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.
To the Editor: Atopic dermatitis (AD) is the most common inflammatory skin disease, affecting up to 20% of children in the United States, and is characterized by an increased susceptibility to ...cutaneous infections.1,2 One in 10 subjects with AD has difficulty clearing cutaneous infections with a host of viruses including herpes simplex, vaccinia, human papilloma, and/or molluscum contagiosum.1 This typically manifests as more extensive cutaneous and sometimes systemic disease and/or resistance to standard therapies.
Background The genetic determinants of the human innate immune response are poorly understood. Apolipoprotein (Apo) E, a lipid-trafficking protein that affects inflammation, has well-described ...wild-type (ε3) and disease-associated (ε2 and ε4) alleles, but its connection to human innate immunity is undefined. Objective We sought to define the relationship of APOε4 to the human innate immune response. Methods We evaluated APOε4 in several functional models of the human innate immune response, including intravenous LPS challenge in human subjects, and assessed APOε4 association to organ injury in patients with severe sepsis, a disease driven by dysregulated innate immunity. Results Whole blood from healthy APOε3 / APOε4 volunteers induced higher cytokine levels on ex vivo stimulation with Toll-like receptor (TLR) 2, TLR4, or TLR5 ligands than blood from APOε3 / APOε3 patients, whereas TLR7/8 responses were similar. This was associated with increased lipid rafts in APOε3/APOε4 monocytes. By contrast, APOε3 / APOε3 and APOε3 / APOε4 serum neutralized LPS equivalently and supported similar LPS responses in Apoe -deficient macrophages, arguing against a differential role for secretory APOE4 protein. After intravenous LPS, APOε3/APOε4 patients had higher hyperthermia and plasma TNF-α levels and earlier plasma IL-6 than APOε3/APOε3 patients. APOE4-targeted replacement mice displayed enhanced hypothermia, plasma cytokines, and hepatic injury and altered splenic lymphocyte apoptosis after systemic LPS compared with APOE3 counterparts. In a cohort of 828 patients with severe sepsis, APOε4 was associated with increased coagulation system failure among European American patients. Conclusions APOε4 is a determinant of the human innate immune response to multiple TLR ligands and associates with altered patterns of organ injury in human sepsis.
Background Atopic dermatitis (AD) is a chronic inflammatory skin disease that is characterized by a defective skin barrier function. Recent studies have reported mutations of the skin barrier gene ...encoding filaggrin in a subset of patients with AD. Objective We investigated whether reduced filaggrin expression was found in patients with AD who were not carriers of known filaggrin mutations and whether filaggrin expression was modulated by the atopic inflammatory response. Methods Filaggrin expression was measured in skin biopsies and cultured keratinocytes using real-time RT-PCR and immunohistochemistry. Filaggrin loss-of-function mutations were screened in a total of 69 subjects. Results Compared with normal skin, filaggrin expression was significantly reduced ( P < .05) in acute AD skin, with further reduction seen in acute lesions from 3 European American subjects with AD who were heterozygous for the 2282del4 mutation. This was confirmed by using immunohistochemistry. AD skin is characterized by the overexpression of IL-4 and IL-13. Keratinocytes differentiated in the presence of IL-4 and IL-13 exhibited significantly reduced filaggrin gene expression (0.04 ± 0.01 ng filaggrin/ng glyceraldehyde 3-phosphate dehydrogenase; P < .05) compared with media alone (0.16 ± 0.03). Conclusion Patients with AD have an acquired defect in filaggrin expression that can be modulated by the atopic inflammatory response. Clinical implications The atopic immune response contributes to the skin barrier defect in AD; therefore, neutralization of IL-4 and IL-13 could improve skin barrier integrity.
Background Atopic dermatitis (AD) is characterized by dry skin and a hyperactive immune response to allergens, 2 cardinal features that are caused in part by epidermal barrier defects. Tight ...junctions (TJs) reside immediately below the stratum corneum and regulate the selective permeability of the paracellular pathway. Objective We evaluated the expression/function of the TJ protein claudin-1 in epithelium from AD and nonatopic subjects and screened 2 American populations for single nucleotide polymorphisms in the claudin-1 gene (CLDN1). Methods Expression profiles of nonlesional epithelium from patients with extrinsic AD, nonatopic subjects, and patients with psoriasis were generated using Illumina's BeadChips. Dysregulated intercellular proteins were validated by means of tissue staining and quantitative PCR. Bioelectric properties of epithelium were measured in Ussing chambers. Functional relevance of claudin-1 was assessed by using a knockdown approach in primary human keratinocytes. Twenty-seven haplotype-tagging SNPs in CLDN1 were screened in 2 independent populations with AD. Results We observed strikingly reduced expression of the TJ proteins claudin-1 and claudin-23 only in patients with AD, which were validated at the mRNA and protein levels. Claudin-1 expression inversely correlated with TH 2 biomarkers. We observed a remarkable impairment of the bioelectric barrier function in AD epidermis. In vitro we confirmed that silencing claudin-1 expression in human keratinocytes diminishes TJ function while enhancing keratinocyte proliferation. Finally, CLDN1 haplotype-tagging SNPs revealed associations with AD in 2 North American populations. Conclusion Collectively, these data suggest that an impairment in tight junctions contributes to the barrier dysfunction and immune dysregulation observed in AD subjects and that this may be mediated in part by reductions in claudin-1.
Background Helminth infections are associated with protection against allergies. It is postulated that IL-10 production after helminth infection suppresses skin hypersensitivity and increases IgG4 ...production, protecting against allergies. Objective We aimed to determine whether IL10 polymorphisms are associated with helminth infection and the risk of wheeze and allergy. Methods Twelve IL10 single nucleotide polymorphisms were genotyped in 1353 children aged 4 to 11 years living in a poor urban area in Salvador, Brazil. Wheezing status, Ascaris lumbricoides and Trichuris trichiura infection, IL-10 production by peripheral blood leukocytes stimulated with A lumbricoides extract, serum total IgE levels, specific IgE levels, skin prick test responses to common aeroallergens, and IgG4 and IgE anti– A lumbricoides antibody levels were measured in all children. Association tests were performed by using logistic or linear regression when appropriate, including sex, age, helminth infection, and principal components for ancestry informative markers as covariates by using PLINK. Results Allele G of marker rs3024496 was associated with the decreased production of IL-10 by peripheral blood leukocytes in response to A lumbricoides stimulation. Allele C of marker rs3024498 was negatively associated with helminth infection or its markers. Marker rs3024492 was positively associated with the risk of atopic wheeze, total IgE levels, and skin prick test responses to cockroach. Conclusions Our findings suggest that IL10 polymorphisms might play a role in the production of IL-10, helminth infection, and allergy. We hypothesize that polymorphisms related to protection against helminths, which would offer an evolutionary advantage to subjects in the past, might be associated with increased risk of allergic diseases.
Background Atopic dermatitis (AD) is a chronic inflammatory skin disease that is characterized by a defective skin barrier function. Recent studies have reported mutations of the skin barrier gene ...encoding filaggrin in a subset of patients with AD. Objective We investigated whether reduced filaggrin expression was found in patients with AD who were not carriers of known filaggrin mutations and whether filaggrin expression was modulated by the atopic inflammatory response. Methods Filaggrin expression was measured in skin biopsies and cultured keratinocytes using real-time RT-PCR and immunohistochemistry. Filaggrin loss-of-function mutations were screened in a total of 69 subjects. Results Compared with normal skin, filaggrin expression was significantly reduced ( P < .05) in acute AD skin, with further reduction seen in acute lesions from 3 European American subjects with AD who were heterozygous for the 2282del4 mutation. This was confirmed by using immunohistochemistry. AD skin is characterized by the overexpression of IL-4 and IL-13. Keratinocytes differentiated in the presence of IL-4 and IL-13 exhibited significantly reduced filaggrin gene expression (0.04 ± 0.01 ng filaggrin/ng glyceraldehyde 3-phosphate dehydrogenase; P < .05) compared with media alone (0.16 ± 0.03). Conclusion Patients with AD have an acquired defect in filaggrin expression that can be modulated by the atopic inflammatory response. Clinical implications The atopic immune response contributes to the skin barrier defect in AD; therefore, neutralization of IL-4 and IL-13 could improve skin barrier integrity.
Background Historically, patients with a prior Fontan procedure for complex congenital heart disease (CHD) have been considered at higher risk for death after heart transplant (HT) compared with ...other HT transplant candidates. With the overall trend of improved survival of pediatric HT recipients, it is unclear of Fontan patient post-HT survival has also improved in the current era. Methods Data from the Pediatric Heart Transplant Study database for Fontan patients who underwent HT was compared between the early era (1993 to 2006, n = 150) and late era (2007 to 2014, n = 252). Post-HT survival and pre-HT characteristics were compared among eras and also with non-Fontan CHD patients. Results At time of HT, Fontan patients in the late era were more likely to require inotropic support, have protein-losing enteropathy, have failure to thrive, and be further from time of Fontan, although less likely to be on ventilator support. Only ventilator support and earlier year of HT were significant risk factors for death in the multivariate analysis. Post-HT Fontan patient survival significantly improved from the early to late era ( p = 0.02), particularly in the early phase, with 1-year survival of 77% in the early era and 89% in the late era. Late era non-Fontan CHD patient 1-year post-HT survival was similar to Fontan patients at 92%. Conclusions Survival of Fontan patients after HT has significantly improved in the current era. Currently, expected post-HT survival for Fontan patients is on par with other CHD patients. Fontan patients should not be excluded from consideration for HT solely on a history of Fontan.
Background A subset of subjects with atopic dermatitis (AD) are susceptible to serious infections with herpes simplex virus, called eczema herpeticum, or vaccina virus, called eczema vaccinatum. ...Objective This National Institute of Allergy and Infectious Diseases–funded multicenter study was performed to establish a database of clinical information and biologic samples on subjects with AD with and without a history of eczema herpeticum (ADEH+ and ADEH− subjects, respectively) and healthy control subjects. Careful phenotyping of AD subsets might suggest mechanisms responsible for disseminated viral infections and help identify at-risk individuals. Methods We analyzed the data from 901 subjects (ADEH+ subjects, n = 134; ADEH− subjects, n = 419; healthy control subjects, n = 348) enrolled between May 11, 2006, and September 16, 2008, at 7 US medical centers. Results ADEH+ subjects had more severe disease based on scoring systems (Eczema Area and Severity Index and Rajka-Langeland score), body surface area affected, and biomarkers (circulating eosinophil counts and serum IgE, thymus and activation-regulated chemokine, and cutaneous T cell–attracting chemokine) than ADEH− subjects ( P < .001). ADEH+ subjects were also more likely to have a history of food allergy (69% vs 40%, P < .001) or asthma (64% vs 44%, P < .001) and were more commonly sensitized to many common allergens ( P < .001). Cutaneous infections with Staphylococcus aureus or molluscum contagiosum virus were more common in ADEH+ subjects (78% and 8%, respectively) than in ADEH− subjects (29% and 2%, respectively; P < .001). Conclusion Subjects with AD in whom eczema herpeticum develops have more severe TH 2-polarized disease with greater allergen sensitization and more commonly have a history of food allergy, asthma, or both. They are also much more likely to experience cutaneous infections with S aureus or molluscum contagiosum.
Background A subset of atopic dermatitis is associated with increased susceptibility to eczema herpeticum (ADEH+). We previously reported that common single nucleotide polymorphisms (SNPs) in the ...IFN-γ (IFNG) and IFN-γ receptor 1 (IFNGR1) genes were associated with the ADEH+ phenotype. Objective We sought to interrogate the role of rare variants in interferon pathway genes for the risk of ADEH+. Methods We performed targeted sequencing of interferon pathway genes ( IFNG , IFNGR1 , IFNAR1 , and IL12RB1 ) in 228 European American patients with AD selected according to their eczema herpeticum status, and severity was measured by using the Eczema Area and Severity Index. Replication genotyping was performed in independent samples of 219 European American and 333 African American subjects. Functional investigation of loss-of-function variants was conducted by using site-directed mutagenesis. Results We identified 494 single nucleotide variants encompassing 105 kb of sequence, including 145 common, 349 (70.6%) rare (minor allele frequency <5%), and 86 (17.4%) novel variants, of which 2.8% were coding synonymous, 93.3% were noncoding (64.6% intronic), and 3.8% were missense. We identified 6 rare IFNGR1 missense variants, including 3 damaging variants (Val14Met V14M, Val61Ile, and Tyr397Cys Y397C) conferring a higher risk for ADEH+ ( P = .031). Variants V14M and Y397C were confirmed to be deleterious, leading to partial IFNGR1 deficiency. Seven common IFNGR1 SNPs, along with common protective haplotypes (2-7 SNPs), conferred a reduced risk of ADEH+ ( P = .015-.002 and P = .0015-.0004, respectively), and both SNP and haplotype associations were replicated in an independent African American sample ( P = .004-.0001 and P = .001-.0001, respectively). Conclusion Our results provide evidence that both genetic variants in the gene encoding IFNGR1 are implicated in susceptibility to the ADEH+ phenotype.
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