The burden of disease associated with filaggrin mutations: a population-based, longitudinal birth cohort study

Histamine suppresses epidermal keratinocyte differentiation and impairs skin barrier function in a human skin model

Background

Defects in keratinocyte differentiation and skin barrier are important features of inflammatory skin diseases like atopic dermatitis. Mast cells and their main mediator histamine are abundant in inflamed skin and thus may contribute to disease pathogenesis.

Methods

Human primary keratinocytes were cultured under differentiation-promoting conditions in the presence and absence of histamine, histamine receptor agonists and antagonists. The expression of differentiation-associated genes and epidermal junction proteins was quantified by real-time PCR, Western blot, and immunofluorescence labeling. The barrier function of human skin models was tested by the application of biotin as tracer molecule.

Results

The addition of histamine to human keratinocyte cultures and organotypic skin models reduced the expression of the differentiation-associated proteins keratin 1/10, filaggrin, and loricrin by 80–95%. Moreover, the addition of histamine to skin models resulted in the loss of the granular layer and thinning of the epidermis and stratum corneum by 50%. The histamine receptor H1R agonist, 2-pyridylethylamine, suppressed keratinocyte differentiation to the same extent as did histamine. Correspondingly, cetirizine, an antagonist of H1R, virtually abrogated the effect of histamine. The expression of tight junction proteins zona occludens-1, occludin, claudin-1, and claudin-4, as well as that of desmosomal junction proteins corneodesmosin and desmoglein-1, was down-regulated by histamine. The tracer molecule biotin readily penetrated the tight junction barrier of skin cultures grown in the presence of histamine, while their diffusion was completely blocked in nontreated controls.

Conclusions

Our findings suggest a new mechanism by which mast cell activation and histamine release contribute to skin barrier defects in inflammatory skin diseases.

Early eczema and the risk of childhood asthma: a prospective, population-based study

Background

Severe eczema in young children is associated with an increased risk of developing asthma and rhino-conjunctivitis. In the general population, however, most cases of eczema are mild to moderate. In an unselected cohort, we studied the risk of current asthma and the co-existence of allergy-related diseases at 6 years of age among children with and without eczema at 2 years of age.

Methods

Questionnaires assessing various environmental exposures and health variables were administered at 2 years of age. An identical health questionnaire was completed at 6 years of age. The clinical investigation of a random subsample ascertained eczema diagnoses, and missing data were handled by multiple imputation analyses.

Results

The estimate for the association between eczema at 2 years and current asthma at 6 years was OR=1.80 (95% CI 1.10-2.96). Four of ten children with eczema at 6 years had the onset of eczema after the age of 2 years, but the co-existence of different allergy-related diseases at 6 years was higher among those with the onset of eczema before 2 years of age.

Conclusions

Although most cases of eczema in the general population were mild to moderate, early eczema was associated with an increased risk of developing childhood asthma. These findings support the hypothesis of an atopic march in the general population.

Trial registration

The Prevention of Allergy among Children in Trondheim study has been identified as ISRCTN28090297 in the international Current Controlled Trials database

Low frequency of filaggrin null mutations in Croatia and their relation with allergic diseases

Filaggrin gene (FLG) null mutations are considered associated with atopic dermatitis. This study was conducted to determine the prevalence of FLG null mutations R501X, 2282del4, R2447X and S3247X in the Croatian population and their role in the occurrence of allergic diseases including atopic dermatitis, allergic rhinitis, asthma and allergic contact dermatitis (ACD). Study enrolled 440 freshmen with defined allergic diseases by means of both present symptoms in International Study of Asthma and Allergies in Childhood questionnaire (relevant respiratory and/or skin symptoms) and markers of allergic sensitization (positive skin prick and/or patch test). FLG null mutations were successfully genotyped in 423 students of which 11 (2.6%) were carriers of FLG null mutation: 1/423 (0.2%) was heterozygous for R501X and 10/423 (2.4%) were heterozygous for 2282del4. No carriers of R2447X and S3247X mutations were identified. In wild-type FLG carriers (412 subjects), atopic dermatitis was present in 45 (11%), allergic rhinitis in 70 (17%) and allergic asthma in 29 (7%) students. Twenty-five of 393 (7%) patch-tested wild-type FLG carriers had ACD. Among 11 FLG null mutation carriers, four had one or more allergic diseases, and five had reported skin symptoms without defined allergic sensitization (positive skin prick test and/or patch test). FLG null mutations were not confirmed as a predictor of analysed allergic diseases, but were confirmed as an independent predictor of skin symptoms (OR 17.19, 95% CI 3.41-86.6, P < 0.001). Our results in general indicate a low frequency of FLG null mutations in the studied Croatian population supporting a theory of a latitude-dependent distribution of FGL null mutations in Europe, with a decreasing north-south gradient of R501X and 2282del4 mutation frequency. The relation between FLG null mutations and skin disorders was confirmed.

Ethical issues of genetic susceptibility testing for occupational diseases: opinions of trainees in a high-risk job

PURPOSE

Genetic research has opened up possibilities for identification of persons with an increased susceptibility for occupational disease. However, regulations considering the ethical issues that are inevitably associated with the use of genetic tests for susceptibility for occupational diseases are scarce. We investigated whether opinions of an intended stakeholder group, that is, student nurses, are sufficiently addressed by existing recommendations.

METHODS

Attitudes and opinions of Dutch student nurses toward a genetic test for susceptibility to occupational contact eczema were studied in a qualitative setup using focus groups, interviews and electronic questionnaires. The results were compared with guidelines and recommendations extracted from the literature.

RESULTS

Sixty-nine percent of the student nurses said they would partake in a genetic test for susceptibility to occupational contact eczema when available. Concerns were expressed regarding the difficulty of interpreting test results, the utility of the test result in practice and the necessity of genetic tests for non-severe diseases. For the issue of privacy and confidentiality, the students expressed few worries and much confidence. The existing guidelines largely covered the students' opinions. Still, the data emphasized the need for good individual risk communication both before and after testing, taking into account that the test concerns susceptibility.

CONCLUSIONS

Comparing the students' statements with the issues addressed by the guidelines, we conclude that the guidelines should pay more attention to risk communication and practical advice accompanying the test results.

Atopic dermatitis results in intrinsic barrier and immune abnormalities: implications for contact dermatitis

Atopic dermatitis (AD), as well as irritant contact dermatitis (ICD) and allergic contact dermatitis (ACD), are common skin diseases. These diseases are characterized by skin inflammation mediated by activated innate immunity or acquired immune mechanisms. Although AD, ICD, and ACD can be encountered in pure forms by allergists and dermatologists, patients with AD often present with increased frequency of ICD and ACD. Although a disturbed barrier alone could potentiate immune reactivity in patients with AD through increased antigen penetration, additional immune mechanisms might explain the increased susceptibility of atopic patients to ICD and ACD. This review discusses cellular pathways associated with increased skin inflammation in all 3 conditions and presents mechanisms that might contribute to the increased rate of ICD and ACD in patients with AD.

The persistence of atopic dermatitis and filaggrin (FLG) mutations in a US longitudinal cohort

BACKGROUND

Atopic dermatitis (AD) is a common skin disease that is characterized by recurrent episodes of itching. Filaggrin (FLG) loss-of-function (FLG null) mutations have been associated with an increased risk of AD.

OBJECTIVE

We sought to evaluate the effect of individual FLG null mutations on the persistence of AD over time.

METHODS

We evaluated a multiyear prospective cohort study of children with AD with respect to FLG null mutations (R501X, 2282del4, R2447X, and S3247X). We evaluated the association of these mutations with the persistence of AD symptoms over time with respect to reports of no symptoms of AD and whether topical medication was needed for symptom resolution.

RESULTS

Eight hundred fifty-seven subjects were followed for 3684 person-years. One or more FLG null mutations were noted in 16.3% of subjects and specifically in 27.5% of white subjects and 5.8% of African American subjects. Subjects with an FLG null mutation were less likely (odds ratio [OR], 0.54; 95% CI, 0.41-0.71) to report that their skin was symptom free at any time compared with those without an FLG null mutation. The effect of these mutations was similar in white subjects (OR, 0.42; 95% CI, 0.31-0.57) and African-American subjects (OR, 0.53; 95% CI, 0.25-1.12; P = .62). Children with the R501X mutation (OR, 0.44; 95% CI, 0.22-0.88) were the least responsive to therapy.

CONCLUSIONS

In a US cohort with AD, FLG null mutations were common. Children with FLG null mutations were more likely to have persistent AD. Although these mutations were more common in those of European ancestry, their effect on persistence was similar in those of African ancestry. Response to therapy was not uniform among children with FLG null mutations.

Epicutaneous exposure to staphylococcal superantigen enterotoxin B enhances allergic lung inflammation via an IL-17A dependent mechanism

Atopic dermatitis (AD) is the initial step of the atopic march: the progression from AD to allergic rhinitis and asthma. There is a close association between skin barrier abnormalities and the development of AD and the atopic march. One of cardinal features of AD is that the lesional skin of the majority of AD patients is chronically colonized with Staphylococcus aureus with half isolates producing superantigen enterotoxin B (SEB). Although diverse roles of SEB in the pathogenesis and severity of AD have been recognized, whether SEB contributes to the dermal inflammation that drives lung inflammation and airway hyperresponsiveness (AHR) has not been examined. Here we show a novel role of S. aureus superantigen SEB in augmenting allergen ovalbumin (Ova) induced atopic march through an IL-17A dependent mechanism. When mice epicutaneously (EC) sensitized with allergen Ova, addition of topical SEB led to not only augmented systemic Th2 responses but also a markedly exaggerated systemic Th17/IL-17 immune environment. The ability of SEB in enhancing Th17/IL-17 was mediated through stimulating lymphocytes in spleen and draining lymph nodes to promote IL-6 production. Epicutaneous sensitization of mice with a combination of Ova and SEB significantly enhanced Ova-induced AHR and granulocytic lung inflammation than Ova allergen alone. When IL-17A was deleted genetically, the effects of SEB on augmenting lung inflammation and AHR were markedly diminished. These findings suggest that chronic heavy colonization of enterotoxin producing S. aureus in the skin of patients with atopic dermatitis may have an important role in the development of atopic march via an IL-17A dependent mechanism.

Retrospective analysis of the natural history of atopic dermatitis occurring in the first year of life in Korean children

The aim of this study was to analyze the natural history of atopic dermatitis (AD) and the risk factors associated with the remission of AD in Korean children. We enrolled 597 children with AD that occurred in the first year of life. A variety of factors influencing the prognosis were assessed by medical records and telephone interviews. Their outcome was classified into complete remission, intermittent, and persistent AD. AD had completely disappeared in 422 cases (70.6%), while 149 (25%) and 26 cases (4.4%) showed intermittent and persistent skin symptoms, respectively. The average healing time was 29.6 months in complete remission group and expected healing time of the AD was 60 months. None of risk factors were significant by multivariate analysis. But, in moderate-to-severe AD group, maternal diet restriction during lactation (P = 0.046) and no sensitization to cow's milk (P = 0.017) were significantly associated with remission of AD in the multivariate analysis. In conclusion, AD occurring in the first year of life disappears in a significant proportion of patients. In addition, in Korean children with moderate-to-severe AD, maternal diet restriction of allergenic food during lactation and sensitization to cow's milk seem to predict the prognosis of AD.

Skin barrier function and its importance at the start of the atopic march

Atopic dermatitis can be due to a variety of causes from nonatopic triggers to food allergy. Control of egress of water and protection from ingress of irritants and allergens are key components of cutaneous barrier function. Current research suggests that a degraded barrier function of the skin allows the immune system inappropriate access to environmental allergens. Epidermal aeroallergen exposure may allow sensitization to allergen possibly initiating the atopic march. Further research into connections between epidermal barrier function and possible allergen sensitization will be important to undertake. Future clinical trials focused on skin barrier protection may be of value as a possible intervention in prevention of the initiation of the atopic march.

Genetic variation in small proline rich protein 2B as a predictor for asthma among children with eczema

BACKGROUND

Small proline rich protein 2B (SPRR2B) is a skin and lung epithelial protein associated with allergic inflammation in mice that has not been evaluated in human atopic diseases.

OBJECTIVE

To determine whether single-nucleotide polymorphisms (SNPs) in SPRR2B are associated with childhood eczema and with the phenotype of childhood eczema combined with asthma.

METHODS

Genotyping for SPRR2B and filaggrin (FLG) was performed in 2 independent populations: the Cincinnati Childhood Allergy & Air Pollution Study (CCAAPS; N = 762; birth-age, 4 years) and the Greater Cincinnati Pediatric Clinical Repository (GCPCR; N = 1152; ages 5-10 years). Eczema and eczema plus asthma were clinical outcomes based on parental report and clinician's diagnosis. Genetic analyses were restricted to whites and adjusted for sex in both cohorts and adjusted for environmental covariates in CCAAPS.

RESULTS

Variants in SPRR2B were not significantly associated with eczema in either cohort after Bonferroni adjustment. Children from both cohorts with the CC genotype of the SPRR2B rs6693927 SNP were at 4 times the risk for eczema plus asthma (adjusted odds ratio, 4.1; 95% confidence interval, 1.5-10.9; P = .005 in CCAAPS; and adjusted odds ratio, 4.0; 95% confidence interval, 1.8-9.1; P < .001 in the GCPCR), however. SNPs in SPRR2B were not in strong linkage disequilibrium with the R501X and del2282 FLG mutations, and these findings were independent of FLG.

CONCLUSIONS

An SNP in SPRR2B was predictive of asthma among white children with eczema from 2 independent populations. SPRR2B polymorphisms may serve as important predictive markers for the combined eczema plus asthma phenotype.

Cohort Profile: the 'children of the 90s'--the index offspring of the Avon Longitudinal Study of Parents and Children

The Avon Longitudinal Study of Parents and Children (ALSPAC) is a transgenerational prospective observational study investigating influences on health and development across the life course. It considers multiple genetic, epigenetic, biological, psychological, social and other environmental exposures in relation to a similarly diverse range of health, social and developmental outcomes. Recruitment sought to enrol pregnant women in the Bristol area of the UK during 1990–92; this was extended to include additional children eligible using the original enrolment definition up to the age of 18 years. The children from 14 541 pregnancies were recruited in 1990–92, increasing to 15 247 pregnancies by the age of 18 years. This cohort profile describes the index children of these pregnancies. Follow-up includes 59 questionnaires (4 weeks–18 years of age) and 9 clinical assessment visits (7–17 years of age). The resource comprises a wide range of phenotypic and environmental measures in addition to biological samples, genetic (DNA on 11 343 children, genome-wide data on 8365 children, complete genome sequencing on 2000 children) and epigenetic (methylation sampling on 1000 children) information and linkage to health and administrative records. Data access is described in this article and is currently set up as a supported access resource. To date, over 700 peer-reviewed articles have been published using ALSPAC data.

The human epidermal differentiation complex: cornified envelope precursors, S100 proteins and the 'fused genes' family

  The skin is essential for survival and protects our body against biological attacks, physical stress, chemical injury, water loss, ultraviolet radiation and immunological impairment. The epidermal barrier constitutes the primordial frontline of this defense established during terminal differentiation. During this complex process proliferating basal keratinocytes become suprabasally mitotically inactive and move through four epidermal layers (basal, spinous, granular and layer, stratum corneum) constantly adapting to the needs of the respective cell layer. As a result, squamous keratinocytes contain polymerized keratin intermediate filament bundles and a water-retaining matrix surrounded by the cross-linked cornified cell envelope (CE) with ceramide lipids attached on the outer surface. These cells are concomitantly insulated by intercellular lipid lamellae and hold together by corneodesmosmes. Many proteins essential for epidermal differentiation are encoded by genes clustered on chromosomal human region 1q21. These genes constitute the 'epidermal differentiation complex' (EDC), which is divided on the basis of common gene and protein structures, in three gene families: (i) CE precursors, (ii) S100A and (iii) S100 fused genes. EDC protein expression is regulated in a gene and tissue-specific manner by a pool of transcription factors. Among them, Klf4, Grhl3 and Arnt are essential, and their deletion in mice is lethal. The importance of the EDC is further reflected by human diseases: FLG mutations are the strongest risk factor for atopic dermatitis (AD) and for AD-associated asthma, and faulty CE formation caused by TG1 deficiency causes life-threatening lamellar ichthyosis. Here, we review the EDC genes and the progress in this field.

[Allergic contact dermatitis and atopy]

Retrospective studies demonstrate that the prevalence of skin sensitization does not significantly differ between atopic and non-atopic patients. In children and adolescents the risk for sensitization seems to occur independently from AD. According to the results of a recent study, AD patients are overrepresented in the group of polysensitized patients. IgE-mediated sensitization as well as an early onset of AD and duration of the disease have been identified as possible risk factors for skin sensitization to contact allergens. A defective permeability barrier with increased epidermal water loss is a hallmark of AD and contributes to sensitization against common allergens. A highly significant association between FLG mutations and the risk of early onset, severe, persistent AD and an increased risk for asthma has been shown in several studies. A more recent study revealed an association between FLG mutations and increased nickel sensitization, but not other contact allergens. However, further large prospective studies with well-characterized patients are necessary to clarify the correlation between impaired skin barrier, atopic dermatitis and allergic contact dermatitis.

Interplay of filaggrin loss-of-function variants, allergic sensitization, and eczema in a longitudinal study covering infancy to 18 years of age

Background

Immune specific genes as well as genes regulating the formation of skin barrier are major determinants for eczema manifestation. There is a debate as to whether allergic sensitization and filaggrin gene (FLG) variants lead to eczema or FLG variants and eczema increase the risk of allergic sensitization. To investigate the time-order between eczema and allergic sensitization with respect to FLG variants, data from a large prospective study covering infancy to late adolescence were analyzed.

Methodology/Principal Findings

Repeated measurements of eczema and allergic sensitization (documented by skin prick tests) at ages 1, 2, 4, 10, and 18 years were ascertained in the Isle of Wight birth cohort (n = 1,456). Three transition periods were analyzed: age 1-or-2 to 4, 4 to 10, and 10 to 18 years. FLG variants were genotyped in 1,150 participants. Over the three transition periods, in temporal sequence analyses of initially eczema-free participants, the combined effect of FLG variants and allergic sensitization showed a 2.92-fold (95% CI: 1.47–5.77) increased risk ratio (RR) of eczema in subsequent examinations. This overall risk was more pronounced at a younger age (transition period 1-or-2 to 4, RR = 6.47, 95% CI: 1.96–21.33). In contrast, FLG variants in combination with eczema showed a weaker, but significant, risk ratio for subsequent allergic sensitization only up to 10 years of age.

Conclusions/Significance

Taking the time order into account, this prospective study demonstrates for the first time, that a combination of FLG variants and allergic sensitization increased the risk of eczema in subsequent years. Also FLG variants interacted with eczema and increased the risk of subsequent allergic sensitization, which, was limited to the younger age. Hence, early restoration of defective skin barrier could prevent allergic sensitization and subsequently reduce the risk of eczema development.

One remarkable molecule: filaggrin

The discovery, in 2006, that loss-of-function mutations in the filaggrin (FLG) gene are the cause of ichthyosis vulgaris-the most common disorder of keratinization-and also a strong genetic risk factor for atopic eczema, marked a significant breakthrough in the understanding of eczema pathogenesis. Subsequent investigations of the role of FLG-null mutations have identified a series of significant associations with atopic disease phenotypes, including atopic asthma, allergic rhinitis, and peanut allergy. However, many questions remain to be answered in relation to the precise mechanisms by which deficiency of an intracellular protein expressed primarily in the differentiating epidermis may contribute to the development of cutaneous and systemic pathology. This review aims to highlight the key milestones in filaggrin research over the past 25 years, to discuss the mechanistic, clinical, and therapeutic implications, and to consider possible future directions for ongoing investigation.

FCER2 T2206C variant associated with chronic symptoms and exacerbations in steroid-treated asthmatic children

BACKGROUND

The T2206C FCER2 variant was found previously to be associated with IgE levels, exacerbation rates and decreased FCER2 expression in children on inhaled corticosteroids (ICS) participating in a clinical trial. This finding has not been replicated. We sought to replicate the association between the FCER2 gene and exacerbations in children with asthma. In addition, we tested the hypothesis that the T2206C variant may be associated with other markers of steroid resistance such as asthma symptom scores and asthma medication use.

METHODS

The influence of the T2206C variant on asthma exacerbations (emergency department visits or hospitalization), symptoms scores and medication use was explored using data from two populations of asthmatic children using ICS: Pharmacogenetics of Asthma medication in Children: Medication with ANti-inflammatory effects study (n = 386) and BREATHE study (n = 939).

RESULTS

The T2206C variant was associated with increased risk of asthma-related hospital visits in both cohorts (OR: 1.91, 95% CI: 1.08-3.40), and meta-analysis with previously published results was highly significant (OR: 2.38, 95% CI: 1.47-3.85, P = 0.0004). The FCER2 variant was also associated with increased risk of uncontrolled asthma measured by Asthma Control Questionnaire (OR: 2.64, 95% CI: 1.00-6.98) and was associated with increased daily steroid dose (OR: 2.46, 95% CI: 1.38-4.39).

CONCLUSION

The association between the FCER2 T2206C variant and asthma-related hospitalizations in steroid-treated asthma appears robust and may also be associated with other indicators of lack of ICS efficacy such as asthma symptoms and a requirement for higher daily doses of ICS. Our results suggest that the FCER2 T2206C variant might be a useful pharmacogenetic predictor of steroid refractory patients.

Epidermal barrier in atopic dermatitis

Atopic dermatitis (AD) is a complex disease that affects up to 20% of children and impacts the quality of patients and families in a significant manner. New insights into the pathophysiology of AD point to an important role of structural abnormalities in the epidermis combined with immune dysregulation. Filaggrin (FLG) is synthesized as a large precursor, profilaggrin, and is expressed in the upper layers of the epidermis. FLG plays a critical role in the epidermal barrier, and FLG mutations cause abnormal epidermal function. FLG mutations are strongly associated with early-onset, and persistent severe AD. In addition, FLG deficiency in the epidermis is related to allergic sensitization and asthma. The basic skin care including repair and protection of the skin barrier with proper hydration and topical anti-inflammatory therapy is important to control the severity of skin disease in patients with AD.

Atopic dermatitis and the atopic march: what is new?

Objective. In this paper the authors review the management of atopic dermatitis (AD) and the association between AD and allergic respiratory diseases. Data Sources. PubMed databases, researching articles in the last 15 years. Results. Studies about atopic march are cross-sectional population studies at different ages. They show that the most important predisposing factor for atopy is a decrease of the filaggrin's expression. Conclusions. The most modern theories seem to show that the most important factor which starts the atopic march is represented by an impaired epidermal barrier. It causes an increase in skin permeability to allergens that could induce sensitization even in the airways. The major predisposing factor is a primary inherited epithelial barrier defect resulting from filaggrin gene mutation, but other factors may play a role in this complex mechanism. Further studies are needed to focus on AD treatment and preventive strategies.

Do early skin care practices alter the risk of atopic dermatitis? A case-control study

The rise in atopic dermatitis prevalence observed in industrialized countries is unexplained. We hypothesized that certain skin care practices early in life may increase the risk for developing atopic dermatitis. Our case-control study could not identify any one practice that increased the odds of developing atopic dermatitis, but it revealed that regular lotion use was very common in infants who later develop atopic dermatitis.

Cedar pollen aggravates atopic dermatitis in childhood monozygotic twin patients with allergic rhino conjunctivitis

We report a case of 7-year-old monozygotic twin patients with atopic dermatitis. The HLA haplotypes were HLA A2, A11, B27, B61, DR1, and DR4. Both serum IgE levels and cedar pollen radioallergosorbent test (RAST) scores were high in the twins (elder/younger sister: IgE: 5170/3980 IU/ml and Japansese cedar pollen: >100/64.0) in contrast to low mite and food RAST scores (Dermatophagoides Pterygonium; 0.59/0.4 and egg white 9.24/4.6). The patients showed positive immediate (20 min in both sisters) and delayed (24 hours in elder sister, 24, 48, 72 hours in younger sister) reactions to a scratch test with Japanese cedar pollen. Skin lesions on the face were aggravated and extended to the trunk and extremities during the Japanese cedar pollen season and gradually subsided in summer. Oral provocation with egg white or cow milk showed no exacerbations, and topical corticosteroid did not improve the eczema. In contrast, successful protection from severe scratching behaviors was achieved by use of topical anti-allergic eye drops and wearing nightgowns made by the mother.

Asthma phenotypes in adults and clinical implications

It is becoming increasingly recognized that asthma is a heterogeneous disease, whether based on clinical factors, including the patient's age at diagnosis, symptom spectrum and treatment response, triggering factors, or the level and type of inflammation. Attempts to analyze the importance of these characteristics to the clinical presentation of asthma have led to the appreciation of numerous separate and overlapping asthma phenotypes. However, these approaches are 'biased' and based on the clinician/scientist's own experience. Recently, unbiased approaches have also been attempted using both molecular and statistical tools. Early results from these approaches have supported and expanded on the clinician's concepts. However, until specific biologic markers are identified for any of these proposed phenotypes, the definitive nature of any phenotype will remain speculative.

Atopic dermatitis: a disease of altered skin barrier and immune dysregulation

Atopic dermatitis (AD) is an important chronic or relapsing inflammatory skin disease that often precedes asthma and allergic disorders. New insights into the genetics and pathophysiology of AD point to an important role of structural abnormalities in the epidermis as well as immune dysregulation not only for this skin disease but also for the development of asthma and allergies. Patients with AD have a unique predisposition to colonization or infection by microbial organisms, most notably Staphylococcus aureus and herpes simplex virus. Measures directed at healing and protecting the skin barrier and addressing the immune dysregulation are essential in the treatment of patients with AD, and early intervention may improve outcomes for both the skin disease as well as other target organs.

Genetics of atopic dermatitis

Atopic dermatitis (AD) is a multifactorial disease, with a strong genetic predisposition. Genome-wide studies as well as candidate gene studies revealed several susceptibility loci. Since the observation of a strong association of "loss of function" mutations in the filaggrin gene with AD, the epidermal barrier was rediscovered as important pathophysiological co-factor of this disease.

Genome-wide linkage study of atopic dermatitis in West Highland White Terriers

BACKGROUND

Canine atopic dermatitis (AD) is a common, heritable, chronic allergic skin condition prevalent in the West Highland White Terrier (WHWT). In canine AD, environmental allergens trigger an inflammatory response causing visible skin lesions and chronic pruritus that can lead to secondary bacterial and yeast infections. The disorder shares many of the clinical and histopathological characteristics of human AD and represents an animal model of this disorder that could be used to further elucidate genetic causes of human AD. Microsatellite markers genotyped in families of WHWTs affected with AD were used to perform a genome-wide linkage study in order to isolate chromosomal regions associated with the disorder.

RESULTS

Blood samples and health questionnaires were collected from 108 WHWTs spanning three families. A linkage simulation using these 108 dogs showed high power to detect a highly penetrant mutation. Ninety WHWTs were genotyped using markers from the Minimal Screening Set 2 (MSS-2). Two hundred and fifty six markers were informative and were used for linkage analysis. Using a LOD score of 2.7 as a significance threshold, no chromosomal regions were identified with significant linkage to AD. LOD scores greater than 1.0 were located in a 56 cM region of chromosome 7.

CONCLUSIONS

The study was unable to detect any chromosomal regions significantly linked to canine AD. This could be a result of factors such as environmental modification of phenotype, incorrect assignment of phenotype, a mutation of low penetrance, or incomplete genome coverage. A genome-wide SNP association study in a larger cohort of WHWTs may prove more successful by providing higher density coverage and higher statistical power.

The eczema risk variant on chromosome 11q13 (rs7927894) in the population-based ALSPAC cohort: a novel susceptibility factor for asthma and hay fever

In a genome-wide association study, a common variant on chromosome 11q13.5 (rs7927894[T]) has been identified as a susceptibility locus for eczema. We aimed to analyze the effect of this risk variant on asthma and hay fever and to determine its impact on the general population level in over 9300 individuals of the prospectively evaluated Avon Longitudinal Study of Parents and Children birth cohort. We demonstrate an association of rs7927894[T] with atopic asthma and with hay fever. The largest effect sizes were found in patients with the combined phenotype atopic asthma plus eczema [odds ratio (OR) = 1.50; 95% confidence interval (CI) 1.20-1.88; P = 3.7 × 10(-4)] and hay fever plus eczema (OR = 1.37; 95% CI 1.15-1.62; P = 3.8 × 10(-4)). We replicated the effects of rs7927894[T] on eczema-associated asthma and hay fever independently in the German GENUFAD (GEnetic studies in NUclear Families with Atopic Dermatitis) study and show that they are significantly larger than the effect observed in eczema. The estimated population attributable risk fractions for eczema, eczema-associated atopic asthma or hay fever were 9.3, 24.9 and 23.5%, respectively. Finally in eczema, we found a synergistic interaction of rs7927894[T] with filaggrin gene (FLG) mutations, which are a major cause of epidermal barrier dysfunction, and replicated the interaction in the German Multicenter Allergy Study birth cohort. The synergistic effect of rs7927894[T] and FLG mutations on eczema risk as well as the association of both variants with eczema-associated atopic asthma and hay fever point to an involvement of rs7927894[T] in a functional pathway that is linked to the barrier defect.

Contrasting pathogenesis of atopic dermatitis and psoriasis--part I: clinical and pathologic concepts

Atopic dermatitis and psoriasis are 2 of the most common inflammatory skin diseases. They are similar in that they are complex inherited diseases involving genes that encode immune components and structural proteins that regulate differentiation of epidermal cells. Each disease is characterized by proliferation of epidermal keratinocytes and abnormal cornification or terminal differentiation in the epidermis; skin lesions contain immune infiltrates of T cells, dendritic cells, and other types of leukocytes. We review similarities between the diseases and differences in epidermal barrier defects and immune cells. We also propose mechanisms of pathogenesis based on differences in the balance of immune cell subsets that could cause the phenotypes that distinguish these diseases. The first part of this 2-part review focuses on the clinical and pathologic features of the diseases; the second part discusses differences in immune cell subsets between atopic dermatitis and psoriasis and recent therapeutic strategies.

Mutations in the filaggrin gene in Han Chinese patients with atopic dermatitis

BACKGROUND

Recently, loss-of-function mutations in the filaggrin gene (FLG) have been identified as the cause of ichthyosis vulgaris (IV) and also predisposing factors for atopic dermatitis (AD) and AD-associated phenotypes. Until now, over thirty mutations in FLG have been identified in patients with IV and AD, but the FLG mutation spectrum is not clear for Chinese Han patients with AD. This study aimed to investigate the role of FLG mutations in AD and AD-associated phenotypes in a Chinese population.

METHODS

We carried out a comprehensive sequencing of the entire FLG coding region in 261 Han AD patients.

RESULTS

In our research, we identified ten novel mutations (R826X, 3222del4, R1140X, 4271delAA, Q1790X, 5757del4, 6834del5, 6950del8, S2706X and K4671X) and eight reported mutations (441delA, R501X, 3321delA, R1474X, Q2417X, E2422X, 7945delA and R4306X) in FLG. FLG mutations were present in 31.4% of our AD patients. Mutations 3321delA and K4671X, with a frequency of 14.6% and 9.2%, respectively, were two of the most common mutations in this AD cohort. FLG null alleles (compound genotypes) were significantly associated with AD (P < 0.001) and AD associated with food sensitization (P = 0.012). However, we did not observe a positive association between FLG mutations and other AD-associated phenotypes, including asthma, allergic rhinitis and elevated total serum IgE level.

CONCLUSION

Our study increases the total number of reported FLG mutations. Moreover, we further confirm that FLG mutations are strong predisposing factors for AD in Han Chinese.

Filaggrin gene defects and the risk of developing allergic disorders

Filaggrin is a key protein that facilitates terminal differentiation of the epidermis and formation of the skin barrier. Mutations in the gene encoding filaggrin (FLG) have been identified as the cause of ichthyosis vulgaris (IV) and have been shown to be major predisposing factors for atopic dermatitis (AD). Approximately 40 loss-of-function FLG mutations have been identified in patients with ichthyosis vulgaris (IV) and/or atopic dermatitis (AD) in Europe and Asia. Major differences exist in the spectra of FLG mutations observed between different ancestral groups. Notably, prevalent FLG mutations are distinct between European and Asian populations. Many cohort studies on FLG mutations in AD have revealed that approximately 25-50% of AD patients harbour filaggrin mutations as a predisposing factor. In addition, FLG mutations are significantly associated with AD-associated asthma. The risk for developing allergic rhinitis is also significantly higher with a FLG mutation, both with and without accompanying AD. Recent studies have hypothesized that skin barrier defects caused by FLG mutations allows allergens to penetrate the epidermis and to interact with antigen-presenting cells, leading to the development of atopic disorders including asthma. The restoration of skin barrier function seems a feasible and promising strategy for prophylactic treatment of AD patients with FLG mutations.

Filaggrin gene defects are independent risk factors for atopic asthma in a Polish population: a study in ECAP cohort

Background

FLG null variants of which 2282del4 and R501X are the most frequent in Caucasians are established risk factors for atopic dermatitis (AD) with an effect probably mediated through impairment of epidermal barrier. Among subjects with AD FLG defects are also consistently associated with asthma and allergic rhinitis (AR) but it is less clear to what extent these associations are also present independently from skin disease. The aim of the present study was to evaluate the role of 2282del4 and R501X in predisposing to these allergic phenotypes in a Polish population.

Methodology

2282del4 and R501X were typed among 3,802 participants of the Epidemiology of Allergic Diseases in Poland (ECAP) survey, a cross-sectional population-based study using ECRHS II and ISAAC questionnaires, and ambulatory examination.

Principal Findings

The FLG null variants were associated with AD (OR = 2.01, CI: 1.20–3.36, P = 0.007), allergic rhinitis (in particular persistent form, OR = 1.69, CI:1.12–2.54, P = 0.011), and asthma (in particular atopic asthma, OR = 2.22, CI:1.24–3.96, P = 0.006). Association with atopic asthma (but not persistent allergic rhinitis) was also present in the absence of AD, (OR = 2.02, CI: 1.07–3.81, P = 0.027) as well as in the absence of AD and history of broadly defined inflammatory skin disease (OR = 2.30, CI: 1.07–4.93, P = 0.03). Association to atopic asthma would have not been found if diagnosis was made by questionnaire only (OR = 1.15, CI: 0.58–2.32, P = 0.8). We did not observe an association between FLG variants and allergic sensitizations (P = 0.8) or total IgE. (P = 0.6).

Conclusions/Significance

In a Polish population FLG 2282del4 and R501X carriage increases risk for development of AD and atopic asthma (also in the absence of AD or history thereof). This suggests that interventions aimed at restoring epidermal barrier may have a general role in asthma prophylaxis/treatment.

The atopic march: progression from atopic dermatitis to allergic rhinitis and asthma

Atopic dermatitis (AD) is an inflammatory disease characterized by pruritic skin lesions. The pathogenesis of AD may include disrupted epidermal barrier function, immunodysregulation, and IgE-mediated sensitization to food and environmental allergens. AD is also part of a process called the atopic march, a progression from AD to allergic rhinitis and asthma. This has been supported by multiple cross-sectional and longitudinal studies and experimental data. Research on the mechanisms of AD has been centered on the adaptive immune system with an emphasis on the T-helper 1 (Th1)-Th2 paradigm. Recently, the conceptual focus has largely shifted to include a primary defect in the epithelial barrier as an initial event in AD providing a significant insight into the disease initiation and pointing to a complex secondary interplay of environmental and immunological sequelae with barrier disruption. Further understanding of AD will help the development of more effective treatment for AD and ultimately, preventative algorithms for the atopic march. In this review we highlight recent advances in our understanding of the pathogenesis of AD and the atopic march.

Latex allergy and filaggrin null mutations

OBJECTIVES

Natural rubber latex (NRL) contains over 200 proteins of which 13 have been identified as allergens and the cause of type I latex allergy. Health care workers share a high occupational risk for developing latex allergy. Filaggrin null mutations increase the risk of type I sensitizations to aeroallergens and it is possible that filaggrin null mutations also increase the risk of latex allergy. The aim of this paper was to examine the association between filaggrin null mutations and type I latex allergy.

METHODS

Twenty latex allergic and 24 non-latex allergic dentists and dental assistants, occupationally exposed to latex, were genotyped for filaggrin null mutations R501X and 2282del4. Latex allergy was determined by a positive reaction or a historical positive reaction to a skin prick test with NRL.

RESULTS

41 individuals were successfully genotyped. Three individuals were filaggrin mutation carriers. One (2.4%) was a 2282del4 heterozygote and two (4.9%) were R501X heterozygote. No homozygote or compound heterozygote carriers were detected. No association between filaggrin null mutations and type I latex allergy was found (p=0.24). Patients with type I latex allergy more often reported contact dermatitis.

CONCLUSIONS

This is the first study to examine a highly plausible association between filaggrin null mutations and type I latex allergy. The study subjects were occupationally exposed to latex but no association between latex allergy and filaggrin mutations were detected. Sensitization to latex in the cases in this study may not have occurred through direct skin contact but through the respiratory organs via latex proteins that are absorbed in glove powder and aerosolized.

Filaggrin null mutations and association with contact allergy and allergic contact dermatitis: results from a tertiary dermatology clinic

BACKGROUND

Filaggrin null (FLG) mutations lead to skin barrier disruption with a reduced resistance towards exogenous agents and also influence the course of disease in atopic dermatitis.

OBJECTIVES

To examine the association between FLG mutations and contact allergy, polysensitization, hand eczema at first appearance of disease, occurrence, and course of dermatitis.

METHODS

A venous blood sample from 430 individuals was genotyped for FLG mutations R501X and 2282del4 with polymerase chain reaction followed by typing through hybridization to paramagnetic polystyrene beads and analysis on a BioPlex 200. All individuals had a minimum of one positive patch test reaction.

RESULTS

In all, 3.5% were 2282del4 heterozygote and 5.1% were R501X heterozygote. An odds ratio (OR) of 1.49 [95% confidence interval (CI) 0.74-3.00] was found for nickel allergy, OR 0.84 (95% CI 0.41-1.74) for polysensitization, OR 0.78 (95% CI 0.25-2.43) for dermatitis, OR 0.96 (95% CI 0.48-1.92) for hand eczema at debut, OR 1.25 (95% CI 0.99-1.57) for duration of disease, and OR 0.76 (95% CI 0.59-0.97) for age at onset.

CONCLUSIONS

No association between nickel allergy, polysensitization, hand eczema at first appearance or occurrence of dermatitis, and FLG mutations was found. However, patients with FLG mutations had an earlier age of onset compared with the wild-type genotype and a trend towards longer duration of disease.

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.

Food allergy and atopic dermatitis: separating fact from fiction

The relationship between food and atopic dermatitis (AD) is complex. A common misunderstanding is that food allergies have a significant impact on the course of AD, resulting in uncontrolled attempts at elimination diets and undertreatment of the skin itself. Studies have shown that only a small portion of cutaneous reactions to food in the form of late, eczematous eruptions will directly exacerbate AD in young infants who have moderate-to-severe AD. Given the low frequency of food allergies actually inducing flares of AD, the focus should return to appropriate skin therapy, and identification of true food allergies should be reserved for recalcitrant AD in children in whom the suspicion for food allergy is high. A different relationship between food and AD involves delaying or preventing AD in high-risk infants by exclusive breastfeeding during the first 4 months of life. Finally, the skin barrier defect in AD may allow for easier and earlier sensitization of food and airborne allergens; therefore, exposure of food proteins on AD skin may act as a risk factor for development of food allergies.

Lower prevalence of common filaggrin mutations in a community sample of atopic eczema: is disease severity important?

BACKGROUND

Recent studies have shown an association of loss-of-function mutations in the filaggrin gene (FLG) with ichthyosis vulgaris and atopic eczema (AE). Case selection may have distorted the hitherto reported prevalence of FLG mutations and their relation to atopic disease. The aim of the study was to determine the true population prevalence of FLG mutations in unselected children with and without reported physician diagnoses of asthma, allergic rhinitis and AE and their relationship with family history of atopic disease.

METHODS

We used a nested case-control design by sampling children with reported doctor's diagnoses of AE, asthma and allergic rhinitis and randomly selected controls from a larger cross-sectional study (n = 1263). Most common FLG mutations R501X, 2282del4, and R2447X were screened in DNA extracted from defrosted urine samples. The relationship of the combined FLG variants with atopic diseases and with reported family history of AE, asthma, and rhinitis was assessed.

RESULTS

In the patient group one homozygote (R501X/R501X), 4 compound heterozygotes (3 R501X/2282del4, one 2282del4/R2447X), and 17 heterozygotes (10 R501X/wt, 5 2282del4/wt, and 2 R2447X/wt), in the control group 9 heterozygotes (5 R501X/wt, 4 2282del4/wt) were detected. The combined prevalence of FLG loss-of-function alleles was 5% in the control group and 9% in the atopic sample. In a subgroup analysis, the combination of allergic rhinitis and AE showed a significant relationship with FLG mutations, OR = 3.7 (1.01-12.67, p = 0.024). Likewise, significant relations with reported family history of asthma, OR = 4.35 (1.78-10.62, p = 0.0012), allergic rhinitis, OR = 2.33 (1.49-3.63, p = 0.0002), and AE, OR = 5.08 (2.78-9.30, p ≤ 0.0001) were observed. In contrast to clinical studies with higher percentages of severely affected persons, FLG mutations here showed a moderate association with atopic disease.

CONCLUSIONS

Case selection may be responsible for overestimating the prevalence of FLG mutations in atopic disease.

Long-term studies of the natural history of asthma in childhood

Segmentation of children with asthma and other wheezy disorders remains the main research challenge today, as it was when described 2 centuries ago. Early childhood wheezy disorders follow different temporal trajectories, probably representing different underlying mechanisms (endophenotypes). Prospective identification of endophenotypes allowing accurate prediction of the clinical course is currently not possible. The variability of the clinical course remains an enigma and difficult to predict. Three of 4 school-aged children with asthma have outgrown disease by midadulthood. The risk of persistence increases with severity, sensitization, smoking, and female sex. Genetic risk variants might help disentangle the heterogeneity of asthma and other wheezy disorders. At early school age, children with asthma have reduced lung function. It is an important and unresolved question whether the airflow limitation associated with asthma already existed at birth or developed along with symptoms. Likewise, the association between the infant's bronchial responsiveness and development of asthma and other wheezy disorders is unclear. Neither primary prevention through manipulation of environmental factors nor secondary prevention through the use of inhaled corticosteroids can effectively halt the long-term disease progression in childhood. In conclusion, the natural history of asthma and the associated airway changes is still poorly understood, and we have not managed to translate findings from long-term studies into a deeper understanding of the underlying endophenotypes or improved disease management. We propose the need for a translational research approach based on long-term clinical studies of birth cohorts with comprehensive and objective assessments of intermediate phenotypes and environmental exposures combined with interdisciplinary basic research and a systems biology approach.

Filaggrin gene variants and atopic diseases in early childhood assessed longitudinally from birth

Copenhagen Prospective Study on Asthma in Childhood (COPSAC) was one of the discovery cohorts of the association between eczema and variants in the filaggrin coding gene (FLG). Here, we study the FLG-associated risk of asthma symptoms in early life and describe the temporal relationship in the development of the different FLG-associated atopic outcomes: asthma, sensitization and eczema, assessed longitudinally from birth. A high-risk cohort of 411 children was assessed in a prospective clinical study from birth to school-age. Asthma, acute severe asthma exacerbations, sensitization and eczema were diagnosed prospectively by the investigators. FLG variants R501X and Del4 were determined in 382 Caucasians. Filaggrin variants increased risk of developing recurrent wheeze, asthma and asthma exacerbations (hazard ratio 1.82 [1.06-3.12], p = 0.03), which was expressed within the first 1.5 yr of life. Children with filaggrin variants had a marked and persistent increase in acute severe asthma exacerbations from 1 yr of age (incidence ratio 2.40 [1.19-4.81], p = 0.01) and increased risk of asthma by age 5 (odds ratio 2.62 [1.12-6.11], p = 0.03). FLG variants increased the risk of eczema, manifesting fully in the first year of life (point prevalence ratio for age 0-5 was 1.75 [1.29-2.37]; p-value = 0.0003) contrasting the increased risk of specific sensitization by age 4 (odds ratio 3.52 [1.72-7.25], p = 0.0007) but not age 1.5. This study describes a FLG-associated pattern of atopic diseases characterized by the early onset of asthma symptoms and eczema and later development of sensitization. The association of filaggrin variants with asthma suggests skin barrier dysfunction as a novel, and potentially modifiable, mechanism driving early childhood asthma.

Application of genetic/genomic approaches to allergic disorders

Completion of the human genome project and rapid progress in genetics and bioinformatics have enabled the development of large public databases, which include genetic and genomic data linked to clinical health data. With the massive amount of information available, clinicians and researchers have the unique opportunity to complement and integrate their daily practice with the existing resources to clarify the underlying cause of complex phenotypes, such as allergic diseases. The genome itself is now often used as a starting point for many studies, and multiple innovative approaches have emerged applying genetic/genomic strategies to key questions in the field of allergy and immunology. There have been several successes that have uncovered new insights into the biologic underpinnings of allergic disorders. Herein we will provide an in-depth review of genomic approaches to identifying genes and biologic networks involved in allergic diseases. We will discuss genetic and phenotypic variation, statistical approaches for gene discovery, public databases, functional genomics, clinical implications, and the challenges that remain.

The infectious aspects of atopic dermatitis

Atopic dermatitis is characterized by Staphylococcus aureus colonization and recurrent skin infections. In addition to an increased risk of invasive infections by herpes simplex or vaccinia viruses, there is ample evidence that microbial pathogens, particularly S aureus and fungi, contribute to the cutaneous inflammation of atopic dermatitis. The authors describe recent developments in the pathogenesis of atopic dermatitis in relation to the role of microbial pathogens. Understanding how microbial pathogens interact or evade the cutaneous immunity of atopic dermatitis may be crucial in preventing infections or cutaneous inflammation in this disease.

Unravelling the skin barrier: a new paradigm for atopic dermatitis and house dust mites

Atopic dermatitis (AD) is a chronic relapsing inflammatory skin disease caused by complex interactions between genetics and environmental factors. In human beings, impairment of the skin barrier is demonstrated and thought to be responsible for enhanced penetration of allergens and increased risk for allergic sensitization. Once inflammation is triggered, further impairment of the skin barrier occurs, leading to self-perpetuating cycles of sensitizations. Canine AD appears to share many similarities with the human counterpart, clinically and immunologically. It is hypothesized that a primary defect of skin barrier function also exists in subsets of atopic dogs (e.g. in an experimental model using high IgE-producing beagles), particularly in young dogs, and in sites predisposed to the development of lesions. This impairment is present in clinically normal skin, worsens with development of lesions and can be quantified by measurement of transepidermal water loss. Therefore, the distribution of lesions in AD may be linked to a primary skin barrier defect in those sites and not simply due to contact with allergens, and increased susceptibility to penetration of allergen may exist early in life. Ultrastructurally, transmission electron microscopy reveals that clinically normal skin in atopic dogs has abnormalities in lamellar body secretion and extracellular lamellar bilayer structure when compared with normal dogs. Development of lesions worsens these changes (e.g. widening of intercellular spaces, release of lamellar bodies, and disorganization of lipid lamellae). It is proposed that the paradigm of canine AD as primarily due to immunologic aberration ('inside/outside') should be shifted to include a primary defect in barrier function ('outside/inside').