Genetic linkage of childhood atopic dermatitis to psoriasis susceptibility loci

Genes in asthma: new genes and new ways

PURPOSE OF REVIEW

Asthma is a disease of unknown aetiology characterized by intermittent inflammation of the small airways of the lung. Asthma is familial due to an interaction between strong genetic and environmental factors. This article aims to review the current understanding of the genetic factors underlying asthma, looking historically as well as highlighting the latest developments in the field.

RECENT FINDINGS

Findings from recent candidate gene studies and microsatellite genome screens have continued to highlight the importance of the epithelial barrier and its defence mechanisms in asthma. Completion of the human genome sequence and the advent of genome-wide association studies have resulted in the identification of two novel asthma susceptibility genes, ORMDL3 and CHI3L1, in the past year.

SUMMARY

With the advances in genetics and genomics substantial steps have been taken in the last decade in understanding the genetic factors underlying asthma. Studies have highlighted the importance of the role of the epithelium with many of the genes so far identified being expressed in this key barrier. With the application of genome-wide expression, microRNA studies, metagenomics, proteomics and metabolomics the next decade will undoubtedly result in a further substantial increment in our understanding of the mechanisms underlying asthma.

Variation in genes encoding eosinophil granule proteins in atopic dermatitis patients from Germany

Background

Atopic dermatitis (AD) is believed to result from complex interactions between genetic and environmental factors. A main feature of AD as well as other allergic disorders is serum and tissue eosinophilia. Human eosinophils contain high amounts of cationic granule proteins, including eosinophil cationic protein (ECP), eosinophil-derived neurotoxin (EDN), eosinophil peroxidase (EPO) and major basic protein (MBP). Recently, variation in genes encoding eosinophil granule proteins has been suggested to play a role in the pathogenesis of allergic disorders. We therefore genotyped selected single nucleotide polymorphisms within the ECP, EDN, EPO and MBP genes in a cohort of 361 German AD patients and 325 healthy controls.

Results

Genotype and allele frequencies did not differ between patients and controls for all polymorphisms investigated in this study. Haplotype analysis did not reveal any additional information.

Conclusion

We did not find evidence to support an influence of variation in genes encoding eosinophil granule proteins for AD pathogenesis in this German cohort.

Polymorphisms within the C3 gene are associated with specific IgE levels to common allergens and super-antigens among atopic dermatitis patients

Atopic dermatitis (AD) is a chronic inflammatory skin disease. Twin and family studies suggest a strong genetic component of the disease. The keratinocytes secrete high amounts of C3 after stimulation with pro-inflammatory cytokines, which may play a functional role in skin inflammation. In this study, we genotyped four different single nucleotide polymorphisms (SNPs) by melting curve analysis using sequence specific hybridization probes in a well-characterized cohort of AD patients. Among four SNPs within C3 gene, higher frequencies of rs10410674 (23.5% vs 12.2%) and rs366510 (13.8% vs 6.5%) were observed in AD patients as compared with control group. None of the tested polymorphisms showed significant association with the risk of the disease phenotype. Analysis of rs10402876 SNP revealed its association with less severe AD disease expression (low SCORAD). Total serum IgE levels were not different among AD patients having any of the four SNPs. However, we observed significantly less serum-specific IgE levels to common allergens (Dermatophagoides pteronyssinus and birch pollens) and Staphylococcal enterotoxin B in AD patients having rs366510 SNP. Thus, associations of polymorphism within C3 gene with less severe AD disease expression and a weaker sensitization to common allergens suggest the role of these SNPs in the development of AD.

Filaggrin null mutations are associated with atopic dermatitis and elevated levels of IgE in the Japanese population: a family and case-control study

Filaggrin (FLG) plays an important role in the barrier function of the skin. Several loss-of-function mutations in the FLG gene have been identified in patients with ichthyosis vulgaris, and these null mutations are associated with atopic dermatitis (AD) development. In this study, we examined tag single nucleotide polymorphisms (tSNPs) and null mutations in FLG for possible associations with AD and atopic phenotypes in a Japanese population. Transmission disequilibrium test of 105 AD families showed that the null allele of the S2554X variant of FLG tended to be overtransmitted to AD-affected offspring; however, the P value did not reach statistical significance. In a case-control comparison of 376 AD cases and 923 nonallergic controls, the null allele of S2554X was significantly associated with AD (P = 0.0012), and the association was strengthened in subjects with AD alone (P = 0.000024). We found that 3321delA and S2554X were also associated with elevated levels of immunoglobulin E (IgE). Combined null mutation carriers were observed more in AD patients and in subjects with high IgE than in control subjects. The combined P value for the family and case-control data was significant for the S2554X and combined null mutations. Our data further support the importance of FLG in AD development.

Filaggrin and the great epidermal barrier grief

One of the principal functions of human skin is to form an effective mechanical barrier against the external environment. This involves the maturation and death of epidermal keratinocytes as well as the assembly of a complex network of differentially and spatially expressed proteins, glycoproteins and lipids into the keratinocyte cell membrane and surrounding extracellular space. In 2006, the key role of the granular cell layer protein filaggrin (filament-aggregating protein) in maintaining the skin barrier was determined with the identification of loss-of-function mutations in the profilaggrin gene (FLG). These mutations have been shown to be the cause of ichthyosis vulgaris and a major risk factor for the development of atopic dermatitis, asthma associated with atopic dermatitis as well as systemic allergies. Mutations in the FLG gene are extremely common, occurring in approximately 9% of individuals from European populations. The remarkable discovery of these widespread mutations is expected to have a major impact on the classification and management of many patients with ichthyosis and atopic disease. It is also hoped that the genetic discovery of FLG mutations will lead to the future development of more specific, non-immunosuppressive treatments capable of restoring effective skin barrier function and alleviating or preventing disease in susceptible individuals.

Filaggrin loss-of-function mutations and association with allergic diseases

Human skin constitutes a highly organized barrier against environmental agents. Its unrestricted function depends on a complex interplay between multiple proteins and lipids expressed in the terminally differentiating epithelium. Recently, attention has been drawn to the protein filaggrin, an integral part of the epidermis that plays a key role in engineering and maintaining the barrier function. Common loss-of-function mutations within the filaggrin gene have been demonstrated to cause ichthyosis vulgaris, one of the most common heritable disorders of cornification, and to represent major risk factors for atopic eczema and secondary allergic diseases. The observations on filaggrin provide striking new insights into the etiology of atopic diseases and might pave the way for the development of new therapeutic approaches.

The genetics of atopic dermatitis

BACKGROUND

Atopic dermatitis (AD) is a complex genetic disorder influenced by environmental factors. The mode of inheritance and genes involved are not clear.

RESULTS

This report here is focusing on the current progress in searching the disease-susceptibility genes of AD via both the linkage studies and candidate gene approaches. Genome-wide linkage studies have identified multiple susceptibility loci on 3q and 17q. Candidate region linkage studies identify other susceptibility loci on 5q23-33, 11q13, and 13q12-14. At least 28 candidate genes have to date been verified in association studies, but only association with genes of interleukin (IL)-4, IL-13, IL-4RA, mast cell chymase, and serine protease inhibitor, kazal-type 5 have been replicated in more than two different studies. More halpotype tests and family-based association studies may help to shed more light for the candidate gene approach.

CONCLUSION

Determining the candidate susceptibility genes for AD is not only helping understanding the pathophysiology but also affecting the response to therapy, which is important in pharmacogenetics. The effect of environmental trigger may also have to be considered to elucidate the real face of the disease.

Cutaneous perspectives on adaptive immunity

The skin, situated at the critical juncture between the host and the environment, is subject to a variety of potentially damaging agents including microbial organisms, toxins, and gene-altering radiation. Diverse immunocytes, including those resident in the skin and those with the capacity to traffic to and from the skin, direct two major types of immune responses: more immediate and less discriminate defenses (so-called innate immunity), and more coordinated and antigen-specific responses (so-called adaptive immunity). This review will focus on features of the adaptive immune system operative within the skin and consider the roles of dendritic cells, lymphocytes, endothelial cells, chemokines, and cytokines. In particular, the major subsets of T cells and the mechanisms by which they endow and regulate the features of adaptive immunity in the skin will be considered, including: the efficient surveillance and recognition of diverse foreign-antigens while limiting reactivity against self-antigens; differentiation into various effector cells capable of inducing apoptosis of infected/damaged cells and/or directing the activities of other immunocytes; and providing for immunologic memory whereby subsequent antigen exposure elicits a rapid and augmented antigen-specific response. It is within this context that the adaptive immune system will be considered for its role in the skin in mediating microbial defense with direct relevance to tumor immunosurveillance and inflammatory disease.

Mice deficient in involucrin, envoplakin, and periplakin have a defective epidermal barrier

The cornified envelope is assembled from transglutaminase cross-linked proteins and lipids in the outermost epidermal layers and is essential for skin barrier function. Involucrin, envoplakin, and periplakin form the protein scaffold on which the envelope assembles. To examine their combined function, we generated mice deficient in all three genes. The triple knockouts have delayed embryonic barrier formation and postnatal hyperkeratosis (abnormal accumulation of cornified cells) resulting from impaired desquamation. Cornified envelopes form but are ultrastructurally abnormal, with reduced lipid content and decreased mechanical integrity. Expression of proteases is reduced and the protease inhibitor, serpina1b, is highly upregulated, resulting in defective filaggrin processing and delayed degradation of desmoglein 1 and corneodesmosin. There is infiltration of CD4⁺ T cells and a reduction in resident γδ⁺ T cells, reminiscent of atopic dermatitis. Thus, combined loss of the cornified envelope proteins not only impairs the epidermal barrier, but also changes the composition of T cell subpopulations in the skin.

Genetic effect of CCR3 and IL5RA gene polymorphisms on eosinophilia in asthmatic patients

BACKGROUND

Eosinophilic infiltration and peripheral blood eosinophilia in asthma require the cooperation of eosinophil-specific cytokines and chemokines and their receptors.

OBJECTIVE

We investigated the association of polymorphisms in CCR3 and IL5RA with asthma susceptibility or peripheral blood eosinophilia and the effects of the polymorphisms on receptor expression.

METHODS

Polymorphisms in CCR3 and IL5RA were identified and genotyped in 576 asthmatic patients and 180 healthy control subjects. CCR3 and IL-5 receptor alpha (IL-5R alpha) protein expression on eosinophils was measured by means of flow cytometry.

RESULTS

Although polymorphisms in CCR3 were not associated with asthma susceptibility, the CCR3 haplotype ht2 showed a negative gene dose effect on the eosinophil count (P = .003-.009). IL5RA c.-5091G>A was weakly associated with eosinophil count. The effects of ht2 were greater when paired with IL5RA c.-5091A (P = .001-.002). CCR3 protein expression was higher on eosinophils of asthmatic patients without ht2 than in those with ht2. Asthmatic patients with the IL5RA c.-5091A allele showed higher IL-5R alpha expression than those who were homozygous for the G allele.

CONCLUSION

The genetic association between CCR3 polymorphisms and the number of circulating eosinophils was revealed as a novel finding. These associations were more pronounced when the CCR3 polymorphisms were paired with polymorphisms in IL5RA. The protein expression levels of CCR3 and IL-5R alpha on peripheral blood eosinophils are associated with the polymorphisms on their own genes.

CLINICAL IMPLICATIONS

The identification of single nucleotide polymorphisms and haplotypes of CCR3 and IL5RA might be useful in developing markers for intermediate phenotypes of eosinophil number and in designing strategies to control diseases related to hypereosinophilia.

Clinical correlations of recent developments in the pathogenesis of atopic dermatitis

Atopic dermatitis is a chronic inflammatory skin disease with a steadily increasing prevalence affecting 10-20 of infants and 1-3 of adults globally. It is often the first clinical manifestation of atopic disease preceding asthma and allergic rhinitis. Probably half of the children with atopic dermatitis develop some other form of atopic disease later in life. The pathogenesis involves a complex interplay of factors including genetic predisposition due to altered immune or skin barrier function, interactions with the environment such as food and allergen exposures, and infectious triggers of inflammation. In this review, we summarize the recent advances in understanding the contribution of different factors in the pathophysiology of atopic dermatitis and how insights provide new therapeutic potential for its treatment.

Molecular basis of atopic dermatitis

PURPOSE OF REVIEW

Atopic dermatitis is a common chronic inflammatory skin disease and there are numerous publications on this topic. This review will focus on developments in understanding the molecular basis of atopic dermatitis while considering the genetic background, skin barrier impairment, immune system deviation and microbial superinfections.

RECENT FINDINGS

Atopic dermatitis is a complex genetic disease in which gene-gene and gene-environment interactions play a key role. Surprisingly some genetic regions of interest were found to be overlapping with loci identified to play a role in another very common inflammatory skin disease, psoriasis, while no overlap has so far been observed with asthma. Impairment of the skin barrier followed by antigens trespassing seems to play an important role, favouring sensitization via transepidermal penetration which is the focus of current investigations. Superinfections by pathogens such as Staphylococcus aureus due to a weak innate defence seem to be significant in atopic dermatitis as they elicit a strong inflammatory response.

SUMMARY

Atopic dermatitis is a chronic inflammatory skin disease with a high incidence in school children and adults. Disease pathogenesis is complex and the background is multifactorial, making the underlying predispositions elusive. Understanding new pathogenic pathways may lead to the development of new drugs with enhanced benefit for the patient.

Evidence for linkage of a new region (11p14) to eczema and allergic diseases

Asthma, allergic rhinitis (AR) and atopic dermatitis also called eczema are allergic co-morbidites, which are likely to depend on pleiotropic genetic effects as well as on specific genetic factors. After a previous genome-wide linkage screen conducted for asthma and AR in a sample of 295 French EGEA families ascertained through asthmatic subjects, the aim here was to search for genetic factors involved in eczema and more particularly the ones shared by the three allergic diseases using the same EGEA data. In this sake, eczema and phenotypes of "allergic disease" accounting for the joint information on the presence/absence of the three diseases were examined by linkage analyses using the maximum likelihood binomial method. A fine mapping was carried out in regions detected for potential linkage, followed by association studies using the family-based association test (FBAT). Evidence for linkage to 11p14 region was shown for "allergic disease" and eczema. Linkage was also indicated between eczema and 5q13 and between "allergic disease" and both 5p15 and 17q21 regions. Fine mapping supported the evidence of linkage to 11p14 and FBAT analyses showed the association between "allergic disease" and a marker located at the linkage peak on 11p14. Further investigations in this region will allow identifying genetic factor(s) which could have pleiotropic effect in the three allergic diseases.

Psoriasis: advances in pathophysiology and management

Psoriasis is an inflammatory skin disease that affects 1-3% of Caucasian populations and may be persistent, disfiguring and stigmatizing. There is a range of severity, but even when the affected body surface area is relatively limited the impact on day-to-day activities and social interactions may be significant. An understanding of the psychological burden and an appreciation that many patients are currently dissatisfied with their management has driven the development of more effective treatment. In recent years psoriasis has been the focus of intense investigation resulting in an improved understanding of the immunopathogenesis, and the development of new, targeted biological treatments.

Variants in a novel epidermal collagen gene (COL29A1) are associated with atopic dermatitis

Atopic dermatitis (AD) is a common chronic inflammatory skin disorder and a major manifestation of allergic disease. AD typically presents in early childhood often preceding the onset of an allergic airway disease, such as asthma or hay fever. We previously mapped a susceptibility locus for AD on Chromosome 3q21. To identify the underlying disease gene, we used a dense map of microsatellite markers and single nucleotide polymorphisms, and we detected association with AD. In concordance with the linkage results, we found a maternal transmission pattern. Furthermore, we demonstrated that the same families contribute to linkage and association. We replicated the association and the maternal effect in a large independent family cohort. A common haplotype showed strong association with AD (p = 0.000059). The associated region contained a single gene, COL29A1, which encodes a novel epidermal collagen. COL29A1 shows a specific gene expression pattern with the highest transcript levels in skin, lung, and the gastrointestinal tract, which are the major sites of allergic disease manifestation. Lack of COL29A1 expression in the outer epidermis of AD patients points to a role of collagen XXIX in epidermal integrity and function, the breakdown of which is a clinical hallmark of AD.

Atopic dermatitis (AD, eczema) is a common chronic inflammatory skin disorder and a major manifestation of allergic disease. Typically, AD first occurs in early childhood, often preceding the onset of allergic airways disease, such as asthma and hay fever. A family history of allergic disorders is the single strongest predictor for AD, showing that genetic factors play a major role in the disease development. We have previously mapped a disease locus for AD on Chromosome 3q21, Now we have used a dense map of microsatellite markers and single nucleotide polymorphisms (SNPs) to find the underlying disease gene. We identified genetic markers in a subregion that showed association with AD, and replicated this finding in a large independent family cohort. The associated region contained a single gene, COL29A1, which encodes a novel collagen. We demonstrate that AD patients lack COL29A1 expression in the outer epidermis, implicating collagen XXIX in epidermal integrity and function. The gene expression pattern of COL29A1 in other organs, including the lung and the gut, suggests that this gene could have a role in a wider spectrum of allergic diseases and may provide a molecular link between AD and respiratory airways disease and food allergies.

The gene underlying atopic dermatitis susceptibility has been identified by gene mapping as expressing a novel collagen, whose expression is lacking in the outer epidermis of atopic dermatitis patients.

Atopic Dermatitis: an Update and Review of the Literature

Atopic eczema/dermatitis from the aspects of immunologic background, genetics, skin barrier dysfunction, IgE receptors, and triggers of AD (including allergens, microorganisms, and autoantigens) is described. Also reviewed are diagnostic procedures, treatment modalities with topical treatment (emollients, topical corticosteroids, topical calcineurin inhibitors, wet wrap therapy, and topical antimicrobial therapy), systemic management (antimicrobials, systemic corticosteroids, cyclosporine A, azathioprine, antihistamines), and phototherapy. Primary and secondary prevention are discussed and the role of the different cell receptors and their up-and down-regulation in this setting are emphasized.

Single nucleotide polymorphism-based genome-wide linkage analysis in Japanese atopic dermatitis families

Background

Atopic dermatitis develops as a result of complex interactions between several genetic and environmental factors. To date, 4 genome-wide linkage studies of atopic dermatitis have been performed in Caucasian populations, however, similar studies have not been done in Asian populations. The aim of this study was to identify chromosome regions linked to atopic dermatitis in a Japanese population.

Methods

We used a high-density, single nucleotide polymorphism genotyping assay, the Illumina BeadArray Linkage Mapping Panel (version 4) comprising 5,861 single nucleotide polymorphisms, to perform a genome-wide linkage analysis of 77 Japanese families with 111 affected sib-pairs with atopic dermatitis.

Results

We found suggestive evidence for linkage with 15q21 (LOD = 2.01, NPL = 2.87, P = .0012) and weak linkage to 1q24 (LOD = 1.26, NPL = 2.44, P = .008).

Conclusion

We report the first genome-wide linkage study of atopic dermatitis in an Asian population, and novel loci on chromosomes 15q21 and 1q24 linked to atopic dermatitis. Identification of novel causative genes for atopic dermatitis will advance our understanding of the pathogenesis of atopic dermatitis.

ADAM33, a new candidate for psoriasis susceptibility

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

The prevalence of atopic triad in children with physician-confirmed atopic dermatitis

BACKGROUND

Atopic dermatitis (AD) is often associated with comorbidities such as allergic rhinitis and asthma.

OBJECTIVE

We sought to describe the frequency of these comorbidities in children with AD.

METHODS

We conducted a cross-sectional study of the first 2270 children with physician-confirmed AD enrolled in a large postmarketing cohort. All were queried for information on comorbidities using a questionnaire from the International Study of Asthma and Allergies in Childhood.

RESULTS

In all, 71.3% reported at least one additional form of atopy (symptoms of asthma or allergic rhinitis). A total of 33.3% reported only symptoms of asthma or allergic rhinitis whereas 38.0% reported symptoms of asthma and allergic rhinitis. By age 3 years, nearly 66% reported at least one additional form of atopy. A statistically significant trend toward poorer disease control was observed for those with additional atopic illnesses (P < .001).

LIMITATIONS

This is a cross-sectional study.

CONCLUSION

Individuals with AD exhibit a predisposition to additional atopic illnesses by age 3 years and in turn the presence of these illnesses correlates with poor disease control.

Genetik der Psoriasis

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

The skin barrier, atopic dermatitis and allergy: a role for Langerhans cells?

The skin barrier (stratum corneum) is a major factor for determining the nature of immune response to antigens presented at the skin surface. Genetic abnormalities in skin barrier function are associated with allergy and atopic dermatitis, and removal of the skin barrier by tape stripping results in dominant Th2 responses to protein antigens. Langerhans cells take up antigen applied to skin from which the skin barrier has been removed; they then migrate to draining lymph nodes and initiate typical Th2 responses. These observations lead us to propose that the high frequency of allergic disease in the industrialized world might be due to lifestyle choices that result in loss of integrity of the skin barrier such as excessive washing and exfoliation of the skin.

Sequence variants in the genes for the interleukin-23 receptor (IL23R) and its ligand (IL12B) confer protection against psoriasis

Psoriasis is an inflammatory skin disorder that is inherited as a multifactorial trait. Genetic analyses have repeatedly identified a primary disease susceptibility locus lying within the major histocompatibility complex (MHC), on chromosome 6p21. A small number of non-MHC susceptibility loci have also been identified. These regions tend to overlap with susceptibility intervals for Crohn's disease and atopic dermatitis, suggesting the possibility that genetic variants affecting inflammatory pathways may contribute to the pathogenesis of multiple disorders. Here, we report a genetic analysis of the interleukin 23 receptor gene (IL23R), which was recently identified as a susceptibility determinant for Crohn's disease. We initially examined the results of a whole-genome association scan, carried out on 318 cases and 288 controls. We observed a significant increase of a non-synonymous substitution (p.Arg381Gln) among controls (P = 0.00036). We validated this finding by extending our cohort to include a further 519 cases and 528 controls. In the overall sample, the frequency of the 381Gln allele was 3.6% in cases and 7% in controls, yielding a P value of 0.00014. Next, we examined genetic variation at the IL12RB1, IL23A and IL12B genes, respectively, encoding the second subunit of the IL23R receptor and the two subunits of its ligand. This analysis identified independent associations for IL12B SNPs rs10045431 (P value for the extended dataset = 0.0001) and rs3212227 (P = 0.036). Altogether, these findings indicate that genes participating in IL23 signalling play a significant role in the pathogenesis of chronic epithelial inflammation.

On the role of the epidermal differentiation complex in ichthyosis vulgaris, atopic dermatitis and psoriasis

Undisturbed epidermal differentiation is crucial for an intact skin barrier function. The epidermal differentiation complex (EDC) is a cluster of genes on chromosome 1q21 encoding proteins that fulfil important functions in terminal differentiation in the human epidermis, including filaggrin, loricrin, S100 proteins and others. Recently, evidence emerged that variation within EDC genes plays an important role in the pathogenesis of three common skin disorders, ichthyosis vulgaris, atopic dermatitis (AD) and psoriasis. Two loss-of-function mutations in the filaggrin (FLG) gene, R501X and 2282del4, were identified as causative for ichthyosis vulgaris in 15 affected European families, and the mode of inheritance was found to be semidominant. As ichthyosis vulgaris and AD often occur concomitantly in affected individuals, these two mutations were subsequently investigated in AD patients and found to be strongly associated with the disease. Following this first report, seven replication studies have been performed that all confirm an association of these two mutations with AD (or AD subtypes) in several European cohorts. Additionally, two unique loss-of-function mutations in the FLG gene were identified in Japanese ichthyosis vulgaris families and found to be associated with AD in a Japanese cohort. Thus, the FLG mutations are among the most consistently replicated associations for AD. Additionally, linkage analysis has suggested that variation within the EDC might also predispose for psoriasis but the exact susceptibility variation(s) have not yet been elucidated. Taken together, these findings convincingly demonstrate the important role of barrier dysfunction in various common skin disorders.

Susceptibility to asthma and eczema from mucosal and epidermal expression of distinctive genes

The past several years have seen an increase in the rate at which genes that are associated with allergic asthma and eczema are discovered. This review -examines genetic association, gene expression, and functional studies that have identified genes that are expressed in the epithelial cells of the skin and lung and are involved in the pathogenesis of allergic asthma and eczema. This includes the genes encoding thymic stromal lympho-poietin (TSLP) and suppressor of cytokine signaling (SOCS3) that are involved in the activation of T-helper 2 cells, the microbial pattern recognition receptors nucleotide-binding oligomerization domain (NOD) genes (CARD4 and CARD15), Toll-like receptors (TLR2 and TLR4), and filaggrin, a protein required for effective barrier defense of the skin. Therefore, the development of allergic disease involves both the adaptive and innate immune systems, and the expression of these genes in the skin and lungs suggests a link to environmental -triggers at body surfaces.

Comprehensive analysis of the gene encoding filaggrin uncovers prevalent and rare mutations in ichthyosis vulgaris and atopic eczema

We recently reported two common filaggrin (FLG) null mutations that cause ichthyosis vulgaris and predispose to eczema and secondary allergic diseases. We show here that these common European mutations are ancestral variants carried on conserved haplotypes. To facilitate comprehensive analysis of other populations, we report a strategy for full sequencing of this large, highly repetitive gene, and we describe 15 variants, including seven that are prevalent. All the variants are either nonsense or frameshift mutations that, in representative cases, resulted in loss of filaggrin production in the epidermis. In an Irish case-control study, the five most common European mutations showed a strong association with moderate-to-severe childhood eczema (chi2 test: P = 2.12 x 10(-51); Fisher's exact test: heterozygote odds ratio (OR) = 7.44 (95% confidence interval (c.i.) = 4.9-11.3), and homozygote OR = 151 (95% c.i. = 20-1,136)). We found three additional rare null mutations in this case series, suggesting that the genetic architecture of filaggrin-related atopic dermatitis consists of both prevalent and rare risk alleles.

Filaggrin null alleles are not associated with psoriasis

Psoriasis is a common skin disease with an etiology consistent with a multifactorial trait. Several psoriasis susceptibility loci are known, a number of which are also implicated in a predisposition to atopic dermatitis (AD), including the epidermal differentiation complex on chromosome 1q21. It has recently been shown in several replicate studies that prevalent null alleles for the filaggrin gene (FLG) on 1q21 are an important genetic factor in AD. Here, we examined the role of these FLG variants in psoriasis using case:control association studies comparing Irish and UK psoriasis cohorts (combined n=691) to ethnically matched populations (combined n=2117). No association was present for the two common European FLG mutations R501X and 2282del4 (combined chi2 P=0.989). In addition, the 3' end of the FLG open-reading frame was sequenced in a number of patients with differing types of psoriasis (plaque, guttate, palmoplantar, and late-onset), which excluded the possibility of a gain-of-function frameshift mutation such as those found in loricrin or certain keratin genes. These data suggest that FLG mutations are unlikely to be involved in genetic susceptibility to psoriasis and implies that there may be within-locus heterogeneity in chromosomal regions involved in both AD and psoriasis.

Unique mutations in the filaggrin gene in Japanese patients with ichthyosis vulgaris and atopic dermatitis

BACKGROUND

Filaggrin is a key protein involved in skin barrier function. Recently, mutations in the filaggrin gene, FLG, were identified in European families with ichthyosis vulgaris (IV) and shown to be an important predisposing factor for atopic dermatitis (AD).

OBJECTIVE

To study the role of FLG mutations in IV/AD in Japan.

METHODS

The known filaggrin mutations were studied by genotyping and new mutations identified by DNA sequencing.

RESULTS

The European-specific mutations R501X and 2282del4 were absent from 253 Japanese individuals. We therefore sequenced the FLG gene in 4 Japanese families with IV and identified 2 novel mutations, 3321delA and S2554X. Immunohistologic and ultrastructural observations indicated that both truncation mutations lead to a striking reduction of keratohyalin granules in the epidermis. We screened 143 Japanese patients with AD for these FLG null mutations and identified them in 8 patients with AD (5.6%), including S2554X in 6 patients (4.2%) and 3321delA in 2 patients (1.4%). Both null variants were absent from 156 unrelated Japanese nonatopic and nonichthyotic controls, giving a significant statistical association between the FLG mutations and AD (chi(2)P value, .0015). This is the first report of FLG mutations in a non-European population.

CONCLUSION

Our data indicate that FLG mutations in Japan are unique from those found in European-origin populations.

CLINICAL IMPLICATIONS

Filaggrin null variants are also significant predisposing factors for AD in Japan and, on the basis of the recent European studies, may predict a more severe and persistent form of atopy.

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.

Cutaneous side-effects in patients with rheumatic diseases during application of tumour necrosis factor-? antagonists

BACKGROUND

Patients with rheumatic diseases receiving antitumour necrosis factor (TNF)-alpha-based treatment may develop cutaneous reactions.

OBJECTIVES

To analyse the new onset or aggravation of skin lesions in patients with a rheumatic disease during treatment with TNF-alpha antagonists.

METHODS

We conducted a prospective analysis of 35 of 150 patients with a long history of rheumatic disease, including rheumatoid arthritis, ankylosing spondylitis (Bechterew's disease) and psoriatic arthritis, to test for the development of cutaneous manifestations during anti-TNF-alpha (infliximab, adalimumab or etanercept) treatment.

RESULTS

Chronic inflammatory skin diseases such as psoriasis and eczema-like manifestations represented the majority of cases (16 of 35). Cutaneous infections caused by viral, bacterial and fungal agents were also observed in many patients (13 of 35). Skin diseases such as dermatitis herpetiformis, leucocytoclastic vasculitis and alopecia occurred in single cases only.

CONCLUSIONS

We observed a broad, diverse clinical spectrum with a majority of chronic inflammatory and infectious skin diseases. However, we did not identify individual risk factors and a discontinuation of the anti-TNF-alpha treatment was not necessary if adequate dermatological treatment was performed. The onset of cutaneous side-effects in anti-TNF-alpha-based treatments should be determined by nationwide registries.

Filaggrin mutations in children with severe atopic dermatitis

Atopic dermatitis (AD) results from strong genetic and environmental interactions. AD shows genetic linkage to Chromosome 1q21. This region contains the epidermal differentiation complex (EDC), which consists of genes that form essential components of epidermal surfaces. Filaggrin (FLG) is one of these. Mutations in FLG/(R501X and 2282del4) are reported to be strongly associated with AD and to influence asthma accompanying AD. We investigated these effects in families recruited through a child with severe AD. We genotyped two panels of families, totalling 426, containing 990 affected and unaffected children. We found significant associations with AD (P=0.0001), asthma (P=0.006), and atopy (P=0.002). The FLG mutations were present in 26.7% of patients with AD, but were also present in 14.4% of children without AD. They were weakly associated with disease severity. The variants were not independently associated with asthma. The overall LOD score for genetic linkage of markers to the region was 3.57. This fell to 2.03 after accounting for the FLG mutations, indicating the presence of other genetic variants influencing AD at this locus. Our results provide further confirmation of the importance of mutations in FLG and the skin barrier in AD pathogenesis. The results indicate that investigations of other genes within the EDC should be undertaken.

Association of a chromosome 1q21 locus in close proximity to a late cornified envelope-like proline-rich 1 (LELP1) gene with total serum IgE levels

The chromosomal region 1q21 has been linked to atopic dermatitis in previous studies. Seven polymorphic repeats were identified in a 0.5 Mb region of chromosome 1q21 encompassing a small proline-rich protein (SPRR) gene cluster, a few S100 gene family members, loricin, and several uncharacterized genes. These repeats were genotyped by fragment length polymorphism analysis in 133 atopic case-parent trios, of which 111 probands had atopic asthma. Our trio-based analysis for association with atopy and atopic asthma revealed no significant allelic or genotypic association for any of the seven loci tested. However, a significant association was observed with locus 5 (3.65 Mb of contig NT_032962) and log(10) serum IgE levels (F = 3.93, P = 0.0008). Results were also replicated in an independent case-control cohort (N (p) = 165, N (c) = 166), where a significant association with log(10) serum IgE levels was observed in the patient group (P = 0.0005). Interestingly, locus 5 is 6.2 kb upstream of a late cornified envelope-like proline-rich 1 (LELP1) gene which encodes a novel small proline rich protein. Further, we have also found a significant association of rs7534334 (tagged SNP from LELP1) SNP with log(10) serum IgE levels in the patient group (P = 0.0029). Thus, our results identify a chromosomal region in close proximity to a novel gene and highlight the need for intense research on LELP1 and other genes close by with respect to atopic disorders.

Relationship of serum brain-derived neurotrophic factor level with other markers of disease severity in patients with atopic dermatitis

Elevated serum levels of neurotrophins such as nerve growth factor (NGF) and brain-derived neurotrophic factor (BDNF) have been reported in allergic and autoimmune diseases. The aim of this study was to assess serum levels of BDNF in patients with atopic dermatitis (AD) and to investigate the relationship of the BDNF level with other markers of disease severity. Serum BDNF concentration was significantly higher in patients with AD (n=62) compared to control subjects (n=20) (P<0.01). Stepwise multiple regression analysis showed a significant influence of the peripheral blood eosinophil counts (F=6.90) and the percentage of CD4(+)IL-4(+) (Th2) cells (F=6.61). Moreover, after remission of AD patients with conventionally treated AD patients (n=14), serum levels of BDNF, eosinophil counts and percentage of Th2 cells were decreased significantly. These results suggest that serum BDNF may be a useful marker of disease activity in AD and that both eosinophils and Th2 cells are major cellular sources of serum BDNF.

Loss-of-function variants of the filaggrin gene are not major susceptibility factors for psoriasis vulgaris or psoriatic arthritis in German patients

Psoriasis vulgaris and atopic dermatitis share a number of features such as chronic cutaneous inflammation and disturbed epidermal barrier function. Genome-wide scans have revealed a conspicuous overlap of susceptibility loci for both diseases involving chromosomal regions 1q21, 3q21, 17q25, and 20p12. Recently, two loss-of-function variants in the gene encoding filaggrin at 1q21 were shown to be strongly associated with atopic dermatitis. In view of a possible genetic overlap of the two skin diseases, we investigated 375 patients suffering from psoriasis vulgaris, 375 patients with psoriatic arthritis, and 376 control probands. Moreover we directly studied expression of filaggrin in 10 patients suffering from psoriasis vulgaris. Our immunohistochemical analysis revealed a checkered pattern with alternating positive broadened or almost absent filaggrin expression. However, no association was found for the two variants of filaggrin (FLG). We conclude that despite a markedly altered filaggrin expression in psoriatic skin, loss-of-function variants of the FLG gene are neither associated with psoriasis vulgaris nor with psoriatic arthritis. The abnormal staining might reflect the altered epidermal differentiation. Our findings imply that the genetic background underlying the epidermal barrier defect in psoriasis is distinct from that found in atopic dermatitis.

Association analysis of CD40 polymorphisms with asthma and the level of serum total IgE

RATIONALE

The CD40 protein plays important roles in cell-mediated and humoral immune responses, especially in immunoglobulin class-switching to IgE.

OBJECTIVES

We tested the association of CD40 polymorphisms with the risk of asthma and the level of serum IgE and investigated the functional effect of associated polymorphisms on the expression of CD40.

METHODS

We identified 17 CD40 single-nucleotide polymorphisms (SNPs) in the Korean population by direct sequencing, and we genotyped 7 of these in 487 subjects with asthma and in 161 normal subjects. Cell-surface expression of CD40 for B-cell lines of various SNP genotypes was measured using flow cytometry. The effects of SNPs in the promoter and 5'-untranslated regions (UTRs) of CD40 were assessed using pGL3 luciferase and enhanced green fluorescent protein (EGFP) reporter systems, respectively.

MEASUREMENTS AND RESULTS

None of the SNPs was associated with asthma risk, but total serum IgE levels were associated with the -580G>A and -1C>T polymorphisms in subjects with asthma (p = 0.007 and 0.005, respectively). The total amount of IgE was highest in the -580A or -1C homozygotes. More CD40 was expressed in B cells with the -1C allele than in those with the -1T allele (p < 0.001). EGFP expression from the CD40 5'-UTR-EGFP construct was higher for the -1C allele than the -1T allele. The -580G>A SNP did not affect promoter activity, even after IFN-gamma stimulation.

CONCLUSIONS

CD40 gene polymorphisms exert a genetic effect on IgE production in patients with asthma through translational regulation of CD40 expression on B cells.

Upregulating promoter polymorphisms of RANTES relate to atopic dermatitis

It has been reported that a functional polymorphism in the promoter of the RANTES gene (-403G/A) is associated with atopic dermatitis in a German population. Although there are several reports on the association of RANTES promoter polymorphisms (-403G/A and -28C/G) with asthma, the association of these polymorphisms with atopic dermatitis has not yet been confirmed in other populations. We therefore aimed to test whether the RANTES promoter polymorphisms relate to atopic dermatitis in a well-defined Japanese population. We conducted an association study of upregulating promoter polymorphisms of RANTES (-403G/A and -28C/G) in 389 patients with atopic dermatitis and 177 healthy control subjects. There was a significant association between the upregulating variant of RANTES -28G and atopic dermatitis, while -403A variant showed a significant association with atopic dermatitis with high IgE productivity. These results support a role for RANTES promoter polymorphisms in susceptibility to atopic dermatitis.

Association screen for atopic dermatitis candidate gene regions using microsatellite markers in pooled DNA samples

Atopic dermatitis (AD) is a chronic inflammatory skin disease affecting up to 16% of children in developed countries. A complex genetic background for AD has been suggested, with genetic as well as environmental factors influencing disease susceptibility. Among other factors, dysregulation in both the innate and the adaptive immune system has been proposed to play a role in AD pathophysiology. We present here an extended association screen for AD using microsatellite markers in 154 genes related to innate and adaptive immunity in pooled DNA samples from 150 German children with AD and 100 controls. After Bonferroni correction, no marker revealed a significant association with AD. Yet, markers representing the nuclear factor kappa B (NFKB)1 and chemokine receptor (CCR)4 genes showed differences in allelic distributions between cases and controls for both pooled DNA analysis and individual genotyping and were thus further investigated. Evaluation of additional single nucleotide polymorphisms (SNP) in the NFKB1 and CCR4 genes revealed no association of individual SNPs with AD. In contrast, haplotype analyses showed a significantly different haplotype distribution between patients and controls for CCR4 (P < 0.001). Furthermore, when SNP-SNP interaction effects were analysed for these two genes, we found significant evidence for epistatic interactions between SNPs within each of the two genes but no evidence for a gene-gene interaction, suggesting that variation in or near both the CCR4 and the NFKB1 genes might individually contribute to AD pathogenesis.

Psoriasis: genetic associations and immune system changes

Psoriasis is a common inflammatory skin disease characterized by infiltration of inflammatory cells into the epidermis and altered keratinocyte differentiation. Psoriasis is currently thought of as a T-cell mediated 'Type-1' autoimmune disease. Gene expression changes in psoriasis lesions have been well documented, and strongly support an important role for tumor necrosis factor and interferon gamma signal pathways in its pathogenesis. The strongest genetic determinant of psoriasis identified to date lies within the class I region of the multiple histocompatibility locus antigen cluster, although its low penetrance implicates a requirement for other genetic risk factors. Multiple genome-wide linkage and an increasing number of association studies have been carried out, leading to multiple linkage peaks, and the identification of potential low risk variants. A number of these variants lie within genes encoding components of the immune system. However, the functional relationships between predisposing genetic variation is unclear, and presumably involves genetic susceptibility factors affecting both immune cell activation and keratinocyte differentiation. The interaction of environmental trigger factors with genetic effects is also not understood, but provide further evidence for the complex basis of this disease.