEN, is in absolute linkage disequilibrium with human leukocyte antigen-B*5801, which is in strong association with allopurinol-induced SJS/TEN. The ease of typing rs9263726 makes it a useful biomarker for allopurinol-related SJS/TEN in Japanese.

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.

High-throughput DNA typing of HLA-A, -B, -C, and -DRB1 loci by a PCR-SSOP-Luminex method in the Japanese population

We have developed a new high-throughput, high-resolution genotyping method for the detection of alleles at the human leukocyte antigen (HLA)-A, -B, -C, and -DRB1 loci by combining polymerase chain reaction (PCR) and sequence-specific oligonucleotide probes (SSOPs) protocols with the Luminex 100 xMAP flow cytometry dual-laser system to quantitate fluorescently labeled oligonucleotides attached to color-coded microbeads. In order to detect the HLA alleles with a frequency of more than 0.1% in the Japanese population, we created 48 oligonucleotide probes for the HLA-A locus, 61 for HLA-B, 34 for HLA-C, and 51 for HLA-DRB1. The accuracy of the PCR-SSOP-Luminex method was determined by comparing it to the nucleotide sequencing method after subcloning into the plasmid vector using 150 multinational control samples obtained from the International HLA DNA Exchange University of California Los Angeles. In addition, we performed the PCR-SSOP-Luminex method for HLA allele typing on DNA samples collected from 1,018 Japanese volunteers. Overall, the genotyping method exhibited an accuracy of 85.91% for HLA-A, 85.03% for HLA-B, 97.32% for HLA-C, and 90.67% for HLA-DRB1 using 150 control samples, and 100% for HLA-A and -C, 99.90% for HLA-B, and 99.95% for HLA-DRB1 in 1,018 Japanese samples. The PCR-SSOP-Luminex method provides a simple, accurate, and rapid approach toward multiplex genotyping of HLA alleles to the four-digit or higher level of resolution in the Japanese population. It takes only approximately 5 h from DNA extraction to the definition of HLA four-digit alleles at the HLA-A, HLA-B, HLA-C, and HLA-DRB1 loci for 96 samples when handled by a single typist.

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.

A microarray study of MPP+-treated PC12 Cells: Mechanisms of toxicity (MOT) analysis using bioinformatics tools

Background

This paper describes a microarray study including data quality control, data analysis and the analysis of the mechanism of toxicity (MOT) induced by 1-methyl-4-phenylpyridinium (MPP⁺) in a rat adrenal pheochromocytoma cell line (PC12 cells) using bioinformatics tools. MPP⁺ depletes dopamine content and elicits cell death in PC12 cells. However, the mechanism of MPP⁺-induced neurotoxicity is still unclear.

Results

In this study, Agilent rat oligo 22K microarrays were used to examine alterations in gene expression of PC12 cells after 500 μM MPP⁺ treatment. Relative gene expression of control and treated cells represented by spot intensities on the array chips was analyzed using bioinformatics tools. Raw data from each array were input into the NCTR ArrayTrack database, and normalized using a Lowess normalization method. Data quality was monitored in ArrayTrack. The means of the averaged log ratio of the paired samples were used to identify the fold changes of gene expression in PC12 cells after MPP⁺ treatment. Our data showed that 106 genes and ESTs (Expressed Sequence Tags) were changed 2-fold and above with MPP⁺ treatment; among these, 75 genes had gene symbols and 59 genes had known functions according to the Agilent gene Refguide and ArrayTrack-linked gene library. The mechanism of MPP⁺-induced toxicity in PC12 cells was analyzed based on their genes functions, biological process, pathways and previous published literatures.

Conclusion

Multiple pathways were suggested to be involved in the mechanism of MPP⁺-induced toxicity, including oxidative stress, DNA and protein damage, cell cycling arrest, and apoptosis.

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.

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.

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.

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.

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.

Novel transcription factors in human CD34 antigen-positive hematopoietic cells

Transcription factors (TFs) and the regulatory proteins that control them play key roles in hematopoiesis, controlling basic processes of cell growth and differentiation; disruption of these processes may lead to leukemogenesis. Here we attempt to identify functionally novel and partially characterized TFs/regulatory proteins that are expressed in undifferentiated hematopoietic tissue. We surveyed our database of 15 970 genes/expressed sequence tags (ESTs) representing the normal human CD34(+) cells transcriptosome (http://westsun.hema.uic.edu/cd34.html), using the UniGene annotation text descriptor, to identify genes with motifs consistent with transcriptional regulators; 285 genes were identified. We also extracted the human homologues of the TFs reported in the murine stem cell database (SCdb; http://stemcell.princeton.edu/), selecting an additional 45 genes/ESTs. An exhaustive literature search of each of these 330 unique genes was performed to determine if any had been previously reported and to obtain additional characterizing information. Of the resulting gene list, 106 were considered to be potential TFs. Overall, the transcriptional regulator dataset consists of 165 novel or poorly characterized genes, including 25 that appeared to be TFs. Among these novel and poorly characterized genes are a cell growth regulatory with ring finger domain protein (CGR19, Hs.59106), an RB-associated CRAB repressor (RBAK, Hs.7222), a death-associated transcription factor 1 (DATF1, Hs.155313), and a p38-interacting protein (P38IP, Hs. 171185). The identification of these novel and partially characterized potential transcriptional regulators adds a wealth of information to understanding the molecular aspects of hematopoiesis and hematopoietic disorders.

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.

Genetic aspects of psoriasis

Epidemiological studies indicate that genes play an important role in the pathogenesis of psoriasis. Multiple genes are likely to be involved, interacting not only with each other but also with the environment to cause disease expression. Molecular genetic studies indicate that there are multiple susceptibility loci present throughout the human genome. It is clear that a gene or genes of major impact on psoriasis is present on chromosome 6 within the major histocompatibility complex (MHC). Linkage disequilibrium studies indicate this gene to reside within a 300 kb interval centred around the centromeric end of class I MHC. Known candidate genes in this region are HLA-C, corneodesmosin and HCR, although novel genes, as yet unknown, may also exist. There is accumulating evidence that HLA-C is not itself the causative gene but rather a marker for it. Identification of the genes involved in psoriasis susceptibility will represent a step forward in our understanding of the disease and our future ability to help patients with psoriasis.

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).