Rare diseases of ectoderm: Translating discovery to therapy

Heritable conditions known as ectodermal dysplasias are rare and can be associated with marked morbidity, mortality, and a reduced quality of life. The diagnosis and care of individuals affected by one of the many ectodermal dysplasias presents myriad challenges due to their rarity and the diverse phenotypes. These conditions are caused by abnormalities in multiple genes and signaling pathways that are essential for the development and function of ectodermal derivatives. During a 2021 international conference focused on translating discovery to therapy, researchers and clinicians gathered with the goal of advancing the diagnosis and treatment of conditions affecting ectodermal tissues with an emphasis on skin, hair, tooth, and eye phenotypes. Conference participants presented a variety of promising treatment strategies including gene or protein replacement, gene editing, cell therapy, and the identification of druggable targets. Further, barriers that negatively influence the current development of novel therapeutics were identified. These barriers include a lack of accurate prevalence data for rare conditions, absence of an inclusive patient registry with deep phenotyping data, and insufficient animal models and cell lines. Overcoming these barriers will need to be prioritized in order to facilitate the development of novel treatments for genetic disorders of the ectoderm.

Ectodermal dysplasias: Classification and organization by phenotype, genotype and molecular pathway

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., non-syndromic hypodontia or missing teeth associated with pathogenic variants of EDA "ectodysplasin"). Information for categorization and cataloging includes the phenotypic features, Online Mendelian Inheritance in Man number, mode of inheritance, genetic alteration, major developmental pathways involved (e.g., EDA, WNT "wingless-type," TP63 "tumor protein p63") or the components of complex molecular structures (e.g., connexins, keratins, cadherins).

Growth failure in focal dermal hypoplasia

Focal dermal hypoplasia (FDH) is a rare genetic disorder caused by mutations in the PORCN gene located on the X chromosome. Short stature was previously noted to be a common finding in FDH, however the etiology of this is unclear. The present study sought to elucidate specific causes for short stature by assessing growth charts, determining bone ages and auxologic measurements, examining laboratory data for the common causes of growth failure, assessing dietary intake, and performing a growth hormone stimulation test. Sixteen patients with FDH between the ages of 3 and 18 years of age consented to the study. While 11 out of 16 patients had short stature based on height less than 2 standard deviations below mid-parental target height percentile and bone age not suggestive of likely catch-up growth, only four had a BMI less than the 5th percentile for age. Laboratory studies did not support a gastrointestinal, allergy or autoimmune cause of growth failure. Three patients had results suggestive of possible growth hormone deficiency. Although short stature is a common feature in FDH, our data suggests that severe undernutrition is not common in this group and that there may be underlying treatable causes for this short stature in some patients.

Growth, nutritional, and gastrointestinal aspects of focal dermal hypoplasia (Goltz-Gorlin syndrome)

Focal dermal hypoplasia (FDH) is a rare genetic disorder caused by mutations in the PORCN gene located on the X-chromosome. In the present study, we characterized the pattern of growth, body composition, and the nutritional and gastrointestinal aspects of children and adults (n = 19) affected with this disorder using clinical anthropometry and a survey questionnaire. The mean birth length (P < 0.06) and weight (P < 0.001) z-scores of the participants were lower than the reference population. The mean head circumference (P < 0.001), height (length) (P < 0.001), weight (P < 0.01), and BMI (P < 0.05) for age z-scores of the participants were lower than the reference population. The height-for-age and weight-for-age z-scores of the participants did not differ significantly between birth and current measurements. Three-fourths of the group reported having one or more nutritional or gastrointestinal problems including short stature (65%), underweight (77%), oral motor dysfunction (41%), gastroesophageal reflux (24%), gastroparesis (35%), and constipation (35%). These observations provide novel clinical information about growth, body composition, and nutritional and gastrointestinal aspects of children and adults with FDH and underscore the importance of careful observation and early clinical intervention in the care of individuals affected with this disorder.

International research symposium on Goltz syndrome

The International Research Symposium on Goltz Syndrome was held at Texas Children's Hospital on July 22 and 23, 2013. This unique research, educational, and family-oriented symposium was sponsored by the National Foundation for Ectodermal Dysplasias, Baylor College of Medicine and Texas Children's Hospital. Goltz syndrome, or Focal Dermal Hypoplasia (FDH), is a highly variable X-linked dominant disorder with abnormalities in tissues derived from the ectoderm and mesoderm. Classic clinical features include patchy hypoplastic skin, split hand/foot deformities, and ocular manifestations. FDH is caused by PORCN gene mutations. PORCN is involved in the secretion and signaling of Wnt proteins, which play a role in embryonic tissue development. The purpose of the International Research Symposium on Goltz Syndrome was to review the progress that has been made in recent years in research related to this rare disorder and to explore potential future research directions and treatments. This issue of American Journal of Medical Genetics contains the research findings from the evaluations from multiple subspecialties. There is a recommendation for a new diagnostic guideline to aid clinicians in identifying individuals with Focal Dermal Hypoplasia. A tissue repository has been instituted at Texas Children's Hospital, to aid future researchers in this area.

Second International Conference on a classification of ectodermal dysplasias: development of a multiaxis model

Ectodermal dysplasias (EDs) comprise a large clinically and etiologically heterogeneous group of genetic disorders characterized by abnormalities in tissues derived from the embryonic ectoderm. Controversy exists over which syndromes should be classified as EDs and which should be excluded from the classification. 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 EDs. The overarching goal of the Second International Conference was to develop a consensus on EDs classifications, with the ultimate goal of creating a system that integrates clinical and molecular knowledge, using an interactive Internet-based database that clinicians, researchers, and laymen can use. The Conference, brought together a group of experts from around the world, including a diverse health-care providers, researchers, patient advocate representatives, and administrators. The Conference was modeled after the 2008 conference, with plenary sessions, scientific updates, and small group discussions. Based on the present clinical knowledge, new molecular advances and both coupled with new bioinformatics developments, the participants agree to develop a multi-axis system approach for the classification of EDs. The multi-axis approach will include a clinical/phenotype axis, a gene-based axis, and a functional/pathways axis. The significance of the conference outcomes includes, a new classification approach that will foster a better understanding of EDs, open new fields of research and develop a nosologic approach that may have broad implications for classifying other hereditary conditions.

X-linked hypohidrotic ectodermal dysplasia (XLHED): clinical and diagnostic insights from an international patient registry

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.

Modeling AEC-New approaches to study rare genetic disorders

Ankyloblepharon-ectodermal defects-cleft lip/palate (AEC) syndrome is a rare monogenetic disorder that is characterized by severe abnormalities in ectoderm-derived tissues, such as skin and its appendages. A major cause of morbidity among affected infants is severe and chronic skin erosions. Currently, supportive care is the only available treatment option for AEC patients. Mutations in TP63, a gene that encodes key regulators of epidermal development, are the genetic cause of AEC. However, it is currently not clear how mutations in TP63 lead to the various defects seen in the patients' skin. In this review, we will discuss current knowledge of the AEC disease mechanism obtained by studying patient tissue and genetically engineered mouse models designed to mimic aspects of the disorder. We will then focus on new approaches to model AEC, including the use of patient cells and stem cell technology to replicate the disease in a human tissue culture model. The latter approach will advance our understanding of the disease and will allow for the development of new in vitro systems to identify drugs for the treatment of skin erosions in AEC patients. Further, the use of stem cell technology, in particular induced pluripotent stem cells (iPSC), will enable researchers to develop new therapeutic approaches to treat the disease using the patient's own cells (autologous keratinocyte transplantation) after correction of the disease-causing mutations.

Characterization of X-linked hypohidrotic ectodermal dysplasia (XL-HED) hair and sweat gland phenotypes using phototrichogram analysis and live confocal imaging

Hypohidrotic ectodermal dysplasia (HED) is the most common type of ectodermal dysplasia (ED), which encompasses a large group of syndromes that share several phenotypic features such as missing or malformed ectodermal structures, including skin, hair, sweat glands, and teeth. X-linked hypohidrotic ectodermal dysplasia (XL-HED) is associated with mutations in ectodysplasin (EDA1). Hypohidrosis due to hypoplastic sweat glands and thin, sparse hair are phenotypic features that significantly affect the daily lives of XL-HED individuals and therefore require systematic analysis. We sought to determine the quality of life of individuals with XL-HED and to quantify sweat duct and hair phenotypes using confocal imaging, pilocarpine iontophoresis, and phototrichogram analysis. Using these highly sensitive and non-invasive techniques, we demonstrated that 11/12 XL-HED individuals presented with a complete absence of sweat ducts and that none produced sweat. We determined that the thin hair phenotype observed in XL-HED was due to multiple factors, such as fewer terminal hairs with decreased thickness and slower growth rate, as well as fewer follicular units and fewer hairs per unit. The precise characterization of XL-HED phenotypes using sensitive and non-invasive techniques presented in our study will improve upon larger genotype-phenotype studies and the assessment of future therapies in XL-HED.

Psychoeducational characteristics of children with hypohidrotic ectodermal dysplasia

OBJECTIVE

Hypohidrotic ectodermal dysplasia (HED) is an X-linked hereditary disorder characterized by hypohidrosis, hypotrichosis, and anomalous dentition. Estimates of up to 50% of affected children having intellectual disability are controversial.

METHOD

In a cross-sectional study, 45 youth with HED (77% males, mean age 9.75 years) and 59 matched unaffected controls (70% males, mean age 9.79 years) were administered the Kaufman Brief Intelligence Test and the Kaufman Test of Educational Achievement, and their parents completed standardized neurodevelopmental and behavioral measures, educational, and health-related information regarding their child, as well as standardized and nonstandardized data regarding socioeconomic information for their family.

RESULTS

There were no statistically significant differences between the two groups in intelligence quotient composite and educational achievement scores, suggesting absence of learning disability in either group. No gender differences within or between groups were found on any performance measures. Among affected youth, parental education level correlated positively with (1) cognitive vocabulary scores and cognitive composite scores; (2) educational achievement for mathematics, reading, and composite scores.

CONCLUSION

Youth affected with HED and unaffected matched peers have similar profiles on standardized measures of cognition, educational achievement, and adaptive functioning although children with HED may be at increased risk for ADHD.

International Research Symposium on Ankyloblepharon-Ectodermal Defects-Cleft Lip/Palate (AEC) syndrome

Ankyloblepharon-ectodermal defects-cleft lip/palate (AEC) syndrome (Hay-Wells syndrome, MIM #106220) is a rare autosomal dominant ectodermal dysplasia syndrome. It is due to mutations in the TP63 gene, known to be a regulatory gene with many downstream gene targets. TP63 is important in the differentiation and proliferation of the epidermis, as well as many other processes including limb and facial development. It is also known that mutations in TP63 lead to skin erosions. These erosions, especially on the scalp, are defining features of AEC syndrome and cause significant morbidity and mortality in these patients. It was this fact that led to the 2003 AEC Skin Erosion Workshop. That conference laid the groundwork for the International Research Symposium for AEC Syndrome held at Texas Children's Hospital in 2006. The conference brought together the largest cohort of individuals with AEC syndrome, along with a multitude of physicians and scientists. The overarching goals were to define the clinical and pathologic findings for improved diagnostic criteria, to obtain tissue samples for further study and to define future research directions. The symposium was successful in accomplishing these aims as detailed in this conference report. Following our report, we also present 11 manuscripts within this special section that outline the collective clinical, pathologic, and mutational data from 18 individuals enrolled in the concurrent Baylor College of Medicine IRB-approved protocol: Characterization of AEC syndrome. These collaborative findings will hopefully provide a stepping-stone to future translational projects of TP63 and TP63-related syndromes.

Perceptions of outcomes of implant therapy in patients with ectodermal dysplasia syndromes

PURPOSE

The purpose of this study was to evaluate patient-specific outcomes and satisfaction using dental implants in a population affected with ectodermal dysplasia.

MATERIALS AND METHODS

Patient-based data were collected using a self-reported survey instrument sent to patients belonging to a private patient foundation and/or treated previously at a government clinic. A standardized survey instrument was developed to evaluate patient satisfaction, outcomes, and potential complications using dental implants.

RESULTS

The survey instrument was mailed to 253 affected individuals self-reported to have various forms of ectodermal dysplasia and who were voluntarily participants in the National Foundation for Ectodermal Dysplasias and/or were participants in the US National Institute for Dental Craniofacial Research Intramural Ectodermal Dysplasia clinical research program. A total of 109 responses were obtained (43% response rate). The duration following completion of implant therapy ranged from to 1 to 23 years. Of the 109 participants, 50% reported either an implant or prosthetic complication with implant treatment, and 24% reported some form of failure with implant therapy. However, 91% of participants reported being either satisfied or very satisfied with dental implants, and 95% reported that the treatment was worth the time and cost.

CONCLUSIONS

Affected individuals receiving tooth replacement therapy with dental implants reported satisfaction with the outcome. A higher level of complications, including infection, mechanical problems, and implant loss, relative to the unaffected population was reported.