An international advisory group met at the National Institutes of Health in Bethesda, Maryland in 2017, to discuss a new classification system for the ectodermal dysplasias (EDs) that would integrate both clinical and molecular information. We propose the following, a working definition of the EDs building on previous classification systems and incorporating current approaches to diagnosis: EDs are genetic conditions affecting the development and/or homeostasis of two or more ectodermal derivatives, including hair, teeth, nails, and certain glands. Genetic variations in genes known to be associated with EDs that affect only one derivative of the ectoderm (attenuated phenotype) will be grouped as non-syndromic traits of the causative gene (e.g., nonsyndromic hypodontia or missing teeth associated with pathogenic variants of EDA "ectodysplasin"). Information for categorization and cataloging includes the phenotypic features, Online Dedication: We dedicate this article to the late Dr. Carlos Salinas, long-time leader who sought continuous improvement in our understanding and classification of the ectodermal dysplasias.

The web-based Ectodermal Dysplasia International Registry (EDIR) is a comprehensive patient-reported survey contributing to an understanding of ectodermal dysplasia (ED). XLHED is the most common of the genetic ED syndromes and was the primary diagnosis reported by 223/835 respondents (141 males and 82 females). Overall, 96% of XLHED registrants reported as least one other affected family member and 21% reported a family history of infant or childhood deaths, consistent with the published mortality data in this disorder. In general, XLHED is diagnosed by the triad of decreased sweating, reduced hair, and hypodontia (present in 89%, 74%, and 74% of XLHED respondents). Additionally, the registry dataset confirmed a spectrum of life-long XLHED clinical complications including recurrent sinus infections (49% males, 52% females), nasal congestion often foul smelling and interfering with feeding (73% males, 27% females), eczema (66% males, 40% females), wheezing (66% males, 45% females), and a hoarse, raspy voice (67% males, 23% females). The Registry results also highlighted features consistently differentiating XLHED from the non-hypohidrotic ED syndromes including the frequency of infant/childhood deaths, the presence of limb/digit abnormalities, feeding issues related to nasal discharge, dentures, and a diagnosis of asthma. These results represent the largest collection of data on a broad-spectrum of health-related issues affecting ED patients. This project provides information for expanding knowledge of the natural history of XLHED, and as such may facilitate the diagnosis and treatment of its varied and lifelong medical challenges.

Background Ectodermal dysplasia (ED) syndromes are a diverse group of disorders that affect multiple ectodermally derived tissues. Small studies and case reports suggest an increase in atopy and primary immunodeficiencies (PIDs) among patients with ED syndromes. Objective To determine the prevalence of clinical symptoms suggestive of atopy or immunodeficiency among a large cohort of children with ED syndromes. Methods A 9-page questionnaire was mailed to families who were members of the National Foundation for Ectodermal Dysplasias. The surveys were completed by parents of children younger than 18 years with a diagnosis of an ED syndrome or carrier state. Portions of the questionnaire were adapted from previously validated questionnaires developed by the International Study of Asthma and Allergies in Childhood (ISAAC). Results We received 347 completed questionnaires (41%). When compared with the 13- to 14-year-old children surveyed by ISAAC, we found both all-aged and age-matched children with ED syndromes, respectively, had significantly higher rates of asthma (32.2% and 37.2% vs 16.4%), rhinitis symptoms (76.1% and 78.3% vs 38.9%), and eczema (58.9% and 48.9% vs 8.2%). The prevalence of physician-diagnosed food allergies (20.7%) and PIDs (6.1%) in these ED patients also exceeded known rates in the general pediatric population. Conclusion This large-scale, retrospective study demonstrates a greater reported prevalence of symptoms suggestive of atopic disorders and PIDs among children with ED syndromes than the general pediatric population. A combination of genetic and environmental factors in ED syndromes may contribute to breaches of skin and mucosal barriers, permitting enhanced transmission and sensitization to irritants, allergens, and pathogens.

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There are many ways to classify ectodermal dysplasia syndromes. Clinicians in practice use a list of syndromes from which to choose a potential diagnosis, paging through a volume, such as Freire-Maia and Pinheiro's corpus, matching their patient's findings to listed syndromes. Medical researchers may want a list of syndromes that share one (monothetic system) or several (polythetic system) traits in order to focus research on a narrowly defined group. Special interest groups may want a list from which they can choose constituencies, and insurance companies and government agencies may want a list to determine for whom to provide (or deny) health care coverage. Furthermore, various molecular biologists are now promoting classification systems based on gene mutation (e.g. TP63 associated syndromes) or common molecular pathways. The challenge will be to balance comprehensiveness within the classification with usability and accessibility so that the benefits truly serve the needs of researchers, health care providers and ultimately the individuals and families directly affected by ectodermal dysplasias. It is also recognized that a new classification approach is an ongoing process and will require periodical reviews or updates. Whatever scheme is developed, however, will have far-reaching application for other groups of disorders for which classification is complicated by the number of interested parties and advances in diagnostic acumen. Consensus among interested parties is necessary for optimizing communication among the diverse groups whether it be for equitable distribution of funds, correctness of diagnosis and treatment, or focusing research efforts.