Low filaggrin monomer repeats in African American pediatric patients with moderate to severe atopic dermatitis

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.

Racial and Ethnic Differences in Sociodemographic, Clinical, and Treatment Characteristics Among Patients with Atopic Dermatitis in the United States and Canada: Real-World Data from the CorEvitas Atopic Dermatitis Registry

INTRODUCTION

This real-world, cross-sectional study compared sociodemographic, clinical and treatment characteristics, and patient-reported outcomes (PROs) among racial/ethnic groups in patients with atopic dermatitis (AD) who are candidates for systemic therapy.

METHODS

This study included adults with dermatologist- or dermatology practitioner-diagnosed AD enrolled in the CorEvitas AD Registry (July 2020-July 2021). All patients initiated systemic therapy within 12 months prior to or at enrollment or had moderate-to-severe AD (vIGA-AD® ≥ 3 and Eczema Area and Severity Index [EASI] ≥ 12) at enrollment. Patients were categorized into five mutually exclusive racial/ethnic groups: non-Hispanic White, Black, Asian, Other/Multiracial, and Hispanic (any race). Patient, clinical, and treatment characteristics were captured at enrollment. Differences in means or proportions of characteristics among racial/ethnic groups were descriptively summarized using effect sizes. Adjusted prevalence ratios and mean differences were estimated (White race/ethnicity group as the reference category) with 95% confidence intervals (CI).

RESULTS

Among 1288 patients, 64% (n = 822) were White, 13% (n = 167) Black, 10% (n = 129) Asian, 8% (n = 97) Hispanic, and 6% (n = 73) Other/Multiracial. In adjusted analyses, statistically more severe EASI lichenification was noted among Black compared with White patients at the head and neck (mean difference, 0.21, [95% CI 0.06, 0.36]; p = 0.01), trunk (0.32, [0.17, 0.47]; p < 0.001), upper extremities (0.27, [0.09, 0.44]; p = 0.008), and lower extremities (0.39, [0.21, 0.57]; p < 0.001). Statistically more severe EASI lichenification was observed among Asian vs White patients in certain areas (mean difference, head and neck, 0.22 [0.04, 0.39], p = 0.01; trunk, 0.25 [0.07, 0.43], p < 0.001; lower extremities, 0.22 [0.01, 0.43], p < 0.001) and SCORing for AD lichenification (mean difference: 0.34 [0.15, 0.52]; p < 0.001). Significantly higher mean pruritus over the past 7 days for Black (mean difference: 0.63 [0.01, 1.26] and Hispanic patients (0.60 [0.11, 1.09]; p = 0.03) vs White patients was observed. Among AD clinical features, the prevalence of facial erythema was significantly lower among Black compared with White patients (prevalence ratio = 0.38, [0.22, 0.67]; p = 0.007).

CONCLUSION

Racial/ethnic differences exist in sociodemographic, clinical and treatment characteristics, disease severity, and PROs among real-world AD patients who are candidates for systemic therapy. Recognizing these variations may be of critical importance for dermatologists for the design and delivery of targeted/personalized medicine approaches.

RELEVANCE OF CODING VARIATION IN FILAGGRIN AND DOCK8 IN FINNISH PEDIATRIC PATIENTS WITH EARLY-ONSET MODERATE-TO-SEVERE ATOPIC DERMATITIS

Early-onset, persistent atopic dermatitis (AD) is proposed as a distinct subgroup that may have specific genotypic features. FLG gene loss-of-function variants are the best known genetic factors contributing to epidermal barrier impairment and eczema severity. In a cohort of 140 Finnish children with early-onset moderate-to-severe AD, we investigated the effect of coding variation in FLG and 13 other genes with epidermal barrier or immune function through the use of targeted amplicon sequencing and genotyping. A FLG loss-of-function variant (Arg501Ter, Ser761fs, Arg2447Ter, or Ser3247Ter) was identified in 20 of 140 patients showing higher transepidermal water loss values than patients without these variants. Total FLG loss-of-function variant frequency (7.14%) was significantly higher than in the general Finnish population (2.34%). When tested separately, only Arg2447Ter showed a significant association with AD (P = 0.003104). In addition, a modest association with moderate-to-severe pediatric AD was seen for rs12730241 and rs6587667 (FLG2:Gly137Glu). Loss-of-function variants, previously reported pathogenic variants, or statistically significant enrichment of nonsynonymous coding region variants were not found in the 13 candidate genes studied by amplicon sequencing. However, higher IgE and eosinophil counts were found in carriers of potentially pathogenic DOCK8 missense variants, suggesting that the role of DOCK8 variation in AD should be further investigated in larger cohorts.

Art of prevention: Atopic dermatitis in women and families of color-prevalence, recognition, and prevention

Atopic dermatitis (AD) is one of the most common skin conditions encountered by dermatologists. Skin of color (SOC) patients, in particular, are 50% more likely to visit a dermatologist for AD than non-SOC patients. While the misdiagnosis of AD in SOC patients is rare, the misinterpretation of severity or undertreatment of disease experienced by this patient population is a common occurrence. Herein, we present this Art of Prevention piece focused on the epidemiology, presentation, treatment, and management of AD in skin of color patients.

No Association of filaggrin copy number variation and atopic dermatitis risk in White and Black Americans

Atopic dermatitis (AD) is a chronic, inflammatory skin condition with a multifactorial pathophysiology. The filaggrin gene (FLG) has particularly been implicated given loss of function (LoF) mutations in this gene lead to skin barrier dysfunction and such mutations can increase a patient's likelihood of developing AD. FLG has intragenic copy number variation (CNV), which impacts the total amount of filaggrin produced. Previous research reported a dose-dependent effect such that as amount of FLG increases, risk of AD decreases. To gain a better understanding, we evaluated FLG CNV in a large case-control study of Whites and Blacks with and without AD. The goal of our study was to determine whether FLG CNV has a dose-dependent effect on the risk of developing AD and to determine whether FLG CNV varies by race. The frequencies and odds ratios comparing a given CNV by race or race within those with AD did not significantly vary. It had been thought that FLG CNV might vary by race and represent an important association with AD in Black AD subjects. However, our work suggests that while there are racial differences with respect to CNV, these differences do not appear to explain AD risk.

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 gene mutations with special reference to atopic dermatitis

Purpose of review

Mutations in the Filaggrin gene can cause absent or reduced filaggrin protein, leading to impaired keratinization and skin barrier defect, which produce characteristic phenotypes. In this short review, we report current evidence on the topic with special reference to atopic dermatitis, suggest future directions, and discuss therapeutic implications.

Recent findings

Numerous candidate gene association studies, genome-wide association studies, studies on copy number variations and most recently, sequencing studies, have confirmed the robust association of mutations in the Filaggrin gene with atopic dermatitis, and have also linked these mutations with several other disorders.

Summary

Filaggrin gene defects remain the strongest identified genetic risk factors for atopic dermatitis. Taken in conjunction with other genes found to be associated with this condition, genetic screening and identification of individuals at risk for atopic dermatitis could lead to personalized therapy. Manipulation of genetic regulatory elements to increase the amount of filaggrin protein in deficient individuals is an attractive treatment option for the future.

Common Skin Disorders in Pediatric Skin of Color

Children with skin of color represent a large proportion of the pediatric population. There are numerous skin conditions that commonly occur in this population, including but not limited to acne, atopic dermatitis, pityriasis alba, tinea versicolor, progressive macular hypomelanosis, traction alopecia, and confluent and reticulated papillomatosis. This article highlights the clinical presentations of these conditions in skin of color and briefly addresses pathophysiology and treatment modalities.

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.

Tiled array-based sequencing identifies enrichment of loss-of-function variants in the highly homologous filaggrin gene in African-American children with severe atopic dermatitis

Filaggrin (FLG) loss-of-function (LOF) variants are a major risk factor for the common inflammatory skin disease, atopic dermatitis (AD) and are often population-specific. African-American (AA) children are disproportionately affected with AD, often later developing asthma and/or allergic rhinitis and comprise an atopy health disparity group for which the role of FLG LOF is not well known. Discovery of FLG LOF using exome sequencing is challenging given the known difficulties for accurate short-read alignment to FLG's high homology repeat variation. Here, we employed an array-based sequencing approach to tile across each FLG repeat and discover FLG LOF in a well-characterized cohort of AA children with moderate-to-severe AD. Five FLG LOF were identified in 23% of our cohort. Two novel FLG LOF singletons, c.488delG and p.S3101*, were discovered as well as p.R501*, p.R826* and p.S3316* previously reported for AD. p.S3316* (rs149484917) is likely an African ancestral FLG LOF, reported in African individuals in ExAC (Exome Aggregation Consortium), Exome Variant Server (ESP), and 4 African 1000G population databases (ESN, MSL, ASW, and ACB). The proportion of FLG LOF (11.5%) among the total FLG alleles in our cohort was significantly higher in comparisons with FLG LOF reported for African individuals in ExAC (2.5%; P = 4.3 × 10^-4 ) and ESP (1.7%; P = 3.5 × 10^-5 ) suggesting a disease-enrichment effect for FLG LOF. Our results demonstrate the utility of array-based sequencing in discovering FLG LOF, including novel and population-specific, which are of higher prevalence in our AA severe AD group than previously reported.

Intragenic Copy Number Variation in the Filaggrin Gene in Ethiopian Patients with Atopic Dermatitis

Genetic variants in filaggrin (FLG) involving truncating mutations or intragenic copy number variation are strongly associated with the risk of developing atopic dermatitis (AD) in European and Asian populations. Few loss-of-function mutations have been identified in Africans, although an association between FLG copy number variation and AD severity in a small African American cohort has been proposed. We studied the association between FLG copy number and AD in 132 Ethiopians and found no association between AD severity and FLG copy number, suggesting that other, still unidentified genetic factors are of more importance in predisposing Ethiopians to AD.

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.

The genetics of the skin barrier in eczema and other allergic disorders

PURPOSE OF REVIEW

We summarize current knowledge on the genetic determinants of skin barrier deficiency in relation to eczema and disease progression to other allergic manifestations.

RECENT FINDINGS

There is increasing evidence that impairment of epidermal barrier function is not only a risk factor for the development of eczema but also for disease progression to allergic airway disease and food allergy. Support comes from recent association studies linking genetic variants in epidermal genes with eczema and food allergy, from monogenic diseases with severe skin barrier defects which display multiple allergic manifestations, and from mouse models providing a mechanism from skin inflammation to allergic reactions in the lung and intestine.

SUMMARY

The key role of the skin barrier defect in the development of eczema and eczema-associated allergic diseases may have important implications for prevention and treatment strategies. Initial clinical trials with moisturizing creams revealed promising results for the prevention of eczema in early infancy. Their long-term effects will be critical to demonstrate the potential benefit of barrier repair therapy in allergic disease prevention.