No evidence for an association between a variant of the mast cell chymase gene and atopic dermatitis based on case-control and haplotype-relative-risk analyses

Association analysis of single nucleotide polymorphisms at five loci: comparison between atopic dermatitis and asthma in the Chinese Han population

Atopic diseases, such as atopic dermatitis (AD) and asthma, are closely related to clinical phenotypes with hypersensitivity, and often share some similar genetic and pathogenic bases. Our recent GWAS identified three susceptibility gene/loci FLG (rs11204971 and rs3126085), 5q22.1 (rs10067777, rs7701890, rs13360927 and rs13361382) and 20q13.33 (rs6010620) to AD. The effect of these AD associated polymorphisms in asthma is so far unknown. To investigate whether AD relevant genetic variants is identical to asthma and reveal the differences in genetic factors between AD and asthma in Chinese Han population, seven AD associated single nucleotide polymorphisms (SNPs) as well as 3 other SNPs (rs7936562 and rs7124842 at 11q13.5 and rs4982958 at 14q11.2) from our previous AD GWAS were genotyped in 463 asthma patients and 985 controls using Sequenom MassArray system. We found rs4982958 at 14q11.2 was significantly associated with asthma (P = 3.04×10⁻⁴, OR = 0.73). We also detected one significant risk haplotype GGGA from the 4 SNPs (rs10067777, rs7701890, rs13360927 and rs13361382) at 5q22.1 in AD cases (P_correction = 3.60×10⁻¹⁰, OR = 1.26), and the haplotype was suggestive of risk in asthma cases in this study (P = 0.014, P_correction = 0.084, OR = 1.38). These SNPs (rs11204971, rs3126085, rs7936562, rs712484 and rs6010620) at AD susceptibility genes/loci FLG, 11q13.5 and 20q13.33 were not associated with asthma in this study. Our results further comfirmed that 14q11.2 was an important candidate locus for asthma and demonstrated that 5q22.1 might be shared by AD and asthma in Chinese Han population.

Eczema in early life: genetics, the skin barrier, and lessons learned from birth cohort studies

Eczema is a chronic inflammatory disorder of the skin that affects up to 30% of children. It often afflicts infants in the first few months of life and can be the first indicator of the atopic march. Recent results from birth cohort studies have uncovered novel information regarding genetic and environmental factors that promote the development of eczema. Birth cohort studies provide an optimal study design to elucidate these associations and prospectively track longitudinal data including exposure assessment and health outcomes from birth into early life and childhood. This is especially relevant for eczema given the age specific emergence of this disease. In this review, we will provide a general overview of pediatric eczema and discuss the important findings in the literature with respect to genetics and environmental exposures, highlighting those derived from birth cohort studies. Additionally, we will review how these relate to the atopic march, the hygiene hypothesis and the integrity of the skin barrier.

An update on the genetics of atopic dermatitis: scratching the surface in 2009

A genetic basis for atopic dermatitis (AD) has long been recognized. Historic documents allude to family history of disease as a risk factor. Before characterization of the human genome, heritability studies combined with family-based linkage studies supported the definition of AD as a complex trait in that interactions between genes and environmental factors and the interplay between multiple genes contribute to disease manifestation. A summary of more than 100 published reports on genetic association studies through mid-2009 implicates 81 genes, in 46 of which at least 1 positive association with AD has been demonstrated. Of these, the gene encoding filaggrin (FLG) has been most consistently replicated. Most candidate gene studies to date have focused on adaptive and innate immune response genes, but there is increasing interest in skin barrier dysfunction genes. This review examines the methods that have been used to identify susceptibility genes for AD and how the underlying pathology of this disease has been used to select candidate genes. Current challenges and the potential effect of new technologies are discussed.

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.

Genetic susceptibility to atopic dermatitis

Atopic dermatitis (AD) is a chronic inflammatory skin disorder with an increasing prevalence in industrialized countries. AD belongs to the group of allergic disorders that includes food allergy, allergic rhinitis, and asthma. A multifactorial background for AD has been suggested, with genetic as well as environmental factors influencing disease development. Recent breakthroughs in genetic methodology have greatly augmented our understanding of the contribution of genetics to susceptibility to AD. A candidate gene association study is a general approach to identify susceptibility genes. Fifty three candidate gene studies (50 genes) have identified 19 genes associated with AD risk in at least one study. Significant associations between single nucleotide polymorphisms (SNPs) in chemokines (chymase 1-1903A > G), cytokines (interleukin13 Arg144Gln), cytokine receptors (interleukin 4 receptor 1727G > A) and SPINK 1258G > A have been replicated in more than one studies. These SNPs may be promising for identifying at-risk individuals. SNPs, even those not strongly associated with AD, should be considered potentially important because AD is a common disease. Even a small increase in risk can translate to a large number of AD cases. Consortia and international collaborative studies, which may maximize study efficacy and overcome the limitations of individual studies, are needed to help further illuminate the complex landscape of AD risk and genetic variations.

Association study of mast cell chymase polymorphisms with atopy

BACKGROUND

Atopic disorders are the result of complex interactions between genetic and environmental factors. Associations analyses between the promoter polymorphism rs1800875 in the mast cell chymase gene (CMA1) and atopy-related phenotypes have yielded inconsistent results.

METHODS

We sequenced the CMA1 locus in 24 unrelated healthy individuals with serum IgE levels <50% percentile and 24 individuals with atopic eczema and serum IgE levels >90% percentile. Seven CMA1 single nucleotide polymorphisms (SNPs) were evaluated for evidence of associations with atopic phenotypes within a large population of German adults (n = 1875). Subjects were phenotyped by standardized questionnaires and interviews, skin prick testing and serum IgE measurements. Genotyping was performed using MALDI-TOF MS (Matrix-Assisted Laser Desorption Ionization-Time of Flight mass spectrometry).

RESULTS

Promoter polymorphism rs1800875 was significantly associated with atopic eczema. No associations between any other single SNP and atopic phenotypes could be detected. Haplotype reconstruction revealed four of 128 possible haplotypes reaching estimated frequencies of 3% or more. Two of these haplotypes showed a borderline-significant association with atopic eczema, which did not remain significant after correction for multiple testing.

CONCLUSIONS

Results confirm previous observations of a significant association between the CMA1 promoter polymorphism rs1800875 and atopic eczema, but not with serum IgE levels, and support the hypothesis that CMA1 serves as candidate gene for atopic eczema.

A novel (TG)n(GA)m repeat polymorphism 254 bp downstream of the mast cell chymase (CMA1) gene is associated with atopic asthma and total serum IgE levels

The gene for mast cell chymase (CMA1) is an ideal candidate for investigating genetic predisposition to atopic asthma, as it is an important mediator of inflammation and remodeling in the asthmatic lung. Various studies have examined the association between -1903 G/A polymorphism and allergic phenotypes, but inconsistent results have been obtained. We investigated the association of this SNP and a novel (TG)(n)(GA)(m) repeat polymorphism (accession no. BV210164) 254 bp downstream of the gene with asthma and its associated traits in a case-control study in two independent cohorts recruited from the Indian population. A significant association was observed for the (TG)(n)(GA)(m) repeat with asthma (p<0.05) in both the cohorts. Although no association was observed for the -1903 G/A SNP with asthma, a significant association was observed between the genotypes and serum IgE levels (p=0.003 and 0.0004 for cohort A and B). When haplotypes were compared between patients and controls, the haplotype G_43 was found at higher frequency in controls (p=0.05). Also, on comparing major haplotypes (>5%) with respect to log total serum IgE levels, a significant difference was obtained (p=0.018 and p=0.046 for cohorts A and B). These results suggest that the CMA1 gene contributes to asthma susceptibility and may be involved in regulating IgE levels in atopic asthma.

The genetics of atopic dermatitis: recent findings and future options

Atopic dermatitis (AD) is a chronic pruritic skin disease affecting up to 15% of children in industrialized countries. AD belongs to the group of allergic disorders that include food allergy, allergic rhinitis, and asthma. A multifactorial background for AD has been suggested, with genetic as well as environmental factors influencing disease development. Genome-wide screens for AD have been completed in four different populations to date. Interestingly, the susceptibility regions identified for AD show little overlap with asthma susceptibility regions, suggesting that, at least in part, separate genes might be involved in the pathogenesis of the different atopic disorders. Instead, some of the identified regions overlap with susceptibility regions for psoriasis, another chronic skin disease. Thus, genes expressed in the skin might play an important role in AD pathogenesis, in addition to genes influencing atopic diatheses. Although no veritable "AD gene" has been identified by positional cloning to date, examples from other complex genetic disorders such as asthma show that this goal is likely to be reached in the near future. Candidate gene studies, on the other hand, have identified 19 genes that were shown to be associated with AD in at least one study. The results of genome-wide screens as well as candidate gene studies are evaluated here in detail.

Mast cell chymase is increased in chronic atopic dermatitis but not in psoriasis

Mast cell chymase is a chymotrypsin-like serine proteinase primarily stored in secretory mast cell granules. Mast cell chymase has various effects on angiotensin, metalloproteases, lipoproteins, procollagen, neuropeptides and cytokines. Recent studies have demonstrated that chymase inhibitors inhibit skin inflammation. In this study we sought to determine the role of mast cell chymase in atopic dermatitis (AD) in comparison with its role in psoriasis and normal skin. Skin biopsy specimens were obtained from non-lesional and lesional skin of patients with chronic AD and psoriasis and from normal skin of non-atopic and non-psoriatic controls. The number of mast cells containing chymase was determined by immunohistochemistry using a chymase-specific monoclonal antibody. A significantly (P < 0.05) enhanced number of chymase-positive cells was found in lesional AD skin as compared to normal skin as well as to lesional and non-lesional skin of patients with psoriasis. A significant (P < 0.05) increase in the number of chymase-positive cells was also found in non-lesional AD skin in comparison to psoriasis. An enhanced, albeit not statistically significant difference was noted in non-lesional AD skin as compared to normal skin. In conclusion, these results suggest that mast cell chymase may play an integral part in eliciting and maintaining cutaneous inflammation in AD but not in psoriasis. The increased proteinase activity of mast cell chymase may also be involved in promoting a skin barrier defect in AD, which subsequently enhances the skin's permeability to allergens and microbes and thereby aggravates the eczema.

Polymorphism of the mast cell chymase gene (CMA1) promoter region: lack of association with asthma but association with serum total immunoglobulin E levels in adult atopic dermatitis

BACKGROUND

Mast cell chymase has the potential to be an important mediator of inflammation and remodelling in the asthmatic lung. Previous studies have examined association between promoter polymorphism of the chymase gene (CMA1) and allergic phenotypes but the significance of this polymorphism is unclear. We have examined association of a CMA1 variant in relation to asthma in a large UK Caucasian family cohort.

METHODS

A polymorphism of the CMA1 gene promoter (-1903G/A) was genotyped in 341 asthmatic families and in 184 non-asthmatic adults recruited from the UK PCR-RFLP based genotyping. Association with asthma diagnosis, atopy, specific and total IgE, and atopy and asthma severity was examined.

RESULTS

Case-control studies did not reveal a significant difference in allele frequency between asthmatics and controls. A significant association was found between CMA1 genotypes and total IgE levels in subjects with self-reported eczema that remained significant after correction for multiple testing (median total serum IgE GG 297 kU/L, GA 144 kU/L, AA 48.4 kU/L, Pc=0.0032).

CONCLUSION

These data suggest that CMA1 promoter polymorphism does not contribute to asthma susceptibility or severity but may be involved in regulating IgE levels in patients with eczema.

Therapeutic potential of a specific chymase inhibitor in atopic dermatitis

A novel therapeutic mechanism may be the key to improving the chief symptoms and signs of atopic dermatitis (AD), which are persistent pruritus and high serum IgE. We demonstrate here that mast cell chymase may be a possible initiating factor and that the orally active specific inhibitor Y-40613 may have a therapeutic potential in the treatment of AD. We found that Y-40613 (2-[5-amino-2-(4-fluorophenyl)-1,6-dihydro-6-oxo-1-pyrimidinyl]-N-[1-[(5-methoxycarbonyl-2-benzoxazolyl)carbonyl]-2-phenylethyl]acetamide) dose-dependently suppressed the scratching response in a mouse pruritus model, with inhibitory efficacy enhanced by combination with conventional drugs, suggesting that chymase contributes to the development of pruritus by a unique mechanism or mechanisms. In fact, chymase injected in the model induced the scratching response. In vitro IgE production from mouse B cells was increased by purified rat chymase and suppressed by Y-40613. Increased serum IgE observed in Brown Norway rats injected with mercury chloride was suppressed by Y-40613. Furthermore, Y-40613 lowered ear thickness as well as serum IgE level in a mouse contact dermatitis model. Taken together, these findings suggest that the specific chymase inhibitor Y-40613 may ameliorate symptoms of AD through the dual inhibition of the chymase-dependent IgE production pathway and itching sensation.

The genetics of atopic dermatitis

PURPOSE OF REVIEW

Atopic dermatitis is typified by itchy, inflamed skin. It is increasingly common in the developed world and is a major cause of morbidity in infants and young children. Most children with the disease have high levels of immunoglobulin E and many have concomitant asthma. The cause of the disease is unknown, but it is highly heritable. Identification of the genes and genetic variants underlying atopic dermatitis may lead to new treatments and better classification of children with the disease.

RECENT FINDINGS

Preliminary genetic studies have identified genes or clusters of genes that are expressed in the outermost layer of the skin to be just as important as genes that may modify the atopic process. These genes may influence other diseases, including psoriasis. Genome screens in mouse models seem to indicate involvement of some of the equivalent chromosomal regions as for human disease.

SUMMARY

The findings suggest that atopy in atopic dermatitis may be a secondary process, rather than the cause of the disease. The barrier function of the skin is seen not to be merely passive. Identification of the genes underlying atopic dermatitis is feasible and likely within a few years.

Interactions between genes and environmental factors in asthma and atopy: new developments

Asthma and associated phenotypes are complex traits most probably caused by an interaction of multiple disease susceptibility genes and environmental factors. Major achievements have occurred in identifying chromosomal regions and polymorphisms in candidate genes linked to or associated with asthma, atopic dermatitis, IgE levels and response to asthma therapy. The aims of this review are to explain the methodology of genetic studies of multifactorial diseases, to summarize chromosomal regions and polymorphisms in candidate genes linked to or associated with asthma and associated traits, to list genetic alterations that may alter response to asthma therapy, and to outline genetic factors that may render individuals more susceptible to asthma and atopy due to environmental changes.

The role of cutaneous dendritic cells in the immunopathogenesis of atopic dermatitis

We review the immunology of atopic dermatitis (AD) and focus attention on the role of cutaneous dendritic cells. AD is a complex immune-mediated skin disorder characterized by the recruitment of both CD4+ and CD8+ T cells into the skin. T-helper (Th) 2-type cytokines are dominant in acute AD skin, while both Th1- and Th2-type cytokines are present in chronic AD. Cutaneous dendritic cells, which are present in increased numbers within AD skin, are believed to play a key part in the activation of T cells in the skin. They may also help to determine the pattern of cytokines produced by activated effector T cells.

Synthesis, structure-activity relationships, and pharmacokinetic profiles of nonpeptidic alpha-keto heterocycles as novel inhibitors of human chymase

We designed nonpeptidic chymase inhibitors based on the structure of a peptidic compound (1) and demonstrated that the combination of a pyrimidinone skeleton as a P3-P2 scaffold and heterocycles as P1 carbonyl-activating groups can function as a nonpeptidic chymase inhibitor. In particular, introduction of heterobicycles such as benzoxazole resulted in more potent chymase-inhibitory activity. Detailed structure-activity relationship studies on the benzoxazole moiety and substituents at the 2-position of the pyrimidinone ring revealed that 2r (Y-40079) had the most potent chymase-inhibitory activity (K(i) = 4.85 nM). This compound was also effective toward chymases of nonhuman origin and showed good selectivity for chymases over other proteases. Pharmacokinetic studies in rats indicated that 2r was absorbed slowly after oral administration and showed satisfactory bioavailability (BA) (T(max) = 6.0 +/- 2.3 h, BA = 19.3 +/- 6.6%, t(1/2) = 35.7 +/- 13.3 h). In conclusion, 2r is a novel, potent, and orally active chymase inhibitor which would be a useful tool in elucidating the pathophysiological roles of chymase.

Absence of association between a variant of the mast cell chymase gene and atopic dermatitis in an Italian population

Atopic dermatitis (AD) is a chronic dermatitis which belongs to the group of atopy-related diseases together with asthma and rhinitis. IgE and mast cell chymase (MCC) play a key role in atopic or allergic inflammation of the skin. An association between AD and a genetic variant of the MCC has been reported in a Japanese population, but failure of confirmation has rendered this association questionable. We have tested for genetic association to an MCC variant in relation to AD in an Italian population. No significant association was found between AD and MCC genotypes. These data suggest that BstXI MCC polymorphism may not be involved in AD.

Non-peptidic inhibitors of human chymase. Synthesis, structure-activity relationships, and pharmacokinetic profiles of a series of 5-amino-6-oxo-1,6-dihydropyrimidine-containing trifluoromethyl ketones

Chymase possesses a wide variety of actions, including promotion of angiotensin II production and histamine release from mast cells. However, due to a lack of effective inhibitors featuring both high inhibitory activity and high metabolic stability, the pathophysiological role of chymase has not been fully elucidated. We designed non-peptidic inhibitors based on the predicted binding mode of the peptidic chymase inhibitor Val-Pro-Phe-CF3 and demonstrated that the Val-Pro unit is replaceable with a (5-amino-6-oxo-2-phenyl-1,6-dihydro-1-pyrimidinyl)acetyl moiety. Structure-activity relationship studies revealed that phenyl substitution at the 2-position of the pyrimidinone ring is indispensable for high activity. The most potent compound 1h (Ki = 0.0506 microM) is superior in potency to the parent peptidic inhibitor Val-Pro-Phe-CF3 and has good selectivity for chymase over other proteases. The related analogue 1e was orally absorbed and maintained high plasma levels for at least 2h. These results suggest that the derivatives reported here could be developed as agents for treatment of chymase-induced disease.

Atopic dermatitis: pathogenetic mechanisms

Atopic dermatitis (AD) is a chronic inflammatory skin disease with increasing incidence and socio-economical relevance. The diagnosis is made on clinical grounds and different diagnostic criteria sets have been established. The majority of all AD cases is associated with a sensitization to environmental allergens and increased serum IgE (so-called extrinsic AD), but about 10--30% of all cases suffer from the so-called intrinsic AD, which obviously lacks any link to the classical atopic diathesis. The genetic background of AD has been investigated by target gene approach by different groups with mostly contradictory results for each of the genes under study. An imbalance in the spectrum of Th1/Th2 responses, a disturbed prostaglandin metabolism, intrinsic defects in keratinocyte function, delayed eosinophil apoptosis, IgE-mediated facilitated antigen presentation by epidermal dendritic cells, a two phase model of the inflammatory response and staphylococcal superantigen effects are among the currently studied pathogenetical aspects of extrinsic AD, which are reviewed in this paper.

Molecular genetics of allergic diseases

Allergic diseases affect approximately one third of the general population. This class of disease, characterized by elevated serum IgE levels and hypersensitivity to normally innocuous antigen, can manifest in practically any mucosal tissue or as a systemic response. A few examples of serious allergic diseases include asthma, dermatitis, bee sting allergy, food allergy, conjunctivitis, and severe systemic anaphylaxis. Taken together, allergic diseases constitute one of the major problems of modern day medicine. A considerable portion of the healthcare budget is expended in the treatment of allergic disease, and morbidity rates of inner city asthmatics are rising steadily. Due to the enormity of the problem, there has been a worldwide effort to identify factors that contribute to the etiology of allergic diseases. Epidemiologic studies of multigeneration families and large numbers of twins clearly indicate a strong genetic component to atopic diseases. At least two independently segregating diseasesusceptibility genes are thought to come together with environmental factors to result in allergic inflammation in a particular tissue. On the basis of the strong genetic studies, multiple groups have attempted to identify disease-susceptibility genes via either a candidate gene approach or by genome-wide scans. Both of these approaches have implicated multiple regions in the human and mouse genomes, which are currently being evaluated as harboring putative atopy genes.

No association between atopy/asthma and the ILe50Val polymorphism of IL-4 receptor

Susceptibility to atopic diseases is known to involve genetic factors. The interleukin-4 (IL-4) receptor- alpha gene (IL4R) reportedly is involved in the development of atopy. A recent study has shown the Ile50 allele of a polymorphism (Ile50Val) of IL4R to be associated with atopy. The objective of this study was to replicate this association and confirm the possible role of the Ile50Val polymorphism of IL4R in the etiology of atopic asthma in a Japanese population. We conducted a transmission disequilibrium test in 86 families identified through asthmatic children. A case-control study was also carried out using both atopic and control subjects. The IL4R Ile50Val polymorphism was genotyped by a PCR-restriction fragment length polymorphism method using an intronic upstream primer. The IL4R Ile50 allele was not preferentially transmitted to atopy- or to asthma-affected children. Neither the Ile50 allele nor the Ile50/Ile50 genotype was more prevalent in the atopic subjects than in the control subjects. Our findings indicate that the Ile50Val polymorphism of IL4R does not play a substantial role in genetic predisposition for the etiology of atopy or asthma in this Japanese population.