Natural gene therapy may occur in all patients with generalized non-Herlitz junctional epidermolysis bullosa with COL17A1 mutations

Strategy for the Optimization of Read-Through Therapy for Junctional Epidermolysis Bullosa with COL17A1 Nonsense Mutation

Read-through therapy suppresses premature termination codons and induces read-through activity, consequently restoring missing proteins. Aminoglycosides are widely studied as read-through drugs in different human genetic disorders, including hereditary skin diseases. Our previous work revealed that aminoglycosides affect COL17A1 nonsense mutations and represent a therapeutic option to alleviate disease severity. However, the amount of restored type XVII collagen (C17) in C17-deficient junctional epidermolysis bullosa keratinocytes was <1% relative to that in normal keratinocytes and was achieved only after high-dose gentamicin treatment, which induced deep transcriptional changes. Therefore, in this study, we designed a strategy combining aminoglycosides with compounds known to reduce their side effects. We developed translational read-through-inducing drug cocktail, version 5 containing low dosage of aminoglycosides, CC-90009, NMDI-14, melatonin, and apocynin that was able to induce about 20% of missing C17 without cell toxicity or an effect on in vitro wound closure. Translational read-through-inducing drugs cocktail, version 5 significantly induced COL17A1 expression and reverted the proinflammatory phenotype of C17-deficient junctional epidermolysis bullosa keratinocytes. Evaluation of this drug cocktail regarding its stability, penetration, and efficacy as a topical treatment remains to be determined. Translational read-through-inducing drug cocktail, version 5 might represent an improved therapeutic strategy for junctional epidermolysis bullosa and for other genetic skin disorders.

Emerging Gene Therapeutics for Epidermolysis Bullosa under Development

The monogenetic disease epidermolysis bullosa (EB) is characterised by the formation of extended blisters and lesions on the patient's skin upon minimal mechanical stress. Causal for this severe condition are genetic mutations in genes, leading to the functional impairment, reduction, or absence of the encoded protein within the skin's basement membrane zone connecting the epidermis to the underlying dermis. The major burden of affected families justifies the development of long-lasting and curative therapies operating at the genomic level. The landscape of causal therapies for EB is steadily expanding due to recent breakthroughs in the gene therapy field, providing promising outcomes for patients suffering from this severe disease. Currently, two gene therapeutic approaches show promise for EB. The clinically more advanced gene replacement strategy was successfully applied in severe EB forms, leading to a ground-breaking in vivo gene therapy product named beremagene geperpavec (B-VEC) recently approved from the US Food and Drug Administration (FDA). In addition, the continuous innovations in both designer nucleases and gene editing technologies enable the efficient and potentially safe repair of mutations in EB in a potentially permanent manner, inspiring researchers in the field to define and reach new milestones in the therapy of EB.

Revertant Mosaicism in Genodermatoses: Natural Gene Therapy Right before Your Eyes

Revertant mosaicism (RM) is the intriguing phenomenon in which nature itself has successfully done what medical science is so eagerly trying to achieve: correcting the effect of disease-causing germline variants and thereby reversing the disease phenotype back to normal. RM was molecularly confirmed for the first time in a genodermatosis in 1997, the genetic skin condition junctional epidermolysis bullosa (EB). At that time, RM was considered an extraordinary phenomenon. However, several important discoveries have changed this conception in the past few decades. First, RM has now been identified in all major subtypes of EB. Second, RM has also been identified in many other genodermatoses. Third, a theoretical mathematical exercise concluded that reverse mutations should be expected in all patients with a recessive subtype of EB or any other genodermatosis. This has shifted the paradigm from RM being an extraordinary phenomenon to it being something that every physician working in the field of genodermatoses should be looking for in every patient. It has also raised hope for new treatment options in patients with genodermatoses. In this review, we summarize the current knowledge on RM and discuss the perspectives of RM for the future treatment of patients with genodermatoses.

Integrated Management Strategies for Epidermolysis Bullosa: Current Insights

Epidermolysis bullosa (EB) is a group of rare genodermatoses that is characterized by skin fragility resulting from minor trauma. There are four major subtypes, namely, EB simplex, junctional EB, dystrophic EB and Kindler EB, depending upon the localization of defective protein and resulting plane of blister formation. The phenotype is heterogeneous in terms of severity and majority of them present at birth or neonatal period. Currently, the treatment is mainly supportive and requires multidisciplinary care. The complex molecular pathology creates difficulty in discovering a unified curative treatment approach. But with arduous efforts, significant progress has been made in the development of treatment strategies in the last decade. The management strategies range from targeting the underlying causative factor to symptom-relieving approaches, and include gene, mRNA, protein, cell and combination therapies. In this review, we enumerate the promising approaches that are currently under various stages of investigation to provide effective treatment for patients with EB.

Revertant Mosaicism in Epidermolysis Bullosa

Epidermolysis bullosa (EB) is a group of genetic blistering diseases characterized by mechanically fragile skin and mucocutaneous involvement. Historically, disease management has focused on supportive care. The development of new genetic, cellular, and recombinant protein therapies has shown promise, and this review summarizes a unique gene and cell therapy phenomenon termed revertant mosaicism (RM). RM is the spontaneous correction of a disease-causing mutation. It has been reported in most EB subtypes, some with relatively high frequency, and has been observed in both keratinocytes and fibroblasts. RM manifests as identifiable patches of unaffected, blister-resistant skin and can occur through a variety of molecular mechanisms, including true back mutation, intragenic crossover, mitotic gene conversion, and second-site mutation. RM cells represent a powerful autologous platform for therapy, and leveraging RM cells as a therapeutic substrate may avoid the inherent mutational risks of gene therapy/editing. However, further examination of the genomic integrity and long-term functionality of RM-derived cells, as well in vivo testing of systemic therapies with RM cells, is required to realize the full therapeutic promise of naturally occurring RM in EB.

Challenges in Treating Genodermatoses: New Therapies at the Horizon

Genodermatoses are rare inherited skin diseases that frequently affect other organs. They often have marked effects on wellbeing and may cause early death. Progress in molecular genetics and translational research has unravelled many underlying pathological mechanisms, and in several disorders with high unmet need, has opened the way for the introduction of innovative treatments. One approach is to intervene where cell-signaling pathways are dysregulated, in the case of overactive pathways by the use of selective inhibitors, or when the activity of an essential factor is decreased by augmenting a molecular component to correct disequilibrium in the pathway. Where inflammatory reactions have been induced by a genetically altered protein, another possible approach is to suppress the inflammation directly. Depending on the nature of the genodermatosis, the implicated protein or even on the particular mutation, to correct the consequences or the genetic defect, may require a highly personalised stratagem. Repurposed drugs, can be used to bring about a "read through" strategy especially where the genetic defect induces premature termination codons. Sometimes the defective protein can be replaced by a normal functioning one. Cell therapies with allogeneic normal keratinocytes or fibroblasts may restore the integrity of diseased skin and allogeneic bone marrow or mesenchymal cells may additionally rescue other affected organs. Genetic engineering is expanding rapidly. The insertion of a normal functioning gene into cells of the recipient is since long explored. More recently, genome editing, allows reframing, insertion or deletion of exons or disruption of aberrantly functioning genes. There are now several examples where these stratagems are being explored in the (pre)clinical phase of therapeutic trial programmes. Another stratagem, designed to reduce the severity of a given disease involves the use of RNAi to attenuate expression of a harmful protein by decreasing abundance of the cognate transcript. Most of these strategies are short-lasting and will thus require intermittent life-long administration. In contrast, insertion of healthy copies of the relevant gene or editing the disease locus in the genome to correct harmful mutations in stem cells is more likely to induce a permanent cure. Here we discuss the potential advantages and drawbacks of applying these technologies in patients with these genetic conditions. Given the severity of many genodermatoses, prevention of transmission to future generations remains an important goal including offering reproductive choices, such as preimplantation genetic testing, which can allow selection of an unaffected embryo for transfer to the uterus.

Investigational Treatments for Epidermolysis Bullosa

Epidermolysis bullosa (EB) is a heterogeneous group of rare inherited blistering skin disorders characterized by skin fragility following minor trauma, usually present since birth. EB can be categorized into four classical subtypes, EB simplex, junctional EB, dystrophic EB and Kindler EB, distinguished on clinical features, plane of blister formation in the skin, and molecular pathology. Treatment for EB is mostly supportive, focusing on wound care and patient symptoms such as itch or pain. However, therapeutic advances have also been made in targeting the primary genetic abnormalities as well as the secondary inflammatory footprint of EB. Pre-clinical or clinical testing of gene therapies (gene replacement, gene editing, RNA-based therapy, natural gene therapy), cell-based therapies (fibroblasts, bone marrow transplantation, mesenchymal stromal cells, induced pluripotential stem cells), recombinant protein therapies, and small molecule and drug repurposing approaches, have generated new hope for better patient care. In this article, we review advances in translational research that are impacting on the quality of life for people living with different forms of EB and which offer hope for improved clinical management.

Clinical Perspectives of Gene-Targeted Therapies for Epidermolysis Bullosa

New insights into molecular genetics and pathomechanisms in epidermolysis bullosa (EB), methodological and technological advances in molecular biology as well as designated funding initiatives and facilitated approval procedures for orphan drugs have boosted translational research perspectives for this devastating disease. This is echoed by the increasing number of clinical trials assessing innovative molecular therapies in the field of EB. Despite remarkable progress, gene-corrective modalities, aimed at sustained or permanent restoration of functional protein expression, still await broad clinical availability. This also reflects the methodological and technological shortcomings of current strategies, including the translatability of certain methodologies beyond preclinical models as well as the safe, specific, efficient, feasible, sustained and cost-effective delivery of therapeutic/corrective information to target cells. This review gives an updated overview on status, prospects, challenges and limitations of current gene-targeted therapies.

Molecular Therapeutics in Development for Epidermolysis Bullosa: Update 2020

Epidermolysis bullosa (EB) is a group of rare genetic disorders for which significant progress has been achieved in the development of molecular therapies in the last few decades. Such therapies require knowledge of mutant genes and specific mutations, some of them being allele specific. A relatively large number of clinical trials are ongoing and ascertaining the clinical efficacy of gene, protein or cell therapies or of repurposed drugs, mainly in recessive dystrophic EB. It is expected that some new drugs may emerge in the near future and that combinations of different approaches may result in improved treatment outcomes for individuals with EB.

Epigenetic and metabolic regulation of epidermal homeostasis

Continuous exposure of the skin to environmental, mechanical and chemical stress necessitates constant self‐renewal of the epidermis to maintain its barrier function. This self‐renewal ability is attributed to epidermal stem cells (EPSCs), which are long‐lived, multipotent cells located in the basal layer of the epidermis. Epidermal homeostasis – coordinated proliferation and differentiation of EPSCs – relies on fine‐tuned adaptations in gene expression which in turn are tightly associated with specific epigenetic signatures and metabolic requirements. In this review, we will briefly summarize basic concepts of EPSC biology and epigenetic regulation with relevance to epidermal homeostasis. We will highlight the intricate interplay between mitochondrial energy metabolism and epigenetic events – including miRNA‐mediated mechanisms – and discuss how the loss of epigenetic regulation and epidermal homeostasis manifests in skin disease. Discussion of inherited epidermolysis bullosa (EB) and disorders of cornification will focus on evidence for epigenetic deregulation and failure in epidermal homeostasis, including stem cell exhaustion and signs of premature ageing. We reason that the epigenetic and metabolic component of epidermal homeostasis is significant and warrants close attention. Charting epigenetic and metabolic complexities also represents an important step in the development of future systemic interventions aimed at restoring epidermal homeostasis and ameliorating disease burden in severe skin conditions.

Transplantation of autologous single hair units heals chronic wounds in autosomal recessive dystrophic epidermolysis bullosa: A proof-of-concept study

Autosomal recessive dystrophic epidermolysis bullosa (RDEB) is characterized by recurrent mucocutaneous blistering with non-healing ulcers which are often complicated by squamous cell carcinoma (SCC). Despite having as high as 80% death rate from SCC, RDEB still does not have an effective treatment. We report on the efficacy of single follicular unit extract (FUE) grafting to heal chronic ulcers of intermediate RDEB in a 54-year-old woman with extensive chronic wounds covering around 30% of the body surface area. On Day 17 post first graft session, the area of treated ulcers on her right upper back was reduced by 80%. Immunofluorescence study revealed positive type VII collagen expression along the epidermal and follicular basement membrane zone in the donor and recipient sites. A few grafted follicles continued to grow hair on the recipient sites. A total of 360 FUEs were grafted in nine sessions over five years, resulting in healing of most treated ulcers and reduced significantly her time for daily wound dressing. Importantly, FUE grafting using patient's own scalp follicles does not require any laboratory manipulation. It is safe and easy to perform. Autologous follicular grafting appears efficacious for healing of recalcitrant wounds and provides an innovative solution for RDEB patients with such wounds.

Genome-wide association studies for iris pigmentation and heterochromia patterns in Large White pigs

Eye colour genetics have been extensively studied in humans since the rediscovery of Mendel's laws. This trait was first interpreted using simplistic genetic models but soon it was realised that it is more complex. In this study, we analysed eye colour variability in a Large White pig population (n = 897) and report the results of GWASs based on several comparisons including pigs having four main eye colour categories (three with both pigmented eyes of different brown grades: pale, 17.9%; medium, 14.8%; and dark, 54.3%; another one with both eyes completely depigmented, 3.8%) and heterochromia patterns (heterochromia iridis - depigmented iris sectors in pigmented irises, 3.2%; heterochromia iridum - one whole eye iris of depigmented phenotype and the other eye with the iris completely pigmented, 5.9%). Pigs were genotyped with the Illumina PorcineSNP60 BeadChip and GEMMA was used for the association analyses. The results indicated that SLC45A2 (on chromosome 16, SSC16), EDNRB (SSC11) and KITLG (SSC5) affect the different grades of brown pigmentation of the eyes, the bilateral eye depigmentation defect and the heterochromia iridis defect recorded in this white pig population respectively. These genes are involved in several mechanisms affecting pigmentation. Significant associations for the eye depigmented patterns were also identified for SNPs on two SSC4 regions (including two candidate genes: NOTCH2 and PREX2) and on SSC6, SSC8 and SSC14 (including COL17A1 as candidate gene). This study provided useful information to understand eye pigmentation mechanisms, further valuing the pig as animal model to study complex phenotypes in humans.

Consensus reclassification of inherited epidermolysis bullosa and other disorders with skin fragility

BACKGROUND

Several new genes and clinical subtypes have been identified since the publication in 2014 of the report of the last International Consensus Meeting on Epidermolysis Bullosa (EB).

OBJECTIVES

We sought to reclassify disorders with skin fragility, with a focus on EB, based on new clinical and molecular data.

METHODS

This was a consensus expert review.

RESULTS

In this latest consensus report, we introduce the concept of genetic disorders with skin fragility, of which classical EB represents the prototype. Other disorders with skin fragility, where blisters are a minor part of the clinical picture or are not seen because skin cleavage is very superficial, are classified as separate categories. These include peeling skin disorders, erosive disorders, hyperkeratotic disorders, and connective tissue disorders with skin fragility. Because of the common manifestation of skin fragility, these 'EB-related' disorders should be considered under the EB umbrella in terms of medical and socioeconomic provision of care.

CONCLUSIONS

The proposed classification scheme should be of value both to clinicians and researchers, emphasizing both clinical and genetic features of EB. What is already known about this topic? Epidermolysis bullosa (EB) is a group of genetic disorders with skin blistering. The last updated recommendations on diagnosis and classification were published in 2014. What does this study add? We introduce the concept of genetic disorders with skin fragility, of which classical EB represents the prototype. Clinical and genetic aspects, genotype-phenotype correlations, disease-modifying factors and natural history of EB are reviewed. Other disorders with skin fragility, e.g. peeling skin disorders, erosive disorders, hyperkeratotic disorders, and connective tissue disorders with skin fragility are classified as separate categories; these 'EB-related' disorders should be considered under the EB umbrella in terms of medical and socioeconomic provision of care. Linked Comment: Pope. Br J Dermatol 2020; 183:603.

Stem cell competition orchestrates skin homeostasis and ageing

Stem cells underlie tissue homeostasis, but their dynamics during ageing-and the relevance of these dynamics to organ ageing-remain unknown. Here we report that the expression of the hemidesmosome component collagen XVII (COL17A1) by epidermal stem cells fluctuates physiologically through genomic/oxidative stress-induced proteolysis, and that the resulting differential expression of COL17A1 in individual stem cells generates a driving force for cell competition. In vivo clonal analysis in mice and in vitro 3D modelling show that clones that express high levels of COL17A1, which divide symmetrically, outcompete and eliminate adjacent stressed clones that express low levels of COL17A1, which divide asymmetrically. Stem cells with higher potential or quality are thus selected for homeostasis, but their eventual loss of COL17A1 limits their competition, thereby causing ageing. The resultant hemidesmosome fragility and stem cell delamination deplete adjacent melanocytes and fibroblasts to promote skin ageing. Conversely, the forced maintenance of COL17A1 rescues skin organ ageing, thereby indicating potential angles for anti-ageing therapeutic intervention.

Epidermolysis bullosa: Molecular pathology of connective tissue components in the cutaneous basement membrane zone

Epidermolysis bullosa (EB), a group of heritable skin fragility disorders, is characterized by blistering, erosions and chronic ulcers in the skin and mucous membranes. In some forms, the blistering phenotype is associated with extensive mutilating scarring and development of aggressive squamous cell carcinomas. The skin findings can be associated with extracutaneous manifestations in the ocular as well as gastrointestinal and vesico-urinary tracts. The phenotypic heterogeneity reflects the presence of mutations in as many as 20 different genes expressed in the cutaneous basement membrane zone, and the types and combinations of the mutations and their consequences at the mRNA and protein levels contribute to the spectrum of severity encountered in different subtypes of EB. This overview highlights the molecular genetics of EB based on mutations in the genes encoding type VII and XVII collagens as well as laminin-332. The mutations identified in these protein components of the extracellular matrix attest to their critical importance in providing stability to the cutaneous basement membrane zone, with implications for heritable and acquired diseases.

Functional therapies for cutaneous wound repair in epidermolysis bullosa

Chronic wounding as a result of recurrent skin blistering in the painful genetic skin disease epidermolysis bullosa, may lead to life-threatening infections, increased risk of tumor formation, and other serious medical complications. Therefore, epidermolysis bullosa patients have an urgent need for optimal wound care and tissue regeneration. Therapeutic strategies using gene-, protein-, and cell-therapies are being developed to improve clinical symptoms, and some of them have already been investigated in early clinical trials. The most favorable options of functional therapies include gene replacement, gene editing, RNA targeting, and harnessing natural gene therapy. This review describes the current progress of the different approaches targeting autologous skin cells, and will discuss the benefits and challenges of their application.

A "late-but-fitter revertant cell" explains the high frequency of revertant mosaicism in epidermolysis bullosa

Revertant mosaicism, or "natural gene therapy", is the phenomenon in which germline mutations are corrected by somatic events. In recent years, revertant mosaicism has been identified in all major types of epidermolysis bullosa, the group of heritable blistering disorders caused by mutations in the genes encoding epidermal adhesion proteins. Moreover, revertant mosaicism appears to be present in all patients with a specific subtype of recessive epidermolysis bullosa. We therefore hypothesized that revertant mosaicism should be expected at least in all patients with recessive forms of epidermolysis bullosa. Naturally corrected, patient-own cells are of extreme interest for their promising therapeutic potential, and their presence in all patients would open exciting, new treatment perspectives to those patients. To test our hypothesis, we determined the probability that single nucleotide reversions occur in patients' skin using a mathematical developmental model. According to our model, reverse mutations are expected to occur frequently (estimated 216x) in each patient's skin. Reverse mutations should, however, occur early in embryogenesis to be able to drive the emergence of recognizable revertant patches, which is expected to occur in only one per ~10,000 patients. This underestimate, compared to our clinical observations, can be explained by the "late-but-fitter revertant cell" hypothesis: reverse mutations arise at later stages of development, but provide revertant cells with a selective growth advantage in vivo that drives the development of recognizable healthy skin patches. Our results can be extrapolated to any other organ with stem cell division numbers comparable to skin, which may offer novel future therapeutic options for other genetic conditions if these revertant cells can be identified and isolated.

The categories of cutaneous mosaicism: A proposed classification

Mosaic disorders can most easily be studied in the skin. This article presents a comprehensive overview of the different forms of cutaneous mosaicism. Major categories are genomic versus epigenetic mosaicism and nonsegmental versus segmental mosaicism. The class of nonsegmental mosaics includes single point mosaicism as exemplified by solitary benign or malignant skin tumors; disseminated mosaicism as noted in autosomal dominant tumor syndromes such as neurofibromatosis 1; and patchy mosaicism without midline separation as found in giant melanocytic nevus. The class of segmental mosaics includes segmental manifestation of lethal genes surviving by mosaicism as noted in Proteus syndrome; type 1 segmental mosaicism of autosomal dominant skin disorders reflecting heterozygosity for a postzygotic new mutation; type 2 segmental mosaicism of autosomal dominant skin disorders reflecting loss of heterozygosity that occurred at an early developmental stage in a heterozygous embryo; and isolated or superimposed segmental mosaicism of common polygenic skin disorders such as psoriasis or atopic dermatitis. A particular form of genomic mosaicism is didymosis (twin spotting). Revertant mosaicism is recognizable as one or more areas of healthy skin in patients with epidermolysis bullosa or other serious genodermatoses. The category of epigenetic mosaicism includes several X-linked, male lethal disorders such as incontinentia pigmenti, and the patterns of lyonization as noted in X-linked non-lethal disorders such as hypohidrotic ectodermal dysplasia of the Christ-Siemens-Touraine type. An interesting field of future research will be the concept of epigenetic autosomal mosaicism that may explain some unusual cases of autosomal transmission of linear hypo- or hypermelanosis.

Application of quantitative trait locus mapping and transcriptomics to studies of the senescence-accelerated phenotype in rats

Background

Etiology of complex disorders, such as cataract and neurodegenerative diseases including age-related macular degeneration (AMD), remains poorly understood due to the paucity of animal models, fully replicating the human disease. Previously, two quantitative trait loci (QTLs) associated with early cataract, AMD-like retinopathy, and some behavioral aberrations in senescence-accelerated OXYS rats were uncovered on chromosome 1 in a cross between OXYS and WAG rats. To confirm the findings, we generated interval-specific congenic strains, WAG/OXYS-1.1 and WAG/OXYS-1.2, carrying OXYS-derived loci of chromosome 1 in the WAG strain. Both congenic strains displayed early cataract and retinopathy but differed clinically from OXYS rats. Here we applied a high-throughput RNA sequencing (RNA-Seq) strategy to facilitate nomination of the candidate genes and functional pathways that may be responsible for these differences and can contribute to the development of the senescence-accelerated phenotype of OXYS rats.

Results

First, the size and map position of QTL-derived congenic segments were determined by comparative analysis of coding single-nucleotide polymorphisms (SNPs), which were identified for OXYS, WAG, and congenic retinal RNAs after sequencing. The transferred locus was not what we expected in WAG/OXYS-1.1 rats. In rat retina, 15442 genes were expressed. Coherent sets of differentially expressed genes were identified when we compared RNA-Seq retinal profiles of 20-day-old WAG/OXYS-1.1, WAG/OXYS-1.2, and OXYS rats. The genes most different in the average expression level between the congenic strains included those generally associated with the Wnt, integrin, and TGF-β signaling pathways, widely involved in neurodegenerative processes. Several candidate genes (including Arhgap33, Cebpg, Gtf3c1, Snurf, Tnfaip3, Yme1l1, Cbs, Car9 and Fn1) were found to be either polymorphic in the congenic loci or differentially expressed between the strains. These genes may contribute to the development of cataract and retinopathy.

Conclusions

This study is the first RNA-Seq analysis of the rat retinal transcriptome generated with 40 mln sequencing read depth. The integration of QTL and transcriptomic analyses in our study forms the basis of future research into the relationship between the candidate genes within the congenic regions and specific changes in the retinal transcriptome as possible causal mechanisms that underlie age-associated disorders.

Induced pluripotent stem cells from human revertant keratinocytes for the treatment of epidermolysis bullosa

Revertant mosaicism is a naturally occurring phenomenon involving spontaneous correction of a pathogenic gene mutation in a somatic cell. It has been observed in several genetic diseases, including epidermolysis bullosa (EB), a group of inherited skin disorders characterized by blistering and scarring. Induced pluripotent stem cells (iPSCs), generated from fibroblasts or keratinocytes, have been proposed as a treatment for EB. However, this requires genome editing to correct the mutations, and, in gene therapy, efficiency of targeted gene correction and deleterious genomic modifications are still limitations of translation. We demonstrate the generation of iPSCs from revertant keratinocytes of a junctional EB patient with compound heterozygous COL17A1 mutations. These revertant iPSCs were then differentiated into naturally genetically corrected keratinocytes that expressed type XVII collagen (Col17). Gene expression profiling showed a strong correlation between gene expression in revertant iPSC-derived keratinocytes and the original revertant keratinocytes, indicating the successful differentiation of iPSCs into the keratinocyte lineage. Revertant-iPSC keratinocytes were then used to create in vitro three-dimensional skin equivalents and reconstitute human skin in vivo in mice, both of which expressed Col17 in the basal layer. Therefore, revertant keratinocytes may be a viable source of spontaneously gene-corrected cells for developing iPSC-based therapeutic approaches in EB.

Neonatal junctional epidermolysis bullosa: treatment conundrums and ethical decision making

Junctional epidermolysis bullosa (JEB), generalized severe (previously called JEB, Herlitz-type) has an extremely poor prognosis, with a mean age of death at 5 months old and most dead before age 3 years. We describe a typical case of a neonate with JEB who developed failure to thrive before his death from fungal septicemia at 4 months of age. This case highlights the ethical considerations of invasive treatments such as gastrostomy tube placements, intubations, and central line placements in neonates with JEB. We review the literature as well as discuss the ethical conundrums in the care of patients with JEB and other severe forms of epidermolysis bullosa.

Management of manifestations of epidermolysis bullosa

PURPOSE OF REVIEW

Children with epidermolysis bullosa can present with disease(s) of the ears, nose, and throat, often related directly to the pathophysiology of their epidermolysis bullosa. Otolaryngologic diseases in children with epidermolysis bullosa have to be managed having a proper understanding of the diagnosis and pathophysiology of epidermolysis bullosa. The purpose of this review is to describe the current nomenclature and diagnostic algorithms for epidermolysis bullosa, and methods for the management of cutaneous and mucosal lesions.

RECENT FINDINGS

Characterization of the gene defects leading to epidermolysis bullosa has allowed the utilization of immunofluorescent techniques as the primary method for epidermolysis bullosa diagnosis. Recognizing the difficulty in managing patients with epidermolysis bullosa, several multidisciplinary groups have developed guidelines using meta-analysis of the published literature, or expert panels. Though there are currently no effective treatment modalities for epidermolysis bullosa, techniques for gene and protein replacement show promising results for future use.

SUMMARY

Currently, the management of cutaneous and mucosal disease in epidermolysis bullosa is based on the principles of prevention and wound care. Understanding the cause of epidermolysis bullosa types and subtypes, characteristics of skin and mucosal involvement, and prognosis will guide in the development of individualized treatment plans.

The genetics of skin fragility

Genetic skin fragility manifests with diminished resistance of the skin and mucous membranes to external mechanical forces and with skin blistering, erosions, and painful wounds as clinical features. Skin fragility disorders, collectively called epidermolysis bullosa, are caused by mutations in 18 distinct genes that encode proteins involved in epidermal integrity and dermal-epidermal adhesion. The genetic spectrum, along with environmental and genetic modifiers, creates a large number of clinical phenotypes, spanning from minor localized lesions to severe generalized blistering, secondary skin cancer, or early demise resulting from extensive loss of the epidermis. Laboratory investigations of skin fragility have greatly augmented our understanding of genotype-phenotype correlations in epidermolysis bullosa and have also advanced skin biology in general. Current translational research concentrates on the development of biologically valid treatments with therapeutic genes, cells, proteins, or small-molecule compounds in preclinical settings or human pilot trials.

Aberrant expression and altered cellular localization of desmosomal and hemidesmosomal proteins are associated with aggressive clinicopathological features of oral squamous cell carcinoma

Disruption of cell adhesion plays a central role in dedifferentiation, invasion, and metastasis of various cancers. The desmosome and hemidesmosome are anchoring junctions that control cell-cell and cell-matrix adhesion, respectively. To clarify their contributions in mediating the biological properties of oral cancer, we immunohistochemically examined the expression of desmoglein 1 (DSG1), DSG2, DSG3, desmocollin 2 (DSC2), integrin beta 4 (ITGB4), laminin gamma chain 2 (LAMC2), and collagen type 17 alpha 1 (COL17A1) in 51 cases of oral squamous cell carcinoma. On normal oral epithelial cells, DSG1, DSG3, DSC2, and COL17A1 were expressed on the plasma membrane, while ITGB4 and mature LAMC2 were present at the basement membrane. In cancer, the expression of DSG1, DSG3, DSC2, and COL17A1 decreased and internalized to the cytoplasm. Cytoplasmic expression of DSG2, ITGB4, and LAMC2 was induced in the cancer cells facing to the stroma. We scored immunohistochemical expression and correlated this to clinicopathological parameters including histologic differentiation, pattern of invasion, and presence of lymph node metastasis. Decrease of DSG3 and DSC2 expression correlated with a more aggressive cancer phenotype: less differentiated and more invasive histologic features and a higher incidence of nodal metastasis. Lower COL17A1 and higher LAMC2 expression were also associated with a more aggressive phenotype. The present study demonstrates that aberrant expression and altered cellular localization of desmosomal and hemidesmosomal proteins are associated with aggressive clinicopathological features of oral cancer. This reinforces the notion that disturbance of the keratin-associated anchoring junctions confers aggressive features to cancer cells.

Gene therapy for skin diseases

The skin possesses qualities that make it desirable for gene therapy, and studies have focused on gene therapy for multiple cutaneous diseases. Gene therapy uses a vector to introduce genetic material into cells to alter gene expression, negating a pathological process. This can be accomplished with a variety of viral vectors or nonviral administrations. Although results are promising, there are several potential pitfalls that must be addressed to improve the safety profile to make gene therapy widely available clinically.

Inherited blistering skin diseases: underlying molecular mechanisms and emerging therapies

A key function of human skin is the formation of a structural barrier against the external environment. In part, this is achieved through the formation of a cornified cell envelope derived from a stratified squamous epithelium attached to an epithelial basement membrane. Resilient in health, the structural integrity of skin can become impaired or break down in a collection of inherited skin diseases, referred to as the blistering genodermatoses. These disorders arise from inherited gene mutations in a variety of structural and signalling proteins and manifest clinically as blisters or erosions following minor skin trauma. In some patients, blistering can be severe resulting in significant morbidity. Furthermore, a number of these conditions are associated with debilitating extra-cutaneous manifestations including gastro-intestinal, cardiac, and ocular complications. In recent years, an improved understanding of the molecular basis of the blistering genodermatoses has led to better disease classification and genetic counselling. For patients, this has also advanced translational research with the advent of new clinical trials of gene, protein, cell, drug, and small molecule therapies. Although curing inherited blistering skin diseases still remains elusive, significant improvements in patients' quality of life are already being achieved.

Mechanisms of natural gene therapy in dystrophic epidermolysis bullosa

Revertant mosaicism has been reported in several inherited diseases, including the genetic skin fragility disorder epidermolysis bullosa (EB). Here, we describe the largest cohort of seven patients with revertant mosaicism and dystrophic EB (DEB), associated with mutations in the COL7A1 gene, and determine the underlying molecular mechanisms. We show that revertant mosaicism occurs both in autosomal dominantly and recessively inherited DEB. We found that null mutations resulting in complete loss of collagen VII and severe disease, as well as missense or splice-site mutations associated with some preserved collagen VII function and a milder phenotype, were corrected by revertant mosaicism. The mutation, subtype, and severity of the disease are thus not decisive for the presence of revertant mosaicism. Although collagen VII is synthesized and secreted by both keratinocytes and fibroblasts, evidence for reversion was only found in keratinocytes. The reversion mechanisms included back mutations/mitotic recombinations in 70% of the cases and second-site mutations affecting splicing in 30%. We conclude that revertant mosaicism is more common than previously assumed in patients with DEB, and our findings will have implications for future therapeutic strategies using the patient's naturally corrected cells as a source for cell-based therapies.

Treatment of hereditary epidermolysis bullosa: updates and future prospects

Epidermolysis bullosa (EB) represents a group of inherited blistering skin diseases, some forms of which are associated with considerable morbidity and increased mortality. Notably, in recessive dystrophic EB there can be extensive muco-cutaneous fragility and disease complications such as scars, contractures, anemia, malnutrition, and malignancy. Currently, there is no effective therapy or cure for EB. Over the last decade, however, a number of important advances have been made that are bringing new treatments closer to the clinic, including gene therapy, protein replacement therapy, cell therapies [allogeneic fibroblasts, mesenchymal stromal cells (MSCs), bone marrow stem cell transplantation, culturing/grafting revertant mosaic keratinocytes], gene editing/engineering, and clinical application of inducible pluripotent stem cells. Although a cure for EB still remains elusive, recent data on animal models and initial human clinical trials have raised the expectations of patients, clinicians, and researchers that disease modification and improved quality of life are feasible goals. Furthermore, the lessons learned in treating EB are likely to have significant implications for improving the management of other genetic diseases.

Pigmentation and melanocyte supply to the epidermis depend on type XVII collagen

Genetic deficiency of type XVII collagen (C17), laminin-332 or type VII collagen causes epidermolysis bullosa (EB). Spontaneous correction of the deficiency, also known as revertant mosaicism, is caused by a second somatic mutation that restores protein expression resulting in clinically healthy (revertant) patches surrounded by fragile (mutant) skin. Interestingly, in some patients, patches of revertant skin show hyperpigmentation. To study the possible role of affected proteins in pigmentation and melanocyte distribution, we investigated clinical documentation and skin biopsy specimens of 13 revertant EB patients having correcting mutations in the COL17A1, LAMB3 or COL7A1 genes. Analysis revealed that lack of C17 led to decreased melanin intensity and melanocyte density in the epidermis when compared with the revertant patches. Reversions of LAMB3 and COL7A1 in keratinocytes did not influence clinical pigmentation or density of melanocytes. We conclude that in human skin, melanocyte supply to the epidermis depends on C17 expression in keratinocytes.

Disorders of the cutaneous basement membrane zone--the paradigm of epidermolysis bullosa

The cutaneous basement membrane zone (BMZ) is a highly specialized functional complex that provides the skin with structural adhesion and resistance to shearing forces. Its regulatory functions include control of epithelial-mesenchymal interactions under physiological and pathological conditions. Mutations in genes encoding components of the BMZ are associated with inherited skin disorders of the epidermolysis bullosa (EB) group, characterized by skin fragility, mechanically induced blisters and erosions of the skin and mucous membranes. Although most disease-associated genes are known, the genetic basis of new EB subtypes linked to mutations in genes for focal adhesion proteins was uncovered only recently. The molecular mechanisms leading to blistering, abnormal wound healing, predisposition to skin cancer, and other complications in EB have been elucidated using animal models and disease proteomics. The rapid progress in understanding the molecular basis of EB has enabled the development of strategies for biologically valid causal therapies.

Bone marrow transplantation in epidermolysis bullosa

Epidermolysis bullosa (EB) is a heterogeneous group of inherited blistering skin diseases. Severe forms of EB are associated with increased morbidity and mortality, and there is currently no effective treatment. To combat severe complications of EB, such as chronic erosions, scarring and malignancy, effective therapy needs to be given systemically and at an early age. One recent therapeutic advancement has been a clinical trial of whole bone marrow (BM) transplantation in children with the dystrophic form of EB. This led to correction of the inherent skin basement membrane defect and better skin integrity in some individuals. The challenge now is to precisely identify which BM cells contribute to skin recovery and what mechanisms are involved in tissue regeneration. An improved understanding of the key aspects of BM skin repair is likely to lead to significant health improvements for patients with EB and other skin diseases.

New findings in genodermatoses

New technologies are accelerating the pace at which genetic defects leading to inherited skin disease are elucidated. Translation of these genetic discoveries into new therapies for patients with inherited skin diseases has not been as rapid but the pace is now accelerating. This article summarizes recent findings in genetic skin diseases, the scope of advances being made, the role of new DNA analysis technologies in these discoveries, as well as highlighting some examples of how an understanding of the genetic cause of inherited skin diseases can lead to therapeutic interventions for patients.

[What's new in pediatric dermatology?]

This paper is based on a review of the literature focused on pediatric dermatology, from October 2011 to september 2012. Our objective was to highlight the main advances in fields such as atopic dermatitis, infantile hemangiomas, infectious diseases, inflammatory disorders, and genodermatoses.

Laminin 332 in junctional epidermolysis bullosa

Laminin 332 is an essential component of the dermal-epidermal junction, a highly specialized basement membrane zone that attaches the epidermis to the dermis and thereby provides skin integrity and resistance to external mechanical forces. Mutations in the LAMA3, LAMB3 and LAMC2 genes that encode the three constituent polypeptide chains, α3, β3 and γ2, abrogate or perturb the functions of laminin 332. The phenotypic consequences are diminished dermal-epidermal adhesion and, as clinical symptoms, skin fragility and mechanically induced blistering. The disorder is designated as junctional epidermolysis bullosa (JEB). This article delineates the signs and symptoms of the different forms of JEB, the mutational spectrum, genotype-phenotype correlations as well as perspectives for future molecular therapies.