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Filaggrin null mutations and childhood atopic eczema: A population-based case-control study

Published:February 29, 2008DOI:https://doi.org/10.1016/j.jaci.2008.01.013

      Background

      Null mutations within the filaggrin gene (FLG) are associated with moderate-to-severe atopic eczema; their role in mild-to-moderate eczema in the general population is unknown.

      Objective

      We sought to investigate the significance of 5 common FLG null mutations in childhood atopic eczema in an unselected population cohort.

      Methods

      Eight hundred eleven English children aged 7 to 9 years were screened for FLG mutations. Eczema cases were defined by using United Kingdom diagnostic criteria and skin examination. Asthma and seasonal rhinitis cases were defined by parental questionnaire. Association between phenotype and genotype was investigated using Fisher exact test and logistic regression analysis.

      Results

      The 12-month period prevalence of atopic eczema was 24.2% (95% CI, 21.2% to 27.2%), with 96% (115/120) of cases having mild-to-moderate disease. The combined null genotype (carriage of ≥1 FLG mutations) was significantly associated with atopic eczema (P = 1.2 × 10−4). The odds ratio (OR) for individuals carrying 2 null mutations was 26.9 (95% CI, 3.3-217.1), but heterozygote carriers showed no significant increase in risk (OR, 1.2; 95% CI, 0.7-1.9). Eight of 190 eczema cases (4.2%) carried 2 FLG null mutations and thus might be attributed to filaggrin deficiency. Asthma in the context of eczema showed significant association with the FLG null mutations (P = 7.1 × 10−4). There was no association of FLG with asthma independent of eczema (P = .15) and no association with seasonal rhinitis (P = .66).

      Conclusion

      FLG null mutations are significantly associated with mild-to-moderate atopic eczema in childhood, with a recessive pattern of inheritance.

      Key words

      Abbreviations used:

      FLG (Filaggrin gene), OR (Odds ratio), UK (United Kingdom)
      Atopic eczema
      • Johansson S.G.
      • Bieber T.
      • Dahl R.
      • Friedmann P.S.
      • Lanier B.Q.
      • Lockey R.F.
      • et al.
      Revised nomenclature for allergy for global use: report of the Nomenclature Review Committee of the World Allergy Organization, October 2003.
      is an itchy inflammatory skin condition that follows a chronic relapsing course. It can cause significant morbidity as a result of pruritus, sleep deprivation, and emotional distress.
      • Chamlin S.L.
      • Cella D.
      • Frieden I.J.
      • Williams M.L.
      • Mancini A.J.
      • Lai J.S.
      • et al.
      Development of the Childhood Atopic Dermatitis Impact Scale: initial validation of a quality-of-life measure for young children with atopic dermatitis and their families.
      Eczema is a complex trait; that is, multiple genetic and environmental factors contribute to the phenotype. There is an increasing recognition of the role of epithelial barrier dysfunction in the pathogenesis of atopic eczema,
      • Hudson T.J.
      Skin barrier function and allergic risk.
      • Taieb A.
      • Hanifin J.
      • Cooper K.
      • Bos J.D.
      • Imokawa G.
      • David T.J.
      • et al.
      Proceedings of the 4th Georg Rajka International Symposium on Atopic Dermatitis, Arcachon, France, September 15-17, 2005.
      and it has been suggested that allergen penetration might predate the development of asthma and allergic rhinitis
      • Hudson T.J.
      Skin barrier function and allergic risk.
      in the so-called atopic march.
      • Hahn E.L.
      • Bacharier L.B.
      The atopic march: the pattern of allergic disease development in childhood.
      Filaggrin (filament-aggregating protein) plays a key role in epidermal differentiation and skin barrier function. Filaggrin aggregates the keratin cytoskeleton to facilitate the collapse and flattening of keratinocytes in the outermost skin layer.
      • Manabe M.
      • Sanchez M.
      • Sun T.T.
      • Dale B.A.
      Interaction of filaggrin with keratin filaments during advanced stages of normal human epidermal differentiation and in ichthyosis vulgaris.
      The protein-lipid cornified envelope, which replaces the plasma membrane of terminally differentiated keratinocytes, is extensively cross-linked and forms an important barrier to prevent water loss and minimize the entry of allergens and microorganisms.
      • Candi E.
      • Schmidt R.
      • Melino G.
      The cornified envelope: a model of cell death in the skin.
      Filaggrin is subsequently degraded to produce a mixture of hygroscopic amino acids, which can also contribute to barrier function.
      • Rawlings A.V.
      • Harding C.R.
      Moisturization and skin barrier function.
      Genotypes resulting in relative or absolute filaggrin deficiency might therefore contribute to epidermal barrier dysfunction by more than 1 mechanism.
      At least 15 different loss-of-function (null) mutations in the filaggrin gene (FLG) have been reported to date, of which 5 are prevalent in the European population.
      • Sandilands A.
      • Terron-Kwiatkowski A.
      • Hull P.R.
      • O'Regan G.M.
      • Clayton T.H.
      • Watson R.M.
      • et al.
      Comprehensive analysis of the gene encoding filaggrin uncovers prevalent and rare mutations in ichthyosis vulgaris and atopic eczema.
      FLG null mutations cause the dry, scaly skin condition ichthyosis vulgaris
      • Smith F.J.
      • Irvine A.D.
      • Terron-Kwiatkowski A.
      • Sandilands A.
      • Campbell L.E.
      • Zhao Y.
      • et al.
      Loss-of-function mutations in the gene encoding filaggrin cause ichthyosis vulgaris.
      ; the 5 most common European mutations are also significantly associated with atopic eczema when analyzed individually and as a combined null genotype.
      • Sandilands A.
      • Terron-Kwiatkowski A.
      • Hull P.R.
      • O'Regan G.M.
      • Clayton T.H.
      • Watson R.M.
      • et al.
      Comprehensive analysis of the gene encoding filaggrin uncovers prevalent and rare mutations in ichthyosis vulgaris and atopic eczema.
      The association with atopic eczema has been replicated in at least 12 separate studies, most of which contain further within-study replication, with no negative or equivocal results,
      • Irvine A.D.
      Fleshing out filaggrin phenotypes.
      making this an unusually well-replicated finding in the field of complex genetics.
      The clinical phenotype of eczema is heterogeneous and likely to encompass considerable etiologic heterogeneity.
      • Brown S.
      • Reynolds N.J.
      Atopic and non-atopic eczema.
      The studies published to date looking at FLG null mutations have focused on moderate-to-severe atopic eczema cases recruited through specialist clinics
      • Sandilands A.
      • Terron-Kwiatkowski A.
      • Hull P.R.
      • O'Regan G.M.
      • Clayton T.H.
      • Watson R.M.
      • et al.
      Comprehensive analysis of the gene encoding filaggrin uncovers prevalent and rare mutations in ichthyosis vulgaris and atopic eczema.
      • Palmer C.N.
      • Irvine A.D.
      • Terron-Kwiatkowski A.
      • Zhao Y.
      • Liao H.
      • Lee S.P.
      • et al.
      Common loss-of-function variants of the epidermal barrier protein filaggrin are a major predisposing factor for atopic dermatitis.
      • Weidinger S.
      • Illig T.
      • Baurecht H.
      • Irvine A.D.
      • Rodriguez E.
      • Diaz-Lacava A.
      • et al.
      Loss-of-function variations within the filaggrin gene predispose for atopic dermatitis with allergic sensitizations.
      • Marenholz I.
      • Nickel R.
      • Ruschendorf F.
      • Schulz F.
      • Esparza-Gordillo J.
      • Kerscher T.
      • et al.
      Filaggrin loss-of-function mutations predispose to phenotypes involved in the atopic march.
      • Ruether A.
      • Stoll M.
      • Schwarz T.
      • Schreiber S.
      • Folster-Holst R.
      Filaggrin loss-of-function variant contributes to atopic dermatitis risk in the population of Northern Germany.
      • Barker J.N.
      • Palmer C.N.
      • Zhao Y.
      • Liao H.
      • Hull P.R.
      • Lee S.P.
      • et al.
      Null mutations in the filaggrin gene (FLG) determine major susceptibility to early-onset atopic dermatitis that persists into adulthood.
      • Stemmler S.
      • Parwez Q.
      • Petrasch-Parwez E.
      • Epplen J.T.
      • Hoffjan S.
      Two common loss-of-function mutations within the filaggrin gene predispose for early onset of atopic dermatitis.
      • Weidinger S.
      • Rodriguez E.
      • Stahl C.
      • Wagenpfeil S.
      • Klopp N.
      • Illig T.
      • et al.
      Filaggrin mutations strongly predispose to early-onset and extrinsic atopic dermatitis.
      • Morar N.
      • Cookson W.O.
      • Harper J.I.
      • Moffatt M.F.
      Filaggrin mutations in children with severe atopic dermatitis.
      and on children with eczema as part of atopy-related birth cohort studies.
      • Palmer C.N.
      • Irvine A.D.
      • Terron-Kwiatkowski A.
      • Zhao Y.
      • Liao H.
      • Lee S.P.
      • et al.
      Common loss-of-function variants of the epidermal barrier protein filaggrin are a major predisposing factor for atopic dermatitis.
      • Marenholz I.
      • Nickel R.
      • Ruschendorf F.
      • Schulz F.
      • Esparza-Gordillo J.
      • Kerscher T.
      • et al.
      Filaggrin loss-of-function mutations predispose to phenotypes involved in the atopic march.
      We therefore aimed to investigate whether the 5 most prevalent FLG null mutations make a significant contribution to the mild-to-moderate atopic eczema that is common in the English population. We also aimed to assess the association of FLG null mutations with other signs of dry skin (eg, xerosis, ichthyosis, keratosis pilaris, and hyperlinear palms) to further define the filaggrin-deficiency phenotype.

      Methods

       Study design and case definition

      We used a population cohort (n = 7737) from the northwest of England for whom DNA samples had been collected at birth,
      • Chase D.S.
      • Tawn E.J.
      • Parker L.
      • Jonas P.
      • Parker C.O.
      • Burn J.
      The North Cumbria Community Genetics Project.
      representing more than 85% of all deliveries in one hospital (West Cumberland Hospital, Whitehaven) between 1996 and 2003. This geographic area is particularly useful for epidemiologic research because of the relatively low rates of population movement. Children within the birth cohort catchment region who had not previously been included in the cohort were offered the opportunity to provide a saliva sample for DNA extraction so that they could be included in this study.
      Children between 7 and 9 years of age (n ≈ 4000) were chosen for this study as an optimal group in which to assess atopic disease (eczema, asthma, and seasonal rhinitis). Eczema is most prevalent in infancy and early childhood; 85% of children are affected before the age of 5 years,
      • Kay J.
      • Gawkrodger D.J.
      • Mortimer M.J.
      • Jaron A.G.
      The prevalence of childhood atopic eczema in a general population.
      and 50% to 70% of children “grow out” of their eczema by the age of 10 years,
      • Akdis C.A.
      • Akdis M.
      • Bieber T.
      • Bindslev-Jensen C.
      • Boguniewicz M.
      • Eigenmann P.
      • et al.
      Diagnosis and treatment of atopic dermatitis in children and adults: European Academy of Allergology and Clinical Immunology/American Academy of Allergy, Asthma and Immunology/PRACTALL Consensus Report.
      • Illi S.
      • von Mutius E.
      • Lau S.
      • Nickel R.
      • Gruber C.
      • Niggemann B.
      • et al.
      The natural course of atopic dermatitis from birth to age 7 years and the association with asthma.
      although they have an increased risk of recurrence in adulthood,
      • Williams H.C.
      • Wuthrich B.
      The natural history of atopic dermatitis.
      as well as an increased incidence of asthma and rhinitis.
      • Hahn E.L.
      • Bacharier L.B.
      The atopic march: the pattern of allergic disease development in childhood.
      Asthma shows a peak age of onset of 5 years, and therefore the majority of cases should be captured in our study age group.
      The study protocol was approved by the local research ethics committee, and a parent or guardian of each child provided written informed consent.
      All 57 primary and junior schools within the birth cohort catchment area were requested to participate in the study to allow distribution of questionnaires to all children aged 7 to 9 years. Questionnaire design used the well-validated United Kingdom (UK) Diagnostic Criteria
      • Williams H.C.
      • Burney P.G.
      • Pembroke A.C.
      • Hay R.J.
      Validation of the U.K. diagnostic criteria for atopic dermatitis in a population setting. U.K. Diagnostic Criteria for Atopic Dermatitis Working Party.
      to assess the 12-month period prevalence of eczema (the full questionnaire appears as Fig E1 in the Online Repository at www.jacionline.org). Additional, more detailed phenotypic data were gathered by a single dermatologist (S.J.B.) who had experience of working in a pediatric dermatology clinic. The skin on each child's face, limbs, and abdomen was examined. Eczema cases were defined according to the UK diagnostic criteria (representing a 12-month period prevalence), flexural eczema on examination by the dermatologist (a point prevalence), or both. Children not included in either of these categories were classified as control subjects.
      Eczema was graded by using the Three Item Severity score,
      • Wolkerstorfer A.
      • de Waard van der Spek F.B.
      • Glazenburg E.J.
      • Mulder P.G.
      • Oranje A.P.
      Scoring the severity of atopic dermatitis: three item severity score as a rough system for daily practice and as a pre-screening tool for studies.
      a simple validated scale that allows the rapid assessment and recording of clinically significant features
      • Charman C.R.
      • Venn A.J.
      • Williams H.
      Measuring atopic eczema severity visually: which variables are most important to patients?.
      : 1 to 2 represents mild eczema, 3 to 5 represents moderate eczema, and 6 to 9 represents severe eczema.
      • Oranje A.P.
      • Glazenburg E.J.
      • Wolkerstorfer A.
      • de Waard-van der Spek F.B.
      Practical issues on interpretation of scoring atopic dermatitis: the SCORAD index, objective SCORAD and the three-item severity score.
      The association between FLG mutations and the other atopic disorders, asthma and seasonal rhinitis, was investigated as a secondary analysis. Asthma and seasonal rhinitis prevalence were defined by parental replies to the following questions: “Has your child ever suffered from asthma? By asthma we mean bouts of wheezing and coughing” and “Has your child ever suffered from hay fever? By hay fever we mean bouts of sneezing with a runny nose or itchy eyes in the summer.”
      • Williams H.C.
      • Burney P.G.
      • Pembroke A.C.
      • Hay R.J.
      Validation of the U.K. diagnostic criteria for atopic dermatitis in a population setting. U.K. Diagnostic Criteria for Atopic Dermatitis Working Party.

       Genotypic analysis

      DNA was extracted from umbilical cord blood or umbilical cord tissue from the birth cohort individuals using standard procedures. Saliva samples were collected from the remainder using Oragene DNA self-collection kits.
      DNA samples were screened for the 5 FLG null mutations most prevalent in the European population,
      • Sandilands A.
      • Terron-Kwiatkowski A.
      • Hull P.R.
      • O'Regan G.M.
      • Clayton T.H.
      • Watson R.M.
      • et al.
      Comprehensive analysis of the gene encoding filaggrin uncovers prevalent and rare mutations in ichthyosis vulgaris and atopic eczema.
      as previously described: TaqMan allelic discrimination assay (Applied Biosystems, Foster City, Calif) for R501X, 2282del4, R2447X, and S3247X and size analysis of fluorescently labeled PCR products using an Applied Biosystems 3100 DNA sequencer for 3702delG.
      • Sandilands A.
      • O'Regan G.M.
      • Liao H.
      • Zhao Y.
      • Terron-Kwiatkowski A.
      • Watson R.M.
      • et al.
      Prevalent and rare mutations in the gene encoding filaggrin cause ichthyosis vulgaris and predispose individuals to atopic dermatitis.
      Homozygote and heterozygote results were confirmed by means of restriction enzyme digestion
      • Smith F.J.
      • Irvine A.D.
      • Terron-Kwiatkowski A.
      • Sandilands A.
      • Campbell L.E.
      • Zhao Y.
      • et al.
      Loss-of-function mutations in the gene encoding filaggrin cause ichthyosis vulgaris.
      • Sandilands A.
      • O'Regan G.M.
      • Liao H.
      • Zhao Y.
      • Terron-Kwiatkowski A.
      • Watson R.M.
      • et al.
      Prevalent and rare mutations in the gene encoding filaggrin cause ichthyosis vulgaris and predispose individuals to atopic dermatitis.
      or sequencing.
      • Sandilands A.
      • Terron-Kwiatkowski A.
      • Hull P.R.
      • O'Regan G.M.
      • Clayton T.H.
      • Watson R.M.
      • et al.
      Comprehensive analysis of the gene encoding filaggrin uncovers prevalent and rare mutations in ichthyosis vulgaris and atopic eczema.

       Statistical analysis

      Calculations based on an estimated 11% prevalence of eczema
      • Williams H.C.
      • Wuthrich B.
      The natural history of atopic dermatitis.
      and combined null allele frequency of 0.078
      • Palmer C.N.
      • Irvine A.D.
      • Terron-Kwiatkowski A.
      • Zhao Y.
      • Liao H.
      • Lee S.P.
      • et al.
      Common loss-of-function variants of the epidermal barrier protein filaggrin are a major predisposing factor for atopic dermatitis.
      predicted that recruitment of 1000 children would give a 91% power at a P value of .001 to detect an allelic odds ratio (OR) of 3 (at the lower end of published data
      • Palmer C.N.
      • Irvine A.D.
      • Terron-Kwiatkowski A.
      • Zhao Y.
      • Liao H.
      • Lee S.P.
      • et al.
      Common loss-of-function variants of the epidermal barrier protein filaggrin are a major predisposing factor for atopic dermatitis.
      • Marenholz I.
      • Nickel R.
      • Ruschendorf F.
      • Schulz F.
      • Esparza-Gordillo J.
      • Kerscher T.
      • et al.
      Filaggrin loss-of-function mutations predispose to phenotypes involved in the atopic march.
      ). A similar calculation predicted that there would be insufficient power to detect an association between each individual mutation and eczema.
      The rationale for counting the 5 screened FLG null mutations as a single null allele is based on biochemical and immunohistochemical studies demonstrating that each of these null mutations produce truncated forms of profilaggrin, which results in a marked reduction or absence of processed filaggrin when present in the homozygote or compound heterozygote state.
      • Sandilands A.
      • Terron-Kwiatkowski A.
      • Hull P.R.
      • O'Regan G.M.
      • Clayton T.H.
      • Watson R.M.
      • et al.
      Comprehensive analysis of the gene encoding filaggrin uncovers prevalent and rare mutations in ichthyosis vulgaris and atopic eczema.
      • Smith F.J.
      • Irvine A.D.
      • Terron-Kwiatkowski A.
      • Sandilands A.
      • Campbell L.E.
      • Zhao Y.
      • et al.
      Loss-of-function mutations in the gene encoding filaggrin cause ichthyosis vulgaris.
      Allele and genotype frequencies in case and control groups and different phenotypic groups were compared by using the Fisher exact test under the null hypothesis that there is no association with genotype. Logistic regression analysis was used to estimate the OR and penetrance of the FLG null allele using both allele- and genotype-based models of disease to investigate the pattern of inheritance. Analysis was performed with the statistical analysis package Stata (version 9, Stata for Linux; StataCorp LP, College Station, Tex).

      Results

      Seventy-five percent (43/57) of eligible schools agreed to take part in the research by distributing study literature and facilitating skin examinations by the visiting dermatologist. An estimated 3086 children in these schools were within the target age range, and consent to participate was given by the parents/guardians of 811 (26%) children. Eight hundred one questionnaires were completed, 792 children underwent skin examination, and 805 DNA samples were located from the birth cohort stores (n = 577) or extracted from saliva (n = 228), giving complete phenotypic and genotypic information on 784 individuals (Fig 1). Individuals with incomplete phenotypic data, genotypic data, or both were included in the statistical analyses unless the missing data precluded this (eg, insufficient criteria to define UK diagnosis or insufficient genotyping results to identify the combined genotype).
      Figure thumbnail gr1
      Fig 1Flow diagram showing recruitment of children to the study.
      The demographic data for this cohort plus clinical features relating to eczema and atopy are summarized in Table I.
      Table IDemographic data and clinical features of 811 children aged 7 to 9 years
      Demographic dataNo.Percentage
      Sex417 male51
      394 female49
      Prevalence of atopic eczema195/80624
      Eczema severity70/120 mild58
      45/120 moderate38
      5/120 severe4
      Prevalence of asthma205/79426
      Children with eczema and asthma83/79311% of total cohort 43% of eczema cases
      41% of asthma cases
      Prevalence of seasonal rhinitis152/79319
      The prevalence of atopic eczema was defined using a questionnaire based on the UK diagnostic criteria
      • Williams H.C.
      • Burney P.G.
      • Pembroke A.C.
      • Hay R.J.
      Validation of the U.K. diagnostic criteria for atopic dermatitis in a population setting. U.K. Diagnostic Criteria for Atopic Dermatitis Working Party.
      (12-month period prevalence) plus skin examination by a dermatologist (point prevalence). Eczema severity was assessed using the Three Item Severity score.
      • Wolkerstorfer A.
      • de Waard van der Spek F.B.
      • Glazenburg E.J.
      • Mulder P.G.
      • Oranje A.P.
      Scoring the severity of atopic dermatitis: three item severity score as a rough system for daily practice and as a pre-screening tool for studies.
      The lifetime prevalence of asthma and seasonal rhinitis was defined by parental questionnaire. The denominator varies to maximize the use of available data.
      Screening for all 5 mutations achieved results for 789 of 805 DNA samples (Table II). Approximately 1 in 7 children (14.2%) of the study cohort are carriers of 1 or more of the FLG mutations. Of eczema cases, 18.4% carried 1 or more FLG null mutations compared with 12.9% of control subjects. The combined null genotype is significantly associated with atopic eczema (P = 1.2 × 10−4).
      Table IIFLG genotypes in a cohort of English schoolchildren compared by using the Fisher exact test
      Atopic eczema
      No. (%) of casesNo. (%) of control subjects
      FLG null genotypeAA155 (81.6)522 (87.1)
      Aa27 (14.2)76 (12.7)
      aa8 (4.2)1 (0.2)
      Total190599
      Fisher exact testP = 1.2 × 10−4
      A, Wild-type form of FLG; a, null mutant form, either R501X, 2282del4, R2447X, S3247X, or 3702delG; aa, individuals including 1 homozygote (R501X/R501X) and 8 compound heterozygotes (6 are R501X/2282del4, including the aa in the control group; 1 is 2282del4/R2447X; and 1 is R501X/R2447X). Each of the 5 variants is in Hardy-Weinberg equilibrium within the cohort.
      Complete genotypic data (results on screening for all 5 mutations) were obtained on a total of 789 children. The genotyping results for each individual mutation are available in Table E1 in this article's Online Repository at www.jacionline.org.
      Genotyping results can be analyzed by using either a genotypic model (comparing frequencies of wild-type with heterozygote and homozygote mutants) or using an allele-based model (which presumes that carriage of 2 mutations results in twice the effect of 1 mutation on a log odds scale). A comparison of these 2 models for our data is shown in Fig 2. The genotypic model fits the data significantly better (P = .0018, likelihood ratio test), and hence this model is preferable because it makes fewer assumptions about the mode of inheritance. This indicates that FLG null mutations have a recessive mode of inheritance because the heterozygotes have no significant increased risk of eczema (OR, 1.2; 95% CI, 0.7-1.9), but individuals carrying 2 copies of the FLG null mutations (homozygotes and compound heterozygotes) have an approximately 27 times greater risk of having childhood eczema (OR, 26.9; 95% CI, 3.3-217.1).
      Figure thumbnail gr2
      Fig 2Logistic regression analysis to estimate odds of disease (atopic eczema) with FLG null mutations comparing genotype- and allele-based models. The 95% CIs are as follows: genotypic model heterozygotes versus wild type, 0.7 to 1.9; homozygote mutants versus wild type, 3.3 to 217.1; allelic model, 1.2 to 8.6. The likelihood ratio test, to test whether the allelic model can be nested in full within the genotypic model of disease, shows that the genotypic model fits the data significantly better (P = 1.8 × 10−3).
      There was no association between parental report of asthma (P = .15) or seasonal rhinitis (P = .66) and FLG null mutations, but there was evidence of an association between the phenotype of asthma with eczema, which was significant even after allowing for multiple testing (P = 7.1 × 10−4; OR for carriers of 2 null mutations, 11.9; 95% CI, 3.1-45.6). Of children with eczema and asthma, 23.2% carry 1 or more of the FLG null mutations compared with 11.8% of control subjects. The results of logistic regression analysis and the Fisher exact test to test association of these and other phenotypes with the FLG genotype are summarized in Table III.
      Table IIIPrevalence, logistic regression ORs, and P values for the Fisher exact test for different phenotypes and the combined FLG null genotype
      Phenotype or clinical featureNo. (denominator)OR (95% CI)Fisher exact test
      Atopic eczema (UK criteria + flexural)195 (806)Hets: 1.2 (0.7–1.9)P = 1.2 × 10−4
      Homs: 26.9 (3.3–217.1)
      Nonflexural eczema
      Cases with nonflexural eczema only (ie, no flexural involvement).
      35 (792)Hets: 0.4 (0.1–1.8)P = .52
      Homs:
      OR cannot be estimated because there are no homozygotes in the control group.
      Asthma205 (794)Hets: 1.0 (0.6–1.6)P = .15
      Homs: 3.6 (1.0–13.7)
      Atopic eczema with asthma83 (793)Hets: 1.5 (0.8–2.8)P = 7.1 × 10−4
      Homs: 11.9 (3.1–45.6)
      Seasonal rhinitis152 (793)Hets: 1.2 (0.7–2.0)P = .66
      Homs: 0.5 (0.1–4.4)
      Ichthyosis vulgaris10 (792)Hets: >100
      Insufficient data for reliable estimation of OR.
      P = 4.1 × 10−16
      Homs: >100
      Insufficient data for reliable estimation of OR.
      Milder ichthyosis54 (792)Hets: 5.5 (3.0–10.0)P = 1.7 × 10−7
      Homs: 5.8 (1.2–29.1)
      Xerosis193 (792)Hets: 1.5 (0.9–2.4)P = .04
      Homs:
      OR cannot be estimated because there are no homozygotes in the control group.
      Hyperlinear palms (marked)52 (792)Hets: 17.5 (9.0–34.2)P = 1.2 × 10−23
      Homs: 152.1 (29.1-794.3)
      Hyperlinear palms (any)167 (792)Hets: 19.3 (11.7–31.7)P = 6.8 × 10−42
      Homs:
      OR cannot be estimated because there are no homozygotes in the control group.
      Keratosis pilaris (marked)77 (792)Hets: 8.9 (5.2–15.2)P = 2.8 × 10−18
      Homs: 35.1 (8.4–146.1)
      Keratosis pilaris (any)273 (792)Hets: 3.6 (2.3–5.5)P = 2.2 × 10−12
      Homs:
      OR cannot be estimated because there are no homozygotes in the control group.
      Hets, Individuals who are heterozygous for any of the 5 FLG null mutations (R501X, 2282del4, R2447X, S3247X, and 3702delG); Homs, individuals with any 2 FLG mutations, including homozygotes and compound heterozygotes.
      Atopic eczema is defined by using the UK diagnostic criteria
      • Williams H.C.
      • Burney P.G.
      • Pembroke A.C.
      • Hay R.J.
      Validation of the U.K. diagnostic criteria for atopic dermatitis in a population setting. U.K. Diagnostic Criteria for Atopic Dermatitis Working Party.
      and skin examination by a dermatologist; asthma and seasonal rhinitis are defined by parental questionnaire. The diagnoses of ichthyosis vulgaris (scaly skin on extensor surfaces plus hyperlinear palms and keratosis pilaris), milder ichthyosis (scaly skin), and xerosis (dry skin) are based on clinical examination by a dermatologist on a single occasion for each child during the winter months. These analyses use the genotypic model of disease, which is less powerful than the allele-based model but makes no assumption about the mode of inheritance, which is currently unknown. Statistically significant results (P < .01) are highlighted in boldface.
      Cases with nonflexural eczema only (ie, no flexural involvement).
      OR cannot be estimated because there are no homozygotes in the control group.
      Insufficient data for reliable estimation of OR.
      In our cohort 10 of 792 children had classical ichthyosis vulgaris (fine gray-white scaling on extensor skin surfaces plus hyperlinear palms and keratosis pilaris) on clinical examination, a prevalence of approximately 1 in 80. One was homozygous for the R501X mutation, 6 were compound heterozygotes, and 3 were heterozygotes (each carrying the R501X mutation). Three of the 10 patients with ichthyosis vulgaris had no eczema by either of our definitions and no parental report of eczema at any time in the child's life, and interestingly, these were the 3 R501X heterozygotes. There were a further 54 children with milder ichthyosis (scaling of the skin), as well as 193 with xerosis (dryness of the skin).
      Looking at the genotype-phenotype correlation, all 9 of the homozygous/compound heterozygous individuals in our cohort had ichthyosis vulgaris or milder ichthyosis, and 8 of these 9 had eczema. Conversely, in the 103 heterozygous individuals, 75 (73%) did not have ichthyosis vulgaris or milder ichthyosis, but 20 (27%) of this subgroup (heterozygotes without any ichthyosis) did have eczema. However, using logistic regression to model the effect of genotype on eczema status, having controlled for the effect of ichthyosis vulgaris, showed that any additional effect of FLG genotype is not statistically significant (P = .43).
      The physical signs of hyperlinear palms and keratosis pilaris in childhood are each strongly and significantly associated with the combined FLG null genotype (Table III). Marked hyperlinear palms also show significant association with the 4 most prevalent FLG null mutations (R501X, 2282del4, R2447X, and S3247X) when they are analyzed individually (P < .01 for each variant). Similarly, marked keratosis pilaris shows significant and independent association with the 2 most prevalent null mutations (R501X and 2282del4, P < .01 for each). These figures translate into a positive predictive value of 71% for marked hyperlinear palms; that is, 71% of children with marked hyperlinear palms carry 1 or more of the 5 common FLG null mutations. The negative predictive value is 90%, meaning 90% of children without hyperlinear palms are not carriers of these mutations. The predictive values for marked keratosis pilaris in this age group are 53% (positive) and 90% (negative predictive value).

      Discussion

      There have, to date, been no published studies investigating the role of FLG mutations in the mild-to-moderate eczema that predominates in our society. We used a unique resource in the northwest of England, an unselected birth cohort with DNA samples, to investigate this question. We were careful to define eczema using a well-validated method (the UK modification of Hanifin and Rajka's diagnostic criteria)
      • Williams H.C.
      • Burney P.G.
      • Pembroke A.C.
      • Hay R.J.
      Validation of the U.K. diagnostic criteria for atopic dermatitis in a population setting. U.K. Diagnostic Criteria for Atopic Dermatitis Working Party.
      in addition to skin examination by an experienced dermatologist. This allowed us to gather more detailed information on phenotypic features, such as xerosis, ichthyosis and keratosis pilaris, which have not been documented in previous studies. Diagnostic accuracy and careful phenotype documentation are particularly important in genetic studies if individual genetic factors are to be identified on the background of complex environmental effects.
      • Morar N.
      • Willis-Owen S.A.
      • Moffatt M.F.
      • Cookson W.O.
      The genetics of atopic dermatitis.
      The low response rate of only 26% reflects our method of recruitment, requiring informed consent before questionnaire completion.
      • Angus V.C.
      • Entwistle V.A.
      • Emslie M.J.
      • Walker K.A.
      • Andrew J.E.
      The requirement for prior consent to participate on survey response rates: a population-based survey in Grampian.
      This raises the possibility that bias has been introduced by self-selection in our study cohort. We addressed this question in 2 ways.
      First, comparison of the prevalence of eczema and asthma in our cohort with a recently published study of atopy prevalence in the northeast of England by using a case definition based on the International Study of Asthma and Allergies in Childhood questionnaire (90% response rate, n = 3000, 6- to 7-year-olds)
      • Shamssain M.
      Trends in the prevalence and severity of asthma, rhinitis and atopic eczema in 6- to 7- and 13- to 14-yr-old children from the north-east of England.
      showed very similar findings: “rash with typical distribution,” 21.1% for boys and 23.8% for girls; “current rash,” 23.3% for boys and 25.0% for girls compared with a prevalence of 24.2% in our study (boys and girls combined). Similarly, asthma lifetime prevalence from this comparable study is reported as 29.8% for boys and 24.1% of girls compared with 26.2% in our study.
      Second, we compared the allele frequencies for each of the 5 FLG mutations in our study cohort with those of an unselected 1000 samples from age-matched children in the same birth cohort (screened as part of another study
      • Brown S.J.
      • Sandilands A.
      • Zhao Y.
      • Liao H.
      • Relton C.L.
      • Meggitt S.J.
      • et al.
      Prevalent and low-frequency null mutations in the filaggrin gene are associated with early-onset and persistent atopic eczema.
      ) and found no significant difference (P > .05, Fisher exact test; these data are available in Table E2 in the Online Repository at www.jacionline.org). We therefore conclude that our cohort is representative of the local population, and hence we can use it to estimate the true risk (or penetrance) associated with FLG mutations and not just their relative risk, which would be estimated from a selected case-control study. From our data, we calculate that the probability of disease (ie, having mild-to-moderate eczema) is 22.9% in wild-type individuals (95% CI, 19.7% to 26.1%), 26.2% in heterozygotes (95% CI, 17.7% to 34.7%), and 88.9% (95% CI, 68.4% to 109.4%) for homozygotes.
      In our cohort the prevalence of ichthyosis vulgaris is approximately 1 in 80. This is significantly higher than that reported in the only previous population cohort study, when 1 in 250 English schoolchildren were found to have the disorder.
      • Wells R.S.
      • Kerr C.B.
      Clinical features of autosomal dominant and sex-linked ichthyosis in an English population.
      This higher prevalence might reflect more careful disease ascertainment with a dermatology specialist. Furthermore, the prevalence of FLG null mutations in the population (9/789 individuals carrying 2 mutations) would support these examination findings, with a predicted prevalence of ichthyosis vulgaris of approximately 1 in 88 (presuming 100% penetrance and not including the effect of semidominant inheritance). Ichthyosis vulgaris and milder ichthyosis were each significantly associated with FLG status in our cohort. This is consistent with data from previous studies that FLG shows semidominant inheritance (ie, heterozygote carriers tend to have a milder phenotype than homozygotes).
      • Palmer C.N.
      • Irvine A.D.
      • Terron-Kwiatkowski A.
      • Zhao Y.
      • Liao H.
      • Lee S.P.
      • et al.
      Common loss-of-function variants of the epidermal barrier protein filaggrin are a major predisposing factor for atopic dermatitis.
      This study adds to our understanding of the genetic basis of eczema in several ways. The phenotype studied (mild-to-moderate atopic eczema in 7- to 9-year-olds) is significantly associated with FLG loss-of-function mutations in the population of the northwest of England. This contrasts with the cases of nonflexural eczema within the cohort, a group likely to include those with discoid eczema and contact dermatitis, who do not show an association with FLG null mutations, although the numbers are too small to draw firm conclusions.
      In these cases of predominantly mild-to-moderate atopic eczema, FLG shows a recessive pattern of inheritance, rather than the semidominant pattern reported in the original group of eczema cases in families with ichthyosis vulgaris.
      • Palmer C.N.
      • Irvine A.D.
      • Terron-Kwiatkowski A.
      • Zhao Y.
      • Liao H.
      • Lee S.P.
      • et al.
      Common loss-of-function variants of the epidermal barrier protein filaggrin are a major predisposing factor for atopic dermatitis.
      The fact that we only have 9 individuals in our cohort that are homozygous for FLG null mutations is reflected in the wide confidence intervals around the ORs in Fig 2. However, we can still be confident that the data demonstrate a recessive pattern of inheritance because 8 (4.0%) of the 190 cases carry 2 FLG null mutations compared with only 1 (0.2%) of 599 control subjects, and hence these 9 individuals provide good evidence for a strong homozygote effect. The CIs do not overlap, and there is a very small chance (P = 1.8 × 10−3) of observing these data under an allele-based model (semidominant inheritance) rather than a genotype-based model (recessive inheritance).
      The association of mild-to-moderate eczema with FLG is closely related to the presence of ichthyosis vulgaris because logistic regression modeling showed no additional effect of genotype, having allowed for the presence/absence of ichthyosis vulgaris. This is perhaps unsurprising, given that FLG mutations are known to cause ichthyosis vulgaris and that 50% to 70% of patients with ichthyosis vulgaris also have eczema. This chain of reasoning emphasizes the role of epidermal barrier dysfunction, which is characteristic of filaggrin deficiency, in the pathogenesis of eczema. An alternative explanation is that FLG is associated with eczema only through linkage disequilibrium with another gene. However, this seems unlikely given the independent association of 5 different FLG mutations with atopic eczema in the European population
      • Sandilands A.
      • Terron-Kwiatkowski A.
      • Hull P.R.
      • O'Regan G.M.
      • Clayton T.H.
      • Watson R.M.
      • et al.
      Comprehensive analysis of the gene encoding filaggrin uncovers prevalent and rare mutations in ichthyosis vulgaris and atopic eczema.
      • Sandilands A.
      • O'Regan G.M.
      • Liao H.
      • Zhao Y.
      • Terron-Kwiatkowski A.
      • Watson R.M.
      • et al.
      Prevalent and rare mutations in the gene encoding filaggrin cause ichthyosis vulgaris and predispose individuals to atopic dermatitis.
      and Asian-specific FLG null mutations that have arisen independently from the European variants,
      • Nomura T.
      • Sandilands A.
      • Akiyama M.
      • Liao H.
      • Evans A.T.
      • Sakai K.
      • et al.
      Unique mutations in the filaggrin gene in Japanese patients with ichthyosis vulgaris and atopic dermatitis.
      as well as a reduction in filaggrin expression in atopic skin
      • Seguchi T.
      • Cui C.Y.
      • Kusuda S.
      • Takahashi M.
      • Aisu K.
      • Tezuka T.
      Decreased expression of filaggrin in atopic skin.
      and biochemical studies demonstrating a similar reduction/absence of processed filaggrin as a result of FLG null mutations.
      • Smith F.J.
      • Irvine A.D.
      • Terron-Kwiatkowski A.
      • Sandilands A.
      • Campbell L.E.
      • Zhao Y.
      • et al.
      Loss-of-function mutations in the gene encoding filaggrin cause ichthyosis vulgaris.
      The OR of having moderate-to-severe eczema given the presence of 1 or more FLG mutations has varied between 2.03 and 13.4 in previous reports.
      • Irvine A.D.
      Fleshing out filaggrin phenotypes.
      • Palmer C.N.
      • Irvine A.D.
      • Terron-Kwiatkowski A.
      • Zhao Y.
      • Liao H.
      • Lee S.P.
      • et al.
      Common loss-of-function variants of the epidermal barrier protein filaggrin are a major predisposing factor for atopic dermatitis.
      • Morar N.
      • Cookson W.O.
      • Harper J.I.
      • Moffatt M.F.
      Filaggrin mutations in children with severe atopic dermatitis.
      The equivalent OR for our predominantly mild-to-moderate cases would be 1.53 (95% CI, 0.99-2.37) if we had used a dominant model of analysis (combining the heterozygotes with the homozygote mutants to compare carriers of ≥1 FLG null mutations with wild-type individuals). This lower OR indicates a lesser effect of the FLG mutations in mild-to-moderate eczema compared with moderate-to-severe eczema. Possible explanations for this observation include an intuitive “dilution” of effect in the less severe phenotype or a greater effect of other factors, genetic and environmental, which are relatively more important than filaggrin insufficiency in milder eczema. The dominant model gives a nonsignificant result for our data (95% CI overlapping 1.0) because of the large number of heterozygotes and small number of homozygotes in the cohort.
      Recognition of the relative importance of different causative factors in the mild-to-moderate compared with the moderate-to-severe eczema phenotype might be helpful in designing more rational therapies aimed at targeting specific pathology.
      Interestingly, the frequency of carriage of FLG mutations in our cases (18.4%) is similar to that reported in children from a Danish birth cohort whose mothers had asthma (n = 372) in which 17.5% of eczema cases were carriers of 1 or more FLG null alleles.
      • Palmer C.N.
      • Irvine A.D.
      • Terron-Kwiatkowski A.
      • Zhao Y.
      • Liao H.
      • Lee S.P.
      • et al.
      Common loss-of-function variants of the epidermal barrier protein filaggrin are a major predisposing factor for atopic dermatitis.
      In these children there was a strikingly high penetrance: 63% of carriers had atopic eczema by the age of 3 years, suggesting that other influential factors (genetic, environmental, or both) are associated with the maternal history of asthma. Our cohort shows an association of FLG mutations with asthma only in those children who also have eczema, replicating earlier reports
      • Palmer C.N.
      • Irvine A.D.
      • Terron-Kwiatkowski A.
      • Zhao Y.
      • Liao H.
      • Lee S.P.
      • et al.
      Common loss-of-function variants of the epidermal barrier protein filaggrin are a major predisposing factor for atopic dermatitis.
      • Marenholz I.
      • Nickel R.
      • Ruschendorf F.
      • Schulz F.
      • Esparza-Gordillo J.
      • Kerscher T.
      • et al.
      Filaggrin loss-of-function mutations predispose to phenotypes involved in the atopic march.
      and emphasizing the existence of a subgroup of asthma in association with eczema.
      This study demonstrates the usefulness of careful physical examination of the skin because hyperlinear palms and keratosis pilaris are features that can help to predict the presence of an FLG null mutation. The mechanisms by which filaggrin insufficiency produces these clinical signs remain to be elucidated.
      Finally, in spite of the significant effect demonstrated in this cohort, FLG null mutations can only explain a small proportion of the total burden of childhood eczema on a population scale. Eight (4.2%) of 190 atopic eczema cases in our cohort carry 2 null mutations and thus can be attributed to FLG deficiency. The residual 95.8% of cases remain to be explained by other genetic and environmental factors. However, FLG is the single most significant genetic factor in atopic eczema that has been identified to date, and our study supports a significant role for filaggrin insufficiency in the pathogenesis of a small proportion of common, mild-to-moderate atopic eczema cases.
      Clinical implications
      This finding emphasizes the role of ichthyosis vulgaris and filaggrin deficiency in the pathogenesis of approximately 4% of eczema cases in the English population.
      We thank the schools in West Cumbria, the children, and their parents for participating in this research.

      Fig E1.

      Figure thumbnail gr3

      Table E1.

      Tabled 1Genotyping results for all 5 FLG null mutations and the combined null genotype in a cohort of 805 English schoolchildren
      R501X2282del4R2447XS3247X3702delGCombined null genotype
      GenotypeControl populationAtopic eczema casesControl populationAtopic eczema casesControl populationAtopic eczema casesControl populationAtopic eczema casesControl populationAtopic eczema casesControl populationAtopic eczema cases
      AA566177572176592189598192599191522155
      Aa361629188343017627
      Aa010000000018
      Total602194601194601192602195599192599190
      Fisher exact testP = .11P = .03P = .73P = .37P = .24P =1.2 × 10−4
      MAF cases vs control subjects0.0460.0300.0460.0240.0080.0060.0080.0030.0030.0000.1100.065
      MAF combined cases and control subjects0.0340.0300.0070.0040.0010.077
      OR using the genotypic model (95% CI)
       Hets1.4 (0.8-2.6)2.0 (1.1-3.7)1.2 (0.3-4.5)2.3 (0.5-10.5)NA1.2 (0.7-1.9)
       HomsNANANANANA26.9 (3.3-217.1)
      OR using the allelic model (95% CI)1.6 (0.9-2.8)2.0 (1.1-3.7)1.2 (0.3-4.5)2.3 (0.5-10.5)NA1.8 (1.2-2.6)
      LR testP = .0018
      AA, Homozygous wild-type genotype; Aa, heterozygous wild-type/mutant genotype for any of the 5 FLG null mutations (R501X, 2282del4, R2447X, S3247X, or 3702delG); aa, homozygous or compound heterozygous mutant for any of the 5 FLG null mutations; MAF, minor allele frequency; NA, not analyzed because of absent or insufficient numbers of homozygotes; LR, likelihood ratio test to compare genotype and allelic models.

      Table E2.

      Tabled 1FLG minor allele frequencies in a cohort of English schoolchildren and an unselected age-matched population birth cohort from the same geographic area
      Minor allele frequency (95% CIs)
      FLG mutationSchoolchildren participating in the study (n = 803)Unselected birth cohort from the same region (n = 747)
      R501X0.0339 (0.0261-0.044)0.0248 (0.018-0.0339)
      2282del40.0296 (0.0223-0.0391)0.0274 (0.0203-0.0370)
      R2447X0.0069 (0.0039-00124)0.0033 (0.0014-0.078)
      S3247X0.0044 (0.0021-0.009)0.0027 (0.0010-0.0069)
      3702delG0.0006 (0.000-0.0036)0.0007 (0.0000-0.0038)
      Combined null genotype0.0767 (0.0646-0.0909)0.0589 (0.0481-0.0720)
      Using a Fisher exact test to compare allele frequencies between groups, the result was a P value of greater than .05 for each of the mutations when analyzed individually and for the combined null genotype, indicating that there is no significant difference in minor allele frequencies between the study group and the unselected birth cohort.

      References

        • Johansson S.G.
        • Bieber T.
        • Dahl R.
        • Friedmann P.S.
        • Lanier B.Q.
        • Lockey R.F.
        • et al.
        Revised nomenclature for allergy for global use: report of the Nomenclature Review Committee of the World Allergy Organization, October 2003.
        J Allergy Clin Immunol. 2004; 113: 832-836
        • Chamlin S.L.
        • Cella D.
        • Frieden I.J.
        • Williams M.L.
        • Mancini A.J.
        • Lai J.S.
        • et al.
        Development of the Childhood Atopic Dermatitis Impact Scale: initial validation of a quality-of-life measure for young children with atopic dermatitis and their families.
        J Invest Dermatol. 2005; 125: 1106-1111
        • Hudson T.J.
        Skin barrier function and allergic risk.
        Nat Genet. 2006; 38: 399-400
        • Taieb A.
        • Hanifin J.
        • Cooper K.
        • Bos J.D.
        • Imokawa G.
        • David T.J.
        • et al.
        Proceedings of the 4th Georg Rajka International Symposium on Atopic Dermatitis, Arcachon, France, September 15-17, 2005.
        J Allergy Clin Immunol. 2006; 117: 378-390
        • Hahn E.L.
        • Bacharier L.B.
        The atopic march: the pattern of allergic disease development in childhood.
        Immunol Allergy Clin North Am. 2005; 25 (v): 231-246
        • Manabe M.
        • Sanchez M.
        • Sun T.T.
        • Dale B.A.
        Interaction of filaggrin with keratin filaments during advanced stages of normal human epidermal differentiation and in ichthyosis vulgaris.
        Differentiation. 1991; 48: 43-50
        • Candi E.
        • Schmidt R.
        • Melino G.
        The cornified envelope: a model of cell death in the skin.
        Nat Rev Mol Cell Biol. 2005; 6: 328-340
        • Rawlings A.V.
        • Harding C.R.
        Moisturization and skin barrier function.
        Dermatol Ther. 2004; 17: 43-48
        • Sandilands A.
        • Terron-Kwiatkowski A.
        • Hull P.R.
        • O'Regan G.M.
        • Clayton T.H.
        • Watson R.M.
        • et al.
        Comprehensive analysis of the gene encoding filaggrin uncovers prevalent and rare mutations in ichthyosis vulgaris and atopic eczema.
        Nat Genet. 2007; 39: 650-654
        • Smith F.J.
        • Irvine A.D.
        • Terron-Kwiatkowski A.
        • Sandilands A.
        • Campbell L.E.
        • Zhao Y.
        • et al.
        Loss-of-function mutations in the gene encoding filaggrin cause ichthyosis vulgaris.
        Nat Genet. 2006; 38: 337-342
        • Irvine A.D.
        Fleshing out filaggrin phenotypes.
        J Invest Dermatol. 2007; 127: 504-507
        • Brown S.
        • Reynolds N.J.
        Atopic and non-atopic eczema.
        BMJ. 2006; 332: 584-588
        • Palmer C.N.
        • Irvine A.D.
        • Terron-Kwiatkowski A.
        • Zhao Y.
        • Liao H.
        • Lee S.P.
        • et al.
        Common loss-of-function variants of the epidermal barrier protein filaggrin are a major predisposing factor for atopic dermatitis.
        Nat Genet. 2006; 38: 441-446
        • Weidinger S.
        • Illig T.
        • Baurecht H.
        • Irvine A.D.
        • Rodriguez E.
        • Diaz-Lacava A.
        • et al.
        Loss-of-function variations within the filaggrin gene predispose for atopic dermatitis with allergic sensitizations.
        J Allergy Clin Immunol. 2006; 118: 214-219
        • Marenholz I.
        • Nickel R.
        • Ruschendorf F.
        • Schulz F.
        • Esparza-Gordillo J.
        • Kerscher T.
        • et al.
        Filaggrin loss-of-function mutations predispose to phenotypes involved in the atopic march.
        J Allergy Clin Immunol. 2006; 118: 866-871
        • Ruether A.
        • Stoll M.
        • Schwarz T.
        • Schreiber S.
        • Folster-Holst R.
        Filaggrin loss-of-function variant contributes to atopic dermatitis risk in the population of Northern Germany.
        Br J Dermatol. 2006; 155: 1093-1094
        • Barker J.N.
        • Palmer C.N.
        • Zhao Y.
        • Liao H.
        • Hull P.R.
        • Lee S.P.
        • et al.
        Null mutations in the filaggrin gene (FLG) determine major susceptibility to early-onset atopic dermatitis that persists into adulthood.
        J Invest Dermatol. 2007; 127: 564-567
        • Stemmler S.
        • Parwez Q.
        • Petrasch-Parwez E.
        • Epplen J.T.
        • Hoffjan S.
        Two common loss-of-function mutations within the filaggrin gene predispose for early onset of atopic dermatitis.
        J Invest Dermatol. 2007; 127: 722-724
        • Weidinger S.
        • Rodriguez E.
        • Stahl C.
        • Wagenpfeil S.
        • Klopp N.
        • Illig T.
        • et al.
        Filaggrin mutations strongly predispose to early-onset and extrinsic atopic dermatitis.
        J Invest Dermatol. 2007; 127: 724-726
        • Morar N.
        • Cookson W.O.
        • Harper J.I.
        • Moffatt M.F.
        Filaggrin mutations in children with severe atopic dermatitis.
        J Invest Dermatol. 2007; 127: 1667-1672
        • Chase D.S.
        • Tawn E.J.
        • Parker L.
        • Jonas P.
        • Parker C.O.
        • Burn J.
        The North Cumbria Community Genetics Project.
        J Med Genet. 1998; 35: 413-416
        • Kay J.
        • Gawkrodger D.J.
        • Mortimer M.J.
        • Jaron A.G.
        The prevalence of childhood atopic eczema in a general population.
        J Am Acad Dermatol. 1994; 30: 35-39
        • Akdis C.A.
        • Akdis M.
        • Bieber T.
        • Bindslev-Jensen C.
        • Boguniewicz M.
        • Eigenmann P.
        • et al.
        Diagnosis and treatment of atopic dermatitis in children and adults: European Academy of Allergology and Clinical Immunology/American Academy of Allergy, Asthma and Immunology/PRACTALL Consensus Report.
        J Allergy Clin Immunol. 2006; 118: 152-169
        • Illi S.
        • von Mutius E.
        • Lau S.
        • Nickel R.
        • Gruber C.
        • Niggemann B.
        • et al.
        The natural course of atopic dermatitis from birth to age 7 years and the association with asthma.
        J Allergy Clin Immunol. 2004; 113: 925-931
        • Williams H.C.
        • Wuthrich B.
        The natural history of atopic dermatitis.
        in: Williams H.C. Atopic dermatitis. The epidemiology, causes and prevention of atopic eczema. Cambridge University Press, Cambridge2000: 41-59
        • Williams H.C.
        • Burney P.G.
        • Pembroke A.C.
        • Hay R.J.
        Validation of the U.K. diagnostic criteria for atopic dermatitis in a population setting. U.K. Diagnostic Criteria for Atopic Dermatitis Working Party.
        Br J Dermatol. 1996; 135: 12-17
        • Wolkerstorfer A.
        • de Waard van der Spek F.B.
        • Glazenburg E.J.
        • Mulder P.G.
        • Oranje A.P.
        Scoring the severity of atopic dermatitis: three item severity score as a rough system for daily practice and as a pre-screening tool for studies.
        Acta Derm Venereol. 1999; 79: 356-359
        • Charman C.R.
        • Venn A.J.
        • Williams H.
        Measuring atopic eczema severity visually: which variables are most important to patients?.
        Arch Dermatol. 2005; 141: 1146-1151
        • Oranje A.P.
        • Glazenburg E.J.
        • Wolkerstorfer A.
        • de Waard-van der Spek F.B.
        Practical issues on interpretation of scoring atopic dermatitis: the SCORAD index, objective SCORAD and the three-item severity score.
        Br J Dermatol. 2007; 157: 645-648
        • Sandilands A.
        • O'Regan G.M.
        • Liao H.
        • Zhao Y.
        • Terron-Kwiatkowski A.
        • Watson R.M.
        • et al.
        Prevalent and rare mutations in the gene encoding filaggrin cause ichthyosis vulgaris and predispose individuals to atopic dermatitis.
        J Invest Dermatol. 2006; 126: 1770-1775
        • Morar N.
        • Willis-Owen S.A.
        • Moffatt M.F.
        • Cookson W.O.
        The genetics of atopic dermatitis.
        J Allergy Clin Immunol. 2006; 118: 24-36
        • Angus V.C.
        • Entwistle V.A.
        • Emslie M.J.
        • Walker K.A.
        • Andrew J.E.
        The requirement for prior consent to participate on survey response rates: a population-based survey in Grampian.
        BMC Health Serv Res. 2003; 3: 21
        • Shamssain M.
        Trends in the prevalence and severity of asthma, rhinitis and atopic eczema in 6- to 7- and 13- to 14-yr-old children from the north-east of England.
        Pediatr Allergy Immunol. 2007; 18: 149-153
        • Brown S.J.
        • Sandilands A.
        • Zhao Y.
        • Liao H.
        • Relton C.L.
        • Meggitt S.J.
        • et al.
        Prevalent and low-frequency null mutations in the filaggrin gene are associated with early-onset and persistent atopic eczema.
        J Invest Dermatol. 2007; ([Epub ahead of print])
        • Wells R.S.
        • Kerr C.B.
        Clinical features of autosomal dominant and sex-linked ichthyosis in an English population.
        BMJ. 1966; 1: 947-950
        • Nomura T.
        • Sandilands A.
        • Akiyama M.
        • Liao H.
        • Evans A.T.
        • Sakai K.
        • et al.
        Unique mutations in the filaggrin gene in Japanese patients with ichthyosis vulgaris and atopic dermatitis.
        J Allergy Clin Immunol. 2007; 119: 434-440
        • Seguchi T.
        • Cui C.Y.
        • Kusuda S.
        • Takahashi M.
        • Aisu K.
        • Tezuka T.
        Decreased expression of filaggrin in atopic skin.
        Arch Dermatol Res. 1996; 288: 442-446