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

Genetic and Immunological Pathogenesis of Atopic Dermatitis

Type 2 immune-mediated diseases give a clear answer to the issue of nature (genetics) versus nurture (environment). Both genetics and environment play vital complementary roles in the development of atopic dermatitis (AD). As a key component of the atopic march, AD demonstrates the interactive nature of genetic and environmental contributions to atopy. From sequence variants in the epithelial barrier gene encoding FLG to the hygiene hypothesis, AD combines a broad array of contributions into a single syndrome. This review will focus on the genetic contribution to AD and where genetics facilitates the elicitation or enhancement of AD pathogenesis.

Neonatal Filaggrin Genetic Screening and Counseling to Prevent Atopic Dermatitis in High-Risk Infants

Background: Mutations in filaggrin (FLG), the gene that codes for the skin barrier protein, have been shown to be associated with atopic dermatitis (AD). Objective: The objectives of this study were to determine the effects of genetic counseling and parental education on infants at a high risk of AD. Methods: We enrolled 7521 newborns in Taiwan from January 1, 2016, to March 30, 2020, and all of them received genetic testing encompassing 20 known FLG mutations. The genetic counseling and AD prevention and care team consisted of pediatricians, dermatologists, social workers, and genetic counselors. The counseling was arranged for at least 30 minutes within 45 days after delivery. Results: A total of 2963 high-risk infants (39.4%) were identified. Homozygous c.1432C>T was the most commonly identified mutation. A total of 418 neonates' parents were stratified into counseling and noncounseling groups, where the effect of parental education was evaluated. The genetically stratified parental education program was effective in preventing AD development by 63.3% in high-risk infants before 12 months of life (P < 0.0001). Conclusion: Genetic stratification and parental education are effective in preventing the development of AD in high-risk infants before 12 months of life.

Diversity of atopic dermatitis and selection of immune targets

Atopic dermatitis (AD) is a heterogeneous immune-mediated skin disorder affecting people of all ages and ethnicities. Despite the development of targeted therapeutics such as biologics and Janus kinase inhibitors, attaining complete clinical efficacy remains difficult. This therapeutic challenge may be attributed to the complex pathogenesis of AD. Although the TH2 axis has been extensively studied, recent advancements have started to reveal the involvement of additional immune pathways including TH1, TH17, and TH22. Understanding the interplay of these immune axes may contribute to a more personalized therapeutic approach based on patients' molecular profile, with the prospect of improving clinical outcome. This review will discuss studies exploring the molecular profile of AD in both skin and blood across age, ethnicity/race, disease chronicity, IgE levels, filaggrin mutation status, and AD association with other atopic conditions. Moreover, it will explore the potential of personalized treatment strategies based on a patient's distinct immune signature.

Filaggrin and beyond: New insights into the skin barrier in atopic dermatitis and allergic diseases, from genetics to therapeutic perspectives

Atopic dermatitis (AD) is the most common inflammatory skin disease worldwide, affecting 20% of children and 5% of adults. One critical component in the pathophysiology of AD is the epidermal skin barrier, with its outermost layer, the stratum corneum (SC), conferring biochemical properties that enable resilience against environmental threats and maintain homeostasis. The skin barrier may be conceptualized as a key facilitator of complex interactions between genetics, host immunity, the cutaneous microbiome, and environmental exposures. The key genetic risk factor for AD development and persistence is a loss-of-function mutation in FLG, with recent advances in genomics focusing on rare variant discovery, establishment of pathogenic mechanisms, and exploration of the role of other epidermal differentiation complex gene variants in AD. Aberrant type 2 inflammatory responses down-regulate the transcription of key epidermal barrier genes, alter the composition of SC lipids, and induce further injury through a neurocutaneous feedback loop and the itch-scratch cycle. The dysbiotic epidermis exhibits reduced bacterial diversity and enhanced colonization with Staphylococcus and Malassezia species, which contribute to both direct barrier injury through the action of bacterial toxins and perpetuation of the inflammatory cascades. Enhanced understanding of each of the pathogenic mechanisms underpinning barrier disruption has led to the development of novel topical and systemic molecules, including interleukin (IL)-4Ra, IL-13, PDE4, and Janus-associated kinase inhibitors, whose clinical effectiveness exceeds conventional treatment modalities. In this narrative review, we aim to summarize the current understanding of the above-mentioned pathophysiological and therapeutic mechanisms, with a focus on the genetic, cellular, and molecular mechanisms underpinning AD development.

Filaggrin gene variants among Saudi patients with ichthyosis vulgaris

Ichthyoses are a heterogeneous group of cornification disorders. The most common form of ichthyoses is ichthyosis vulgaris (IV) ([OMIM] #146,700), which can be inherited as autosomal semi-dominant mutation in the filaggrin gene (FLG). We present the findings of a study involving 35 Saudi patients with a clinical diagnosis of ichthyosis vulgaris. For identifying the pathogenic mutation of their disease, we used Sanger sequencing analysis of the extracted DNA samples. We also identified the underlying 22 FLG variants, which have been seen before. However, the detected mutations do not involve the common p.R501* c. 2282del4 mutations reported in European populations. Indeed, we did not identify any statistical influence of the homozygous or heterozygous genotypes on the phenotype severity of the disease.

Are Antimicrobial Peptides a 21st-Century Solution for Atopic Dermatitis?

Atopic dermatitis (AD) is a chronic inflammatory skin disorder that is the result of various environmental, bacterial and genetic stimuli, which culminate in the disruption of the skin's barrier function. Characterized by highly pruritic skin lesions, xerosis and an array of comorbidities among which skin infections are the most common, this condition results in both a significant loss of quality of life and in the need for life-long treatments (e.g., corticosteroids, monoclonal antibodies and regular antibiotic intake), all of which may have harmful secondary effects. This, in conjunction with AD's rising prevalence, made the development of alternative treatment strategies the focus of both the scientific community and the pharmaceutical industry. Given their potential to both manage the skin microbiome, fight infections and even modulate the local immune response, the use of antimicrobial peptides (AMPs) from more diverse origins has become one of the most promising alternative solutions for AD management, with some being already used with some success towards this end. However, their production and use also exhibit some limitations. The current work seeks to compile the available information and provide a better understanding of the state of the art in the understanding of AMPs' true potential in addressing AD.

Candidate Gene Association Studies in Atopic Dermatitis in Participants of European and Asian Ancestry: A Systematic Review and Meta-Analysis

Atopic dermatitis (AD) has been extensively investigated for genetic associations utilizing both candidate gene approaches and genome-wide scans. Here, we comprehensively evaluated the available literature to determine the association of candidate genes in AD to gain additional insight into the etiopathogenesis of the disease. We systematically screened all studies that explored the association between polymorphisms and AD risks in cases of European and Asian ancestry and synthesized the available evidence through a random-effects meta-analysis. We identified 99 studies that met our inclusion/exclusion criteria that examined 17 candidate loci in Europeans and 14 candidate genes in Asians. We confirmed the significant associations between FLG variants in both European and Asian populations and AD risk, while synthesis of the available data revealed novel loci mapped to IL18 and TGFB1 genes in Europeans and IL12RB1 and MIF in Asians that have not yet been identified by genome-wide association studies. Our findings provide comprehensive evidence for AD risk loci in cases of both European and Asian ancestries, validating previous associations as well as revealing novel loci that could imply previously unexplored biological pathways.

Pimecrolimus for the Treatment of Atopic Dermatitis in Infants: An Asian Perspective

Atopic dermatitis (AD) is a common chronic, multisystem inflammatory skin disease in pediatric patients. There has been an increase in the incidence of AD in the pediatric population of the Asia-Pacific region. Studies have shown that genetic, epigenetic, environmental and cultural factors may lead to differences in the clinical manifestation and prevalence of AD between races. Early treatment of AD is necessary to prevent the atopic march leading to comorbidities such as asthma and allergic rhinitis. Topical corticosteroids (TCS) are used as first-line therapy for the treatment of AD, but their long-term usage poses a risk to the patient's health. Pimecrolimus (1%) is a topical calcineurin inhibitor (TCI) that is indicated for the treatment of mild to moderate AD. Pimecrolimus has no apparent increase in adverse events compared to TCS, and it causes less of a burning sensation than tacrolimus. The safety and efficacy of pimecrolimus has been established through various clinical trials; yet, in many Asian countries, the use of pimecrolimus in infants is still restricted due to safety concerns. Based on the available evidence, the expert panel recommends pimecrolimus in infants between 3 months and 2 years of age in the Asian population.

Ichthyosis

The ichthyoses are a large, heterogeneous group of skin cornification disorders. They can be inherited or acquired, and result in defective keratinocyte differentiation and abnormal epidermal barrier formation. The resultant skin barrier dysfunction leads to increased transepidermal water loss and inflammation. Disordered cornification is clinically characterized by skin scaling with various degrees of thickening, desquamation (peeling) and erythema (redness). Regardless of the type of ichthyosis, many patients suffer from itching, recurrent infections, sweating impairment (hypohidrosis) with heat intolerance, and diverse ocular, hearing and nutritional complications that should be monitored periodically. The characteristic clinical features are considered to be a homeostatic attempt to repair the skin barrier, but heterogeneous clinical presentation and imperfect phenotype-genotype correlation hinder diagnosis. An accurate molecular diagnosis is, however, crucial for predicting prognosis and providing appropriate genetic counselling. Most ichthyoses severely affect patient quality of life and, in severe forms, may cause considerable disability and even death. So far, treatment provides only symptomatic relief. It is lifelong, expensive, time-consuming, and often provides disappointing results. A better understanding of the molecular mechanisms that underlie these conditions is essential for designing pathogenesis-driven and patient-tailored innovative therapeutic solutions.

Factors associated with severity of atopic dermatitis - a Finnish cross-sectional study

BACKGROUND

Severity-associated factors in atopic dermatitis (AD) have focussed on early onset, concomitant atopic diseases, markers of Th2-shifted inflammation and filaggrin mutations.

OBJECTIVES

To investigate factors associated with severe AD in Finnish patients.

METHODS

We conducted a single-centre, cross-sectional observational study with 502 AD patients aged 4.79 to 79.90 years (mean 32.08 years). Disease severity was assessed with the Rajka-Langeland severity score and EASI and associated clinical signs were evaluated. Data regarding onset, relatives, atopic and other comorbidities was gathered retrospectively. We investigated total serum IgE-levels, a panel of filaggrin null mutations and functional variants of genes associated with skin barrier defects.

RESULTS

Factors more frequent in severe AD included early onset (P = 0.004, 95%CI 0.000-0.024), male sex (P = 0.002, 95%CI 0.000-0.11), history of smoking (P = 0.012, 95%CI 0.000-0.024), concomitant asthma (P = 0.001, 95%CI 0.000-0.011), palmar hyperlinearity (P = 0.013, 95%CI 0.014-0.059), hand dermatitis (P = 0.020, 95%CI 0.000-0.029) and history of contact allergy (P = 0.042, 95%CI 0.037-0.096). Body mass indices (P < 0.000, 95%CI 0.000-0.011) and total serum IgE-levels (P < 0.000, 95%CI 0.000-0.011) were higher in severe AD. No differences were observed for allergic rhinitis, allergic conjunctivitis, food allergy, peanut allergy, prick positivity, keratosis pilaris, history of herpes simplex infections, filaggrin null mutations and other gene variants.

CONCLUSIONS

Severity determinants in Finnish patients seem to be early-onset, male sex, smoking, overweight, concomitant asthma, palmar hyperlinearity, hand dermatitis and high IgE-levels. A sub-typing of patients in relation to confirmed severity determinants may be useful for course prediction, prognosis and targeted AD management.

Quality of life in atopic dermatitis in Asian countries: a systematic review

Atopic dermatitis (AD) is a common chronic inflammatory skin condition which impacts psychological wellbeing and social relationships. There have been studies of AD's impact on quality of life (QoL) in Western countries, but these findings cannot be directly extrapolated to Asian populations with genetic, environmental and cultural differences. Therefore, we aimed to systematically review the literature pertaining to QoL impairment in AD in East and Southeast Asia to characterize the impact of AD on patients and their families, and to identify the factors affecting the degree of QoL impairment. A search of English language papers was conducted on MEDLINE, EMBASE, PSYCInfo, Global Health and Web of Science. Observational studies measuring QoL using single or multi-item instruments in people with self-reported or physician diagnosed atopic dermatitis were included. 27 studies from 29 articles were included and synthesized. There is data documenting QoL impairment in AD sufferers and their families, across a wide range of Asian countries, healthcare settings and ages. Aspects of QoL impacted to a greater extent included symptoms of itch, feelings of embarrassment, and sleep disturbance. Severity of disease affects the degree of impairment of QoL, but there is no apparent link between QoL impairment and patient demographic factors, or other medical factors such as age at diagnosis or duration of illness. Our findings also highlighted the need for clinicians to actively explore the impact of patient's symptoms, especially in an Asian context where healthcare communications are traditionally doctor-centric.

Revisiting the Roles of Filaggrin in Atopic Dermatitis

The discovery in 2006 that loss-of-function mutations in the filaggrin gene (FLG) cause ichthyosis vulgaris and can predispose to atopic dermatitis (AD) galvanized the dermatology research community and shed new light on a skin protein that was first identified in 1981. However, although outstanding work has uncovered several key functions of filaggrin in epidermal homeostasis, a comprehensive understanding of how filaggrin deficiency contributes to AD is still incomplete, including details of the upstream factors that lead to the reduced amounts of filaggrin, regardless of genotype. In this review, we re-evaluate data focusing on the roles of filaggrin in the epidermis, as well as in AD. Filaggrin is important for alignment of keratin intermediate filaments, control of keratinocyte shape, and maintenance of epidermal texture via production of water-retaining molecules. Moreover, filaggrin deficiency leads to cellular abnormalities in keratinocytes and induces subtle epidermal barrier impairment that is sufficient enough to facilitate the ingress of certain exogenous molecules into the epidermis. However, although FLG null mutations regulate skin moisture in non-lesional AD skin, filaggrin deficiency per se does not lead to the neutralization of skin surface pH or to excessive transepidermal water loss in atopic skin. Separating facts from chaff regarding the functions of filaggrin in the epidermis is necessary for the design efficacious therapies to treat dry and atopic skin.

Classifying atopic dermatitis: a systematic review of phenotypes and associated characteristics

Atopic dermatitis is a heterogeneous disease, accompanied by a wide variation in disease presentation and the potential to identify many phenotypes that may be relevant for prognosis and treatment. We aimed to systematically review previously reported phenotypes of atopic dermatitis and any characteristics associated with them. Ovid EMBASE, Ovid MEDLINE and Web of Science were searched from inception till the 12th of February 2021 for studies attempting to classify atopic dermatitis. Primary outcomes are atopic dermatitis phenotypes and characteristics associated with them in subsequent analyses. A secondary outcome is the methodological approach used to derive them. In total, 8,511 records were found. By focusing only on certain clinical phenotypes, 186 studies were eligible for inclusion. The majority of studies were hospital-based (59%, 109/186) and cross-sectional (76%, 141/186). The number of included patients ranged from seven to 526,808. Data-driven approaches to identify phenotypes were only used in a minority of studies (7%, 13/186). Ninety-one studies (49%) investigated a phenotype based on disease severity. A phenotype based on disease trajectory, morphology and eczema herpeticum was investigated in 56 (30%), 22 (12%) and 11 (6%) studies, respectively. Thirty-six studies (19%) investigated morphological characteristics in other phenotypes. Investigated associated characteristics differed between studies. In conclusion, we present an overview of phenotype definitions used in literature for severity, trajectory, morphology and eczema herpeticum, including associated characteristics. There is a lack of uniform and consistent use of atopic dermatitis phenotypes across studies.

Review article: Emerging issues in pediatric skin of color, Part 2

Dermatology for pediatric skin of color is the application of dermatology to the genetically diverse and distinctive segment of the pediatric population that includes children of non-White racial and ethnic groups with increased pigmentation including individuals of Asian, Hispanic/LatinX, African, Native American, Pacific Island descent, indigenous people among others with overlap in particular individuals, and mixtures thereof. The discipline of pediatric skin of color can be challenging with difficulty in diagnosis of common conditions due to underlying pigmentation, variations in common hair styling practices, and differences in demographics of cutaneous disease. Whereas some conditions are more common in children of color, other conditions have nuances in clinical appearance and therapeutics with regard to skin color. This article, the second of the series, focuses on inflammatory skin disease nuances, melanocytic disorders, and hypopigmented mycosis fungoides.

Moisturisers from birth in at-risk infants of atopic dermatitis - a pragmatic randomised controlled trial

Background

Atopic dermatitis (AD) is a common, chronic dermatosis, with onset of disease often manifesting in early infancy. Past studies evaluating the early use of moisturisers in the prevention of AD had mixed results.

Objectives

To compare the incidence of moderate or severe AD and total incidence of AD in a cohort of ‘at‐risk’ infants treated with moisturisers from the first 2 weeks of life, to a similar group without moisturisers.

Methods

We performed a single‐centre, prospective, parallel‐group, randomised study in infants with at least 2 first‐degree relatives with atopy. Subjects were randomised into either a treatment group with moisturisers or a control group without moisturisers. Participants were assessed at 2, 6, and 12 months for AD and if present, the severity was assessed using SCORAD index. We also compared the overall incidence of AD, trans‐epidermal water loss (TEWL), stratum corneum (SC) hydration, pH, and incidence of food and environmental sensitisation and allergies between both groups. Genotyping for loss‐of‐functions mutations in the FLG gene was conducted.

Results

A total of 200 subjects were recruited, with 100 subjects in each arm. There was no significant difference in incidence of moderate or severe AD, and total incidence of AD at 12 months between the treatment and control groups. There was a lower mean SCORAD in the treatment group than in the control group, but no significant difference in TEWL, SC hydration, and skin pH. No significant side‐effects were reported.

Conclusions

The early use of moisturisers in ‘at‐risk’ infants does not reduce the incidence of moderate‐to‐severe AD and overall incidence of AD in infancy.

New Treatments for Atopic Dermatitis Targeting Skin Barrier Repair via the Regulation of FLG Expression

Atopic dermatitis (AD) is one of the most common chronic, inflammatory skin disorders with a complex etiology and a broad spectrum of clinical phenotypes. Despite its high prevalence and effect on the quality of life, safe and effective systemic therapies approved for long-term management of AD are limited. A better understanding of the pathogenesis of atopic dermatitis in recent years has contributed to the development of new therapeutic approaches that target specific pathophysiological pathways. Skin barrier dysfunction and immunological abnormalities are critical in the pathogenesis of AD. Recently, the importance of the downregulation of epidermal differentiation complex (EDC) molecules caused by external and internal stimuli has been extensively emphasized. The purpose of this review is to discuss the innovations in the therapy of atopic dermatitis, including biologics, small molecule therapies, and other drugs by highlighting regulatory mechanisms of skin barrier-related molecules, such as filaggrin (FLG) as a crucial pathway implicated in AD pathogenesis.

Filaggrin Polymorphisms and the Uptake of Chemicals through the Skin-A Human Experimental Study

BACKGROUND

The filaggrin protein is important for skin barrier structure and function. Loss-of-function (null) mutations in the filaggrin gene FLG may increase dermal absorption of chemicals.

OBJECTIVE

The objective of the study was to clarify if dermal absorption of chemicals differs depending on FLG genotype.

METHOD

We performed a quantitative real-time polymerase chain reaction (qPCR)-based genetic screen for loss-of-function mutations (FLG null) in 432 volunteers from the general population in southern Sweden and identified 28 FLG null carriers. In a dermal exposure experiment, we exposed 23 FLG null and 31 wild-type (wt) carriers to three organic compounds common in the environment: the polycyclic aromatic hydrocarbon pyrene, the pesticide pyrimethanil, and the ultraviolet-light absorber oxybenzone. We then used liquid-chromatography mass-spectrometry to measure the concentrations of these chemicals or their metabolites in the subjects' urine over 48 h following exposure. Furthermore, we used long-range PCR to measure FLG repeat copy number variants (CNV), and we performed population toxicokinetic analysis.

RESULTS

Lag times for the uptake and dermal absorption rate of the chemicals differed significantly between FLG null and wt carriers with low (20-22 repeats) and high FLG CNV (23-24 repeats). We found a dose-dependent effect on chemical absorption with increasing lag times by increasing CNV for both pyrimethanil and pyrene, and decreasing area under the urinary excretion rate curve (AUC(0-40h)) with increasing CNV for pyrimethanil. FLG null carriers excreted 18% and 110% more metabolite (estimated by AUC(0-40h)) for pyrimethanil than wt carriers with low and high CNV, respectively.

CONCLUSION

We conclude that FLG genotype influences the dermal absorption of some common chemicals. Overall, FLG null carriers were the most susceptible, with the shortest lag time and highest rate constants for skin absorption, and higher fractions of the applied dose excreted. Furthermore, our results indicate that low FLG CNV resulted in increased dermal absorption of chemicals. https://doi.org/10.1289/EHP7310.

Global differences in atopic dermatitis

Atopic dermatitis (AD) is a chronic inflammatory skin disorder, with a highly variable prevalence worldwide. Recent evidence, however, has shown an increase in prevalence in the Asia Pacific region. Nevertheless, most of the published literature has focused mainly on Western populations, and only few clinical trials have included subgroups of other ethnic populations. Reasons for the observed ethnic and geographical differences in AD are not well established. This calls into question the need for a better understanding of AD pathogenesis and inter-ethnic differences in clinical and immuno-phenotypes. These differences may reflect inherent variability in disease mechanisms between populations, which in turn may impact upon treatment responses such as biologics that are currently tailored mainly to a specific immuno-phenotype (T-helper type 2 dominant). In this article, we reviewed existing literature on the prevalence of AD globally, highlighting differences, if any, in the clinical and immuno-phenotypes of AD between different ethnicities. We discussed genetic and environmental factors that affect AD in different populations and therapeutic considerations. Our review highlights AD as a disease with ethnic-dependent clinical and immunological heterogeneity and calls for greater inclusion of ethnic diversity in future research in order to develop targeted treatments.

Practical Recommendations for the Topical Treatment of Atopic Dermatitis in South and East Asia

Introduction

There is some evidence to suggest that the prevalence of atopic dermatitis (AD) in Asia is rising. We have therefore developed an algorithm for the topical treatment of AD throughout South and East Asia for use by primary care physicians, pediatricians and dermatologists.

Methods

Nine AD experts from South and East Asia and one from Europe developed the algorithm based upon treatment guidelines, relevant literature and local treatment practices. The algorithm outlines current best practice for the use of emollients, topical corticosteroids (TCS) and topical calcineurin inhibitors (TCI), with the intention of simplifying the treatment regimen of mild-to-moderate AD in South and East Asia.

Results

Patients with AD should bathe and cleanse affected skin to remove crusts and scales daily. Emollients should also be applied daily as a maintenance treatment. When selecting appropriate topical anti-inflammatory treatment for AD flares, several factors should be taken into consideration, including the patient’s age, attitude to treatment options and site of AD lesions. Given the concerns regarding the risk of skin atrophy with use of TCS, a TCI should be used to treat AD lesions in sensitive skin areas: pimecrolimus is recommended for mild-to-moderate AD in these locations, while tacrolimus should be considered for moderate and severe cases. Either pimecrolimus or tacrolimus is recommended for flares in other, non-sensitive body locations. A proactive or intermittent maintenance treatment strategy involving regular emollient use and twice-weekly application of a TCI to previously affected areas is encouraged to reduce the risk of flares.

Conclusions

The algorithm proposed here is intended to simplify the topical treatment of mild-to-moderate AD in daily practice in South and East Asian countries.

Which Way Do We Go? Complex Interactions in Atopic Dermatitis Pathogenesis

Atopic dermatitis (AD) is a common, chronic, inflammatory skin condition characterized by recurrent and pruritic skin eruptions. Multiple factors contribute to the pathogenesis of AD, including skin barrier dysfunction, microbial dysbiosis, and immune dysregulation. Interactions among these factors form a complex, multidirectional network that can reinforce atopic skin disease but can also be ameliorated by targeted therapies. This review summarizes the complex interactions among contributing factors in AD and the implications on disease development and therapeutic interventions.

Atopic dermatitis

Atopic dermatitis is a common inflammatory skin disorder characterised by recurrent eczematous lesions and intense itch. The disorder affects people of all ages and ethnicities, has a substantial psychosocial impact on patients and relatives, and is the leading cause of the global burden from skin disease. Atopic dermatitis is associated with increased risk of multiple comorbidities, including food allergy, asthma, allergic rhinitis, and mental health disorders. The pathophysiology is complex and involves a strong genetic predisposition, epidermal dysfunction, and T-cell driven inflammation. Although type-2 mechanisms are dominant, there is increasing evidence that the disorder involves multiple immune pathways. Currently, there is no cure, but increasing numbers of innovative and targeted therapies hold promise for achieving disease control, including in patients with recalcitrant disease. We summarise and discuss advances in our understanding of the disease and their implications for prevention, management, and future research.

Uncrossed corticospinal tracts in a patient with ichthyosis and hemiparesis: a case report

Background

Anomalies of pyramidal tract decussation are rare phenomena that can be caused by ectodermal dysplasia. Herein, we describe a patient with ichthyosis who exhibited ipsilateral hemiparesis after stroke and whose neuroimaging results showed evidence of motor control being provided by the ipsilateral motor cortex.

Case presentation

A 24-year-old right-handed man presented with skin abnormalities, sudden-onset left hemiparesis, and dysarthria. He exhibited a mild-to-moderate left-sided weakness (grade 4 on the Medical Research Council scale). Magnetic resonance imaging revealed an acute infarct in the left corona radiata. Diffusion tensor imaging revealed uncrossed corticospinal tracts. Next-generation sequencing identified heterozygous FLG mutations. The patient was diagnosed with cerebral infarction and ichthyosis vulgaris and was treated with aspirin (100 mg/d). His symptoms gradually dissipated.

Conclusions

This case suggests that pyramidal decussation anomalies can be associated with ichthyosis. Patients with ichthyosis should therefore be evaluated for nerve involvement.

Epigenetic Regulation of Filaggrin Gene Expression in Human Epidermal Keratinocytes

Background

Loss-of-function mutations in the filaggrin gene (FLG), which encodes an epidermal protein crucial for the formation of a functional skin barrier, have been identified as a major predisposing factor in the etiopathogenesis of atopic dermatitis (AD). Recent reports of relatively low frequencies of FLG-null mutations among specific ethnic groups with AD necessitated analysis of the epigenetic regulation which may control FLG expression without altering its DNA sequence.

Objective

The study aimed to identify DNA methylation-dependent regulation of FLG expression.

Methods

Quantitative polymerase chain reaction was performed to determine the restoration of FLG mRNA expression in normal human epidermal keratinocyte (NHEK) cells after treatment with epigenetic modulating agents. Bisulfite genomic sequencing and pyrosequencing analyses of the FLG promoter region were conducted to identify the citical CpG sites relevant to FLG expression. We performed small-scale pilot study for epidermal tissues obtained from Korean patients with severe AD.

Results

We here show that DNA methylation in the FLG with non-CpG island promoter is responsible for the transcriptional regulation of FLG in undifferentiated NHEK cells. The methylation frequencies in a single CpG site of the FLG promoter were significantly higher in lesional epidermis than those in matched nonlesional epidermis of subjects with severe AD.

Conclusion

Our in vitro and clinical studies point to this unique CpG site as a potential DNA methylation marker of FLG, which can be a promising therapeutic target in the complications of filaggrin-related skin barrier dysfunction as well as in AD.

Correlation of age-of-onset of Atopic Dermatitis with Filaggrin loss-of-function variant status

The genetic background of Atopic Dermatitis (AD) with chronic pruritus is complex. Filaggrin (FLG) is an essential gene in the epidermal barrier formation s. Loss-of-function (LOF) variants in FLG associated with skin barrier dysfunction constitute the most well-known genetic risk factor for AD. In this study, we focused on the frequency and effect of FLG loss-of-function variants in association with self-reported age-of-onset of AD. The dataset consisted of 386 whole-genome sequencing (WGS) samples. We observe a significant association between FLG LOF status and age-of-onset, with earlier age of onset of AD observed in the FLG LOF carrier group (p-value 0.0003, Wilcoxon two-sample test). We first tested this on the two most prevalent FLG variants. Interestingly, the effect is even stronger when considering all detected FLG LOF variants. Having two or more FLG LOF variants associates with the onset of AD at 2 years of age. In this study, we have shown enrichment of rare variants in the EDC region in cases compared with controls. Age-of-onset analysis shows not only the effect of the FLG and likely EDC variants in terms of the heightened risk of AD, but foremost enables to predict early-onset, lending further credence to the penetrance and causative effect of the identified variants. Understanding the genetic background and risk of early-onset is suggestive of skin barrier dysfunction etiology of AD with chronic pruritus

Atopic Dermatitis in Adults

Atopic dermatitis (AD) was once thought to be a benign childhood disease that remitted with increasing age. However, recent studies have transformed the understanding of AD, particularly in adult patients. AD is common in adults and can lead to substantial disability by negatively affecting sleep, mental health, and quality of life. There seem to be different genetic, immunologic, and epidemiologic risk factors for AD in adults than in children. This article examines the pathophysiology, epidemiology, heterogeneous clinical presentation, burden, diagnosis, and treatment of adult AD.

Prevalence of FLG loss-of-function mutations R501X, 2282del4, and R2447X in Spanish children with atopic dermatitis

BACKGROUND/OBJECTIVES

Atopic dermatitis (AD) is the most prevalent inflammatory skin disorder, and is often associated with a personal or family history of atopic disease. The presence of loss-of-function mutations in the filaggrin gene (FLG) is the main predisposing factor for AD FLG mutations show ethnic and geographical variations, even between European populations. We sought to determine the frequency of the 3 most common FLG null mutations in a population of Spanish children consisting of healthy controls and AD patients. We also investigated the association between these 3 FLG mutations and AD.

METHODS

A total of 214 participants (111 AD patients and 103 healthy controls) were enrolled in this study. Genotyping for 3 FLG null mutations (R501X, 2282del4, and R2447X) was performed by conventional Sanger sequencing.

RESULTS

The combined mutation frequency was 1.9% in the control group and 12.6% in the AD group. The most common FLG mutation in AD patients was R501X (9.9%), followed by R2447X (2.7%) and 2282del4 (1.8%).

CONCLUSION

These findings further our understanding of the prevalence of FLG null mutations in the Spanish population, and suggest that the frequency of FLG mutations in AD patients in Spain is slightly higher than that of other Mediterranean countries.

Case report: two novel VPS13B mutations in a Chinese family with Cohen syndrome and hyperlinear palms

BACKGROUND

Cohen syndrome (CS) is an uncommon developmental disease with evident clinical heterogeneity. VPS13B is the only gene responsible for CS. Only few sporadic cases of CS have been reported in China.

CASE PRESENTATION

A Chinese family with two offspring-patients affected by developmental delay and intellectual disability was investigated in this study. Exome sequencing was performed, and compound heterozygous mutations in VPS13B were segregated for family members with autosomal recessive disorder. Splicing mutation c.3666 + 1G > T (exon 24) and nonsense mutation c. 9844 A > T:p.K3282X (exon 54) were novel. We revisited the family and learned that both patients are affected by microcephaly, developmental delay, neutropenia, and myopia and have a friendly disposition, all of which are consistent with CS phenotypes. We also found that both patients have hyperlinear palms, which their parents do not have. VPS13B mutations reported among the Chinese population were reviewed accordingly.

CONCLUSIONS

This study presents two novel VPS13B mutations in CS. The identification of hyperlinear palms in a family affected by CS expands the phenotype spectrum of CS.

The role of filaggrin in atopic dermatitis and allergic disease

OBJECTIVE

To provide an overview of filaggrin biology and the role of filaggrin variants in atopic dermatitis (AD) and allergic disease.

DATA SOURCES

We performed a PubMed literature review consisting mainly of studies relating to filaggrin in the last 5 years.

STUDY SELECTIONS

We selected articles that were found in PubMed using the search terms filaggrin, atopic dermatitis, skin barrier, and atopy.

RESULTS

Filaggrin plays an important role in the development of AD and allergic disease. Novel methods in measuring filaggrin expression and identifying filaggrin mutations aid in stratifying this patient cohort. We review new insights into understanding the role of filaggrin in AD and allergic disease.

CONCLUSION

Filaggrin remains a very important player in the pathogenesis of atopic dermatitis and allergic disease. This review looks at recent studies that aid our understanding of this crucial epidermal protein.

PEBBLES study protocol: a randomised controlled trial to prevent atopic dermatitis, food allergy and sensitisation in infants with a family history of allergic disease using a skin barrier improvement strategy

INTRODUCTION

The skin is an important barrier against environmental allergens, but infants have relatively impaired skin barrier function. There is evidence that impaired skin barrier function increases the risk of allergic sensitisation, atopic dermatitis (AD) and food allergy. We hypothesise that regular prophylactic use of emollients, particularly those that are designed to improve skin barrier structure and function, will help prevent these conditions. With the aim of determining if application of a ceramide-dominant emollient two times per day reduces the risk of AD and food allergy, we have commenced a multicentre phase III, outcome assessor blinded, randomised controlled trial of this emollient applied from birth to 6 months.

METHODS AND ANALYSIS

Infants (n=760) with a family history of allergic disease will be recruited from maternity hospitals in Melbourne. The primary outcomes are as follows: the presence of AD, assessed using the UK Working Party criteria, and food allergy using food challenge, in the first 12 months of life as assessed by a blinded study outcome assessor. Secondary outcomes are as follows: food sensitisation (skin prick test), skin barrier function, AD severity, the presence of new onset AD after treatment cessation (between 6 and 12 months) and the presence of parent reported AD/eczema. Recruitment commenced in March 2018.

ETHICS AND DISSEMINATION

The PEBBLES Study is approved by the Human Research Ethics Committees of the Royal Children's Hospital (RCH) (#37090A) and the Mercy Hospital for Women (2018-008). Parents or guardians will provide written informed consent. Outcomes will be disseminated through peer-reviewed publications and presented at scientific conferences.

TRIAL REGISTRATION NUMBERS

ACTRN12617001380381 and NCT03667651.

Racial differences in atopic dermatitis

OBJECTIVE

To summarize studies investigating ethnical and racial differences in atopic dermatitis (AD) epidemiology, clinical features, and skin and blood phenotypes.

DATA SOURCES

PubMed literature review (years 2000-2018).

STUDY SELECTIONS

Articles discussing primarily human disease.

RESULTS

Higher overall rates of AD were found in Africa and Oceania as opposed to India and Northern and Eastern Europe. In the United States, AD prevalence was found to be higher in African American (19.3%) compared with European American (16.1%) children. Although several studies have consistently found FLG loss-of-function mutations in up to 50% of European and 27% of Asian patients with AD, FLG mutations were 6 times less common in African American than in European American patients, even in patients with severe AD. Thus, FLG mutations seem to play less a pathogenic role in patients of African origin than in individuals of European or Asian ancestry. The immune phenotype of all ethnic groups was characterized by strong T_H2 activation, but important differences in immune polarization exist among the different ethnicities. Asian patients with AD had stronger T_H17/T_H22 activation than African American and European American patients with AD, whereas African American patients had the highest serum IgE levels among all groups, while largely lacking T_H1 and T_H17 activation.

CONCLUSION

AD is a heterogeneous disease that has differences among various ethnic and racial groups, which might be important for the development of future, targeted treatments and for personalized medicine approaches.

A clinician's reference guide for the management of atopic dermatitis in Asians

Background

Atopic dermatitis (AD) is a common skin condition among Asians. Recent studies have shown that Asian AD has a unique clinical and immunologic phenotype compared with European/American AD.

Objective

The Asian Academy of Dermatology and Venereology Expert Panel on Atopic Dermatitis developed this reference guide to provide a holistic and evidence-based approach in managing AD among Asians.

Methods

Electronic searches were performed to retrieve relevant systematic reviews and guidelines on AD. Recommendations were appraised for level of evidence and strength of recommendation based on the U.K. National Institute for Health and Care Excellence and Scottish Intercollegiate Guidelines Network guidelines. These practice points were based on the consensus recommendations discussed during the Asia Pacific Meeting of Experts in Dermatology held in Bali, Indonesia in October 2016 and April 2017.

Results

The Expert Panel recommends an approach to treatment based on disease severity. The use of moisturizers is recommended across all levels of AD severity, while topical steroids are recommended only for flares not controlled by conventional skin care and moisturizers. Causes of waning efficacy must be explored before using topical corticosteroids of higher potency. Topical calcineurin inhibitors are recommended for patients who have become recalcitrant to steroid, in chronic uninterrupted use, and when there is steroid atrophy, or when there is a need to treat sensitive areas and pediatric patients. Systemic steroids have a limited role in AD treatment and should be avoided if possible. Educational programs that allow a patient-centered approach in AD management are recommended as an adjunct to conventional therapies. Recommendations on the use of phototherapy, systemic drugs, and emerging treatments are also included.

Conclusion

The management of AD among Asians requires a holistic approach, integrating evidence-based treatments while considering accessibility and cultural acceptability.

A systematic review and meta-analysis of the regional and age-related differences in atopic dermatitis clinical characteristics

BACKGROUND

Previous studies found conflicting results about the commonality of different atopic dermatitis (AD) signs and symptoms.

OBJECTIVE

To determine the prevalences of AD characteristics and differences by region and age.

METHODS

A systematic review was performed of all published studies in MEDLINE, EMBASE, SCOPUS, LILACS, Cochrane, China National Knowledge Infrastructure, Taiwan Electronic Periodical Services, and CiNii that analyzed the proportion of AD characteristics. Two reviewers performed a review study titles and/or abstracts and data abstraction.

RESULTS

In all, 101 studies reported proportion of AD features with sufficient data for meta-analysis. The most prevalent AD features were pruritus, lichenification, and xerosis. There were differences in AD characteristics by study region. Flexural involvement was less commonly reported in India, the Americas, and Iran. Studies from East Asian reported more erythroderma and truncal, extensor, scalp, and auricular involvement. Studies from Southeast Asia reported more exudative eczema, truncal involvement, lichenification, and prurigo nodularis. Studies from Iran reported more head, face, and neck involvement; pityriasis alba; and xerosis. Studies from Africa reported more papular lichenoid lesions, palmar hyperlinearity, ichthyosis, and orbital darkening.

LIMITATIONS

Heterogeneity between studies and limited reporting of certain AD clinical characteristics.

CONCLUSIONS

AD characteristics are heterogeneous and vary by region and age.

Keratosis Pilaris and its Subtypes: Associations, New Molecular and Pharmacologic Etiologies, and Therapeutic Options

Keratosis pilaris is a common skin disorder comprising less common variants and rare subtypes, including keratosis pilaris rubra, erythromelanosis follicularis faciei et colli, and the spectrum of keratosis pilaris atrophicans. Data, and critical analysis of existing data, are lacking, so the etiologies, pathogeneses, disease associations, and treatments of these clinical entities are poorly understood. The present article aims to fill this knowledge gap by reviewing literature in the PubMed, EMBASE, and CINAHL databases and providing a comprehensive, analytical summary of the clinical characteristics and pathophysiology of keratosis pilaris and its subtypes through the lens of disease associations, genetics, and pharmacologic etiologies. Histopathologic, genomic, and epidemiologic evidence points to keratosis pilaris as a primary disorder of the pilosebaceous unit as a result of inherited mutations or acquired disruptions in various biomolecular pathways. Recent data highlight aberrant Ras signaling as an important contributor to the pathophysiology of keratosis pilaris and its subtypes. We also evaluate data on treatments for keratosis pilaris and its subtypes, including topical, systemic, and energy-based therapies. The effectiveness of various types of lasers in treating keratosis pilaris and its subtypes deserves wider recognition.

The Epidemiology of Food Allergy in the Global Context

There is a lack of high-quality evidence based on the gold standard of oral food challenges to determine food allergy prevalence. Nevertheless, studies using surrogate measures of food allergy, such as health service utilization and clinical history, together with allergen-specific immunoglobulin E (sIgE), provide compelling data that the prevalence of food allergy is increasing in both Western and developing countries. In Western countries, challenge-diagnosed food allergy has been reported to be as high as 10%, with the greatest prevalence noted among younger children. There is also growing evidence of increasing prevalence in developing countries, with rates of challenge-diagnosed food allergy in China and Africa reported to be similar to that in Western countries. An interesting observation is that children of East Asian or African descent born in a Western environment are at higher risk of food allergy compared to Caucasian children; this intriguing finding emphasizes the importance of genome-environment interactions and forecasts future increases in food allergy in Asia and Africa as economic growth continues in these regions. While cow’s milk and egg allergy are two of the most common food allergies in most countries, diverse patterns of food allergy can be observed in individual geographic regions determined by each country’s feeding patterns. More robust studies investigating food allergy prevalence, particularly in Asia and the developing world, are necessary to understand the extent of the food allergy problem and identify preventive strategies to cope with the potential increase in these regions.

Recent evolution of the human skin barrier

The skin is the first line of defense against the environment, with the epidermis as the outermost tissue providing much of the barrier function. Given its direct exposure to and encounters with the environment, the epidermis must evolve to provide an optimal barrier for the survival of an organism. Recent advances in genomics have identified a number of genes for the human skin barrier that have undergone evolutionary changes since humans diverged from chimpanzees. Here, we highlight a selection of key and innovative genetic findings for skin barrier evolution in our divergence from our primate ancestors and among modern human populations.

Epidemiology of adult atopic dermatitis

Atopic dermatitis (AD) is driven by a complex gene-environment interaction. Many of the risk factors and genetic underpinning previously observed for pediatric AD may not apply to adult atopic dermatitis, suggesting that these may largely be different disorders. Whereas AD is classically thought of as a pediatric disease, recent studies have shown high rates of disease in adults as well. Risk factors for persistence of childhood-onset AD, as well as adult-onset AD, are reviewed. Adults with AD are particularly vulnerable to exogenous insults from the outside environment, including climate, ultraviolet exposure, pollution, irritants and pruritogens, and microbes. Finally, adult AD is associated with a substantial health care burden, with increased utilization, direct and indirect costs of care, and lost work productivity.

How Different Parts of the World Provide New Insights Into Food Allergy

The prevalence and patterns of food allergy are highly variable in different parts of the world. Differences in food allergy epidemiology may be attributed to a complex interplay of genetic, epigenetic, and environmental factors, suggesting that mechanisms of food allergy may differ in various global populations. Genetic polymorphisms, migration, climate, and infant feeding practices all modulate food allergy risk, and possibly also the efficacy of interventions aimed at primary prevention of food allergy development. Approaches to diagnosis, treatment, and prevention of food allergy should thus be tailored carefully to each population's unique genetic and environmental make-up. Future research in the context of food allergy prevention should focus on elucidating factors determining differential responses between populations.

Immunologic, microbial, and epithelial interactions in atopic dermatitis

OBJECTIVE

To provide an overview of studies contributing to the understanding of immunologic, microbial, and epithelial interactions in atopic dermatitis.

DATA SOURCES

PubMed literature review (2000-2017) and meeting abstracts from recent international dermatology conferences.

STUDY SELECTIONS

Articles discussing primarily human disease.

RESULTS

Clinical studies showed that atopic dermatitis is a type 2 immune-centered disease with a systemic inflammatory component but with heterogeneous treatment responses. This suggests that other factors are likely involved in shaping the skin disease phenotype, including microbial dysbiosis and epidermal barrier dysfunction.

CONCLUSION

Recent clinical investigation has significantly expanded our knowledge on disease pathogenesis in atopic dermatitis, and current and future clinical trials will most likely further help to elucidate this complex, heterogeneous skin disease.

Differences in Genetic Variations Between Treatable and Recalcitrant Atopic Dermatitis in Korean

Purpose

Variations in barrier- or immune response-related genes are closely related to the development of atopic dermatitis (AD). This study was designed to identify genetic variations and clinical features to predict ‘recalcitrant AD.’

Methods

AD patients were classified as treatable and recalcitrant. Treatable AD patients showed satisfactory clinical improvement with basic and topical treatments. Recalcitrant AD patients used systemic immune-suppressants for over 4 weeks as they had not shown clinical improvement with basic and topical treatments. The frequency of gene variations in barrier- (FLG 3321delA, FLG K4022X, KLK7, SPINK 1156, SPINK 1188, SPINK 2475) and immune response- (DEFB1, KDR, IL-5RA, IL-9, and IL-12RB1a, b) related genes were compared between each AD group and the controls.

Results

Of all, 249 treatable AD and 32 recalcitrant AD were identified. Heterozygous mutations (Hetero) in KLK7 was more frequent in recalcitrant AD patients than treatable AD, without statistical significance. Hetero in DEFB1 was more frequent in treatable AD patients. However, no other significant genetic differences between treatable and recalcitrant AD was observed. Instead, higher initial Eczema Area Severity Index (EASI) score, serum immunoglobulin E (IgE) level, allergen specific IgE for house dust mites, and family history of atopic diseases were associated with recalcitrant AD with statistical significance.

Conclusions

According to our study, no genetic variation to predict recalcitrant AD was identified, suggesting that clinical manifestation, rather than genetic variations of AD patients is more likely to be an important factor in predicting the prognosis of AD. Further large-scale studies on the correlation between genetic variation and recalcitrant AD are needed.

Filaggrin Mutation in Korean Patients with Atopic Dermatitis

PURPOSE

Atopic dermatitis (AD) is a chronic, relapsing eczematous inflammatory skin disease. Mutations in the filaggrin gene (FLG) are major predisposing factors for AD. Ethnic differences exist between Asian and European populations in the frequency and spectrum of FLG mutations. Moreover, a distinct set of FLG mutations has been reported in Asian populations. The aim of this study was to examine the spectrum of FLG mutations in Koreans with AD. We also investigated the association of FLG mutations and clinical features of AD and compared the Korean FLG landscape with that of other East Asian countries.

MATERIALS AND METHODS

Seventy Korean patients with AD were enrolled in this study. Fourteen FLG mutations previously detected in Korean, Japanese, and Chinese patients were screened by genotyping.

RESULTS

Four FLG null mutations (3321delA, K4022X, S3296X, and S2889X) were identified in eleven patients (15.7%). The most commonly detected mutations in Korean patients with AD were 3321delA (n=6, 9.1%) and K4022X (n=3, 4.5%). FLG mutations were significantly associated with elevated IgE (≥200 KIU/L and/or MAST-CLA >3+, p=0.005), palmar hyperlinearity (p<0.001), and a family history of allergic disease (p=0.021).

CONCLUSION

This study expanded our understanding of the landscape of FLG mutations in Koreans and revealed an association between FLG mutations and AD phenotype.

A functional SNP associated with atopic dermatitis controls cell type-specific methylation of the VSTM1 gene locus

BACKGROUND

Expression quantitative trait loci (eQTL) databases represent a valuable resource to link disease-associated SNPs to specific candidate genes whose gene expression is significantly modulated by the SNP under investigation. We previously identified signal inhibitory receptor on leukocytes-1 (SIRL-1) as a powerful regulator of human innate immune cell function. While it is constitutively high expressed on neutrophils, on monocytes the SIRL-1 surface expression varies strongly between individuals. The underlying mechanism of regulation, its genetic control as well as potential clinical implications had not been explored yet.

METHODS

Whole blood eQTL data of a Chinese cohort was used to identify SNPs regulating the expression of VSTM1, the gene encoding SIRL-1. The genotype effect was validated by flow cytometry (cell surface expression), correlated with electrophoretic mobility shift assay (EMSA), chromatin immunoprecipitation (ChIP) and bisulfite sequencing (C-methylation) and its functional impact studied the inhibition of reactive oxygen species (ROS).

RESULTS

We found a significant association of a single CpG-SNP, rs612529T/C, located in the promoter of VSTM1. Through flow cytometry analysis we confirmed that primarily in the monocytes the protein level of SIRL-1 is strongly associated with genotype of this SNP. In monocytes, the T allele of this SNP facilitates binding of the transcription factors YY1 and PU.1, of which the latter has been recently shown to act as docking site for modifiers of DNA methylation. In line with this notion rs612529T associates with a complete demethylation of the VSTM1 promoter correlating with the allele-specific upregulation of SIRL-1 expression. In monocytes, this upregulation strongly impacts the IgA-induced production of ROS by these cells. Through targeted association analysis we found a significant Meta P value of 1.14 × 10^-6 for rs612529 for association to atopic dermatitis (AD).

CONCLUSION

Low expression of SIRL-1 on monocytes is associated with an increased risk for the manifestation of an inflammatory skin disease. It thus underlines the role of both the cell subset and this inhibitory immune receptor in maintaining immune homeostasis in the skin. Notably, the genetic regulation is achieved by a single CpG-SNP, which controls the overall methylation state of the promoter gene segment.

Atopic Dermatitis Susceptibility Variants in Filaggrin Hitchhike Hornerin Selective Sweep

Human skin has evolved rapidly, leaving evolutionary signatures in the genome. The filaggrin (FLG) gene is widely studied for its skin-barrier function in humans. The extensive genetic variation in this gene, especially common loss-of-function (LoF) mutations, has been established as primary risk factors for atopic dermatitis. To investigate the evolution of this gene, we analyzed 2,504 human genomes and genotyped the copy number variation of filaggrin repeats within FLG in 126 individuals from diverse ancestral backgrounds. We were unable to replicate a recent study claiming that LoF of FLG is adaptive in northern latitudes with lower ultraviolet light exposure. Instead, we present multiple lines of evidence suggesting that FLG genetic variation, including LoF variants, have little or no effect on fitness in modern humans. Haplotype-level scrutinization of the locus revealed signatures of a recent selective sweep in Asia, which increased the allele frequency of a haplotype group (Huxian haplogroup) in Asian populations. Functionally, we found that the Huxian haplogroup carries dozens of functional variants in FLG and hornerin (HRNR) genes, including those that are associated with atopic dermatitis susceptibility, HRNR expression levels and microbiome diversity on the skin. Our results suggest that the target of the adaptive sweep is HRNR gene function, and the functional FLG variants that involve susceptibility to atopic dermatitis, seem to hitchhike the selective sweep on HRNR. Our study presents a novel case of a locus that harbors clinically relevant common genetic variation with complex evolutionary trajectories.

Role of environmental exposures and filaggrin mutations on associations of ethnic origin with risk of childhood eczema. The Generation R Study

BACKGROUND

The prevalence of childhood eczema varies considerably between ethnic groups. However, data from longitudinal studies remain scarce.

METHODS

We examined the associations of ethnic origin with the development of eczema from birth until the age of 4 years, and whether known environmental and genetic risk factors explain these associations. This study was performed in a multiethnic population-based prospective cohort among 5,082 children. Ethnic origin was based on the parents' country of birth. Data on physician-diagnosed eczema were obtained by annual questionnaires. Information on environmental risk factors was mostly obtained by questionnaires. Filaggrin (FLG) mutations (2282del4, R2447X, R501X, and S3247X) were genotyped for 3,096 children. We used generalized estimating equation models to examine the associations of ethnic origin with the longitudinal odds of eczema at 6 months and 1, 2, 3, and 4 years of age overall and independently.

RESULTS

Compared with Dutch children, Cape Verdean, Dutch Antillean, Surinamese-Creole, and Surinamese-Hindustani children had overall increased risks of eczema (OR (95%-CI): 1.53 (1.15, 2.03), 1.60 (1.21, 2.12), 1.95 (1.56, 2.44), and 2.06 (1.65, 2.57), respectively). Effect estimates for the associations of Cape Verdean and Dutch Antillean origin with eczema became non-significant after adjustment for genetic risk factors or both environmental and genetic risk factors, respectively. Surinamese-Creole and Surinamese-Hindustani children remained to have increased risks of eczema.

CONCLUSIONS

Cape Verdean, Dutch Antillean, Surinamese-Creole, and Surinamese-Hindustani children had increased risks of eczema in the first 4 years of life. Environmental and genetic risk factors partly weakened these associations.