Pathologic changes of skin and hair in ankyloblepharon-ectodermal defects-cleft lip/palate (AEC) syndrome

Molecular and Cellular Function of p63 in Skin Development and Genetic Diseases

The transcription factor p63 is a master regulator of multiple ectodermal derivatives. During epidermal commitment, p63 interacts with several chromatin remodeling complexes to transactivate epidermal-specific genes and repress transcription of simple epithelial and nonepithelial genes. In the postnatal epidermis, p63 is required to control the proliferative potential of progenitor cells, maintain epidermal integrity, and contribute to epidermal differentiation. Autosomal dominant sequence variant in p63 cause a spectrum of syndromic disorders that affect several tissues, including or derived from stratified epithelia. In this review, we describe the recent studies that have provided novel insights into disease pathogenesis and potential therapeutic targets.

Hair Evaluation in Orthodontic Patients with Oligodontia

Oligodontia can be isolated or syndromic, associated with other ectodermal abnormalities. The aim of the study was to perform hair examination in orthodontic patients diagnosed with oligodontia with a low clinical expression of symptoms of ectodermal origin. All available orthodontic patients diagnosed with oligodontia in the permanent dentition were enrolled. Hair examination included clinical evaluation of the patients' hair, trichoscopy, trichogram and evaluation of the hair shafts under a polarized light microscope. In total, 25 patients, 18 males and 7 females, aged 6 to 24 years were evaluated for the presence of dental and hair abnormalities. The number of congenitally absent teeth ranged from 6 to 24 teeth and diastemas, microdontia, taurodontism and altered tooth shape were found in 23 patients. Hair disorders were found in 68% of the subjects. Hypotrichosis, the heterogeneity of shaft color and loss of pigment, androgenetic alopecia, telogen effluvium, trichoschisis, pili canaliculi, trichorrhexis nodosa and pseudomoniletrix were observed. Trichoscopy and trichogram are valid non-invasive diagnostic tests which could be used to differentiate between isolated and syndromic oligodontia in patients with a low clinical expression of ectodermal symptoms.

Molecular Modeling Analysis Provides Genotype-Phenotype Correlation Insights in a Patient with Ankyloblepharon-Ectodermal Dysplasia-Clefting Syndrome

Ankyloblepharon-ectodermal defects-cleft lip/palate (AEC) syndrome is a rare autosomal dominant disorder. AEC is caused by mutations in the TP63 gene that encodes the tumor suppressor p63 protein, itself involved in the regulation of epidermal proliferation, development, and differentiation. We present here a typical AEC case of a four-year-old girl with extensive skin erosions and erythroderma of the scalp and the trunk, and to a lesser extent of the limbs, nail dystrophy on the fingers and toes, xerophthalmia, a high-arched palate, oligodontia, and hypohidrosis. Mutation analysis of the TP63 gene detected a de novo missense mutation in exon 14 (c.1799G>T; p.Gly600Val). We discuss the phenotype-genotype correlation by presenting the clinical features of AEC in the patient, and the effect of the detected mutation in p63 structure and function using protein structural modeling, in view of similar cases in the literature. We performed a molecular modeling study in order to link the effect on the protein structure level of the missense mutation G600V. We noted that the introduction of the bulkier Valine residue in place of the slim Glycine residue caused a significantly altered 3D conformational arrangement of that protein region, pushing away the adjacent antiparallel α helix. We propose that the introduced locally altered structure of the G600V mutant p63 has a significant functional effect on specific protein-protein interactions, thus affecting the clinical phenotype.

Pili Torti: A Feature of Numerous Congenital and Acquired Conditions

Pili torti is a rare condition characterized by the presence of the hair shaft, which is flattened at irregular intervals and twisted 180° along its long axis. It is a form of hair shaft disorder with increased fragility. The condition is classified into inherited and acquired. Inherited forms may be either isolated or associated with numerous genetic diseases or syndromes (e.g., Menkes disease, Björnstad syndrome, Netherton syndrome, and Bazex-Dupré-Christol syndrome). Moreover, pili torti may be a feature of various ectodermal dysplasias (such as Rapp-Hodgkin syndrome and Ankyloblepharon-ectodermal defects-cleft lip/palate syndrome). Acquired pili torti was described in numerous forms of alopecia (e.g., lichen planopilaris, discoid lupus erythematosus, dissecting cellulitis, folliculitis decalvans, alopecia areata) as well as neoplastic and systemic diseases (such as cutaneous T-cell lymphoma, scalp metastasis of breast cancer, anorexia nervosa, malnutrition, cataracts, and chronic graft-vs.-host disease). The condition may also be induced by several drugs (epidermal growth factor receptor inhibitors, oral retinoids, sodium valproate, and carbamide perhydrate). The diagnosis of pili torti is based on trichoscopic or microscopic examination. As pili torti is a marker of numerous congenital and acquired disorders, in every case, the search for the signs of underlying conditions is recommended.

Ankyloblepharon-ectodermal Defects-cleft Lip-palate Syndrome Due to a Novel Missense Mutation in the SAM Domain of the TP63 Gene

Ankyloblepharon-ectodermal defects-cleft lip/palate (AEC) syndrome is a rare genetic disease with an autosomal dominant transmission, characterized by several congenital anomalies. Clinical features include ectodermal defects affecting the skin, hair, teeth, nails and sweat glands, associated with typical eyelid fusion in addition to a cleft lip and/or palate. The diagnosis is based on clinical criteria and molecular genetic testing of TP63 gene, the gene related to AEC syndrome. In this context, most reported mutations induce an amino acid change in the sterile alpha motif (SAM) domain, and are predicted to disrupt protein-protein interactions. We here describe the case of a 2-year-old Moroccan girl diagnosed with AEC syndrome on the basis of clinical features. The molecular studies and bioinformatics tools revealed a novel heterozygous missense mutation c.1798G>C (p.Gly600Arg) in exon 14 of the TP63 gene, that was not found in her parents. The molecular analysis and the early diagnosis of this syndrome are important to offer appropriate genetic counseling and management to patients and their families.

Functional and Mechanistic Insights into the Pathogenesis of P63-Associated Disorders

The p53 family member p63 is a master regulator of gene expression in stratified epithelia, such as the epidermis. One of the main functions of p63 is to sustain mechanical resistance, positively regulating several epidermal genes involved in cell-matrix adhesion and cell-cell adhesion (Ferone et al., 2015).

Scanning Electron Microscopic Hair Shaft Analysis in Ectodermal Dysplasia Syndromes

OBJECTIVES

The objective of the current study was to catalog hair shaft abnormalities in individuals with ectodermal dysplasia (ED) syndromes using scanning electron microscopy (SEM) and to compare the findings with those in unaffected controls. This is the second of a two-part study, the first of which used light microscopy as the modality and was previously published.

METHODS

Scanning electron microscopy was performed in a blinded manner on hair shafts from 65 subjects with seven types of ED syndromes and 41 unaffected control subjects. Assessment was performed along the length of the shaft and in cross section.

SETTING

Hair donations were collected at the 28th Annual National Family Conference held by the National Foundation for Ectodermal Dysplasia. Control subjects were recruited from a private dermatology practice and an academic children's hospital outpatient dermatology clinic.

RESULTS

SEM identified various pathologic hair shaft abnormalities in each type of ED and in control patients. When hairs with all types of ED were grouped together and compared with those of control patients, the difference in the presence of small diameter and shallow and deep grooves was statistically significant (p < 0.05). When the EDs were separated according to subtype, statistically significant findings were also seen.

CONCLUSION

SEM is a possible adjuvant tool in the diagnosis of ED syndromes. There are significant differences, with high specificity, between the hairs of individuals with ED and those of control subjects and between subtypes.

Trichoscopic Hair Evaluation in Patients with Ectodermal Dysplasia

Hair abnormalities in ectodermal dysplasia may be difficult to identify. Among 16 patients with ectodermal dysplasia trichoscopy (hair dermoscopy) revealed predominance of pilosebaceous units with 1 hair (69%), abnormalities of hair shaft pigmentation (gray hair with single dark hairs, 56%), pili torti, trichothiodystrophy, trichorrhexis nodosa, and rarely, cicatricial alopecia.

Epidermal cell junctions and their regulation by p63 in health and disease

As the outermost tissue of the body, the epidermis is the first physical barrier for any pressure, stress or trauma. Several specialized cell-matrix and cell-cell adhesion structures, together with an intracellular network of dedicated intermediate filaments, are required to confer critical resilience to mechanical stress. The transcription factor p63 is a master regulator of gene expression in the epidermis and in other stratified epithelia. It has been extensively demonstrated that p63 positively controls a large number of tissue-specific genes, including those encoding a large fraction of tissue-restricted cell adhesion molecules. Consistent with p63 functions in cell adhesion and in epidermal differentiation, heterozygous mutations clustered mainly in the p63 C-terminus are causative of AEC syndrome, an autosomal dominant disorder characterized by cleft palate, ankyloblepharon and ectodermal dysplasia associated with severe skin erosions, bleeding and infections. The molecular basis of skin erosions in AEC patients is not fully understood, although defects in desmosomes and in other cell junctions are likely to be involved. Here, we provide an extensive review of the different epidermal cell junctions that cooperate to withstand mechanical stress and on the mechanisms by which p63 regulates gene expression of their components in healthy skin and in AEC syndrome. Collectively, advancement in understanding the molecular mechanisms by which epidermal cell junctions precisely exert their functions and how p63 orchestrates their coordinated expression, will ultimately lead to insight into developing future strategies for the treatment of AEC syndrome and more in generally for diseases that share an overlapping phenotype.

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.

p63 control of desmosome gene expression and adhesion is compromised in AEC syndrome

Ankyloblepharon, ectodermal defects, cleft lip/palate (AEC) syndrome is a rare autosomal dominant disorder caused by mutations in the p63 gene, essential for embryonic development of stratified epithelia. The most severe cutaneous manifestation of this disorder is the long-lasting skin fragility associated with severe skin erosions after birth. Using a knock-in mouse model for AEC syndrome, we found that skin fragility was associated with microscopic blistering between the basal and suprabasal compartments of the epidermis and reduced desmosomal contacts. Expression of desmosomal cadherins and desmoplakin was strongly reduced in AEC mutant keratinocytes and in newborn epidermis. A similar impairment in desmosome gene expression was observed in human keratinocytes isolated from AEC patients, in p63-depleted keratinocytes and in p63 null embryonic skin, indicating that p63 mutations causative of AEC syndrome have a dominant-negative effect on the wild-type p63 protein. Among the desmosomal components, desmocollin 3, desmoplakin and desmoglein 1 were the most significantly reduced by mutant p63 both at the RNA and protein levels. Chromatin immunoprecipitation experiments and transactivation assays revealed that p63 controls these genes at the transcriptional level. Consistent with reduced desmosome function, AEC mutant and p63-deficient keratinocytes had an impaired ability to withstand mechanical stress, which was alleviated by epidermal growth factor receptor inhibitors known to stabilize desmosomes. Our study reveals that p63 is a crucial regulator of a subset of desmosomal genes and that this function is impaired in AEC syndrome. Reduced mechanical strength resulting from p63 mutations can be alleviated pharmacologically by increasing desmosome adhesion with possible therapeutic implications.

Ectodermal dysplasias: a clinical and molecular review

The ectodermal dysplasias are a large group of hereditary disorders characterized by alterations of structures of ectodermal origin. Although some syndromes can have specific features, many of them share common clinical characteristics. Two main groups of ectodermal dysplasias can be distinguished. One group is characterized by aplasia or hypoplasia of ectodermal tissues, which fail to develop and differentiate because of a lack of reciprocal signaling between ectoderm and mesoderm, the other has palmoplantar keratoderma as its most striking feature, with additional manifestations when other highly specialized epithelia are also involved. In recent decades, the genes responsible for at least 30 different types of ectodermal dysplasia have been identified, throwing light on the pathogenic mechanisms involved and their correlation with clinical findings.

Light microscopic hair shaft analysis in ectodermal dysplasia syndromes

The objective of the study was to catalog hair shaft abnormalities in individuals with ectodermal dysplasia (ED) syndromes using light microscopy and to compare findings with those in unaffected controls. Light microscopy was performed in a nonblinded manner on hair shafts from 65 participants with seven types of ED (hypohidrotic ED, ED-ectrodactyly-cleft lip or palate, ankyloblepharon-ectodermal defects-cleft lip and palate, Clouston syndrome, Goltz syndrome, Schopf-Schulz Passarge syndrome, and oculodentodigital dysplasia) and 41 unaffected controls. Hair donations were collected at the 28th Annual National Family Conference held by the National Foundation for Ectodermal Dysplasia. Control participants were recruited from a private dermatology practice and an academic children's hospital outpatient dermatology clinic. Sixty-five affected participants and 41 unaffected controls were included in the analysis. We assessed the hair shafts of ED and control participants for abnormalities visible using LM. Light microscopy identified various pathologic hair shaft abnormalities in each type of ED, although none of the findings were statistically significantly different from those of the control group. Light microscopy is a poor adjuvant tool in the diagnosis of ED syndromes. Most findings are nonspecific and not sufficiently sensitive.

Mutations in AEC syndrome skin reveal a role for p63 in basement membrane adhesion, skin barrier integrity and hair follicle biology

BACKGROUND

AEC (ankyloblepharon-ectodermal defects-clefting) syndrome is an autosomal dominant ectodermal dysplasia disorder caused by mutations in the transcription factor p63. Clinically, the skin is dry and often fragile; other features can include partial eyelid fusion (ankyloblepharon), hypodontia, orofacial clefting, sparse hair or alopecia, and nail dystrophy.

OBJECTIVES

To investigate how p63 gene mutations affect gene and protein expression in AEC syndrome skin.

METHODS

We performed microarray analysis on samples of intact and eroded AEC syndrome skin compared with control skin. Changes were verified by quantitative real-time reverse transcription-polymerase chain reaction and, for basal keratinocyte-associated genes, by immunohistochemistry and analysis of microdissected skin.

RESULTS

We identified significant upregulation of six genes and downregulation of 69 genes in AEC syndrome skin, with the main changes in genes implicated in epidermal adhesion, skin barrier formation and hair follicle biology. There was reduced expression of genes encoding the basement membrane proteins FRAS1 and collagen VII, as well as the skin barrier-associated small proline-rich proteins 1A and 4, late cornified envelope protein 5A, hornerin, and lipid transporters including ALOX15B. Reduced expression of the hair-associated keratins 25, 27, 31, 33B, 34, 35, 81 and 85 was also noted. We also confirmed similar alterations in gene expression for 26 of the 75 genes in eroded AEC scalp skin.

CONCLUSIONS

This study identifies specific changes in skin structural biology and signalling pathways that result from mutant p63 and provides new molecular insight into the AEC syndrome phenotype.

Mutant p63 causes defective expansion of ectodermal progenitor cells and impaired FGF signalling in AEC syndrome

Ankyloblepharon-ectodermal defects-cleft lip/palate (AEC) syndrome, which is characterized by cleft palate and severe defects of the skin, is an autosomal dominant disorder caused by mutations in the gene encoding transcription factor p63. Here, we report the generation of a knock-in mouse model for AEC syndrome (p63(+/L514F) ) that recapitulates the human disorder. The AEC mutation exerts a selective dominant-negative function on wild-type p63 by affecting progenitor cell expansion during ectodermal development leading to a defective epidermal stem cell compartment. These phenotypes are associated with impairment of fibroblast growth factor (FGF) signalling resulting from reduced expression of Fgfr2 and Fgfr3, direct p63 target genes. In parallel, a defective stem cell compartment is observed in humans affected by AEC syndrome and in Fgfr2b(-/-) mice. Restoring Fgfr2b expression in p63(+/L514F) epithelial cells by treatment with FGF7 reactivates downstream mitogen-activated protein kinase signalling and cell proliferation. These findings establish a functional link between FGF signalling and p63 in the expansion of epithelial progenitor cells and provide mechanistic insights into the pathogenesis of AEC syndrome.

Clinical lessons learned from the International Research Symposium on Ankyloblepharon-Ectodermal Defects-Cleft Lip/Palate (AEC) syndrome

The International Research Symposium on Ankyloblepharon-Ectodermal Defects-Cleft Lip/Palate ((AEC) Syndrome, that was supported by the National Foundation for Ectodermal Dysplasias (NFED) through a grant from the National Institute of Arthritis and Musculoskeletal and Skin Diseases (NIAMS) and the National Institutes of Health Office of Rare Diseases (NIH-ORD), brought together physicians, scientists, and 23 individuals affected by AEC syndrome from 13 families. Eighteen of the AEC-affected individuals were enrolled in an IRB-approved protocol through Baylor College of Medicine. Enrolled participants had clinical evaluations by multiple subspecialists, and additionally submitted blood for mutational analysis and skin specimens for pathologic evaluation. One of the goals of the conference was to define clinical and pathologic findings for improved diagnostic criteria, with the hope of determining genotype-phenotype correlations that might aid in predicting prognosis or directing therapeutics. What we found was wide interfamilial and intrafamilial variability in the manifestations of the syndrome. We were unable to identify any specific genotype-phenotype correlations. This may relate to our small sample size or other unknown epigenetic factors that are also at play in the expression and manifestation of the syndrome in specific individuals.

Dermatologic findings of ankyloblepharon-ectodermal defects-cleft lip/palate (AEC) syndrome

Hay-Wells syndrome, caused by mutations in the p63 gene, is an autosomal dominant ectodermal dysplasia with the main features of ankyloblepharon filiforme adnatum, ectodermal defects, and cleft lip/palate, from which the disorder's other name, AEC syndrome, is derived. The National Foundation for Ectodermal Dysplasias convened the International Research Symposium for AEC Syndrome on November 8-10, 2006, at Texas Children's Hospital/Baylor College of Medicine, Houston, TX with appropriate IRB approval. This multidisciplinary conference was the largest gathering of such patients to date and allowed us to further characterize dermatologic features of AEC syndrome, which included: sparse and wiry hair, nail changes, past or present scalp erosions, decreased sweat production, palmar/plantar changes, and unique pigmentary anomalies. Early recognition of the features of AEC syndrome and subsequent early diagnosis is important in minimizing invasive diagnostic studies, improving morbidity and mortality, and providing genetic counseling. Skin erosions, especially those of the scalp, were identified as the most challenging cutaneous aspect of this syndrome. Although the reasons for the skin erosions and poor healing are not known, mutations of p63 may lead to a diminished store of basal cells capable of replenishing the disrupted barrier. Therapeutic strategies currently under exploration include gene therapy, as well as epidermal stem cell therapy. Until then, gentle wound care and limiting further trauma seem to be the most prudent treatment modalities.

Craniofacial and anthropometric phenotype in ankyloblepharon-ectodermal defects-cleft lip/palate syndrome (Hay-Wells syndrome) in a cohort of 17 patients

Ankyloblepharon-ectodermal dysplasia-cleft lip/palate (AEC) syndrome and Rapp-Hodgkin syndrome are well-characterized clinical entities caused by mutations in the TP63 gene. While AEC and Rapp-Hodgkin had been thought to be clinically distinct entities, the elucidation of their molecular etiology confirmed that they are a clinical continuum as opposed to distinct disorders. We have evaluated 17 patients with AEC syndrome using a systematic clinical approach. In our study, we have identified new features and others that were thought to occur only rarely. These include short stature and poor weight gain with preservation of head circumference in nearly all subjects, trismus in 35% and hypospadias in 78% of males. In addition, we describe the frequency of phenotypic features and demonstrate the extreme clinical variability in the largest cohort of AEC individuals reported in the literature thus far.

DeltaNp63 knockdown mice: A mouse model for AEC syndrome

Dominant mutations in TP63 cause ankyloblepharon ectodermal dysplasia and clefting (AEC), an ectodermal dysplasia characterized by skin fragility. Since DeltaNp63alpha is the predominantly expressed TP63 isoform in postnatal skin, we hypothesized that mutant DeltaNp63alpha proteins are primarily responsible for skin fragility in AEC patients. We found that mutant DeltaNp63alpha proteins expressed in AEC patients function as dominant-negative molecules, suggesting that the human AEC skin phenotype could be mimicked in mouse skin by downregulating DeltaNp63alpha. Indeed, downregulating DeltaNp63 expression in mouse epidermis caused severe skin erosions, which resembled lesions that develop in AEC patients. In both cases, lesions were characterized by suprabasal epidermal proliferation, delayed terminal differentiation, and basement membrane abnormalities. By failing to provide structural stability to the epidermis, these defects likely contribute to the observed skin fragility. The development of a mouse model for AEC will allow us to further unravel the genetic pathways that are normally regulated by DeltaNp63 and that may be perturbed in AEC patients. Ultimately, these studies will not only contribute to our understanding of the molecular mechanisms that cause skin fragility in AEC patients, but may also result in the identification of targets for novel therapeutic approaches aimed at treating skin erosions. (c) 2009 Wiley-Liss, Inc.

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.