FCεRI gene promoter polymorphisms and total IgE levels in susceptibility to atopic dermatitis in Korea

Candidate Gene Association Studies in Atopic Dermatitis in Participants of European and Asian Ancestry: A Systematic Review and Meta-Analysis

Atopic dermatitis (AD) has been extensively investigated for genetic associations utilizing both candidate gene approaches and genome-wide scans. Here, we comprehensively evaluated the available literature to determine the association of candidate genes in AD to gain additional insight into the etiopathogenesis of the disease. We systematically screened all studies that explored the association between polymorphisms and AD risks in cases of European and Asian ancestry and synthesized the available evidence through a random-effects meta-analysis. We identified 99 studies that met our inclusion/exclusion criteria that examined 17 candidate loci in Europeans and 14 candidate genes in Asians. We confirmed the significant associations between FLG variants in both European and Asian populations and AD risk, while synthesis of the available data revealed novel loci mapped to IL18 and TGFB1 genes in Europeans and IL12RB1 and MIF in Asians that have not yet been identified by genome-wide association studies. Our findings provide comprehensive evidence for AD risk loci in cases of both European and Asian ancestries, validating previous associations as well as revealing novel loci that could imply previously unexplored biological pathways.

Interaction between functional polymorphisms in FCER1A and TLR2 and the severity of atopic dermatitis

Dendritic cell toll-like receptors (TLRs) and the high-affinity immunoglobulin E (IgE) receptor (FcεRI) may biologically interact with regard to atopic dermatitis (AD) development and, especially, severity. Our aim here was to test if such interaction can be detected on the genetic level. The combined effect of the TLR2 gene (TLR2) rs4696480 and the FcεRI α-chain gene (FCER1A) rs2252226 and rs2251746 polymorphisms on the AD severity as measured by SCORAD was assessed. The FCER1A rs2252226 and TLR2 rs4696480 polymorphisms interacted with regard to SCORAD. Higher SCORAD was observed in patients being the TLR2 rs4696480 major homozygotes and carrying at the same time the FCER1A rs2252226 minor allele, compared to those characterized by (any other of) the remaining combined rs2252226 and rs4696480 genotypes. The observation of the epistatic effect of TLR2 and FCER1A genetic variants on SCORAD is in line with the involvement of the interaction TLRs-FcεRI in the pathophysiology of AD.

Identification of Novel Biomarkers for Drug Hypersensitivity After Sequencing of the Promoter Area in 16 Genes of the Vitamin D Pathway and the High-Affinity IgE Receptor

The prevalence of allergic diseases and drug hypersensitivity reactions (DHRs) during recent years is increasing. Both, allergic diseases and DHRs seem to be related to an interplay between environmental factors and genetic susceptibility. In recent years, a large effort in the elucidation of the genetic mechanisms involved in these disorders has been made, mostly based on case-control studies, and typically focusing on isolated SNPs. These studies provide a limited amount of information, which now can be greatly expanded by the complete coverage that Next Generation Sequencing techniques offer. In this study, we analyzed the promoters of sixteen genes related to the Vitamin D pathway and the high-affinity IgE receptor, including FCER1A, MS4A2, FCER1G, VDR, GC, CYP2R1, CYP27A1, CYP27B1, CYP24A1, RXRA, RXRB, RXRG, IL4, IL4R, IL13, and IL13RA1. The study group was composed of patients with allergic rhinitis plus asthma (AR+A), patients with hypersensitivity to beta-lactams (BLs), to NSAIDs including selective hypersensitivity (SH) and cross-reactivity (CR), and healthy controls without antecedents of atopy or adverse drug reactions. We identified 148 gene variations, 43 of which were novel. Multinomial analyses revealed that three SNPs corresponding to the genes FCER1G (rs36233990 and rs2070901), and GC (rs3733359), displayed significant associations and, therefore, were selected for a combined dataset study in a cohort of 2,476 individuals. The strongest association was found with the promoter FCER1G rs36233990 SNP that alters a transcription factor binding site. This SNP was over-represented among AR+A patients and among patients with IgE-mediated diseases, as compared with control individuals or with the rest of patients in this study. Classification models based on the above-mentioned SNPs were able to predict correct clinical group allocations in patients with DHRs, and patients with IgE-mediated DHRs. Our findings reveal gene promoter SNPs that are significant predictors of drug hypersensitivity, thus reinforcing the hypothesis of a genetic predisposition for these diseases.

Differences in Genetic Variations Between Treatable and Recalcitrant Atopic Dermatitis in Korean

Purpose

Variations in barrier- or immune response-related genes are closely related to the development of atopic dermatitis (AD). This study was designed to identify genetic variations and clinical features to predict ‘recalcitrant AD.’

Methods

AD patients were classified as treatable and recalcitrant. Treatable AD patients showed satisfactory clinical improvement with basic and topical treatments. Recalcitrant AD patients used systemic immune-suppressants for over 4 weeks as they had not shown clinical improvement with basic and topical treatments. The frequency of gene variations in barrier- (FLG 3321delA, FLG K4022X, KLK7, SPINK 1156, SPINK 1188, SPINK 2475) and immune response- (DEFB1, KDR, IL-5RA, IL-9, and IL-12RB1a, b) related genes were compared between each AD group and the controls.

Results

Of all, 249 treatable AD and 32 recalcitrant AD were identified. Heterozygous mutations (Hetero) in KLK7 was more frequent in recalcitrant AD patients than treatable AD, without statistical significance. Hetero in DEFB1 was more frequent in treatable AD patients. However, no other significant genetic differences between treatable and recalcitrant AD was observed. Instead, higher initial Eczema Area Severity Index (EASI) score, serum immunoglobulin E (IgE) level, allergen specific IgE for house dust mites, and family history of atopic diseases were associated with recalcitrant AD with statistical significance.

Conclusions

According to our study, no genetic variation to predict recalcitrant AD was identified, suggesting that clinical manifestation, rather than genetic variations of AD patients is more likely to be an important factor in predicting the prognosis of AD. Further large-scale studies on the correlation between genetic variation and recalcitrant AD are needed.

Molecular Mechanisms of Cutaneous Inflammatory Disorder: Atopic Dermatitis

Atopic dermatitis (AD) is a multifactorial inflammatory skin disease resulting from interactions between genetic susceptibility and environmental factors. The pathogenesis of AD is poorly understood, and the treatment of recalcitrant AD is still challenging. There is accumulating evidence for new gene polymorphisms related to the epidermal barrier function and innate and adaptive immunity in patients with AD. Newly-found T cells and dendritic cell subsets, cytokines, chemokines and signaling pathways have extended our understanding of the molecular pathomechanism underlying AD. Genetic changes caused by environmental factors have been shown to contribute to the pathogenesis of AD. We herein present a review of the genetics, epigenetics, barrier dysfunction and immunological abnormalities in AD with a focus on updated molecular biology.

Are Podoplanin Gene Polymorphisms Associated with Atopic Dermatitis in Koreans?

Background

The histologic characteristics of atopic dermatitis (AD) include perivascular edema and dilated tortuous vessels in the papillary dermis. A single nucleotide polymorphism (SNP) of the fms-related tyrosine kinase 4 (FLT4) gene is associated with AD.

Objective

To investigate the associations between podoplanin (PDPN) gene SNPs and AD.

Methods

We genotyped 9 SNPs from 5 genes of 1,119 subjects (646 AD patients and 473 controls). We determined the promoter activity of 1 SNP (rs355022) by luciferase assay; this SNP was further investigated using 1,133 independent samples (441 AD patients and 692 controls).

Results

The rs355022 and rs425187 SNPs and the C-A haplotype in the PDPN gene were significantly associated with intrinsic AD in the initial experiment. The rs355022 SNP significantly affected promoter activity in the luciferase assay. However, these results were not replicated in the replication study.

Conclusion

Two SNPs and the C-A haplotype in the PDPN gene are significantly associated with intrinsic AD; although, the results were confirmed by luciferase assay, they could not be replicated with independent samples. Nevertheless, further replication experiments should be performed in future studies.

Molecular biology of atopic dermatitis

Atopic dermatitis (AD) is a chronic inflammatory skin disease with specific genetic and immunological mechanisms. The rapid development of new techniques in molecular biology had ushered in new discoveries on the role of cytokines, chemokines, and immune cells in the pathogenesis of AD. New polymorphisms of AD are continually being reported in different populations. The physical and immunological barrier of normal intact skin is an important part of the innate immune system that protects the host against microbials and allergens that are associated with AD. Defects in the filaggrin gene FLG may play a role in facilitating exposure to allergens and microbial pathogens, which may induce Th2 polarization. Meanwhile, Th22 cells also play roles in skin barrier impairment through IL-22, and AD is often considered to be a Th2/Th22-dominant allergic disease. Mast cells and eosinophils are also involved in the inflammation via Th2 cytokines. Release of pruritogenic substances by mast cells induces scratching that further disrupts the skin barrier. Th1 and Th17 cells are mainly involved in chronic phase of AD. Keratinocytes also produce proinflammatory cytokines such as thymic stromal lymphopoietin (TSLP), which can further affect Th cells balance. The immunological characteristics of AD may differ for various endotypes and phenotypes. Due to the heterogeneity of the disease, and the redundancies of these mechanisms, our knowledge of the pathophysiology of the disease is still incomplete, which is reflected by the absence of a cure for the disease.

Different FCER1A polymorphisms influence IgE levels in asthmatics and non-asthmatics

BACKGROUND

Recently, three genome-wide association studies (GWAS) demonstrated FCER1A, the gene encoding a ligand-binding subunit of the high-affinity IgE receptor, to be a major susceptibility locus for serum IgE levels. The top association signal differed between the two studies from the general population and the one based on an asthma case-control design. In this study, we investigated whether different FCER1A polymorphisms are associated with total serum IgE in the general population and asthmatics specifically.

METHODS

Nineteen polymorphisms were studied in FCER1A based on a detailed literature search and a tagging approach. Polymorphisms were genotyped by the Illumina HumanHap300Chip (6 polymorphisms) or MALDI-TOF MS (13 polymorphisms) in at least 1303 children (651 asthmatics) derived from the German International Study of Asthma and Allergies in Childhood II and Multicentre Asthma Genetics in Childhood Study.

RESULTS

Similar to two population-based GWAS, the peak association with total serum IgE was observed for SNPs rs2511211, rs2427837, and rs2251746 (mean r(2) > 0.8), with the lowest p-value of 4.37 × 10(-6). The same 3 polymorphisms showed the strongest association in non-asthmatics (lowest p = 0.0003). While these polymorphisms were also associated with total serum IgE in asthmatics (lowest p = 0.003), additional polymorphisms (rs3845625, rs7522607, and rs2427829) demonstrated associations with total serum IgE in asthmatics only (lowest p = 0.01).

CONCLUSIONS

These data suggest that FCER1A polymorphisms not only drive IgE levels in the general population but that specific polymorphisms may also influence IgE in association with asthma, suggesting that disease-specific mechanisms in IgE regulation exist.

Current concepts of IgE regulation and impact of genetic determinants

Immunoglobulin E (IgE) mediated immune responses seem to be directed against parasites and neoplasms, but are best known for their involvement in allergies. The IgE network is tightly controlled at different levels as outlined in this review. Genetic determinants were suspected to influence IgE regulation and IgE levels considerably for many years. Linkage and candidate gene studies suggested a number of loci and genes to correlate with total serum IgE levels, and recently genome-wide association studies (GWAS) provided the power to identify genetic determinants for total serum IgE levels: 1q23 (FCER1A), 5q31 (RAD50, IL13, IL4), 12q13 (STAT6), 6p21.3 (HLA-DRB1) and 16p12 (IL4R, IL21R). In this review, we analyse the potential role of these GWAS hits in the IgE network and suggest mechanisms of how genes and genetic variants in these loci may influence IgE regulation.

Atopic dermatitis 2.0: from the clinical phenotype to the molecular taxonomy and stratified medicine

Atopic dermatitis (AD) is a paradigmatic inflammatory chronic skin disease. As for other chronic skin diseases, (i) the spectrum of the clinical phenotype and severity as well as (ii) the genetic background and (iii) the underlying mechanisms strongly suggest a high degree of pathophysiological heterogeneity yet leading to a similar clinical pattern, that is, the eczematous skin lesion, but showing distinct progression patterns. This review suggests to exploit the recent knowledge about AD for a novel approach proposing a tentative first molecular taxonomy of this disease based on the genotype and endophenotype. The consequences in terms of personalized prevention and management are delineated.