Filaggrin Gene Gene Research Articles

DNA methylation profile and expression of the phyllagrin gene in patients with atopic dermatitis: case-control study

Background. Atopic dermatitis (AD) is one of the most common inflammatory skin diseases, affecting up to 20.0% of children and 2.0–8.0% of adults worldwide. Patients with atopic dermatitis usually have dry skin and itching, they are at higher risk of developing asthma, as well as allergic rhinitis. Features of the clinical course of AD are associated with both interaction of genes and influence of environmental factors. Studying epigenetic mechanisms could provide understanding of the most likely mechanisms by which environmental factors influence gene expression and contribute to the development of AD. The aim of the study is to conduct a comprehensive molecular genetic analysis (assessment of the level of global DNA methylation and expression of the filaggrin gene (FLG) in patients with moderate to severe AD. Material and methods: The case-control study was conducted from January 2022, through June 2022. A total of 32 patients with AD and 6 healthy volunteers were recruited. The level of global DNA methylation in the blood of patients with AD and healthy individuals was assessed. The FLG expression was measured by polymerase chain reaction in the leukocyte fraction of blood. A three-stage cycle is used during PCR. To determine the expression level of the FLG gene, total RNA was isolated, followed by a reverse transcription, amplification, and detection reaction. Results. A hypermethylation of the genome in patients with AD is 2.3 times higher than the methylation of genome in controls (p = 0.003),it was also found that the expression level of the FLG gene (exon 3, position 7–8, and exon 1) in the leukocyte fraction of blood in patients with AD did not significantly differ from the control group (p = 0.41). Conclusion. The current study found that the epigenome of AD patients differs from healthy individuals. The study of pathogenetic mechanisms is the basis for the development of new methods of targeted therapy for this socially significant dermatosis.

Асоціація варіацій генів POMP, FLG, MTOR ТА ATG5 із ризиком розвитку бронхіальної астми в дітей

Метою даного дослідження було визначити зв’язок однонуклеотидних поліморфізмів у гені білка дозрівання протеасоми (POMP), філагрину (FLG), білка-мішені рапаміцину (MTOR) та автофагії (ATG5) із розвитком бронхіальної астми в дітей. Методи: клінічні, генетичні — визначення генотипу хворих і здорових дітей за допомогою полімеразної ланцюгової реакції в реальному часі; статистичні. Результати. Установлено, що розподіл генотипів у досліджених групах вірогідно відрізняється при аналізі поліморфізму POMP: GG-варіант виявлений у 9 здорових дітей та відсутній у групі хворих, 32 пацієнти і 37 здорових дітей мали AG-варіант, 62 і 52 відповідно — мали алельний варіант AA, до того ж мінорний варіант взагалі не зустрічався у хворих на бронхіальну астму (р < 0,05 за χ2-критерієм). Варіанти з мінорним генотипом гена FLG виявилися у 2,5 раза частіше у хворих, ніж у контрольній групі: у 5 пацієнтів і у 2 здорових дітей був наявний алельний варіант AA, 27 і 36 — відповідно мали гетерозиготний варіант GА, 67 і 61 — відповідно мали варіант GG. Варіанти з мінорним генотипом у гені MTOR виявилися у 2,4 раза частіше в контрольній групі, ніж серед хворих: у 50 пацієнтів і 43 здорових дітей наявний мажорний алельний варіант ТТ, 36 пацієнтів і 32 здорові дитини мали варіант ТС, 5 і 12 — відповідно мали варіант СС. Отримано статистично вірогідну різницю в розподілі генотипів поліморфізму гена ATG5: у 51 хворої дитини та 43 здорових дітей був гетерозиготний варіант СТ, у 29 та 21 відповідно — мінорний варіант ТТ, у 18 та 33 відповідно — мажорний варіант СС (р < 0,05 за χ2-критерієм). Мінорний генотип поліморфізму гена ATG5 асоціюється з підвищеним ризиком ранньої маніфестації бронхіальної астми (до 3 років життя) (р < 0,05 за χ2-критерієм). За результатами MDR-аналізу виявлено, що поліморфізм гена ATG5 виявився найбільш сильним предиктором розвитку бронхіальної астми, оскільки зменшує рівень ентропії на 7,88 %. При цьому поліморфізм гена POMP зменшує рівень ентропії на 5,21 %, поліморфізм гена MTOR — на 1,18 %, поліморфізм гена FLG — на 1,04 %. Висновки. Досліджені поліморфізми можуть бути використані як прогностичні маркери розвитку бронхіальної астми в дітей.

The role of filaggrin mutations leading to a decrease in the amount of protein in the development of atopic dermatitis and bronchial asthma in children

Atopic diseases remain one of the most common childhood diseases. At the beginning of life, atopic dermatitis (AD) occurs, and only then bronchial asthma (BA). This staged development of sensitization and transformation of clinical manifestations is called the atopic march. Are the genetic factors of predisposition to AD the same for BA? There is still no definite answer to this question. Mutations in the filaggrin gene (FLG) are known to impair skin barrier function. Filaggrin is expressed not only in the skin, but also in the respiratory organs of the nasal mucosa, lungs, and bronchi. Filaggrin defects lead not only to disruption of the skin barrier, but also to an increase in the Th2 response and increased production of IgE, typical of bronchial asthma. Therefore, mutations in the FLG gene can be a risk factor for the development of not only AD, but also BA.The aimof this study was to compare the values of the association of mutations in the FLG gene with AD and BA in the Russian sample.Material and methods.Case-control study design. We used 265 blood samples from children. 4 mutations in the filaggrin gene were identified by real-time PCR. The association of mutations with disease was assessed by odds ratio.Results.We showed a strongly pronounced association of the deletion of 4 nucleotides (2282del4) with AD, but not with BA, although for patients with atopic BA the indicator of the association of this mutation with the disease was higher than for the group with symptoms of bronchial asthma identified by the ISAAC questionnaire. These results lead to the conclusion that the role of the filaggrin gene for BA is much less significant than for AD.

Filaggrin Loss-of-Function Mutations Are Risk Factors for Severe Food Allergy in Children with Atopic Dermatitis.

Atopic dermatitis is frequently associated with the onset of other allergic conditions, such as asthma, rhino-conjunctivitis and food allergy. The etiology of atopic dermatitis is marginally understood in spite of the number of predisposing factors, above all, mutations in the Filaggrin gene (FLG). In this study, the association between loss-of-function variants in the FLG gene and other allergic manifestations, in particular food allergy, was evaluated in an Italian pediatric population affected by atopic dermatitis. The 10 more frequently mutated loci in the FLG gene were genotyped in 238 children affected by atopic dermatitis and tested for association with clinical features of allergic disorders by a multivariate logistic regression model. R501X and 2282del4 were the only two mutations identified; 12.2% of children carry one of these variants, corresponding to an allelic frequency of 6.5%. According to multivariate statistical analysis, loss-of-function variants in the FLG gene represent a risk factor for the onset of severe manifestations of food allergy (OR = 8.9; CI: 3.1–28.3). Peanut and hazelnut were identified as high-risk foods in patients with FLG mutations. This study demonstrates that atopic children carrying FLG mutations represent a high-risk population due to their predisposition to develop severe food allergy reactions, such as anaphylaxis.

Rare occurrence of common filaggrin mutations in Turkish children with food allergy and atopic dermatitis

Background/aimFilaggrin is a protein complex involved in epidermal differentiation and skin barrier formation. Mutations of the filaggrin gene (FLG) are associated with allergen sensitization and allergic diseases like atopic dermatitis (AD), allergic rhinitis, food allergy (FA), and asthma. The aim of the study is to reveal the frequency of change in the FLG gene and determine the association between FLG loss-of-function (LOF) mutations and FA and/or AD in Turkish children.Materials and methodsFour FLG loss-of-function (LOF) mutations known to be common in European populations were analyzed in 128 healthy children, 405 food-allergic children with or without atopic dermatitis, and 61 children with atopic dermatitis. PCR-RFLP was performed for genotyping R501X, 2282del4, and R2447X mutations; S3247X was genotyped using a TaqMan-based allelic discrimination assay. Results were confirmed by DNA sequence analysis in 50 randomly chosen patients for all mutations. ResultsA total of 466 patients [(67% male, 1 (0.7–2.8) years] and 128 healthy controls [59% male, 2.4 (1.4–3.5) years)] were included in this study. Two patients were heterozygous carriers of wild-type R501X, but none of the controls carried this mutation. Three patients and one healthy control were heterozygous carriers of wild-type 2282del4. Neither patients nor controls carried R2447X or S3247X FLG mutations. There were no combined mutations determined in heterozygous mutation carriers. ConclusionsAlthough R501X, 2282del4, R2447X, and S3247X mutations are very common in European populations, we found that FLG mutations were infrequent and there is no significant association with food allergy and/or atopic dermatitis in Turkish individuals.

Thymic stromal lymphopoietin downregulates filaggrin expression by signal transducer and activator of transcription 3 (STAT3) and extracellular signal-regulated kinase (ERK) phosphorylation in keratinocytes

Thymic stromal lymphopoietin downregulates filaggrin expression by signal transducer and activator of transcription 3 (STAT3) and extracellular signal-regulated kinase (ERK) phosphorylation in keratinocytes

Analyses ofFLGmutation frequency and filaggrin expression in isolated ichthyosis vulgaris (IV) and atopic dermatitis-associated IV

Ichthyosis vulgaris (IV; OMIM 146700) is a very common inherited skin disorder. Loss-of-function mutations in the filaggrin gene (FLG) have been identified as the cause of IV. In a previous study, we found that the percentage of FLG null mutations was lower in IV associated with atopic dermatitis (AD) than in IV not associated with AD (isolated IV). We speculated that some clinical manifestations of IV in patients with AD are not induced by FLG mutations. In order to clarify this issue, we collected 21 IV pedigrees, 33 patients with sporadic isolated IV and 116 patients with AD-associated IV to analyse FLG mutation frequency and filaggrin expression in isolated IV and AD-associated IV. A comprehensive sequencing of the FLG gene in all patients was performed using an overlapping polymerase chain reaction (PCR) strategy. We also studied the immunohistochemistry of profilaggrin/filaggrin protein expression in the skin and measured the mRNA expression using real-time PCR in seven patients, including one patient with IV harbouring the mutation c.3321delA, two patients with AD-associated IV harbouring c.3321delA and c.6834del5, and four patients with AD-associated IV without FLG mutations. The percentage of mutations in the FLG gene was 74% and 43% in patients with isolated IV and patients with AD-associated IV, respectively. Immunohistochemical staining revealed that profilaggrin/filaggrin peptides were remarkably reduced in the epidermis of all the patients. All the patients with either AD or IV showed lower FLG mRNA expression compared with the normal control. These results indicate that factors other than FLG gene mutations can downregulate profilaggrin/filaggrin expression, leading to the ichthyosiform phenotype in the context of AD.

DNA methylation of the filaggrin gene adds to the risk of eczema associated with loss‐of‐function variants

Loss-of-function variants within the filaggrin gene (FLG) are associated with a dysfunctional skin barrier that contributes to the development of eczema. Epigenetic modifications, such as DNA methylation, are genetic regulatory mechanisms that modulate gene expression without changing the DNA sequence. To investigate whether genetic variants and adjacent differential DNA methylation within the FLG gene synergistically act on the development of eczema. A subsample (n = 245, only females aged 18 years) of the Isle of Wight birth cohort participants (n = 1456) had available information for FLG variants R501X, 2282del4 and S3247X and DNA methylation levels for 10 CpG sites within the FLG gene. Log-binomial regression was used to estimate the risk ratios (RRs) of eczema associated with FLG variants at different methylation levels. The period prevalence of eczema was 15.2% at age 18 years and 9.0% of participants were carriers (heterozygous) of FLG variants. Of the 10 CpG sites spanning the genomic region of FLG, methylation levels of CpG site 'cg07548383' showed a significant interaction with FLG sequence variants on the risk for eczema. At 86% methylation level, filaggrin haploinsufficient individuals had a 5.48-fold increased risk of eczema when compared to those with wild type FLG genotype (P-value = 0.0008). Our novel results indicated that the association between FLG loss-of-function variants and eczema is modulated by DNA methylation. Simultaneously assessing the joint effect of genetic and epigenetic factors within the FLG gene further highlights the importance of this genomic region for eczema manifestation.

Association of filaggrin gene polymorphism with atopic dermatitis in southern Chinese Han population

To investigate the association of filaggrin gene (FLG) polymorphism with atopic dermatitis (AD) in southern Chinese Han population. The frequencies of the 13 known FLG gene single nucleotide polymorphism(SNPs), including 3321delA, 441delA, 1249insG, E1795X, S3296X, R501X, 2282del4, R2447X, S2889X, 7945delA, 3702delG, Q2417X, R4307X, were detected in a cohort of 50 AD patients and 100 control individuals using polymerase chain reaction (PCR) and DNA sequencing. FLG 3321delA and 441delA were detected in 14 (28%) and 6 (12%) AD patients, respectively. The other 11 SNPs were not detected in the patients. None of the 13 SNPs was detected in the controls. The results suggested that the FLG gene might be associated with atopic dermatitis susceptibility in southern Chinese Han population.

Exacerbation of X-linked ichthyosis phenotype in a female by inheritance of filaggrin and steroid sulfatase mutations

X-linked ichthyosis (XLI) is a relatively common, recessive condition caused by mutations in the steroid sulfatase (STS) gene. Common loss-of-function mutations in the filaggrin gene (FLG) cause ichthyosis vulgaris and predispose individuals to atopic eczema. To test the hypothesis that co-inheritance of FLG mutations can act as a genetic modifier in XLI. An unusually severe XLI phenotype in addition to eczema and mild childhood asthma was investigated in a female Indian patient by fluorescent in situ hybridization (FISH) for the common STS gene deletion. Direct sequencing of the entire FLG gene was also performed. FISH analysis revealed that the proband was homozygous for the common STS genomic deletion mutation. Further investigation revealed a frame-shift mutation 3672del4 in the gene encoding filaggrin (FLG), leading to premature termination of profilaggrin translation. Interestingly, her father, who had a very typical mild presentation of XLI, did not carry this FLG mutation in addition to his STS deletion. Her mother was a heterozygous carrier of the FLG mutation and consistent with this, had mild symptoms of ichthyosis vulgaris; she was also a heterozygous carrier of the STS deletion. This is the second reported case of the modifying effects of FLG null alleles on XLI and strengthens the hypothesis that filaggrin defects can synergize with STS deficiency to exacerbate the ichthyosis phenotype.

Carrier Status for the Common R501X and 2282del4 Filaggrin Mutations Is Not Associated with Hearing Phenotypes in 5377 Children from the ALSPAC Cohort

BackgroundFilaggrin is a major protein in the epidermis. Several mutations in the filaggrin gene (FLG) have been associated with a number of conditions. Filaggrin is expressed in the tympanic membrane and could alter its mechanical properties, but the relationship between genetic variation in FLG and hearing has not yet been tested.Methodology/Principal FindingsWe examined whether loss-of function mutations R501X and 2282del4 in the FLG gene affected hearing in children. Twenty eight hearing variables representing five different aspects of hearing at age nine years in 5,377 children from the Avon Longitudinal Study of Parents and Children (ALSPAC) cohort were tested for association with these mutations. No evidence of association was found between R501X or 2282del4 (or overall FLG mutation carrier status) and any of the hearing phenotypes analysed.Conclusions/SignificanceIn conclusion, carrier status for common filaggrin mutations does not affect hearing in children.

Filaggrin mutations may confer susceptibility to chronic hand eczema characterized by combined allergic and irritant contact dermatitis

The pathogenesis of chronic hand eczema (CHE) is multifactorial and involves both endogenous predisposition and environmental triggers. Filaggrin is a structural protein of the cornified envelope and important for the formation of the epidermal skin barrier. The aim of this investigation was to evaluate the role of mutations in the filaggrin gene (FLG) in the development of CHE. In total, 122 German patients with clearly defined CHE subtypes were screened for the FLG variants R501X and 2282del4 by polymerase chain reaction and restriction enzyme digest analysis. The prevalence of these variants in CHE patients was compared with that in 95 healthy individuals. Overall, allele frequency and the number of mutation carriers were similar in both the CHE and control groups. When classified according to clearly defined CHE subtypes, however, the nonfunctional FLG variants showed an association with CHE involving an aetiological combination of contact allergy and irritant factors [P = 0.04; P (exact test) = 0.06; P (difference in rates) = 0.09; 95% confidence interval (CI) 0-56.8)], or with excessive daily exposure to water and irritants [P = 0.003; P (difference in rates) < 0.001; 95% CI 29.3-67.9]. Heterozygosity for nonfunctional mutations in the FLG gene may contribute to the manifestation and maintenance of a particular CHE subtype that is characterized by the combination of allergic and irritant contact dermatitis.

Identification of a Genetic Locus for Ichthyosis Vulgaris on Chromosome 10q22.3–q24.2

Ichthyosis vulgaris (IV) is one of the most commonly inherited disorders and has an estimated prevalence rate of 2.29% in China. To date, only one gene responsible for IV, the filaggrin gene (FLG), was identified, but genetic heterogeneity exists. In this study, two Chinese families with autosomal-dominant IV were genetically characterized. The FLG gene was first excluded as the disease-causing gene in the two families. The larger family was then characterized by genome-wide linkage analysis to identify a new genetic locus for IV. Significant linkage was identified with markers on chromosome 10q22.3-q24.2 with a maximum LOD score of 3.19. No other markers showed a LOD score of >1.5. Fine mapping defined the new genetic locus within a 20.7 cM region between markers D10S569 and D10S1709. The second family also showed positive linkage to the same 10q22.3-q24.2 region. The combined maximum LOD score in the two families was 3.95. Identification of linkage in two independent families provides strong genetic evidence that a previously unreported gene for IV is located on chromosome 10q22.3-q24.2. Future studies of the candidate genes at the 10q IV locus will identify a specific gene, which will provide insights into the pathogenesis of IV.

Loss-of-function variations within the filaggrin gene predispose for atopic dermatitis with allergic sensitizations

Atopic dermatitis (AD) is a chronic inflammatory skin disease with a strong genetic background. One of the characteristic features of AD and causative factor for the disease is an impaired epidermal skin barrier based on a primary defect of epidermal differentiation. Recently, 2 loss-of-function mutations (R501X and 2282derl4) in the filaggrin gene (FLG) that cause ichthyosis vulgaris, one of the most common inherited skin disorders of keratinization, have been reported to be strong predisposing factors for AD. We evaluated the association of the loss-of-function mutations R501X and 2282del4 within the FLG gene in a large collection of 476 well-characterized white German families with AD by using the transmission-disequilibrium test. Our family-based approach revealed prominent associations between the 2 loss-of-function FLG mutations and AD, as previously observed in a traditional Mendelian linkage analysis and case-control cohort analysis approach. In addition, we observed associations of the FLG mutations in particular with the extrinsic subtype of AD, which is characterized by high total serum IgE levels and concomitant allergic sensitizations. Furthermore, FLG mutations are significantly associated with palmar hyperlinearity in patients with AD, which represents a shared feature of AD and ichthyosis vulgaris. Together these data implicate that FLG is the first really strong genetic factor identified in a common complex disease. These findings underline the crucial role of the skin barrier in preventing allergic sensitization.

Breaking the (Un)Sound Barrier: Filaggrin Is a Major Gene for Atopic Dermatitis

We have recently shown that loss-of-function mutations in the filaggrin gene, carried by about 10% of people of European ethnicity, cause ichthyosis vulgaris and are strong predisposing factors for atopic dermatitis and asthma secondary to atopic dermatitis. These results demonstrate a prominent role for the epidermal barrier in atopic disease and have important implications for the study of complex traits.