Genetic associations of psoriasis in a Pakistani population.

BACKGROUND: Genetic predisposition to psoriasis, an inflammatory skin disease affecting 0·2-4% of the world population, is well established. Thus far, 41 psoriasis susceptibility loci reach genome-wide significance (P ≤ 5 × 10(-8) ). Identification of genetic susceptibility loci in diverse populations will help understand the underlying biology of psoriasis susceptibility. OBJECTIVES: The primary objective of this study was to examine psoriasis susceptibility associations previously reported in Chinese and caucasian populations in a Pakistani cohort. METHODS: Blood samples and phenotype data were collected from psoriasis cases and controls in Islamabad, Pakistan. DNA was isolated and genotypes of selected susceptibility markers were determined. The data were analysed using χ(2) tests or logistic regression for psoriasis association. RESULTS: HLA-Cw6 showed the strongest association [odds ratio (OR) 2·43, P = 2·3 × 10(-12) ]. HLA-Cw1 showed marginally significant association (OR 1·66, P = 0·049), suggesting that the HLA-Cw1-B46 risk haplotype may be present in the Pakistani population. Three other loci (IL4/IL13, NOS2, TRAF3IP2) showed nominally significant association (P < 0·05). CONCLUSIONS: HLA-Cw6 is strongly associated with psoriasis susceptibility in the Pakistani population, as has been found in every other population studied. In addition, HLA-Cw1 showed marginal association, reflecting the relative geographical proximity and thus likely genetic relatedness to other populations in which the HLA-Cw1-B46 haplotype is known to be associated. A larger cohort and a denser marker set will be required for further analysis of psoriasis associations in the South Asian population.

Comparison of MHC class I risk haplotypes in Thai and Caucasian psoriatics shows locus heterogeneity at PSORS1.

Earlier studies have shown that psoriasis in Japan and Thailand is associated with two different major histocompatibility complex (MHC) haplotypes - those bearing HLA-Cw6 and those bearing HLA-Cw1 and HLA-B46. In an independent case-control sample from Thailand, we confirmed the association of psoriasis with both haplotypes. No association was seen in Thai HLA-Cw1 haplotypes lacking HLA-B46, nor was HLA-Cw1 associated with psoriasis in a large Caucasian sample. To assess whether these risk haplotypes share a common origin, we sequenced genomic DNA from a Thai HLA-Cw1-B46 homozygote across the ∼300 kb MHC risk interval, and compared it with sequence of a HLA-Cw6-B57 risk haplotype. Three small regions of homology were found, but these regions share equivalent sequence similarity with one or more clearly non-risk haplotypes, and they contain no polymorphism alleles unique to all risk haplotypes. Differences in psoriasis phenotype were also observed, including lower risk of disease, greater nail involvement, and later age at onset in HLA-Cw1-B46 carriers compared with HLA-Cw6 carriers. These findings suggest locus heterogeneity at PSORS1 (psoriasis susceptibility 1), the major psoriasis susceptibility locus in the MHC, with HLA-Cw6 imparting risk in both Caucasians and Asians, and an allele other than HLA-Cw1 on the HLA-Cw1-B46 haplotype acting as an additional risk variant in East Asians.

The psoriasis-protective TYK2 I684S variant impairs IL-12 stimulated pSTAT4 response in skin-homing CD4+ and CD8+ memory T-cells.

Tyrosine kinase 2 (TYK2) belongs to the Janus kinase (JAK) family of tyrosine kinases, which transmit signals from activated cytokine receptors. GWAS have consistently implicated TYK2 in psoriasis susceptibility. We performed an in-depth association analysis of TYK2 using GWAS and resequencing data. Strong genetic association of three nonsynonymous variants in the exonic regions of the TYK2 gene (rs34536443, rs12720356, and rs2304256) were found. rs12720356 encoding I684S is predicted to be deleterious based on its location in the pseudokinase domain. We analyzed PBMCs from 29 individuals representing the haplotypes containing each of the significantly associated signals. STAT4 phosphorylation was evaluated by phospho-flow cytometry after CD3/CD28 activation of cells followed by IL-12 stimulation. Individuals carrying the protective I684S variant manifested significantly reduced p-STAT4 levels in CD4 + CD25 + CD45RO+ (mean Stimulation Index (S.I.) 48.08, n = 10) and CD8 + CD25 + CD45RO + cells (S.I. 55.71, n = 10), compared to controls homozygous for the ancestral haplotype (S.I. 68.19, n = 10 (p = 0.002) and 76.76 n = 10 (p = 0.0008) respectively). Reduced p-STAT4 levels were also observed in skin-homing, cutaneous lymphocyte associated antigen (CLA)-positive CD4 and CD8 cells from I684S carriers. No significant changes in p-STAT4 for the psoriasis-associated variant rs34536443 was found. These data establish the functional significance of the TYK2 I684S variant in psoriasis susceptibility.

Analysis of RUNX1 binding site and RAPTOR polymorphisms in psoriasis: no evidence for association despite adequate power and evidence for linkage.

BACKGROUND: A previous study identified two peaks of allelic association between psoriasis and single nucleotide polymorphisms (SNPs) mapping to distal chromosome 17q, including a disease associated SNP that leads to loss of a RUNX1 transcription factor binding site, and additional SNPs in the third intron of the RAPTOR gene. Another study found an association with SNPs in the RAPTOR gene, but not with the RUNX1 binding site polymorphism. METHODS: In an effort to confirm these observations, we genotyped 579 pedigrees containing 1285 affected individuals for three SNPs immediately flanking and including the RUNX1 binding site, and for three SNPs in the RAPTOR gene. RESULTS: Here we report further evidence for linkage to distal chromosome 17q, with a linkage peak mapping 1.7 cM distal to the RUNX1 binding site (logarithm of the odds 2.26 to 2.73, depending upon statistic used). However, we found no evidence for association to individual SNPs or haplotypes in either of the previously identified peaks of association. Power analysis demonstrated 80% power to detect significant association at genotype relative risks of 1.2 (additive and multiplicative models) to 1.5 (dominant and recessive models) for the RUNX1 binding site, and 1.3 to 1.4 for the RAPTOR locus under all models except dominant. CONCLUSIONS: Our data provide no support for the previously identified RUNX1 binding site or for the RAPTOR locus as genetic determinants of psoriasis, despite evidence for linkage of psoriasis to distal chromosome 17q.

The EGF receptor ligand amphiregulin controls cell division via FoxM1.

Epidermal growth factor receptor (EGFR) is central to epithelial cell physiology, and deregulated EGFR signaling has an important role in a variety of human carcinomas. Here we show that silencing of the EGF-related factor amphiregulin (AREG) markedly inhibits the expansion of human keratinocytes through mitotic failure and accumulation of cells with ⩾ 4n DNA content. RNA-sequencing-based transcriptome analysis revealed that tetracycline-mediated AREG silencing significantly altered the expression of 2331 genes, 623 of which were not normalized by treatment with EGF. Interestingly, genes irreversibly upregulated by suppression of AREG overlapped with genes involved in keratinocyte differentiation. Moreover, a significant proportion of the irreversibly downregulated genes featured upstream binding sites recognized by forkhead box protein M1 (FoxM1), a key transcription factor in the control of mitosis that is widely dysregulated in cancer. The downregulation of FoxM1 and its target genes preceded mitotic arrest. Constitutive expression of FoxM1 in AREG knockdown cells normalized cell proliferation, reduced the number of cells with ⩾ 4n DNA content and rescued expression of FoxM1 target genes. These results demonstrate that AREG controls G2/M progression and cytokinesis in keratinocytes via activation of a FoxM1-dependent transcriptional program, suggesting new avenues for treatment of epithelial cancer.

Epidemiology and the genetics of psoriasis.

Several lines of compelling epidemiologic evidence indicate that susceptibility to psorasis is inherited, albeit not in a simple monogenic fashion. Psoriasis is one of a number of diseases with a presumed autoimmune pathogenesis that display significant human leukocyte antigen (HLA) associations. However, only a small fraction of those who carry the implicated HLA susceptibility alleles develop disease. Taken together with the epidemiologic data indicative of high heritability, this observations suggests that one or more loci in addition to HLA are necessary for the development of psoriasis. As the identity of these other genes is unknown, genetic linkage analysis offers an attractive strategy for their identification. To this end, we have initiated a large linkage study of multiplex psoriasis kindreds, and PCR-based genotyping of CA repeat polymorphisms has been performed for several markers in the HLA region (6p21.3). As expected given the hypothesis of oligogenic inheritance, these analyses have thus far failed to reveal tight linkage of psoriasis to the 6p21 region. Nevertheless, the substantial homogeneity of the psoriatric phenotype and the clear evidence for increased HLA association and heritability in juvenile onset disease (40 years) indicate that, like insulin-dependent diabetes mellitus, psoriasis is an HLA-associated, genetically complex disease whose etiology is potentially amenable to elucidation through linkage analysis.

Of genes and antigens: the inheritance of psoriasis.

Psoriasis is one of a number of autoimmune diseases that display significant HLA associations. In particular, individuals with onset of disease prior to 40 years of age display striking associations with HLA-Cw6 and are much more likely to have a positive family for psoriasis. However, only about 10% of Cw6-positive individuals develop disease, suggesting that other genetic and/or environmental factors must be involved. Several compelling lines of epidemiologic evidence indicate that psoriasis susceptibility is inherited, albeit not in a simple monogenic fashion, and that genetic, rather than environmental, factors are primarily responsible for the variability in inheritance of psoriasis. Taken together, these observations suggest that one or more loci in addition to HLA are necessary for the development of psoriasis. The number of additional loci is likely to be small, because i) the disease is very common ii) substantial excess risk of psoriasis is observed in first degree relatives, and iii) nevoid variants of psoriasis have been reported, suggestive of somatic mutation of a single gene during development. The substantial homogeneity of the psoriatic phenotype and the clear evidence for increased HLA association and heritability in juvenile onset disease indicate that despite its complexity, psoriasis is a common disease whose etiology is amendable to elucidation through the techniques of modern molecular genetics.

Prenatal exclusion of lamellar ichthyosis based on identification of two new mutations in the transglutaminase 1 gene.

Lamellar ichthyosis is a severe, generalized, autosomal recessive genodermatosis characterized clinically by large, parchment-like scales and histologically by acanthosis and marked hyperkeratosis. Genetic heterogeneity in lamellar ichthyosis has been recognized with reports of two linked loci (on chromosomes 14q11 and 2q33-35). In a cohort of four small families with lamellar ichthyosis we found confirmatory evidence for linkage (p < or = 0.01) to D14S275, a microsatellite marker close to transglutaminase 1 on chromosome 14q11. We also identified two novel transglutaminase 1 mutations in an affected sibling pair from one of these families. The paternal mutation in exon 3, 1387insCAGC, causes a frameshift predicted to result in premature termination of translation within the same exon. The maternal mutation in exon 8, 4561delAC, also causes a frameshift and a premature stop codon in this exon. The mother of these siblings recently became pregnant with twins. Genotyping and direct sequencing of DNA isolated from fetal amniotic fluid cultures revealed the presence of the paternal but the absence of the maternal mutation, thus predicting a normal skin phenotype. Both twins were born with normal-appearing skin. Our findings demonstrate that mutations of both alleles of the transglutaminase 1 gene are the cause of lamellar ichthyosis in this family, and illustrate an emerging clinical application of molecular genetics in dermatology.

Cyclosporin A rapidly inhibits epidermal cytokine expression in psoriasis lesions, but not in cytokine-stimulated cultured keratinocytes.

To better understand the cellular target(s) of cyclosporin action in psoriasis, we have studied the effects of systemic short-term (7 d), low-dose (3-7.5 mg/kg) cyclosporin A administration on the expression of the cytokines interleukin (IL)-8 and IL-1 beta in psoriatic lesions. RNA blot hybridization analysis of pretreatment keratome biopsies revealed that expression of both cytokine mRNAs was highly variable from patient to patient. Significant covariation of both cytokine mRNA levels was noted (r = 0.86, p < 0.0001). However, there was no significant correlation between expression of either cytokine and clinical severity, as measured by the pretreatment Psoriasis Area and Severity Index (PASI). IL-1 beta protein levels measured by enzyme-linked immunosorbent assay (ELISA) were highly correlated with IL-1 beta mRNA levels, indicating that the differences in transcript levels accurately reflect differences in epidermal cytokine protein. Significant reductions in both cytokine transcripts and in IL-1 beta immunoreactive protein were noted in the high expression subgroup after 1 week of cyclosporin A therapy, prior to detectable clinical improvement. In contrast to its pronounced effects on epidermal cytokine expression in vivo and the allogeneic mixed lymphocyte reaction in vitro, cyclosporine A did not inhibit the induction of intercellular adhesion molecule (ICAM)-1 or IL-8 mRNAs by cultured keratinocytes in response to IL-1 beta or the combination of tumor necrosis factor (TNF)-alpha and interferon (IFN)-gamma. These data suggest that epidermal keratinocytes respond to signals produced by activated T cells by coordinate expression of multiple cytokines, and that cyclosporin A acts primarily through blockade of T cells, rather than through keratinocyte activation.

The genetics of psoriasis.

BACKGROUND AND DESIGN: Psoriasis is a member of a class of common, HLA-associated conditions in which disease susceptibility appears to be heritable. However, the mode of inheritance of these diseases has been difficult to define in simple mendelian terms. Psoriasis displays one of the strongest HLA associations of this class of diseases. However, only a small fraction of those who carry the implicated HLA susceptibility alleles develop disease, and it has proven difficult to demonstrate that the HLA associations observed are due to formal genetic linkage between the disease and the HLA locus. Although the role of environmental factors in psoriasis and these other diseases cannot be denied, the participation of additional genes, not necessarily linked to HLA, has long been suspected. OBSERVATIONS: Epidemiologic and immunogenetic data are reviewed and analyzed, which demonstrate that a predisposition to psoriasis is heritable, and which implicate genes of the HLA locus as necessary but not sufficient determinants of psoriasis. Recent developments in human genome research are described, which make possible a systematic search for additional genetic determinants of psoriasis, including those unlinked to HLA. CONCLUSIONS: As one of the most common, most heritable, and most highly HLA-associated examples of this class of HLA-associated diseases, psoriasis represents an ideal target for the application of this emerging genomic technology.

The genetics of psoriasis 2001: the odyssey continues.

Accumulating evidence indicates that psoriasis is a multifactorial disorder caused by the concerted action of multiple disease genes in a single individual, triggered by environmental factors. Some of these genes control the severity of multiple diseases by regulating inflammation and immunity (severity genes), whereas others are unique to psoriasis. Various combinations of these genes can occur even within a single family, accounting in large measure for the many clinical manifestations of psoriasis. The disease-causing variants (alleles) of these genes probably arose early in the history of modern humans. As a result, psoriasis disease alleles are common in the general population, have a worldwide distribution, and often share the same ancestral chromosome with neutral alleles at adjacent loci. This phenomenon, called linkage disequilibrium, explains why psoriasis is strongly associated with HLA-Cw6 worldwide, although HLA-Cw6 is unlikely to be the disease allele. Many unaffected individuals carry 1 or more disease alleles, but lack other genetic and/or environmental factors necessary to produce disease. This explains why psoriasis develops in only about 10% of HLA-Cw6-positive individuals, and why genome-wide linkage scans for psoriasis and other multifactorial genetic disorders have not been uniformly successful. The Human Genome Project is rapidly generating a catalog of human DNA sequence variations. This resource has already allowed precise linkage disequilibrium mapping of the major histocompatibility complex psoriasis gene to just beyond HLA-C, toward HLA-A. This gene is likely to be identified soon. Further development and use of linkage disequilibrium resources will provide a powerful tool for the identification of the remaining psoriasis genes.

Shaped field electron dosimetry for a Philips SL75/10 linear accelerator.

Both small and irregular fields are frequently the treatment of choice in many clinical applications of electron therapy. The fields are often shaped by lead or low melting point alloy placed at the end of the cone or on the patient's surface. The dosimetry for electrons of energies of 4, 6, 8, and 10 MeV is examined with particular emphasis on very small fields for treatment such as the lip, nose, and eye and irregular fields of various area/perimeter ratios. The paper discusses the dosimetry correction due to field shaping as a function of the location of the shield.

Evaluation of fetal dose from megavoltage irradiation of the knee and neonate followup.

A 24-yr-old female patient who was to undergo radiation therapy management for a recurrent low-grade fibrosarcoma on her right knee was found to be 9 weeks pregnant. The patient and her relatives insisted on carrying the pregnancy to maturity, despite undergoing irradiation of her right knee for local control of her disease and to take the teratological risk, if any, that it entails. This paper discusses the measurement of scattered dose in water, fetal dose estimation in an Alderson-Rando human phantom and possible ways of minimizing it.

Dosimetric considerations of d(15) + Be and p(26) + Be neutron beams from an isocentric cyclotron facility.

To select the optimum therapeutic neutron beam available from a CS30 medical cyclotron (manufactured by the Cyclotron Corporation, Berkeley, California), central axis depth dose data and output dose rates were compared for the bombardment of beryllium with either the proton or deuteron beams available from the machine. The effect on these parameters of filtering the beams with either pure polyethylene, polyethylene loaded with 5% boron, or polyethylene loaded with 10% lithium was studied. A 4-cm, 10% lithiated filter used with a 26-MeV proton beam was selected for therapeutic use. Buildup curves, beam profiles at several transverse planes for different field sizes, and comparison of beam profiles with 60Co are given.

A typical patient simulation and dosimetry data sheet.

A typical, comprehensive "Patient Simulation & Dosimetry Data" sheet has been developed. It contains all essential patient simulation, treatment and radiation dosimetry parameters and also relevant anatomical diagrams. The form can be used for any radiation therapy modality.

Radiation dosimetry of 12 MV photons from a CGR Therac 20 MeV Saturne linear accelerator.

Typically useful clinical radiation dosimetry characteristics of 12 MV photon beams from a CGR Therac 20 MeV Saturne linear accelerator are briefly outlined. Central axis percent depth dose data are compared with other published data. Beam profiles for small, medium and large fields are delineated to show the uniformity of beams at various depths.

Certain dosimetric features of electrons from a CGR Therac-20 MeV Saturne linear accelerator.

Some of the useful clinical radiation characteristics required for treatment planning using the 6,9,13,17, and 20 Me V scanning electron beams obtainable in a CGR Therac-20 Me V Saturne linear accelerator are outlined.