The genetic architecture of alopecia areata

Familial patterns of alopecia areata: A systematic review and meta-analysis

BACKGROUND

Alopecia Areata (AA) is a T cell-mediated autoimmune disease characterized by sudden hair loss. It is associated with a significant familial predisposition and comorbidities such as thyroid disease, diabetes, atopic dermatitis, and vitiligo. This study aims to systematically review and meta-analyze the prevalence of familial AA and its associated comorbidities to better understand the hereditary nature of the disease.

METHODS

A systematic review and meta-analysis were conducted following the PRISMA guidelines. Relevant studies were identified from databases including EMBASE, Cochrane Library, PubMed, and Web of Science up to October 15, 2023. Studies were included if they reported on AA patients with a confirmed diagnosis and a family history of AA or related comorbidities. Data extraction and quality assessment were performed by two independent reviewers, with discrepancies resolved by a third reviewer. Pooled prevalence estimates were calculated using a random effects model.

RESULTS

The meta-analysis included 67 studies, encompassing 24,226 AA patients and their relatives. The prevalence of a family history of alopecia areata (AA) was found to be 17.6 %, indicating that 17.6 % of individuals with AA have a positive family history of the condition. (CI: 14.9 %-20.6 %, I2 = 96 %). The prevalence among relatives was 0.90 % (CI: 0.55 %-1.47 %, I2 = 98 %), with the highest prevalence observed in first-degree relatives at 3.22 % (CI: 2.31 %-4.48 %, I2 = 94 %). Comorbid conditions were present in 9.61 % (CI: 6.98 %-13.1 %, I2 = 95 %) of family members across first-, second-, and third-degree relatives of individuals with alopecia areata have comorbid autoimmune or related conditions, including thyroid disease (4.7 %), diabetes (10.1 %), atopic dermatitis (18.9 %), vitiligo (5.5 %), and other autoimmune disease (12.1 %).

CONCLUSION

This systematic review and meta-analysis highlight the significant familial risk and comorbidities in family members of AA patients. The findings emphasize the need for comprehensive family monitoring, which includes regular health screenings for autoimmune and related conditions among relatives of AA patients, and genetic counseling to educate families on hereditary risks and to guide early intervention and monitoring strategies. It can lead to improved outcomes. In the future, large population-based studies focusing on second and third-degree relatives are needed to further elucidate these associations.

Clinical and Genetic Aspects of Alopecia Areata: A Cutting Edge Review

Alopecia areata (AA) is a chronic, non-scarring, immune-mediated skin disease that affects approximately 0.5-2% of the global population. The etiology of AA is complex and involves genetic and environmental factors, with significant advancements in genetic research occurring in recent years. In addition to well-known genes such as PTPN22, CTLA4, and IL2, which have been widely supported as being associated with AA, an increasing number of specific gene-related loci have been discovered through advances in genetic research. For instance, gene analysis of microRNAs can reveal the critical role of miRNAs in regulating gene expression, aiding in the understanding of cellular and organismal functional regulatory mechanisms. Furthermore, numerous studies have confirmed the existence of correlations between AA and other immune-related diseases. Examples include hyperthyroidism and rheumatoid arthritis. By understanding the interrelationships between AA and other immune diseases, we can further comprehend potential shared genetic foundations or pathogenic mechanisms among different diseases. Genetic research plays a crucial role in unraveling the pathogenesis of AA, as the identification of genetic variations associated with AA can assist in formulating more effective and targeted treatment strategies.

How Our Microbiome Influences the Pathogenesis of Alopecia Areata

Alopecia areata is a multifactorial autoimmune-based disease with a complex pathogenesis. As in all autoimmune diseases, genetic predisposition is key. The collapse of the immune privilege of the hair follicle leading to scalp loss is a major pathogenic event in alopecia areata. The microbiota considered a bacterial ecosystem located in a specific area of the human body could somehow influence the pathogenesis of alopecia areata, as it occurs in other autoimmune diseases. Moreover, the Next Generation Sequencing of the 16S rRNA bacterial gene and the metagenomic methodology have provided an excellent characterization of the microbiota. The aim of this narrative review is to examine the published literature on the cutaneous and intestinal microbiota in alopecia areata to be able to establish a pathogenic link. In this review, we summarize the influence of the microbiota on the development of alopecia areata. We first introduce the general pathogenic mechanisms that cause alopecia areata to understand the influence that the microbiota may exert and then we summarize the studies that have been carried out on what type of gut and skin microbiota is found in patients with this disease.

Familial implications of autoimmune disease: Recurrence risks of alopecia areata and associated conditions in first-degree relatives

Alopecia areata (AA), a complex autoimmune hair loss condition, affects approximately 2.1% of the population. Individuals with AA have increased susceptibility to diseases such as atopy and autoimmune disorders, but little is known about first-degree relatives' risk to develop AA and associated conditions. Genetic counseling for multifactorial conditions, including autoimmune disease is complex, but potentially valuable. Anecdotally we know patients with AA ask medical providers about recurrence risk for family members as well as question whether they and their relatives are at risk for other conditions. Data on AA recurrence risks and comorbid conditions among relatives of affected individuals comprise valuable information that may guide clinical management by genetic counselors. This study investigated the recurrence risk of AA and compared the prevalence of associated conditions among first-degree relatives to the general population. The study also assessed the validity of self-reported conditions for a subset of participants. Relatives of individuals with AA (N = 155), recruited from the National Alopecia Areata Foundation Registry, completed telephone surveys about their personal medical history for 70 medical conditions associated with AA. Medical records for 60 participants were compared to self-reported responses. One-sided proportional tests, in which it is assumed the disease prevalence in first-degree relatives is higher than for those in the general population, yielded a 7.8% estimated risk of AA versus the general population prevalence of 2.1%. Furthermore, there are increased risks of 33 associated conditions, including atopy and other autoimmune conditions. Comparison of medical reports to self-reported conditions indicated only 12% was incongruent. The findings may help genetic counselors better serve patients and their families by informing them of lifetime risk estimates of developing AA and comorbid conditions, resulting in early diagnosis of autoimmune diseases in AA families. Findings also provide evidence supporting the validity of self-report data in AA families.

Alopecia areata patients show deficiency of FOXP3+CD39+ T regulatory cells and clonotypic restriction of Treg TCRβ-chain, which highlights the immunopathological aspect of the disease

Alopecia areata (AA) is a hair loss disorder resulting from an autoimmune reaction against hair follicles. T-helper 1 cells are a major contributor to this disorder, but little is known about the role of T-regulatory cells (Tregs) in AA. Here, we analysed the distribution of circulating Treg subsets in twenty AA patients with active hair loss and fifteen healthy subjects by flow cytometry. The Treg suppressor HLA-DR+ subpopulation was significantly reduced in the patients (P<0.001) and there were significantly fewer cells expressing CD39 among the CD4+CD25+Foxp3+ Treg subpopulation in patients (P = 0.001). FOXP3 CD39 Treg cells were also reduced in hair follicles; by 75% in non-lesional skin and 90% in lesional skin, when compared to control healthy skin. To further characterise Treg cells in AA; Tregs (CD4+CD25+FOXP3+) were investigated for their TCRβ sequence. PCR products analysed by Next Generation Sequencing techniques, showed that all frequent public clonotypes in AA Tregs were also present in controls at relatively similar frequencies, excepting two public clonotypes: CATSRDEGGLDEKLFF (V15 D1 J1-4) and CASRDGTGPSNYGYTF (V2 D1 J1-2), which were exclusively present in controls. This suggests that these Treg clonotypes may have a protective effect and that they may be an exciting subject for future therapeutic applications.

Pathogenesis of Alopecia Areata Based on Bioinformatics Analysis

Background:

Alopecia areata (AA) describes a sudden localized patchy alopecia. The cause of AA is not completely clear and its incidence may be related to genetic, autoimmune, and environmental factors.

Aim:

To explore the possible mechanisms of AA and to provide a basis for the early diagnosis and treatment of AA.

Methods:

Gene microarray data from 122 scalp skin biopsy tissue samples from patients with AA or healthy controls from the Gene-Cloud of Biotechnology Information database were analyzed using bioinformatics analysis methods. Molecular network analysis of the differentially expressed genes (DEGs) was conducted by Cytocluster using the Molecular Complex Detection (MCODE) algorithm.

Results:

The gene expression profile of skin lesions from patients with AA was significantly altered, with 111 DEGs found in the skin lesions of AA, compared with that of the healthy skin. The DEGs were mainly related to biological processes such as the development of the epidermis and inflammatory reaction. The protein–protein interaction network analysis of DEGs revealed bone morphogenetic protein 2 (BMP2) as a core protein interaction network. BMP2 acted not only via the inflammatory response but also via the signaling pathways in epithelial cell development and epidermal cell differentiation to affect the epidermal development. MCODE analysis further showed that keratins (KRTs) and keratin-associated proteins (KRTAPs) can affect the epidermal development via the epidermal development pathway.

Conclusions:

The abnormal development of the epidermis and inflammatory reactions in skin tissue play important roles in the pathogenesis of AA and are closely related to BMP2, KRTs, and KRTAPs genes.

Limitations:

Our study was limited by experimental verification.

Alopecia areata: A multifactorial autoimmune condition

Alopecia areata is an autoimmune disease that results in non-scarring hair loss, and it is clinically characterised by small patches of baldness on the scalp and/or around the body. It can later progress to total loss of scalp hair (Alopecia totalis) and/or total loss of all body hair (Alopecia universalis). The rapid rate of hair loss and disfiguration caused by the condition causes anxiety on patients and increases the risks of developing psychological and psychiatric complications. Hair loss in alopecia areata is caused by lymphocytic infiltrations around the hair follicles and IFN-γ. IgG antibodies against the hair follicle cells are also found in alopecia areata sufferers. In addition, the disease coexists with other autoimmune disorders and can come secondary to infections or inflammation. However, despite the growing knowledge about alopecia areata, the aetiology and pathophysiology of disease are not well defined. In this review we discuss various genetic and environmental factors that cause autoimmunity and describe the immune mechanisms that lead to hair loss in alopecia areata patients.

When your patient's parent asks: "My child's alopecia areata is not getting better. Should he or she get tested for celiac disease?"

The relationship between alopecia areata and celiac disease has been suspected for more than 20 years. For a particular individual with alopecia areata, the risk of coexisting celiac disease and the potential benefit of a gluten-free diet on hair loss or regrowth is known. Despite this limited information, patients often aske dermatologists whether they should undergo celiac disease testing or begin a gluten-free diet. We reviewed all available studies of the relationship between alopecia areata and celiac disease to provide guidance to practicing clinicians.

Novel therapies for alopecia areata: The era of rational drug development

Treatments for alopecia areata (AA) have evolved over the decades from broad and nonspecific therapies to those that are now more targeted and rationally selected. This was achieved by means of close cooperation and communication between clinicians and basic scientists, which resulted in the elucidation and understanding of the unique pathophysiology of AA. In this review we discuss this evolution and how novel therapies for AA have changed over the decades, what we have in our current arsenal of drugs for this potentially devastating disease, and what the future holds.

The Changing Landscape of Alopecia Areata: The Translational Landscape

Recent genetic and preclinical studies have increased our understanding of the immunopathogenesis of alopecia areata (AA). This has allowed expedited development of targeted therapies for the treatment of AA, and a paradigm shift in our approach and understanding of autoimmunity and the hair follicle. The synergy between preclinical studies, animal models, and translational studies has led to unprecedented advances in the treatment options for AA, ultimately benefiting patients who have had little recourse. In this review, we summarize the scientific field of contemporary AA research, and look forward to potential new technologies and developments.

Genomewide analysis of copy number variants in alopecia areata in a Central European cohort reveals association with MCHR2

Alopecia areata (AA) is a common hair loss disorder of autoimmune aetiology, which often results in pronounced psychological distress. Understanding of the pathophysiology of AA is increasing, due in part to recent genetic findings implicating common variants at several genetic loci. To date, no study has investigated the contribution of copy number variants (CNVs) to AA, a prominent class of genomic variants involved in other autoimmune disorders. Here, we report a genomewide- and a candidate gene-focused CNV analysis performed in a cohort of 585 patients with AA and 1340 controls of Central European origin. A nominally significant association with AA was found for CNVs in the following five chromosomal regions: 4q35.2, 6q16.3, 9p23, 16p12.1 and 20p12.1. The most promising finding was a 342.5-kb associated region in 6q16.3 (duplications in 4/585 patients; 0/1340 controls). The duplications spanned the genes MCHR2 and MCHR2-AS1, implicated in melanin-concentrating hormone (MCH) signalling. These genes have not been implicated in previous studies of AA pathogenesis. However, previous research has shown that MCHR2 affects the scale colour of barfin flounder fish via the induction of melanin aggregation. AA preferentially affects pigmented hairs, and the hair of patients with AA frequently shows a change in colour when it regrows following an acute episode of AA. This might indicate a relationship between AA, pigmentation and MCH signalling. In conclusion, the present results provide suggestive evidence for the involvement of duplications in MCHR2 in AA pathogenesis.

Alopecia areata

Alopecia areata is an autoimmune disorder characterized by transient, non-scarring hair loss and preservation of the hair follicle. Hair loss can take many forms ranging from loss in well-defined patches to diffuse or total hair loss, which can affect all hair-bearing sites. Patchy alopecia areata affecting the scalp is the most common type. Alopecia areata affects nearly 2% of the general population at some point during their lifetime. Skin biopsies of affected skin show a lymphocytic infiltrate in and around the bulb or the lower part of the hair follicle in the anagen (hair growth) phase. A breakdown of immune privilege of the hair follicle is thought to be an important driver of alopecia areata. Genetic studies in patients and mouse models have shown that alopecia areata is a complex, polygenic disease. Several genetic susceptibility loci were identified to be associated with signalling pathways that are important to hair follicle cycling and development. Alopecia areata is usually diagnosed based on clinical manifestations, but dermoscopy and histopathology can be helpful. Alopecia areata is difficult to manage medically, but recent advances in understanding the molecular mechanisms have revealed new treatments and the possibility of remission in the near future.

Mechanisms of LtxA (Leukotoxin), a Potent New Anti-Inflammatory Agent for the Treatment of Alopecia Areata

Alopecia areata is an autoimmune condition where activated, pro-inflammatory white blood cells (WBCs) attack the hair follicles, resulting in hair loss. Migration of these activated WBCs from the blood stream and into the follicle tissue requires interaction between the integrin, lymphocyte function-associated antigen-1 (LFA-1) on WBCs, and ICAM-1 on vascular endothelial cells. High levels of active LFA-1 are uniquely expressed on WBCs that are involved in autoimmune and inflammatory conditions. The natural biologic agent LtxA (Leukothera) preferentially targets and depletes disease activated and malignant WBCs by binding to active LFA-1. The experimental drug has demonstrated significant therapeutic efficacy against autoimmune/inflammatory conditions such as psoriasis and allergic asthma in mouse models for these diseases. In addition, when injected into rodents, rhesus macaques, and dogs, LtxA was demonstrated to be physiologically active, biologically specific, and extremely well-tolerated. LFA-1 is an attractive target for therapy because it is only normally present on WBCs and has been shown to be activated and overexpressed on WBCs that are responsible for autoimmune/inflammatory conditions.

The scientific legacy of Stephen Rothman

The year 2014 marks the centennial of events that led to the First World War ("the war to end all wars") following the assassination of Archduke Ferdinand of the crumbling Austro-Hungarian Empire. It also marks the 120th anniversary of the birth of Stephen Rothman and the 60th anniversary of the publication of his epic textbook The Physiology and Biochemistry of the Skin. In this review, we document our belief that Rothman had a seismic impact on moving investigative dermatology from a medical backwater to a scientific discipline that can hold its own with any other specialty.