Inherited dystrophic epidermolysis bullosa in inbred dogs: A spontaneous animal model for somatic gene therapy

Systemic Collagen VII Replacement Therapy for Advanced Recessive Dystrophic Epidermolysis Bullosa

Recessive dystrophic epidermolysis bullosa (RDEB) is a genetic skin blistering disease associated with progressive multiorgan fibrosis. RDEB is caused by biallelic mutations in COL7A1 encoding the extracellular matrix protein collagen VII (C7), which is necessary for epidermal‒dermal adherence. C7 is not simply a structural protein but also has multiple functions, including the regulation of TGFβ bioavailability and the inhibition of skin scarring. Intravenous (IV) administration of recombinant C7 (rC7) rescues C7-deficient mice from neonatal lethality. However, the effect on established RDEB has not been determined. In this study, we used small and large adult RDEB animal models to investigate the disease-modulating abilities of IV rC7 on established RDEB. In adult RDEB mice, rC7 accumulated at the basement membrane zone in multiple organs after a single infusion. Fortnightly IV injections of rC7 for 7 weeks in adult RDEB mice reduced fibrosis of skin and eye. The fibrosis-delaying effect was associated with a reduction of TGFβ signaling. IV rC7 in adult RDEB dogs incorporated in the dermal‒epidermal junction of skin and improved disease by promoting wound healing and reducing dermal‒epidermal separation. In both species, IV C7 was well-tolerated. These preclinical studies suggest that repeated IV administration of rC7 is an option for systemic treatment of established adult RDEB.

A COL7A1 Variant in a Litter of Neonatal Basset Hounds with Dystrophic Epidermolysis Bullosa

We investigated three neonatal Basset Hound littermates with lesions consistent with epidermolysis bullosa (EB), a group of genetic blistering diseases. A clinically normal bitch was bred to her grandfather by artificial insemination. Out of a litter of seven puppies, two affected puppies died and one was euthanized, with these puppies being submitted for diagnostic necropsy. All had multiple bullae and ulcers involving the nasal planum and paw pads, as well as sloughing claws; one puppy also had oral and esophageal ulcers. The complete genome of one affected puppy was sequenced, and 37 known EB candidate genes were assessed. We found a candidate causative variant in COL7A1, which encodes the collagen VII alpha 1 chain. The variant is a complex rearrangement involving duplication of a 107 bp region harboring a frameshift deletion of 7 bp. The variant is predicted to truncate more than 75% of the open reading frame, p.(Val677Serfs*11). Targeted genotyping of this duplication confirmed that all three affected puppies were homozygous for the duplication, whereas 12 unaffected Basset Hounds did not carry the duplication. This variant was also not seen in the genomes of more than 600 dogs of other breeds. COL7A1 variants have been identified in humans and dogs with dystrophic epidermolysis bullosa (DEB). The identified COL7A1 variant therefore most likely represents the causative variant and allows the refinement of the preliminary EB diagnosis to DEB.

Nonsense variant in COL7A1 causes recessive dystrophic epidermolysis bullosa in Central Asian Shepherd dogs

A rare hereditary mechanobullous disorder called epidermolysis bullosa (EB) causes blistering in the skin and the mucosal membranes. To date, nineteen EB-related genes have been discovered in human and other species. We describe here a novel EB variant in dogs. Two newborn littermates of Central Asian Shepherd dogs with severe signs of skin blistering were brought to a veterinary clinic and euthanized due to poor prognosis. In post-mortem examination, the puppies were shown to have findings in the skin and the mucosal membranes characteristic of EB. A whole-genome sequencing of one of the affected puppies was performed to identify the genetic cause. The resequencing data were filtered under a recessive model against variants from 31 other dog genomes, revealing a homozygous case-specific nonsense variant in one of the known EB-causing genes, COL7A1 (c.4579C>T, p.R1527*). The variant results in a premature stop codon and likely absence of the functional protein in the basement membrane of the skin in the affected dogs. This was confirmed by immunohistochemistry using a COL7A1 antibody. Additional screening of the variant indicated full penetrance and breed specificity at ~28% carrier frequency. In summary, this study reveals a novel COL7A1 variant causing recessive dystrophic EB and provides a genetic test for the eradication of the disease from the breed.

Novel and emerging therapies in the treatment of recessive dystrophic epidermolysis bullosa

Epidermolysis bullosa (EB) is a clinically and genetically heterogeneous group of inherited blistering diseases that affects ∼ 500,000 people worldwide. Clinically, individuals with EB have fragile skin and are susceptible to blistering following minimal trauma, with mucous membrane and other organ involvement in some subtypes. Within the spectrum of EB, ∼ 5% of affected individuals have the clinically more severe recessive dystrophic (RDEB) variant with a prevalence of 8 per one million of the population. RDEB is caused by loss-of-function mutations in the type VII collagen gene, COL7A1, which leads to reduced or absent type VII collagen (C7) and a paucity of structurally effective anchoring fibrils at the dermal-epidermal junction (DEJ). Currently, there is no cure for RDEB, although considerable progress has been made in testing novel treatments including gene therapy (lentiviral and gamma retroviral vectors for COL7A1 supplementation in keratinocytes and fibroblasts), as well as cell therapy (use of allogeneic fibroblasts, mesenchymal stromal cells (MSCs), and bone marrow transplantation (BMT)). Here, we review current treatment modalities available as well as novel and emerging therapies in the treatment of RDEB. Clinical trials of new translational therapies in RDEB offer hope for improved clinical management of patients as well as generating broader lessons for regenerative medicine that could be applicable to other inherited or acquired abnormalities of wound healing or scarring.

Congenital dystrophic epidermolysis bullosa (DEB) in Sprague Dawley rats: a case series

BACKGROUND

Epidermolysis bullosa is a rare skin disease caused by defects in the basement membrane and/or other dermoepidermal junction components.

HYPOTHESIS/OBJECTIVES

We describe a series of spontaneous cases of dystrophic epidermolysis bullosa (DEB) in a colony of Sprague Dawley rats investigated with histopathology, transmission electron microscopy (TEM) and inheritance pattern.

ANIMALS

Four, 4-day-old pups from a litter of Sprague Dawley rats developed blistering, haemorrhagic skin lesions and were euthanized. Age-matched controls from the same litter were normal. Several months later two more litters presented with identical findings. All three litters had the same sire, suggesting a genetic component.

METHODS

Skin from affected and control animals was evaluated histologically and with TEM. Unaffected sibling pairs from affected litters were bred in order to potentially reproduce the disease and determine the mode of inheritance.

RESULTS

Histologically, there was significant dermoepidermal clefting below the basement membrane with variable amounts of haemorrhage and cellular debris within the clefts. Ultrastructurally, clefting occurred below the basement membrane with an intact lamina densa and normal hemidesmosomes. Anchoring filaments were strikingly absent. Litters produced from phenotypically unaffected sibling pairs resulted in a total of four more litters with approximately a quarter of pups affected.

CONCLUSIONS AND CLINICAL IMPORTANCE

Based on the gross lesions, histopathological features and TEM determination of separation below the lamina densa and lack of normal anchoring fibrils, these cases are most consistent with DEB. This is the first report of naturally occurring, localized and reproducible recessive DEB in Sprague Dawley rats.

Epidermolysis bullosa in animals: a review

Epidermolysis bullosa (EB) is a hereditary mechanobullous disease of animals and humans, characterized by an extreme fragility of the skin and mucous membranes. The main feature of EB in humans and animals is the formation of blisters and erosions in response to minor mechanical trauma. Epidermolysis bullosa is caused by mutations in the genes that code for structural proteins of the cytoskeleton of the basal keratinocytes or of the basement membrane zone. Based on the ultrastructural levels of tissue separation, EB is divided into the following three broad categories: epidermolysis bullosa simplex, junctional epidermolysis bullosa and dystrophic epidermolysis bullosa. Human types of EB are divided into several subtypes based on their ultrastructural changes and the mode of inheritance; subtypes are not fully established in animals. In humans, it is estimated that EB affects one in 17,000 live births; the frequency of EB in different animals species is not known. In all animal species, except in buffalo with epidermolysis bullosa simplex, multifocal ulcers are observed on the gums, hard and soft palates, mucosa of the lips, cheek mucosa and dorsum of the tongue. Dystrophic or absent nails, a frequent sign seen in human patients with EB, corresponds to the deformities and sloughing of the hooves in ungulates and to dystrophy or atrophy of the claws in dogs and cats. This review covers aspects of the molecular biology, diagnosis, classification, clinical signs and pathology of EB reported in animals.

Gene therapy: pursuing restoration of dermal adhesion in recessive dystrophic epidermolysis bullosa

The replacement of a defective gene with a fully functional copy is the goal of the most basic gene therapy. Recessive dystrophic epidermolysis bullosa (RDEB) is characterised by a lack of adhesion of the epidermis to the dermis. It is an ideal target for gene therapy as all variants of hereditary RDEB are caused by mutations in a single gene, COL7A1, coding for type VII collagen, a key component of anchoring fibrils that secure attachment of the epidermis to the dermis. RDEB is one of the most severe variants in the epidermolysis bullosa (EB) group of heritable skin diseases. Epidermolysis bullosa is defined by chronic fragility and blistering of the skin and mucous membranes due to mutations in the genes responsible for production of the basement membrane proteins. This condition has a high personal, medical and socio-economic impact. People with RDEB require a broad spectrum of medications and specialised care. Due to this being a systemic condition, most research focus is in the area of gene therapy. Recently, preclinical works have begun to show promise. They focus on the virally mediated ex vivo correction of autologous epithelium. These corrected cells are then to be expanded and grafted onto the patient following the lead of the first successful gene therapy in dermatology being a grafting of corrected tissue for junctional EB treatment. Current progress, outstanding challenges and future directions in translating these approaches in clinics are reviewed in this article.

Cell therapy in dermatology

Harnessing the regenerative capacity of keratinocytes and fibroblasts from human skin has created new opportunities to develop cell-based therapies for patients. Cultured cells and bioengineered skin products are being used to treat patients with inherited and acquired skin disorders associated with defective skin, and further clinical trials of new products are in progress. The capacity of extracutaneous sources of cells such as bone marrow is also being investigated for its plasticity in regenerating skin, and new strategies, such as the derivation of inducible pluripotent stem cells, also hold great promise for future cell therapies in dermatology. This article reviews some of the preclinical and clinical studies and future directions relating to cell therapy in dermatology, particularly for inherited skin diseases associated with fragile skin and poor wound healing.

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.

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.

The biomechanical properties of canine skin measured in situ by uniaxial extension

INTRODUCTION

A uniaxial extension system was setup to analyze the mechanical properties of dog skin.

MATERIAL AND METHODS

Pads were glued onto dog skin with constant reproducible geometrical parameters and the extension force was measured as a function of the extension values. Forty-one sites (82 cycling tests) were investigated in situ on 11 canine cadavers, half of them after surgically isolating the test area from the surrounding skin. Series of loading-unloading cycles of up to 5N or 10N or both loads were performed on each site. The elastic properties and the dissipative effects were characterized respectively by evaluating the secant Rigidity at maximum loads and the Fraction of dissipated energy.

RESULTS

A hysteresis phenomenon, implying the need for preconditioning to attain equilibrium cycles, was apparent during mechanical characterization. Polynomial expressions were used to relate the measured Rigidities and the Fractions of dissipated energy with or without sample isolation. The latter were less affected by isolation. The ratios between the Rigidities at 5N to those at 10N displayed non-linearity in the investigated extension range in contrary to the Fractions of dissipated energy.

DISCUSSION/CONCLUSION

The parameters confirming the dissipative non-linear elastic behavior of dog skin were identified and the correlation between Rigidity and Fraction of dissipated energy on isolated and non-isolated skin samples was quantitatively determined. This extension setup can now be used as a "true in vivo" mapping tool to determine the mechanical characteristics of the skin during healing processes or during the study of Human skin disease with the dog as an animal model.

Rat model for dominant dystrophic epidermolysis bullosa: glycine substitution reduces collagen VII stability and shows gene-dosage effect

Dystrophic epidermolysis bullosa, a severely disabling hereditary skin fragility disorder, is caused by mutations in the gene coding for collagen VII, a specialized adhesion component of the dermal-epidermal junction zone. Both recessive and dominant forms are known; the latter account for about 40% of cases. Patients with dominant dystrophic epidermolysis bullosa exhibit a spectrum of symptoms ranging from mild localized to generalized skin manifestations. Individuals with the same mutation can display substantial phenotypic variance, emphasizing the role of modifying genes in this disorder. The etiology of dystrophic epidermolysis bullosa has been known for around two decades; however, important pathogenetic questions such as involvement of modifier genes remain unanswered and a causative therapy has yet to be developed. Much of the failure to make progress in these areas is due to the lack of suitable animal models that capture all aspects of this complex monogenetic disorder. Here, we report the first rat model of dominant dystrophic epidermolysis bullosa. Affected rats carry a spontaneous glycine to aspartic acid substitution, p.G1867D, within the main structural domain of collagen VII. This confers dominant-negative interference of protein folding and decreases the stability of mutant collagen VII molecules and their polymers, the anchoring fibrils. The phenotype comprises fragile and blister-prone skin, scarring and nail dystrophy. The model recapitulates all signs of the human disease with complete penetrance. Homozygous carriers of the mutation are more severely affected than heterozygous ones, demonstrating for the first time a gene-dosage effect of mutated alleles in dystrophic epidermolysis bullosa. This novel viable and workable animal model for dominant dystrophic epidermolysis bullosa will be valuable for addressing molecular disease mechanisms, effects of modifying genes, and development of novel molecular therapies for patients with dominantly transmitted skin disease.

A COL7A1 mutation causes dystrophic epidermolysis bullosa in Rotes Höhenvieh cattle

We identified a congenital mechanobullous skin disorder in six calves on a single farm of an endangered German cattle breed in 2010. The condition presented as a large loss of skin distal to the fetlocks and at the mucosa of the muzzle. All affected calves were euthanized on humane grounds due to the severity, extent and progression of the skin and oral lesions. Examination of skin samples under light microscopy revealed detachment of the epidermis from the dermis at the level of the dermo epidermal junction, leading to the diagnosis of a subepidermal bullous dermatosis such as epidermolysis bullosa. The pedigree was consistent with monogenic autosomal recessive inheritance. We localized the causative mutation to an 18 Mb interval on chromosome 22 by homozygosity mapping. The COL7A1 gene encoding collagen type VII alpha 1 is located within this interval and COL7A1 mutations have been shown to cause inherited dystrophic epidermolysis bullosa (DEB) in humans. A SNP in the bovine COL7A1 exon 49 (c.4756C>T) was perfectly associated with the observed disease. The homozygous mutant T/T genotype was exclusively present in affected calves and their parents were heterozygous C/T confirming the assumed recessive mode of inheritance. All known cases and genotyped carriers were related to a single cow, which is supposed to be the founder animal. The mutant T allele was absent in 63 animals from 24 cattle breeds. The identified mutation causes a premature stop codon which leads to a truncated protein representing a complete loss of COL7A1 function (p.R1586*). We thus have identified a candidate causative mutation for this genetic disease using only three cases to unravel its molecular basis. Selection against this mutation can now be used to eliminate the mutant allele from the Rotes Höhenvieh breed.

Inherited junctional epidermolysis bullosa (Herlitz type) in German black-headed mutton sheep

This report describes the microscopical, immunohistochemical and ultrastructural findings in the first ovine cases of the Herlitz type of inherited junctional epidermolysis bullosa. Sixteen German black-headed mutton lambs and one crossbred lamb had blisters and ulceration of the skin and mucous membranes in addition to alterations of the horn of the hooves. Microscopically, there was separation of the dermoepidermal junction, which was confirmed to be located in the lamina lucida of the basement membrane by electron microscopy. In areas of subepidermal splitting the hemidesmosomes were missing and in adjacent areas they appeared to be rudimentary and reduced in number. Immunohistochemistry for laminin 5 revealed a markedly reduced expression of this molecule on the dermal side of the blisters, while expression of collagen VII was normal.

Correction of dog dystrophic epidermolysis bullosa by transplantation of genetically modified epidermal autografts

Recessive dystrophic epidermolysis bullosa (RDEB) is a severe skin blistering condition caused by mutations in the gene coding for collagen type VII. Genetically engineered RDEB dog keratinocytes were used to generate autologous epidermal sheets subsequently grafted on two RDEB dogs carrying a homozygous missense mutation in the col7a1 gene and expressing baseline amounts of the aberrant protein. Transplanted cells regenerated a differentiated and vascularized auto-renewing epidermis progressively repopulated by dendritic cells and melanocytes. No adverse immune reaction was detected in either dog. In dog 1, the grafted epidermis firmly adhered to the dermis throughout the 24-month follow-up, which correlated with efficient transduction (100%) of highly clonogenic epithelial cells and sustained transgene expression. In dog 2, less efficient (65%) transduction of primary keratinocytes resulted in a loss of the transplanted epidermis and graft blistering 5 months after transplantation. These data provide the proof of principle for ex vivo gene therapy of RDEB patients with missense mutations in collagen type VII by engraftment of the reconstructed epidermis, and demonstrate that highly efficient transduction of epidermal stem cells is crucial for successful gene therapy of inherited skin diseases in which correction of the genetic defect confers no major selective advantage in cell culture.

Determination of the depth of excision using a dermatome (Aesculap) to export all hair follicle bulbs from a donor site in the dog

The aim of the study was to determine the depth of excision using a dermatome to excise all hair follicle bulbs from the donor site. Partial-thickness skin samples of different depth, ranging from 0.4 to 1 mm, were excised using a dermatome (Aesculap) from the dorsal aspect of the trunk of the dog. Biopsies, using a 6-mm biopsy punch, were performed in the centre of each donor site and excised sample. They were processed routinely for histological examination and the aspect of the hair follicles was observed. Split-thickness skin grafts of >or=0.7 mm deep performed with a dermatome contain the entire hair follicle.

Current approaches and perspectives in human keratinocyte-based gene therapies

Inherited and acquired disorders are liable to treatment with somatic gene therapy. The skin, and in particular epidermal cells, are particularly suited to genetic manipulation and follow-up of therapeutic effects. Cutaneous gene therapy may be effective for skin defects and systemic abnormalities. The robust basic and preclinical data available today would support the application of keratinocyte-based gene therapy to patients.

Gene therapy of epidermolysis bullosa

Easy access to the organ and identification of underlying mutations in epidermolysis bullosa (EB) facilitated the first cutaneous gene therapy experiments in vitro in the mid-1990s. The leading technology was transduction of the respective cDNA carried by a retroviral vector. Using this approach, the genotypic and phenotypic hallmark features of the recessive forms of junctional EB, which are caused by loss of function of the structural proteins laminin-5 or bullous pemphigoid antigen 2/type XVII collagen of the dermo-epidermal basement membrane zone, have been corrected in vitro and in vivo using xenograft mouse models. Recently, this approach has also been shown to be feasible for the large COL7A1 gene (mutated in dystrophic EB), applying PhiC31 integrase or lentiviral vectors. Neither of these approaches has made it into a successful Phase I study on EB patients. Therefore, alternative approaches to gene correction, including modulation of splicing, are being investigated for gene therapy in EB.

Cloning of laminin gamma2 cDNA and chromosome mapping of the genes for the dog adhesion ligand laminin 5

Overexpression of the gamma2 chain of laminin-5 has been linked to tumor invasion and an unfavorable prognostic value, but the role of this adhesion molecule in cancer progression remains unclear. Because dog models of human cancers provide the opportunity of clarifying the relation between laminin-5 and tumor malignancy we have isolated and characterized the cDNA of dog gamma2 chain. Comparative analysis of the nucleotide sequence revealed high identity between the dog and the human gamma2, including the intermolecular molecule binding sites and the regulatory promoter sequences. Moreover, expression of a recombinant human gamma2 chain in dog keratinocytes results in assembly and secretion of hybrid laminin-5 molecules, which underscore the functional relevance of the gamma2 conserved domains. We have also determined the syntenic location of the dog laminin-5 loci on CFA7. Our study provides a basis for therapeutical approaches of epithelial cancers of gamma2 using dogs as large animal models.

Genetic correction of canine dystrophic epidermolysis bullosa mediated by retroviral vectors

We have assessed the suitability of retroviral vectors for gene therapy of recessive dystrophic epidermolysis bullosa (RDEB) in dogs expressing a mutated collagen type VII. Isolation and analysis of the 9 kb dog collagen type VII cDNA identified the causative genetic mutation G1906S and disclosed the interspecies conservation of collagen type VII. Highly efficient transfer of the wild-type collagen type VII cDNA to both dog RDEB and human primary RDEB collagen type VII-null keratinocytes using recombinant vectors derived from LZRS-Ires-zeo and MSCV retroviruses achieved sustained and permanent expression of the transgene product. The expression and post-translational modification profile of the recombinant collagen type VII was comparable to that of the wild-type counterpart. The recombinant canine collagen type VII in human RDEB keratinocytes and dog cells corrected the observable defects caused by RDEB keratinocytes in cell cultures and in vitro reconstructed skin. Hypermotility was fully reverted in human RDEB keratinocytes, and strongly reduced in the dog RDEB cells. This observation suggests that not only infection efficiency but also high expression levels are required to ensure therapeutic efficacy in the presence of mutated gene products. Our results set the basis for preclinical gene therapy assays in the first immune-competent large animal model for an inherited skin disease and broaden the spectrum of preclinical and clinical applications of retroviral vectors in the transfer of large recombinant genes in epithelial cells.

Genetic reversion of inherited skin disorders

Human epidermis is a squamous stratified epithelium whose integrity relies on balanced processes of cell attachment, proliferation, and differentiation. In monogenic skin dermatoses, such as mecano-bullous diseases, or DNA repair deficiencies such as the xeroderma pigmentosum (XP), alterations of skin integrity may have devastating consequences as illustrated by the extremely high epidermal cancer proneness of XP patients. The lack of efficient pharmacological treatments, the easy accessibility of skin, and the possibility of long term culture and genetic manipulations ex vivo of epidermal keratinocytes, have encouraged approaches toward gene transfer and skin therapy prospects. We review here some of the human genetic disorders that exhibit major traits in skin, as well as requirements and difficulties inherent to approaches aimed at stable phenotypic correction.

Animal models for skin blistering conditions: absence of laminin 5 causes hereditary junctional mechanobullous disease in the Belgian horse

Recent achievements in the genetic correction of keratinocytes isolated from patients with junctional epidermolysis bullosa have paved the way to a gene therapy approach for the disease. Because gene therapy protocols require preclinical validation in animals, we have characterized spontaneous animal models of junctional epidermolysis bullosa. In this study we have elucidated the genetic basis of the hereditary junctional mechanobullous disease in the Belgian horse, a condition characterized by blistering of the skin and mouth epithelia, and exungulation (loss of the hoof). Immunofluorescence analysis associated the condition to the absent expression of the gamma2 chain of laminin 5 and designated Lamc2 as the candidate gene. Comparative analysis of the nucleotide sequence of the full-length gamma2 cDNA isolated by reverse transcription polymerase chain reaction amplification of total RNA purified from the epithelium of a junctional epidermolysis bullosa foal and a healthy control disclosed a homozygous basepair insertion (1368insC) in the affected animal. Mutation 1368insC results in a downstream premature termination codon and is predicted to cause absent expression of the laminin gamma2 polypeptide. Our results also show that: (i) the horse junctional epidermolysis bullosa genetically corresponds to the severe Herlitz form of junctional epidermolysis bullosa in man; (ii) the amino acid sequence and structure of the horse laminin gamma2 chain are virtually identical to the human counterpart; (iii) the moderate eruption of skin blisters in the affected animals with respect to the human Herlitz junctional epidermolysis bullosa patients correlates with the protection provided by hair. Our observations suggest that the affected foals are a convenient source of epithelial cells from tissues that cannot be obtained from human junctional epidermolysis bullosa patients, and imply that hairless strains of animals with recessive skin disorders would be the best models for in vivo gene therapy approaches to skin blistering diseases.

Skin biopsy site selection in small animal dermatology with an introduction to histologic pattern-analysis of inflammatory skin lesions

The skin biopsy is an invaluable diagnostic tool in veterinary dermatology. Biopsy site selection and interpretation of the biopsy report significantly influence the value of this procedure for diagnosing inflammatory skin diseases and are discussed in this article. Skin diseases often present with several different recognizable lesions that change significantly during their evolution. Individual lesions are typically heterogenous--some areas are diagnostic and some are not. Understanding which skin lesions to biopsy, and when and where to sample them, can significantly improve the value of information collected. To increase the information returned to clinicians for a biopsy, veterinary dermatopathologists have adopted the pattern-analysis method of classifying inflammatory skin lesions. This approach is based on recognizing morphologically distinct inflammatory patterns in skin biopsies and their association with particular sets of diseases. A basic knowledge of the pattern-analysis method is essential for maximizing the interpretation of skin biopsy reports.

Cutaneous gene transfer and therapy: the present and the future

The easy accessibility of the skin as a therapeutic target provides an exciting potential for this organ for the development of gene therapy protocols for cutaneous diseases and a variety of metabolic disorders. Thus far, full phenotypic reversion of a diseased phenotype has been achieved in vivo for junctional epidermolysis bullosa and X-linked or lamellar ichthyosis and in vitro for xeroderma pigmentosum. These recessive skin diseases are characterized by skin blistering, abnormalities in epidermal differentiation and increased development of skin cancers, respectively. Corrective gene delivery at both molecular and functional levels was achieved by transduction of cultured skin cells using retroviral vectors carrying the specific curative cDNA. These positive results should prompt clinical trials based on transplantation of artificial epithelia reconstructed ex vivo using genetically modified keratinocytes. Promising results have also been obtained in phenotypic reversion of cells isolated from patients suffering from a number of metabolic diseases such as gyrate atrophy, familial hypercholesterolemia or phenylketonuria. In these diseases transplantation of autologous artificial epithelia expressing the transgenes of interest or direct transfer of the DNA to the skin represents a potential therapeutic approach for the systemic delivery of active molecules. Successful cutaneous gene therapy trials, however, require development of protocols for efficient gene transfer to epidermal stem cells, and information about the host immune response to the recombinant polypeptides produced by the implanted keratinocytes. The availability of spontaneous animal models for genodermatoses will validate the gene therapy approach in preclinical trials.