Analysis of four prevalent filaggrin mutations (R501X, 2282del4, R2447X and S3247X) in Austrian and German patients with atopic dermatitis

Background Recently, mutations in the filaggrin gene (FLG) have been shown to be a major predisposing factor for atopic dermatitis (AD). Objective In this study, we evaluated the influence of four prevalent mutations (R501X, 2282del4, R2447X and S3247X) in a large cohort of 462 Austrian and German AD patients and in 402 control individuals. Results We found a strong association of the FLG mutations with AD. Subgroup analysis revealed a significantly higher proportion of patients with an early age of disease onset and significantly higher median serum IgE levels among mutation carriers. Furthermore, we observed an overrepresentation of null alleles in AD patients with concomitant asthma compared with those without this co‐morbidity. Conclusion Our data confirm and extend the knowledge of the influence of FLG mutations in AD.     

Genotype–phenotype associations in filaggrin loss‐of‐function mutation carriers

Background. Loss‐of‐function mutations in the filaggrin gene (FLG) have been reported to be associated with specific phenotypic characteristics such as hyperlinearity and keratosis pilaris. Objectives. To study phenotypic features in patients with occupational irritant contact eczema of the hands in relation to FLG loss‐of‐function mutations. Materials and methods. In a prospective cohort study, genotype was determined for 459 study subjects for four FLG null alleles, and investigated for selected history, clinical and laboratory features. Results. Overall, 68 patients showed a mutation in the FLG alleles R501X, R2447X, S3247X, and/or 2282del4. Flexural eczema, xerosis cutis, pityriasis alba, dirty neck, pulpitis sicca, hyperlinear palms, keratosis pilaris and family history of eczema were positively associated with FLG mutations (p < 0.05). Although we observed a statistically significant correlation with higher serum IgE in FLG mutation carriers, allergic rhinoconjunctivitis and allergic asthma were not over‐represented in this group. Conclusion. This study shows further genotype–phenotype correlations in patients with occupational irritant contact eczema and FLG mutation carrier status. These features may help to identify those with FLG mutations on a specific phenotype basis.     

Usefulness of a global clinical ichthyosis vulgaris scoring system for predicting common FLG null mutations in an adult caucasian population

Background Loss of function FLG alleles were first identified as causative of ichthyosis vulgaris (IV) and were subsequently found to be major predisposing factors for atopic dermatitis (AD) and atopic disorders. Objectives To identify independent factors associated with the clinical IV phenotype in adult caucasian patients with AD and to assess the performance of a global clinical severity score of IV in predicting common FLG null mutations. Patients and methods This was a prospective study conducted from January 2007 to June 2008. Adult patients attending the department of dermatology with a diagnosis of AD with or without IV were eligible to participate. For each patient, five clinical signs of IV were scored from 0 to 3 – diffuse xerosis, hyperlinearity of palms, scales on legs, scalp desquamation and keratosis pilaris – and a global IV clinical severity score was derived (0–15). Age of onset of AD, SCORAD (SCORing of Atopic Dermatitis), family and personal history for other signs of atopy, and total immunoglobulin E were recorded. Genotyping was performed for R501X and 2282del4. Univariate and multivariate analysis for factors associated with AD or AD + IV were conducted. Results In univariate analysis, family history of atopy, global clinical severity scoring and 2282del4 FLG mutation were positively correlated with the AD + IV phenotype. Using multivariate analysis, SCORAD for AD (OR 0·94, P = 0·01) and global clinical severity scoring for AD + IV (OR 2·62, P < 0·0001) were found to be independent factors. Conclusions The 2282del4 FLG mutation was confirmed as a good marker of early‐onset disease. Moreover, our global clinical severity score yielded a good negative predictive value of common caucasian null FLG mutations.     

Distinct barrier integrity phenotypes in filaggrin-related atopic eczema following sequential tape stripping and lipid profiling

Background Filaggrin gene (FLG) loss‐of‐function mutations have been shown to represent the strongest so far known genetic risk factor for atopic dermatitis (AD). Whereas the barrier characteristics in FLG mutation carriers under baseline conditions have been investigated, there are only limited data on the permeability barrier function in filaggrin‐AD under compromised conditions. Aim We investigated: (i) stratum corneum (SC) integrity/cohesion; (ii) barrier recovery after controlled mechanical and irritant‐induced barrier abrogation; and (iii) the lipid composition of the non‐lesional and lesional skin of AD patients harbouring the European R501X, 2282del4, 3702delG, R2447X or S3247X FLG variants. Methods Thirty‐seven AD patients (14 FLG mutation carriers and 23 non‐carriers) and 20 healthy controls participated in the study. Stratum corneum integrity/cohesion was assessed by measurement of transepidermal water loss (TEWL) and amount of removed protein following sequential tape stripping. Barrier recovery was monitored by repeated measurements of TEWL and erythema up to 96 h after barrier abrogation. Samples for lipid analysis were obtained from non‐lesional and lesional skin using the cyanoacrylate method. Results Tape stripping revealed distinct genotype‐related impairment of the SC integrity/cohesion. No differences in the rate of barrier recovery among the groups were found. The SC lipid analysis revealed significant differences regarding the percentage amount of cholesterol, ceramide/cholesterol ratio and triglycerides in the uninvolved skin as well as the amounts of free fatty acids, CER[EOH] and triglycerides in the skin lesions of the AD FLG mutation carriers. Conclusions Our results provide evidence for discernible FLG‐related barrier integrity phenotypes in atopic eczema.     

Impact of atopic dermatitis and loss‐of‐function mutations in the filaggrin gene on the development of occupational irritant contact dermatitis

Background Atopic dermatitis (AD) and loss‐of‐function mutations in the filaggrin gene (FLG) are both associated with chronic irritant contact dermatitis (ICD). As FLG mutations also are a major risk factor for AD, it is not clear whether FLG mutations are an independent risk factor for ICD or whether the risk is mediated by AD. Objectives To investigate the relative contribution and interaction of FLG mutations and AD in German patients with occupational ICD and controls (vocational school apprentices). Methods A total of 634 patients and 393 controls were genotyped for R501X, 2282del4, R2447X and S3247X. Current or past flexural eczema was used as an indicator of AD. Results FLG mutations were found in 15·9% of the patients with ICD and 8·3% of the controls, with a crude odds ratio (OR) of 2·09 [95% confidence interval (CI) 1·33–3·28] for the combined genotype. The adjusted OR for FLG mutations, corrected for AD, was 1·62 (95% CI 1·01–2·58). Subjects with AD were at approximately three times higher risk of developing ICD than controls (OR 2·89; 95% CI 2·09–3·99). There was no evidence of an interaction between these two risk factors. Conclusions Our results indicate that both FLG mutations and AD increase the risk of ICD. Individuals with concurrent FLG mutations and AD are at the highest risk of developing ICD.     

Mutations analysis in filaggrin gene in northern China patients with atopic dermatitis

Background Recently, we have reported filaggrin mutations (FLG) of atopic dermatitis in southern China. However, there have been few detailed reports of FLG mutations of patients with AD in northern China by now. Objectives The present aim was to establish the mutation spectrum of FLG gene in AD patients in northern China. Methods A total of 339 cases met Hanifin and Rajka diagnostic criteria of AD were recruited. A comprehensive sequencing of the entire FLG coding region in these patients was conducted. All detected FLG null mutations were screened in a cohort of 301 normal controls. Results Seven novel mutations (478insA, Q1070X, 4026delT, Q1712X, Q2397X, 7145del4 and 8001del4) and eleven reported mutations (3222del4, 3321delA, 4271delAA, S1515X, Q1790X, 5757del4, 6834del5, Q2417X, E2422X, 7945delA and K4671X) in AD were identified. Mutations 3321delA and K4671X were two of the most common mutations in AD. FLG null mutations were present in 26.0% of AD patients. FLG null alleles (compound genotypes) were significantly higher in AD (P < 0.001) than in the controls. The compound genotypes for all FLG variants were significantly associated with IV (P < 0.001) and palmar hyperlinearity (P < 0.001). The common mutation, K4671X, was significantly associated with AD‐coexistent allergic rhinitis (P = 0.005). Conclusions Our study increases the total number of FLG mutations. We clearly demonstrated that FLG loss‐of‐function mutations were significantly associated with AD in northern China. The FLG null mutations in the Chinese population differed not only from that in the European population but also from that in sub‐populations of Asians outside of the Chinese mainland.     

Filaggrin mutations are strongly associated with contact sensitization in individuals with dermatitis

Background. Although heterozygous filaggrin gene (FLG) mutation carriers seem to have an increased risk of atopic, irritant and allergic nickel dermatitis, it remains unclear whether the risk of contact sensitization to allergens other than nickel is also elevated in FLG mutation carriers. Objectives. We hypothesized that heterozygous FLG mutation carriers who suffer from dermatitis will have strongly reduced or even absent filaggrin levels during episodes of inflammation, potentially increasing the penetration of contact allergens, and hence the risk of becoming sensitized. Materials and methods. During 2006–2008, 3335 randomly invited 18–69‐year‐old adult Danes participated in a general health examination, filled out a questionnaire, and were genotyped for the R501X and 2282del4 mutations in FLG. Results. A logistic regression analysis restricted to individuals who reported atopic dermatitis and frequent episodes of hand eczema showed a strong association between FLG mutations and contact sensitization to allergens other than nickel (odds ratio 5.71; 95% confidence interval 1.31–24.94). In participants without dermatitis, no association was found between contact sensitization and FLG mutations. Conclusion. FLG mutation carriers with self‐reported dermatitis have an increased risk of contact sensitization to substances other than nickel, whereas FLG mutations alone may not, or may only slightly, increase the risk of sensitization.     

Filaggrin Gene Mutations in African Americans with Both Ichthyosis Vulgaris and Atopic Dermatitis

Atopic dermatitis (AD) and ichthyosis vulgaris (IV) are two common disorders of epidermal homeostasis resulting in dry skin. The profilaggrin gene, located on chromosome 1q22, encodes a keratin filament aggregating protein (filaggrin) that is essential to forming the epidermal barrier and maintaining hydration. Null mutations in filaggrin have been found to underlie IV and are common in patients with AD, but the minority of African Americans with AD or IV show these mutations in filaggrin. We have selectively studied African Americans with both AD and IV to maximize the possibility of finding filaggrin null mutations in this population. DNA was collected using buccal swabs from 18 African American children with both AD and IV and 17 African American controls without either of these diseases. Purified genomic DNA was amplified using polymerase chain reaction from three regions of the filaggrin gene, exon 3, including R501X, 2282del4, E2554X, R2447X, 1249insG, R826X, 2767insT, and E2422X. Of the African American children with both AD and IV, 22.2% were heterozygous for filaggrin null mutations. Out of the control group, one carried a null mutation and was later discovered to have a history of asthma. Null mutations found in this population included R501X (n = 1), 2282del4 (n = 2), and R826X (n = 2, including the control patient). Our data demonstrate a prevalence of filaggrin mutations in the African American population that exceeds previously published data, although the overall prevalence is still lower than in other populations. It is likely that factors other than known FLG mutations are involved in African American patients.     

Association between P478S polymorphism of the filaggrin gene and risk of psoriasis in a Chinese population in Taiwan

Abnormal keratinocyte terminal differentiation is one of the important characteristics of psoriatic lesions. Filaggrin (FLG) is a key protein that facilitates the terminal differentiation of the epidermis. Thus, FLG genetic variants may modify the risk of psoriasis. In total, 314 patients with psoriasis and 611 control subjects were analyzed for the presence of FLG R501X, 2282del4 mutations, and P478S (rs11584340, C/T base change) polymorphism by polymerase chain reaction (PCR). The analysis revealed that both the R501X and 2282del4 mutations were not present in a subset of 200 patients (64%) with psoriasis. In contrast, a marginally significant difference (P = 0.020) was found in the distribution of rs11584340 genotype frequencies between psoriatic patients and controls. The frequency of the TT genotype in psoriasis patients was significantly higher than in controls (37.9% vs. 29.1%, respectively, P = 0.007). The T allele frequency of patients (60.5%) was also significantly higher than that of controls (53.9%) (P = 0.007). After adjusting for age and gender, carriers of the TT genotype were 1.46 (95% CI, 1.08–1.96) times more likely than non-carriers to have psoriasis (P = 0.013). In conclusion, our results suggest that FLG P478S polymorphism may confer susceptibility to the development of psoriasis among Taiwanese Chinese.     

Novel filaggrin mutation but no other loss-of-function variants found in Ethiopian patients with atopic dermatitis

Background Filaggrin is a key protein involved in maintaining skin barrier function and hydration. Mutations in the filaggrin gene (FLG) cause ichthyosis vulgaris (IV) and are a major predisposing factor for atopic dermatitis (AD) in individuals of European and Asian descent. It has been proposed that FLG mutations are population specific and a difference in the spectra of mutations between different ancestral groups has been described. However, it is unknown whether FLG mutations in the African population are a causative genetic factor for IV and predispose to AD, or whether other mechanisms are more prominent. Objectives The present aim was to investigate the role of FLG mutations as predisposing factors for IV or AD among individuals from Ethiopia. Methods A case series of Ethiopian patients with AD (n = 103) and IV (n = 7) together with controls (n = 103; subjects without past or present history of AD, dry skin or atopic manifestations) was collected at the outpatient dermatology clinics at ALERT Dermatology Hospital, Tikur Anbessa Hospital and Gondar University Hospital, Ethiopia. AD was diagnosed by a dermatologist using the U.K. Working Party’s diagnostic criteria. The IV diagnosis was based on clinical examination and genetic testing of the steroid sulphatase gene to exclude X‐linked recessive ichthyosis. Patients were studied with direct sequencing (n = 40) and/or allelic discrimination (n = 110). Immunohistochemical analysis was performed for filaggrin expression in the skin of patients (n = 7) and controls (n = 2). Results The Ethiopian patients and controls were genotyped for the four previously described common European FLG null mutations (R501X, 2282del4, S3247X, R2447X) and no carriers were found. In one patient with AD a novel heterozygous 2‐bp deletion, 632del2, leading to a premature stop codon was revealed by direct sequencing. No additional carrier of this deletion or other mutations was found. In addition, no difference in filaggrin expression was detected in AD or IV skin compared with healthy control skin. Conclusions Our results indicate that FLG loss‐of‐function‐variants are less common in patients with IV and AD in the Ethiopian population, suggesting that other factors may be of importance in the pathogenesis in this ethnic group.     

Filaggrin compound heterozygous patients carry mutations in trans position

More than 40 null mutations in the filaggrin (FLG) gene are described. It is therefore possible to find two different null mutations in one individual (compound heterozygosity). It has been generally perceived that homozygous and compound heterozygous individuals were genotypically comparable; however, this has not been scientifically investigated. Two different FLG null mutations in the same individual may be in trans position, meaning that each mutation locates to a different allele functionally equivalent to homozygosity, or may be in cis position, meaning that both mutations locate to the same allele functionally equivalent to heterozygosity. To experimentally investigate allelic in cis versus in trans configuration of the two most common filaggrin (FLG) mutations (R501X and 2282del4) in compound heterozygous individuals. Testing for in cis or in trans allele configuration was performed by means of allele‐specific PCR amplification and analysis of PCR products by agarose gel electrophoresis. All R501X/2282del4 compound heterozygous samples collected over a 4‐year period of routine FLG mutation testing were investigated. In total, 37 samples were tested. All thirty‐seven R501X/2282del4 compound heterozygous individuals were found to carry the two mutations in trans position. FLG null mutation compound heterozygous individuals can be considered functionally equivalent to FLG null mutation homozygosity for any of the two mutations.     

Novel FLG null mutations in Korean patients with atopic dermatitis and comparison of the mutational spectra in Asian populations

Filaggrin is essential for the development of the skin barrier. Mutations in the gene encoding filaggrin have been identified as major predisposing factors for atopic disorders. Molecular analysis of the FLG gene in this study showed nine null and one unclassified mutation in 13 of 81 Korean patients with atopic dermatitis (AD): five novel null mutations (i.e. p.S1405*, c.5671_5672delinsTA, p.W1947*, p.G2025* and p.E3070*); four reported null mutations (i.e. c.3321delA, p.S1515*, p.S3296* and p.K4022*); and one unclassified mutation (i.e. c.306delAAAGCACAG). These variants are nonsense, premature termination codon or in‐frame deletion expected to cause loss‐of‐function of FLG. Genotype–phenotype correlation is not obvious in Korean AD patients with FLG null mutations. According to a review of the mutational spectra of the FLG gene in the Asian populations, FLG null mutations appeared to be unique in each population but some mutations such as p.R501*, c.3321delA, p.S1515*, p.S3296* and p.K4022* were commonly found in at least two of the selected Asian populations including Korean, Japanese, Chinese, Singaporean Chinese or Taiwanese. Further investigations on a larger group of Korean AD would be necessary to elucidate its clinical pathogenesis and mutational spectrum related to specific FLG null mutations for AD.     

Clinical course of occupational irritant contact dermatitis of the hands in relation to filaggrin genotype status and atopy

Background Filaggrin loss‐of‐function mutations and atopy may alter the clinical course of irritant contact dermatitis (ICD). Objective To investigate the clinical course of patients with occupational ICD according to loss‐of‐function mutations in the filaggrin gene (FLG) and atopy. Methods In a prospective cohort study, the clinical course, use of topical corticosteroids, sick leave, recovery rate and job continuation were investigated in 459 inpatients treated for occupational ICD of the hands. Patients were genotyped for four FLG mutations, examined for atopy and followed for up to 3 years after discharge. Results Our study included 327 (71·2%) atopic individuals and 132 nonatopic individuals. Overall, 68 patients showed a mutation in the FLG alleles R501X, R2447X, S3247X and 2282del4 (60 atopic and eight nonatopic). Nonatopic patients with ICD responded well to therapeutic approaches, while atopy status made subjects more resistant to therapy, resulting in lower rates of recovery and job continuation and higher use of topical corticosteroids. Carriage of FLG loss‐of‐function mutations in combination with atopy worsened the course. The risk of abandoning one’s profession in this group was significantly increased when compared with ‘pure’ ICD (odds ratio 3·1) after 3 years. Conclusions Patients with atopy are a special risk population for ICD. In the presence of atopy, FLG mutations seem to be a modifier of the severity of the clinical course in ICD. Early‐stage identification of this subgroup may result in additional emphasis to these patients regarding the importance of adherence to specific therapeutic interventions.     

Eczema severity in preadolescent children and its relation to sex,filaggrin mutations,asthma, rhinitis,aggravating factors and topical treatment: a report from the BAMSE birth cohort

Background Filaggrin (FLG) mutations are major genetic determinants for eczema, but their role in eczema severity needs further investigation. Children with eczema are at higher risk of having asthma and rhinitis but it is not known if this risk is associated with the severity of eczema. Objectives To investigate eczema severity in relation to sex, FLG mutations, asthma, rhinitis and topical treatment among preadolescent children in a population‐based cohort. Methods Parental questionnaires were used to obtain data on symptoms of eczema, asthma, and rhinitis among 3301 preadolescent children. Eczema severity was evaluated based on sleep disturbance, extent of disease and total time with eczema the previous year. Genotyping was performed in 1854 individuals for three common FLG mutations (R501X, R2447X and 2282del4). Results Eczema was more prevalent among girls (14·5%) than boys (9·4%). FLG mutations were detected in 13·1% of children with mild eczema and 12·5% with moderate‐to‐severe eczema. Of children with moderate‐to‐severe eczema, 45·1% had rhinitis and 22·0% had asthma compared with 32·7% and 13·8% of children with mild eczema, respectively. Children with moderate‐to‐severe eczema used moisturizers and topical glucocorticoids more frequently than children with mild eczema. Boys used moisturizers less frequently than girls. Conclusions More preadolescent girls than boys had eczema. FLG mutations did not influence eczema severity in our population‐based cohort. Prevalence of rhinitis and asthma was associated with eczema severity, with the highest prevalence among boys with moderate‐to‐severe eczema.     

Filaggrin null mutations increase the risk and persistence of hand eczema in subjects with atopic dermatitis: results from a general population study

Summary Background Hand eczema is prevalent in the general population. It remains unclear whether or not filaggrin gene (FLG) null mutations increase the overall risk of hand eczema or only increase the risk of hand eczema in subjects with atopic dermatitis. Objectives To investigate the association between FLG null mutations and hand eczema. Methods A random sample of 3335 adults from the general population in Denmark was patch tested, FLG genotyped for R501X and 2282del4 null mutations and questioned about hand eczema. Results Participants with combined presence of atopic dermatitis and FLG null mutation status had a significantly higher prevalence of hand eczema, an earlier onset of hand eczema and a higher persistence of hand eczema compared with subjects with normal FLG status and absence of atopic dermatitis. Logistic regression analyses revealed positive associations between hand eczema within the past 12 months and FLG null mutation status in participants with a history of atopic dermatitis [odds ratio (OR) 2·98; 95% confidence interval (CI) 1·27–7·01], but not in subjects without atopic dermatitis (OR 0·82; 95% CI 0·41–1·67). Conclusions FLG null mutations were significantly associated with hand eczema (< 12 months) in subjects with atopic dermatitis. Combined atopic dermatitis and filaggrin null mutation status was strongly associated with early onset of hand eczema and hand eczema persistence.     

The filaggrin null genotypes R501X and 2282del4 seem not to be associated with psoriasis: results from general population study and meta‐analysis

Background Psoriasis vulgaris could be associated with the filaggrin null genotype since certain known susceptibility loci for psoriasis are shared with susceptibility loci for atopic dermatitis. Furthermore, filaggrin expression is lowered in psoriatic skin lesions but normally expressed in uninvolved skin. So far five relatively small patient‐based case‐control studies have rejected a possible association between psoriasis and the two most prevalent filaggrin null mutations, 2282del4 and R501X. Objectives To reinvestigate a possible association between psoriasis and filaggrin null mutation status by using cross‐sectional general population questionnaire data. Also, to perform a meta‐analysis including published studies that investigated the relation between filaggrin gene mutations R501X and 2282del4, respectively, and psoriasis vulgaris. Methods Between June 2006 and May 2008, a cross‐sectional study was performed in the general population in Copenhagen. A random sample of 7931 subjects aged 18–69 years was invited to participate in a general health examination including a questionnaire and 3471 (43.7%) participated. A total of 3335 (96.1%) individuals were filaggrin genotyped for the 2282del4 and R501X mutations. A meta‐analysis was undertaken to investigate the relation between filaggrin gene mutations and psoriasis vulgaris. Results The prevalence of self‐reported psoriasis was 6.7% among the 3240 respondents. The prevalence of the R501X and 2282del4 filaggrin null genotypes was 9.3% in subjects who reported psoriasis and 8.0% in subjects who did not report psoriasis (OR = 1.28; 95% CI = 0.74–1.89; P = 0.78). The meta‐analysis found no association between the filaggrin null genotypes R501X and 2282del4 and psoriasis (OR = 1.04; 95% CI = 0.81–1.35). Conclusions Psoriasis was not associated with the R501X and 2282del4 filaggrin null genotypes in a general population study and in a meta‐analysis on published studies.     

The association between null mutations in the filaggrin gene and contact sensitization to nickel and other chemicals in the general population

Background It was recently shown that filaggrin gene (FLG) null mutations are positively associated with nickel sensitization. We have hypothesized that histidine‐rich filaggrin proteins in the epidermis chelate nickel ions and prevent their skin penetration and exposure to Langerhans cells. Furthermore, we have proposed that the low degree of genetic predisposition to nickel sensitization found by a Danish twin study was explained by a high prevalence of ear piercing among participants resulting in ‘bypassing’ of the filaggrin proteins. Objectives To investigate the association between FLG null mutations and (nickel) contact sensitization. Methods A random sample of 3335 adults from the general population in Denmark was patch tested and genotyped for R501X and 2282del4 in the FLG gene. Results The combined carrier frequency of FLG null mutations was 8·1%. Nickel, fragrance and contact sensitization to at least one allergen were not associated with FLG null mutations. A crude analysis on women who did not have ear piercings revealed a positive association between FLG null mutations and nickel sensitization [8·3% vs. 2·4%; odds ratio (OR) 3·71, 95% confidence interval (CI) 0·73–18·96] as well as between FLG null mutations and allergic nickel dermatitis (8·3% vs. 1·3%; OR 6·75, 95% CI 1·17–38·91). FLG mutation status and atopic dermatitis were positively associated with neomycin or ethylenediamine sensitization. Conclusions This study suggests that FLG null mutations may be a risk factor for the development of nickel sensitization. However, ear piercing was a much stronger risk factor in our general population and we could therefore identify a positive association only in women without ear piercings. Contact sensitization to specific chemicals is related to treatment exposure.     

Analyses of FLG mutation frequency and filaggrin expression in isolated ichthyosis vulgaris (IV) and atopic dermatitis‐associated IV

Background 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. Objectives 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. Methods 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. Results 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. Conclusions 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.     

Filaggrin haploinsufficiency is highly penetrant and is associated with increased severity of eczema: further delineation of the skin phenotype in a prospective epidemiological study of 792 school children

Background Null mutations within the filaggrin gene (FLG) cause ichthyosis vulgaris and are associated with atopic eczema. However, the dermatological features of filaggrin haploinsufficiency have not been clearly defined. Objectives This study investigated the genotype–phenotype association between detailed skin phenotype and FLG genotype data in a population‐based cohort of children. Methods Children (n = 792) aged 7–9 years were examined by a dermatologist. Features of ichthyosis vulgaris, atopic eczema and xerosis were recorded and eczema severity graded using the Three Item Severity score. Each child was genotyped for the six most prevalent FLG null mutations (R501X, 2282del4, R2447X, S3247X, 3702delG, 3673delC). Fisher’s exact test was used to compare genotype frequencies in phenotype groups; logistic regression analysis was used to estimate odds ratios and penetrance of the FLG null genotype and a permutation test performed to investigate eczema severity in different genotype groups. Results Ten children in this cohort had ichthyosis vulgaris, of whom five had mild–moderate eczema. The penetrance of FLG null mutations with respect to flexural eczema was 55·6% in individuals with two mutations, 16·3% in individuals with one mutation and 14·2% in wild‐type individuals. Summating skin features known to be associated with FLG null mutations (ichthyosis, keratosis pilaris, palmar hyperlinearity and flexural eczema) showed a penetrance of 100% in children with two FLG mutations, 87·8% in children with one FLG mutation and 46·5% in wild‐type individuals (P < 0·0001, Fisher exact test). FLG null mutations were associated with more severe eczema (P = 0·0042) but the mean difference was only 1–2 points in severity score. Three distinct patterns of palmar hyperlinearity were observed and these are reported for the first time. Conclusions Filaggrin haploinsufficiency appears to be highly penetrant when all relevant skin features are included in the analysis. FLG null mutations are associated with more severe eczema, but the effect size is small in a population setting.     

Wide spectrum of filaggrin-null mutations in atopic dermatitis highlights differences between Singaporean Chinese and European populations

Background  Null mutations in the filaggrin gene (FLG) cause ichthyosis vulgaris (IV) and predispose to atopic dermatitis (AD). Cohort studies in Europe and Japan have reported an FLG mutation carrier frequency of between 14% and 56%, but the prevalent European FLG mutations are rare or absent in Chinese patients with IV and AD. Objectives  To investigate further the spectrum of FLG‐null mutations in Chinese patients and to compare it with that in other populations. Methods  We conducted comprehensive FLG genetic analysis in a discovery cohort of 92 Singaporean Chinese individuals with IV and/or moderate‐to‐severe AD. All detected FLG mutations were then screened in a cohort of 425 patients with AD and 440 normal controls. Results  In total, 22 FLG‐null mutations, of which 14 are novel, were identified in this study; the combined null FLG genotype of 17 mutations detected in cases and controls showed strong association with AD [Fisher’s exact test; P = 5·3 × 10^?9; odds ratio (OR) 3·3], palmar hyperlinearity (Fisher’s exact test; P = 9·0 × 10^?15; OR 5·8), keratosis pilaris (Fisher’s exact test; P = 0·001; OR 4·7) and with increased severity of AD (permutation test; P = 0·0063). Conclusions  This study emphasizes the wider genetic landscape of FLG‐null mutations in Asia that is slowly emerging.