Filaggrin Gene Mutation c.3321delA is Associated with Dry Phenotypes of Atopic Dermatitis in the Chinese Han Population

Phenotypes, endotypes and genotypes of atopic dermatitis and allergy in populations of African ancestry on the continent and diaspora

Atopic dermatitis is a complex inflammatory condition characterized by synergist interactions between epidermal and immune related genotypes, skin barrier defects and immune dysregulation as well as microbial dysbiosis. Ethnicity-specific variations in clinical presentation, immune endotypes and genetic susceptibility have been described in diverse populations. We summarize available data with specific consideration of AD in populations of African ancestry. Some highlights include the observation of AD lesions on extensor surfaces, lichen planus-like AD, prurigo type AD and follicular AD in African populations. In addition, a consistent absence of dominant filaggrin gene defects has been reported. The detection of normal filaggrin protein content in AD skin implicates the contribution of alternative mechanisms in the pathogenesis of AD in African patients. Markedly high IgE has been described in paediatric and adult African AD. While Th2, Th22 and Th17 activation in African AD skin shares the same direction as with other populations, it has been noted that the magnitude of activation is dissimilar. Reduced Th17 cytokines have been observed in the circulation of moderate to severe paediatric 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.

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.

Epidemiology and Characterization of Atopic Dermatitis in East Asian Populations: A Systematic Review

Introduction

As atopic dermatitis (AD) grows increasingly prevalent in Asian populations worldwide, understanding how environmental, genetic, and cultural factors uniquely influence AD in Asians is essential for informing disease management. Our objectives were to characterize the epidemiology of AD in East Asian populations with sensitivity to the changing demographics of AD in these populations and the effects of urbanization and immigration.

Methods

A systematic review was performed on epidemiologic studies of AD in East Asian populations over the past 10 years.

Results

There is a rising prevalence of both pediatric and adult AD in Asian populations worldwide, particularly in Asians living in urban areas. Studies suggest that the children of Asian immigrants may be at higher risk for developing AD, potentially resulting from epigenetic phenomena unique to immigrant populations. A number of genetic polymorphisms implicated in AD are shared by Asian populations around the world and appear to be rare among other ethnic populations.

Conclusions

As the prevalence of AD continues to increase in Asian populations, it is important to understand its distinct genetic and pathophysiologic profile in these populations, as well as characterize the cultural beliefs and practices surrounding its treatment. Future research should aim to capitalize on our growing understanding of pathophysiologic differences to inform the most promising treatments for AD in Asians. Additionally, the impact of immigration on AD suggests that further investigation of these trends may lead to a greater understanding of the epigenetics of AD.

Aryl hydrocarbon receptor polymorphisms are associated with dry skin phenotypes in Chinese patients with atopic dermatitis

BACKGROUND

Epidermal barrier dysfunction is the initial event in the development of atopic dermatitis (AD). Recent studies have identified a crucial role for the aryl hydrocarbon receptor (AHR) in controlling the gene expression of filaggrin and other skin barrier proteins, suggesting an underlying association between AHR and AD pathogenesis.

AIM

To investigate the role of AHR gene polymorphisms in the susceptibility to AD and in AD-associated phenotypes.

METHODS

We enrolled 487 patients with AD, 210 patients with psoriasis and 226 healthy controls (HCs) from the Han Chinese population, and genotyped two AHR single-nucleotide polymorphisms (rs10249788 and rs2066853) by PCR and subsequent DNA sequencing.

RESULTS

The AHR rs10249788 and rs2066853 polymorphisms were found in both sets of patients (AD and psoriasis) and in HCs, but no significant differences were detected in genotype or allele frequencies between the three groups. However, patients with AD with the rs10249788 (CT/TT) or rs2066853 (AG + AA) genotype were more likely to have severe dry skin scores. In the stratification analysis, the AHR rs2066853 (AG + AA) and rs10249788 (CT + TT) genotypes could predict a higher risk of severe dry skin phenotypes in the male, early-onset and allergic rhinitis subgroups. Furthermore, the combined rs10249788 (CT + TT) and rs2066853 (AG + AA) genotypes led to a higher risk for severe dry skin in patients with AD.

CONCLUSION

AHR polymorphisms are not associated with the risk of AD; however, they may predict a dry skin phenotype in patients with AD.