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Khatib CM, Klein-Petersen AW, Rønnstad ATM, Egeberg A, Christensen MO, Silverberg JI, Thomsen SF, Irvine AD, Thyssen JP. Increased loss-of-function filaggrin gene mutation prevalence in atopic dermatitis patients across northern latitudes indicates genetic fitness: A systematic review and meta-analysis. Exp Dermatol 2024; 33:e15130. [PMID: 38989976 DOI: 10.1111/exd.15130] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/12/2023] [Revised: 05/23/2024] [Accepted: 06/24/2024] [Indexed: 07/12/2024]
Abstract
Loss-of-function (LoF) mutations in the filaggrin gene (FLG) constitute the strongest genetic risk for atopic dermatitis (AD). A latitude-dependent difference in the prevalence of LoF FLG mutations was systematically evaluated. A systematic review and meta-analysis were performed to estimate the prevalence of LoF FLG mutations in AD patients and the general population by geography and ethnicity. Risk of bias was assessed by Newcastle-Ottawa Scale and Jadad score. StatsDirect, version 3 software was used to calculate all outcomes. PubMed and EMBASE were searched until 9th December 2021. Studies were included if they contained data on the prevalence of LoF FLG mutations in AD patients or from the general population or associations between AD and LoF FLG mutations and were authored in English. Overall, 248 studies and 229 310 AD patients and individuals of the general population were included in the quantitative analysis. The prevalence of LoF FLG mutations was 19.1% (95% CI, 17.3-21.0) in AD patients and 5.8% (95% CI, 5.3-6.2) in the general population. There was a significant positive association between AD and LoF FLG mutations in all latitudes in the Northern hemisphere, but not in all ethnicities. The prevalence of LoF FLG mutations became gradually more prevalent in populations residing farther north of the Equator but was negligible in Middle Easterners and absent in most African populations. FLG LoF mutations are common and tend to increase with northern latitude, suggesting potential clinical implications for future AD management. The existence of possible genetic fitness from FLG LoF mutations remains unknown.
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Affiliation(s)
- Casper Milde Khatib
- Department of Dermatology, Bispebjerg Hospital, University of Copenhagen, Copenhagen, Denmark
| | | | | | - Alexander Egeberg
- Department of Dermatology, Bispebjerg Hospital, University of Copenhagen, Copenhagen, Denmark
| | | | | | - Simon Francis Thomsen
- Department of Dermatology, Bispebjerg Hospital, University of Copenhagen, Copenhagen, Denmark
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2
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Lunjani N, Kerbelker T, Mdletshe FB, Hlela C, O’Mahony L. Phenotypes, endotypes and genotypes of atopic dermatitis and allergy in populations of African ancestry on the continent and diaspora. FRONTIERS IN ALLERGY 2024; 4:1203304. [PMID: 38327736 PMCID: PMC10847302 DOI: 10.3389/falgy.2023.1203304] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/10/2023] [Accepted: 12/11/2023] [Indexed: 02/09/2024] Open
Abstract
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.
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Affiliation(s)
- N. Lunjani
- APC Microbiome Ireland, University College Cork, Cork, Ireland
- Division of Dermatology, University of Cape Town, Cape Town, South Africa
| | - T. Kerbelker
- Department of Peadiatrics, University of Cape Town, Cape Town, South Africa
| | - F. B. Mdletshe
- Division of Otorhinolaryngology, University of Witwatersrand, Johannesburg, South Africa
| | - C. Hlela
- Division of Dermatology, University of Cape Town, Cape Town, South Africa
| | - L. O’Mahony
- APC Microbiome Ireland, University College Cork, Cork, Ireland
- Department of Medicine, University College Cork, Cork, Ireland
- School of Microbiology, University College Cork, Cork, Ireland
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3
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Grafanaki K, Antonatos C, Maniatis A, Petropoulou A, Vryzaki E, Vasilopoulos Y, Georgiou S, Gregoriou S. Intrinsic Effects of Exposome in Atopic Dermatitis: Genomics, Epigenomics and Regulatory Layers. J Clin Med 2023; 12:4000. [PMID: 37373692 DOI: 10.3390/jcm12124000] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/12/2023] [Revised: 06/03/2023] [Accepted: 06/09/2023] [Indexed: 06/29/2023] Open
Abstract
Atopic dermatitis (AD) or atopic eczema is an increasingly manifested inflammatory skin disorder of complex etiology which is modulated by both extrinsic and intrinsic factors. The exposome includes a person's lifetime exposures and their effects. We recently reviewed the extrinsic exposome's environmental risk factors that contribute to AD. The periods of pregnancy, infancy, and teenage years are recognized as crucial stages in the formation of AD, where the exposome leads to enduring impacts on the immune system. However, research is now focusing on the interactions between intrinsic pathways that are modulated by the extrinsic exposome, including genetic variation, epigenetic modifications, and signals, such as diet, stress, and microbiome interactions. As a result, immune dysregulation, barrier dysfunction, hormonal fluctuations, and skin microbiome dysbiosis are important factors contributing to AD development, and their in-depth understanding is crucial not only for AD treatment but also for similar inflammatory disorders.
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Affiliation(s)
- Katerina Grafanaki
- Department of Dermatology-Venereology, School of Medicine, University of Patras, 26504 Patras, Greece
- Department of Biochemistry, School of Medicine, University of Patras, 26504 Patras, Greece
| | - Charalabos Antonatos
- Laboratory of Genetics, Section of Genetics, Cell Biology and Development, Department of Biology, University of Patras, 26504 Patras, Greece
| | - Alexandros Maniatis
- Department of Biochemistry, School of Medicine, University of Patras, 26504 Patras, Greece
| | - Antonia Petropoulou
- Department of Biochemistry, School of Medicine, University of Patras, 26504 Patras, Greece
| | - Eleftheria Vryzaki
- Department of Dermatology-Venereology, School of Medicine, University of Patras, 26504 Patras, Greece
| | - Yiannis Vasilopoulos
- Laboratory of Genetics, Section of Genetics, Cell Biology and Development, Department of Biology, University of Patras, 26504 Patras, Greece
| | - Sophia Georgiou
- Department of Dermatology-Venereology, School of Medicine, University of Patras, 26504 Patras, Greece
| | - Stamatis Gregoriou
- Department of Dermatology-Venereology, Faculty of Medicine, Andreas Sygros Hospital, National and Kapodistrian University of Athens, 16121 Athens, Greece
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4
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Berna R, Mitra N, Hoffstad O, Wubbenhorst B, Nathanson KL, Margolis DJ. Using a Machine Learning Approach to Identify Low-Frequency and Rare FLG Alleles Associated with Remission of Atopic Dermatitis. JID INNOVATIONS 2021; 1:100046. [PMID: 34909743 PMCID: PMC8659778 DOI: 10.1016/j.xjidi.2021.100046] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/01/2021] [Revised: 06/28/2021] [Accepted: 06/29/2021] [Indexed: 12/29/2022] Open
Abstract
Atopic dermatitis (AD) is a common relapsing inflammatory skin disease. FLG is the gene most consistently associated with AD. Loss-of-function variants in FLG have been previously associated with AD. Low-frequency and rare alleles (minor allele frequency < 5%) in this gene have been given less attention than loss-of-function variants. We fine sequenced the FLG gene in a cohort of individuals with AD. We developed a machine learning‒based algorithm to associate low-frequency and rare alleles with the disease. We then applied this algorithm to the FLG data, searching for associations between groups of low-frequency and rare FLG alleles and AD remission. A group of 46 rare and low-frequency FLG alleles was associated with increased AD remission (P = 2.76e-11). Overall, 16 of these 46 FLG variants were identified in an independent cohort and were associated with decreased AD incidence (P = 0.0007). This study presents an application of statistical methods in AD genetics and suggests that low-frequency and rare alleles may play a larger role in AD pathogenesis than previously appreciated.
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Affiliation(s)
- Ronald Berna
- Department of Dermatology, University of Pennsylvania, Philadelphia, Pennsylvania, USA
| | - Nandita Mitra
- Department of Biostatistics, Epidemiology, and Informatics, University of Pennsylvania, Philadelphia, Pennsylvania, USA
| | - Ole Hoffstad
- Department of Dermatology, University of Pennsylvania, Philadelphia, Pennsylvania, USA
| | - Bradley Wubbenhorst
- Division of Translational Medicine and Human Genetics, Department of Medicine, University of Pennsylvania, Philadelphia, Pennsylvania, USA
| | - Katherine L Nathanson
- Division of Translational Medicine and Human Genetics, Department of Medicine, University of Pennsylvania, Philadelphia, Pennsylvania, USA
| | - David J Margolis
- Department of Dermatology, University of Pennsylvania, Philadelphia, Pennsylvania, USA.,Department of Biostatistics, Epidemiology, and Informatics, University of Pennsylvania, Philadelphia, Pennsylvania, USA
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Cracking the Skin Barrier: Liquid-Liquid Phase Separation Shines under the Skin. JID INNOVATIONS 2021; 1:100036. [PMID: 34909733 PMCID: PMC8659386 DOI: 10.1016/j.xjidi.2021.100036] [Citation(s) in RCA: 8] [Impact Index Per Article: 2.7] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/27/2021] [Revised: 06/07/2021] [Accepted: 06/18/2021] [Indexed: 12/25/2022] Open
Abstract
Central to forming and sustaining the skin’s barrier, epidermal keratinocytes (KCs) fluxing to the skin surface undergo a rapid and enigmatic transformation into flat, enucleated squames. At the crux of this transformation are intracellular keratohyalin granules (KGs) that suddenly disappear as terminally differentiating KCs transition to the cornified skin surface. Defects in KGs have long been linked to skin barrier disorders. Through the biophysical lens of liquid-liquid phase separation (LLPS), these enigmatic KGs recently emerged as liquid-like membraneless organelles whose assembly and subsequent pH-triggered disassembly drive squame formation. To stimulate future efforts toward cracking the complex process of skin barrier formation, in this review, we integrate the key concepts and foundational work spanning the fields of LLPS and epidermal biology. We review the current progress in the skin and discuss implications in the broader context of membraneless organelles across stratifying epithelia. The discovery of environmentally sensitive LLPS dynamics in the skin points to new avenues for dissecting the skin barrier and for addressing skin barrier disorders. We argue that skin and its appendages offer outstanding models to uncover LLPS-driven mechanisms in tissue biology.
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Key Words
- 3D, three-dimensional
- AD, atopic dermatitis
- CE, cornified envelope
- EDC, epidermal differentiation complex
- ER, endoplasmic reticulum
- IDP, intrinsically-disordered protein
- KC, keratinocyte
- KG, keratohyalin granule
- LCST, lower critical solution temperature
- LLPS, liquid-liquid phase separation
- PTM, post-translational modification
- TG, trichohyalin granule
- UCST, upper critical solution temperature
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Fulton RL, Margolis DJ, Sockler PG, Mitra N, Wong XFCC, Common JE. No Association of filaggrin copy number variation and atopic dermatitis risk in White and Black Americans. Exp Dermatol 2021; 31:233-236. [PMID: 34407261 DOI: 10.1111/exd.14449] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/03/2021] [Revised: 08/04/2021] [Accepted: 08/16/2021] [Indexed: 01/10/2023]
Abstract
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.
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Affiliation(s)
- Rachel L Fulton
- Department of Dermatology, University of Pennsylvania Perelman School of Medicine, Philadelphia, PA, USA.,Department of Biostatistics and Epidemiology, University of Pennsylvania Perelman School of Medicine, Philadelphia, PA, USA
| | - David J Margolis
- Department of Dermatology, University of Pennsylvania Perelman School of Medicine, Philadelphia, PA, USA.,Department of Biostatistics and Epidemiology, University of Pennsylvania Perelman School of Medicine, Philadelphia, PA, USA
| | - Patrick G Sockler
- Department of Dermatology, University of Pennsylvania Perelman School of Medicine, Philadelphia, PA, USA
| | - Nandita Mitra
- Department of Biostatistics and Epidemiology, University of Pennsylvania Perelman School of Medicine, Philadelphia, PA, USA
| | | | - John E Common
- A⁎STAR, Skin Research Institute of Singapore, Singapore
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Zhu Y, Mitra N, Feng Y, Tishkoff S, Hoffstad O, Margolis D. FLG Variation Differs between European Americans and African Americans. J Invest Dermatol 2021; 141:1855-1857. [PMID: 33493532 PMCID: PMC8238796 DOI: 10.1016/j.jid.2020.12.022] [Citation(s) in RCA: 5] [Impact Index Per Article: 1.7] [Reference Citation Analysis] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/10/2020] [Revised: 12/07/2020] [Accepted: 12/22/2020] [Indexed: 01/02/2023]
Affiliation(s)
- Yaqian Zhu
- Department of Biostatistics, Epidemiology & Informatics, Perelman School of Medicine, University of Pennsylvania, Philadelphia, Pennsylvania, USA.
| | - Nandita Mitra
- Department of Biostatistics, Epidemiology & Informatics, Perelman School of Medicine, University of Pennsylvania, Philadelphia, Pennsylvania, USA
| | - Yuanqing Feng
- Departments of Genetics, Perelman School of Medicine, University of Pennsylvania, Philadelphia, Pennsylvania, USA
| | - Sarah Tishkoff
- Departments of Genetics, Perelman School of Medicine, University of Pennsylvania, Philadelphia, Pennsylvania, USA; Department of Biology, School of Arts & Sciences, University of Pennsylvania, Philadelphia, Pennsylvania, USA
| | - Ole Hoffstad
- Department of Dermatology, Perelman School of Medicine, University of Pennsylvania, Philadelphia, Pennsylvania, USA
| | - David Margolis
- Department of Biostatistics, Epidemiology & Informatics, Perelman School of Medicine, University of Pennsylvania, Philadelphia, Pennsylvania, USA; Department of Dermatology, Perelman School of Medicine, University of Pennsylvania, Philadelphia, Pennsylvania, USA
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8
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Gilhar A, Reich K, Keren A, Kabashima K, Steinhoff M, Paus R. Mouse models of atopic dermatitis: a critical reappraisal. Exp Dermatol 2021; 30:319-336. [PMID: 33368555 DOI: 10.1111/exd.14270] [Citation(s) in RCA: 28] [Impact Index Per Article: 9.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/09/2020] [Revised: 12/17/2020] [Accepted: 12/17/2020] [Indexed: 12/13/2022]
Abstract
Mouse models for atopic dermatitis (AD) are an indispensable preclinical research tool for testing new candidate AD therapeutics and for interrogating AD pathobiology in vivo. In this Viewpoint, we delineate why, unfortunately, none of the currently available so-called "AD" mouse models satisfactorily reflect the clinical complexity of human AD, but imitate more "allergic" or "irriant" contact dermatitis conditions. This limits the predictive value of AD models for clinical outcomes of new tested candidate AD therapeutics and the instructiveness of mouse models for human AD pathophysiology research. Here, we propose to initiate a rational debate on the minimal criteria that a mouse model should meet in order to be considered relevant for human AD. We suggest that valid AD models should at least meet the following criteria: (a) an AD-like epidermal barrier defect with reduced filaggrin expression along with hyperproliferation, hyperplasia; (b) increased epidermal expression of thymic stromal lymphopoietin (TSLP), periostin and/or chemokines such as TARC (CCL17); (c) a characteristic dermal immune cell infiltrate with overexpression of some key cytokines such as IL-4, IL-13, IL-31 and IL-33; (d) distinctive "neurodermatitis" features (sensory skin hyperinnervation, defective beta-adrenergic signalling, neurogenic skin inflammation and triggering or aggravation of AD-like skin lesions by perceived stress); and (e) response of experimentally induced skin lesions to standard AD therapy. Finally, we delineate why humanized AD mouse models (human skin xenotransplants on SCID mice) offer a particularly promising preclinical research alternative to the currently available "AD" mouse models.
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Affiliation(s)
- Amos Gilhar
- Skin Research Laboratory, Rappaport Faculty of Medicine, Technion -Israel Institute of Technology, Haifa, Israel.,Rambam Health Care Campus, Haifa, Israel
| | - Kristian Reich
- Centre for Translational Research in Inflammatory Skin Diseases, Institute for Health Services Research in Dermatology and Nursing, University Medical Center Hamburg-Eppendorf, Hamburg, Germany.,Skinflammation Center, Hamburg, Germany
| | - Aviad Keren
- Skin Research Laboratory, Rappaport Faculty of Medicine, Technion -Israel Institute of Technology, Haifa, Israel
| | - Kenji Kabashima
- Department of Dermatology, Kyoto University Graduate School of Medicine, Kyoto, Japan.,Singapore Immunology Network (SIgN) and Institute of Medical Biology, Agency for Science, Technology and Research (A*STAR), Biopolis, Singapore, Singapore
| | - Martin Steinhoff
- Department of Dermatology and Venereology, Hamad Medical Corporation, Qatar University, Doha, Qatar.,School of Medicine, Weill Cornell University-Qatar and Qatar University, Doha, Qatar
| | - Ralf Paus
- Dr. Phillip Frost, Department of Dermatology & Cutaneous Surgery, University of Miami Miller School of Medicine, Miami, FL, USA.,Dermatology Research Centre, University of Manchester and NIHR Manchester Biomedical Research Centre, Manchester, UK.,Monasterium Laboratory, Münster, Germany
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