Inherited junctional epidermolysis bullosa in the German Pointer: establishment of a large animal model

Independent COL17A1 Variants in Cats with Junctional Epidermolysis Bullosa

Epidermolysis bullosa (EB), characterized by defective adhesion of the epidermis to the dermis, is a heterogeneous disease with many subtypes in human patients and domestic animals. We investigated two unrelated cats with recurring erosions and ulcers on ear pinnae, oral mucosa, and paw pads that were suggestive of EB. Histopathology confirmed the diagnosis of EB in both cats. Case 1 was severe and had to be euthanized at 5 months of age. Case 2 had a milder course and was alive at 11 years of age at the time of writing. Whole genome sequencing of both affected cats revealed independent homozygous variants in COL17A1 encoding the collagen type XVII alpha 1 chain. Loss of function variants in COL17A1 lead to junctional epidermolysis bullosa (JEB) in human patients. The identified splice site variant in case 1, c.3019+1del, was predicted to lead to a complete deficiency in collagen type XVII. Case 2 had a splice region variant, c.769+5G>A. Assessment of the functional impact of this variant on the transcript level demonstrated partial aberrant splicing with residual expression of wildtype transcript. Thus, the molecular analyses provided a plausible explanation of the difference in clinical severity between the two cases and allowed the refinement of the diagnosis in the affected cats to JEB. This study highlights the complexity of EB in animals and contributes to a better understanding of the genotype-phenotype correlation in COL17A1-related JEB.

Inheritance of Monogenic Hereditary Skin Disease and Related Canine Breeds

The plasticity of the genome is an evolutionary factor in all animal species, including canines, but it can also be the origin of diseases caused by hereditary genetic mutation. Genetic changes, or mutations, that give rise to a pathology in most cases result from recessive alleles that are normally found with minority allelic frequency. The use of genetic improvement increases the consanguinity within canine breeds and, on many occasions, also increases the frequency of these recessive alleles, increasing the prevalence of these pathologies. This prevalence has been known for a long time, but mutations differ according to the canine breed. These genetic diseases, including skin diseases, or genodermatosis, which is narrowly defined as monogenic hereditary dermatosis. In this review, we focus on genodermatosis sensu estricto, i.e., monogenic, and hereditary dermatosis, in addition to the clinical features, diagnosis, pathogeny, and treatment. Specifically, this review analyzes epidermolytic and non-epidermolytic ichthyosis, junctional epidermolysis bullosa, nasal parakeratosis, mucinosis, dermoid sinus, among others, in canine breeds, such as Golden Retriever, German Pointer, Australian Shepherd, American Bulldog, Great Dane, Jack Russell Terrier, Labrador Retriever, Shar-Pei, and Rhodesian Ridgeback.

Genes of Congenital Dermatologic Disorders in Dogs—A Review

This article presents an overview of up-to-date identified genes responsible for congenital canine skin diseases of dogs and the characteristics of these diseases. Congenital skin diseases constitute a specific group of dermatologic disorders that plays an important role in breeding of purebred dogs. They include primary seborrhoea, ichthyosis, hereditary nasal parakeratosis, dermatomyositis, colour dilution alopecia, skin mucinosis, dermoid sinus, lethal acrodermatitis, acral mutilation syndrome, keratoconjunctivitis sicca, ichthyosiform dermatosis, bullous epidermolysis, exfoliative dermal lupus erythematosus, congenital footpad hyperkeratosis and sebaceous adenitis. In the majority of cases, their occurrence is linked to particular breeds. In more than half of these diseases a specific defective gene variant responsible for the disease has been identified. Genetic tests for identification of the relevant defective genes serve as an important tool in the diagnostics of diseases in veterinary practice and in breeding of purebred dogs.

Genetic trend of the junctional epidermolysis bullosa in the German shorthaired pointer in Italy

BACKGROUND

Epidermolysis bullosa (EB) is a hereditary heterogeneous group of mechanobullous disorders caused by mutations in several structural skin proteins observed in both humans and animals. In this work, we report the incidence and the genetic trend of the junctional epidermolysis bullosa (JEB), a major type of EB, in the Italian German Shorthaired Pointer (GSPs) population in a 10 years span.

METHODS

In this study, we monitored the genetic trend of JEB in the Italian population of the GSPs from 2009 to 2018 in 750 animals. The studied mutation was the insertion (4818+207 ins 6.5 kb) of repetitive satellite DNA within intron 35 of the LAMA3 gene.

RESULTS

Allele frequencies showed a reduction of the mutated (C) allele during the years, with the only exception of 2017, when 13 dogs were diagnosed as carrier for the genetic pathology. A regression logistic analysis was performed, including sex, coat colour and their interaction. Our results showed that there was a statistically significant association with coat colour.

CONCLUSIONS

The simplicity and the low cost of the analysis for the detection of this pathology suggests that a deeper identification of carrier dogs will allow better breeding strategies and management, leading to a rapid JEB eradication.

Genetics of inherited skin disorders in dogs

Canine genodermatoses represent a broad spectrum of diseases with diverse phenotypes. Modern genetic technology including whole genome sequencing has expedited the identification of novel genes and greatly simplified the establishment of genetic diagnoses in such heterogeneous disorders. The precise genetic diagnosis of a heritable skin disorder is essential for the appropriate counselling of owners regarding the course of the disease, prognosis and implications for breeding. Understanding the underlying pathophysiology is a prerequisite to developing specific, targeted or individualized therapeutic approaches. This review aims to create a comprehensive overview of canine genodermatoses and their respective genetic aetiology known to date. Raising awareness of genodermatoses in dogs is important and this review may help clinicians to apply modern genetics in daily clinical practice, so that a precise diagnoses can be established in suspected genodermatoses.

Canine junctional epidermolysis bullosa due to a novel mutation in LAMA3 with severe upper respiratory involvement

BACKGROUND

Junctional epidermolysis bullosa (JEB) is a group of congenital blistering skin diseases characterized by clefting through the lamina lucida of the basement membrane zone.

OBJECTIVES

To characterize the clinical and morphological features of a congenital mechanobullous disease in a litter of puppies with severe upper respiratory involvement, and to identify an associated genetic variant.

ANIMALS

Five of eight puppies in an Australian cattle dog cross-bred litter showed signs of skin fragility. Three were stillborn and one died at one month of age. The two surviving puppies were presented with blistering skin disease and severe respiratory distress. Additionally, one unaffected sibling was examined and blood was obtained for genetic testing.

METHODS AND MATERIALS

Post-mortem examination, histopathological evaluation and electron microscopy were performed. Whole genome sequencing (WGS) of one affected puppy was compared to a database of 522 dogs of 55 different breeds for variant analysis. Sanger sequencing of one additional affected and one unaffected sibling confirmed the variant.

RESULTS

Clinically, severe mucocutaneous ulcers occurred in frictional areas with claw sloughing. Histopathological results revealed subepidermal clefts and electron microscopy confirmed the split in the lamina lucida. Post-mortem examination documented extensive pharyngeal and laryngeal lesions with granulation tissue and fibrinous exudate obscuring the airway. Moderate tracheal hypoplasia contributed. The WGS revealed a novel missense variant in the laminin α3-chain XP_537297.2p(Asp2867Val), with an autosomal recessive mode of inheritance.

CONCLUSIONS AND CLINICAL RELEVANCE

A novel variant in LAMA3 caused a generalized and severe phenotype of JEB with an unique clinical presentation of upper airway obstruction.

A de novo mutation in KRT5 in a crossbred calf with epidermolysis bullosa simplex

A 6‐day‐old Belgian Blue‐Holstein calf was referred because of a syndrome resembling epidermolysis bullosa simplex (EBS). The clinical phenotype included irregular and differently sized erosions and ulcerations spread over the body, in particular on the limbs and over bone prominences, as well as in the nasal planum and oral mucosa. Blisters were easily induced by rubbing the skin. The skin lesions displayed a clear dermal‐epidermal separation at the level of the basal cell layer. Post mortem examination revealed erosions in the pharynx, proximal esophagus, and rumen. Whole‐genome sequencing revealed a heterozygous disruptive in‐frame deletion variant in KRT5 (c.534_536delCAA). Genotyping of both parents confirmed the variant as de novo mutation. Clinicopathological and genetic findings were consistent with the diagnosis of KRT5‐related EBS providing the second example of a spontaneous mutation causing epidermolysis bullosa in cattle.

LAMB3 Missense Variant in Australian Shepherd Dogs with Junctional Epidermolysis Bullosa

In a highly inbred Australian Shepherd litter, three of the five puppies developed widespread ulcers of the skin, footpads, and oral mucosa within the first weeks of life. Histopathological examinations demonstrated clefting of the epidermis from the underlying dermis within or just below the basement membrane, which led to a tentative diagnosis of junctional epidermolysis bullosa (JEB) with autosomal recessive inheritance. Endoscopy in one affected dog also demonstrated separation between the epithelium and underlying tissue in the gastrointestinal tract. As a result of the severity of the clinical signs, all three dogs had to be euthanized. We sequenced the genome of one affected puppy and compared the data to 73 control genomes. A search for private variants in 37 known candidate genes for skin fragility phenotypes revealed a single protein-changing variant, LAMB3:c.1174T>C, or p.Cys392Arg. The variant was predicted to change a conserved cysteine in the laminin β3 subunit of the heterotrimeric laminin-322, which mediates the binding of the epidermal basement membrane to the underlying dermis. Loss-of-function variants in the human LAMB3 gene lead to recessive forms of JEB. We confirmed the expected co-segregation of the genotypes in the Australian Shepherd family. The mutant allele was homozygous in two genotyped cases and heterozygous in three non-affected close relatives. It was not found in 242 other controls from the Australian Shepherd breed, nor in more than 600 other controls. These data suggest that LAMB3:c.1174T>C represents the causative variant. To the best of our knowledge, this study represents the first report of a LAMB3-related JEB in domestic animals.

Transcriptome Profiling and Differential Gene Expression in Canine Microdissected Anagen and Telogen Hair Follicles and Interfollicular Epidermis

The transcriptome profile and differential gene expression in telogen and late anagen microdissected hair follicles and the interfollicular epidermis of healthy dogs was investigated by using RNAseq. The genes with the highest expression levels in each group were identified and genes known from studies in other species to be associated with structure and function of hair follicles and epidermis were evaluated. Transcriptome profiling revealed that late anagen follicles expressed mainly keratins and telogen follicles expressed GSN and KRT15. The interfollicular epidermis expressed predominately genes encoding for proteins associated with differentiation. All sample groups express genes encoding for proteins involved in cellular growth and signal transduction. The expression pattern of skin-associated genes in dogs is similar to humans. Differences in expression compared to mice and humans include BMP2 expression mainly in telogen and high KRT17 expression in the interfollicular epidermis of dogs. Our data provide the basis for the investigation of the structure and function of canine skin or skin disease and support the use of dogs as a model for human cutaneous disease by assigning gene expression to specific tissue states.

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.

Genetic testing in veterinary dermatology

BACKGROUND

Molecular genetics has made significant advances in the analysis of hereditary dermatoses during the last several years.

OBJECTIVES

To provide an update on currently available genetic tests for skin diseases of dogs, cats and horses, and to aid the veterinary clinician in the appropriate selection and applications of genetic tests.

METHODS

The scientific literature on the topic was critically reviewed. The list of known causative variants for genodermatoses and hair morphology traits was compiled by searching the Online Mendelian Inheritance in Animals (OMIA) database.

RESULTS

Genetic testing has become an important diagnostic method in veterinary medicine. Genetic tests can help to establish the correct diagnosis in some diseases with relatively nonspecific signs. Genetic tests are also essential for sustainable breeding programmes and to help minimize the frequency of animals with hereditary diseases. Advances in genetic methodology and bioinformatics already allow genome-wide screening for potential disease causing mutations for research purposes. It is anticipated that this will become a routine process in clinical practice in the future.

CONCLUSION AND CLINICAL IMPORTANCE

As specific DNA tests and broad genome-wide analyses come into more common use, it is critical that clinicians understand the proper application and interpretation of these test results.

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.

From caveman companion to medical innovator: genomic insights into the origin and evolution of domestic dogs

The phenotypic and behavioral diversity of the domestic dog has yet to be matched by any other mammalian species. In their current form, which comprises more than 350 populations known as breeds, there is a size range of two orders of magnitude and morphological features reminiscent of not only different species but also different phylogenetic families. The range of both appearance and behavior found in the dog is the product of millennia of human interference, and though humans created the diversity it remains a point of fascination to both lay and scientific communities. In this review we summarize the current understanding of the history of dog domestication based on molecular data. We will examine the ways that canine genetic and genomic studies have evolved and look at examples of dog genetics in the light of human disease.

Combining GWAS and RNA-Seq Approaches for Detection of the Causal Mutation for Hereditary Junctional Epidermolysis Bullosa in Sheep

In this study, we demonstrate the use of a genome-wide association mapping together with RNA-seq in a reduced number of samples, as an efficient approach to detect the causal mutation for a Mendelian disease. Junctional epidermolysis bullosa is a recessive genodermatosis that manifests with neonatal mechanical fragility of the skin, blistering confined to the lamina lucida of the basement membrane and severe alteration of the hemidesmosomal junctions. In Spanish Churra sheep, junctional epidermolysis bullosa (JEB) has been detected in two commercial flocks. The JEB locus was mapped to Ovis aries chromosome 11 by GWAS and subsequently fine-mapped to an 868-kb homozygous segment using the identical-by-descent method. The ITGB4, which is located within this region, was identified as the best positional and functional candidate gene. The RNA-seq variant analysis enabled us to discover a 4-bp deletion within exon 33 of the ITGB4 gene (c.4412_4415del). The c.4412_4415del mutation causes a frameshift resulting in a premature stop codon at position 1472 of the integrin β4 protein. A functional analysis of this deletion revealed decreased levels of mRNA in JEB skin samples and the absence of integrin β4 labeling in immunohistochemical assays. Genotyping of c.4412_4415del showed perfect concordance with the recessive mode of the disease phenotype. Selection against this causal mutation will now be used to solve the problem of JEB in flocks of Churra sheep. Furthermore, the identification of the ITGB4 mutation means that affected sheep can be used as a large mammal animal model for the human form of epidermolysis bullosa with aplasia cutis. Our approach evidences that RNA-seq offers cost-effective alternative to identify variants in the species in which high resolution exome-sequencing is not straightforward.

Epidermolysis bullosa in Danish Hereford calves is caused by a deletion in LAMC2 gene

BACKGROUND

Heritable forms of epidermolysis bullosa (EB) constitute a heterogeneous group of skin disorders of genetic aetiology that are characterised by skin and mucous membrane blistering and ulceration in response to even minor trauma. Here we report the occurrence of EB in three Danish Hereford cattle from one herd.

RESULTS

Two of the animals were necropsied and showed oral mucosal blistering, skin ulcerations and partly loss of horn on the claws. Lesions were histologically characterized by subepidermal blisters and ulcers. Analysis of the family tree indicated that inbreeding and the transmission of a single recessive mutation from a common ancestor could be causative. We performed whole genome sequencing of one affected calf and searched all coding DNA variants. Thereby, we detected a homozygous 2.4 kb deletion encompassing the first exon of the LAMC2 gene, encoding for laminin gamma 2 protein. This loss of function mutation completely removes the start codon of this gene and is therefore predicted to be completely disruptive. The deletion co-segregates with the EB phenotype in the family and absent in normal cattle of various breeds. Verifying the homozygous private variants present in candidate genes allowed us to quickly identify the causative mutation and contribute to the final diagnosis of junctional EB in Hereford cattle.

CONCLUSIONS

Our investigation confirms the known role of laminin gamma 2 in EB aetiology and shows the importance of whole genome sequencing in the analysis of rare diseases in livestock.

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.

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.

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.

Copy number variation in the domestic dog

Differences in the content and organization of DNA, collectively referred to as structural variation, have emerged as a major source of genetic and phenotypic diversity within and between species. In addition, structural variation provides an important substrate for evolutionary innovations. Here, we review recent progress in characterizing patterns of canine structural variation within and between breeds, and in correlating copy number variants (CNVs) with phenotypes. Because of the extensive phenotypic diversity that exists within and between breeds and the tantalizing examples of canine CNVs that influence traits such as skin wrinkling in Shar-Pei, dorsal hair ridge in Rhodesian and Thai Ridgebacks, and short limbs in many breeds such as Dachshunds and Corgis, we argue that domesticated dogs are uniquely poised to contribute novel insights into CNV biology. As new technologies continue to be developed and refined, the field of canine genomics is on the precipice of a deeper understanding of how structural variation and CNVs contribute to canine genetic diversity, phenotypic variation, and disease susceptibility.

A frameshift mutation within LAMC2 is responsible for Herlitz type junctional epidermolysis bullosa (HJEB) in black headed mutton sheep

Junctional epidermolysis bullosa (JEB) is a hereditary mechanobullous skin disease in humans and animals. A Herlitz type JEB was identified in German Black Headed Mutton (BHM) sheep and affected lambs were reproduced in a breeding trial. Affected lambs showed skin and mucous membranes blistering and all affected lambs died within the first weeks of life. The pedigree data were consistent with a monogenic autosomal recessive inheritance. Immunofluorescence showed a reduced expression of laminin 5 protein which consists of 3 subunits encoded by the genes LAMA3, LAMB3 and LAMC2. We screened these genes for polymorphisms. Linkage and genome-wide association analyses identified LAMC2 as the most likely candidate for HJEB. A two base pair deletion within exon 18 of the LAMC2 gene (FM872310:c.2746delCA) causes a frameshift mutation resulting in a premature stop codon (p.A928*) 13 triplets downstream of this mutation and in addition, introduces an alternative splicing of exon 18 LAMC2. This deletion showed a perfect co-segregation with HJEB in all 740 analysed BHM sheep. Identification of the LAMC2 deletion means an animal model for HJEB is now available to develop therapeutic approaches of relevance to the human form of this disease.

Leader of the pack: gene mapping in dogs and other model organisms

The domestic dog offers a unique opportunity to explore the genetic basis of disease, morphology and behaviour. We share many diseases with our canine companions, including cancer, diabetes and epilepsy, making the dog an ideal model organism for comparative disease genetics. Using newly developed resources, whole-genome association in dog breeds is proving to be exceptionally powerful. Here, we review the different trait-mapping strategies, some key biological findings emerging from recent studies and the implications for human health. We also discuss the development of similar resources for other vertebrate organisms.

Man's best friend becomes biology's best in show: genome analyses in the domestic dog

In the last five years, canine genetics has gone from map construction to complex disease deconstruction. The availability of a draft canine genome sequence, dense marker chips, and an understanding of the genome architecture has changed the types of studies canine geneticists can undertake. There is now a clear recognition that the dog system offers the opportunity to understand the genetics of both simple and complex traits, including those associated with morphology, disease susceptibility, and behavior. In this review, we summarize recent findings regarding canine domestication and review new information on the organization of the canine genome. We discuss studies aimed at finding genes controlling morphological phenotypes and provide examples of the way such paradigms may be applied to studies of behavior. We also discuss the many ways in which the dog has illuminated our understanding of human disease and conclude with a discussion on where the field is likely headed in the next five years.

Clinical and immunological heterogeneity of canine subepidermal blistering dermatoses with anti-laminin-332 (laminin-5) auto-antibodies

Laminin-332 (laminin-5) is a basement membrane heterotrimeric protein composed of alpha-3, beta-3 and gamma-2 laminin chains. Laminin-332 polypeptides are targeted by auto-antibodies in human patients with mucous membrane (cicatricial) pemphigoid or, more rarely, subepidermal vesicular diseases that resemble epidermolysis bullosa acquisita (EBA) or bullous pemphigoid (BP). The objectives of this report were to characterize the clinical, histopathological and immunological characteristics of nine dogs with auto-antibodies targeting laminin-332. Immunological investigations consisted of direct immunofluorescence (IF), indirect IF with intact and salt-split canine gingival, and salt-split normal or laminin-332-deficient human skin, immunoblotting with purified human laminin-332 and immunoblotting with recombinant NC1 domain of human collagen VII. All dogs exhibited varying degrees of skin blistering and ulceration associated with microscopic subepidermal vesiculation with or without inflammatory cells. Indirect IF established that circulating IgG auto-antibodies bound the dermal side of salt-split canine lip and human skin. In five dogs, IgG variably recognized the basement membrane of laminin-332-deficient human skin (three dogs negative, two dogs positive). In all nine dogs, IgG auto-antibodies detected purified human laminin-332 by immunoblotting. In two dogs, additional targeting of collagen VII-NC1 was present. These observations establish laminin-332 as a novel basement membrane antigen in dogs with autoimmune blistering diseases with variable clinical phenotypes. The names 'acquired junctional epidermolysis bullosa', 'anti-laminin-332 mucous membrane pemphigoid (MMP)' and 'mixed auto-immune subepidermal blistering dermatosis' are proposed for dogs with clinical signs reminiscent of EBA, MMP or BP respectively.

Two dogs with juvenile-onset skin diseases with involvement of extremities

Two dogs of juvenile-onset skin diseases with involvement of extremities were examined by histopathological, immunohistochemical and ultrastructural analyses. Clinically, both cases showed alopecia and crusts on the face and extremities. Case 1 showed histopathology of dermo-epidermal separation. Ultrastructural analysis revealed that the clefts were recognized between hemidesmosomes and lamina densa. In case 2, histopathology showed follicular atrophy, vacuolar degeneration at lower epidermis and masseter muscle degeneration, without remarkable ultrastructural abnormalities in basement membrane zone of the skin. Thus, the findings in case 1 were compatible to those in junctional epidermolysis bullosa, while those in case 2 were compatible to dermatomyositis-like disease. Combination of histopathological and ultrastructural analyses was useful to distinguish the diseases in two dogs.

A mouse model of generalized non-Herlitz junctional epidermolysis bullosa

Epidermolysis bullosa (EB) is a class of intractable, rare, genetic disorders characterized by fragile skin and blister formation as a result of dermal-epidermal mechanical instability. EB presents with considerable clinical and molecular heterogeneity. Viable animal models of junctional EB (JEB), that both mimic the human disease and survive beyond the neonatal period, are needed. We identified a spontaneous, autosomal recessive mutation (Lamc2(jeb)) due to a murine leukemia virus long terminal repeat insertion in Lamc2 (laminin gamma2 gene) that results in a hypomorphic allele with reduced levels of LAMC2 protein. These mutant mice develop a progressive blistering disease validated at the gross and microscopic levels to closely resemble generalized non-Herlitz JEB. The Lamc2(jeb) mice display additional extracutaneous features such as loss of bone mineralization and abnormal teeth, as well as a respiratory phenotype that is recognized but not as well characterized in humans. This model faithfully recapitulates human JEB and provides an important preclinical tool to test therapeutic approaches.

Animal models of epidermolysis bullosa

For more than 2 decades, animal models have been used to clarify the pathogenic mechanisms of human diseases and develop new therapeutics for these diseases. Several therapies for human diseases have become available through trials using animal models. Epidermolysis bullosa (EB) is one of the most severe inherited skin disorders, whose effective treatments have not been fully available. EB is characterized by abnormalities of the proteins that consist of the dermoepidermal junction. EB has been classified into three major subtypes according to the level of skin cleavage: EB simplex, junctional EB, and dystrophic EB. To date, 13 genes have been shown to cause EB phenotype. After the discovery of the causative genes responsible for each EB subtype, many researchers have tried to develop EB animal models by genetically manipulating the corresponding genes.

Partial deletion of the LAMA3 gene is responsible for hereditary junctional epidermolysis bullosa in the American Saddlebred Horse

Laminin 5 is a heterotrimeric basement membrane protein integral to the structure and function of the dermal-epidermal junction. It consists of three glycoprotein subunits: the alpha3, beta3 and gamma2 chains, which are encoded by the LAMA3, LAMB3 and LAMC2 genes respectively. A mutation in any of these genes results in the condition known as hereditary junctional epidermolysis bullosa (JEB). A 6589-bp deletion spanning exons 24-27 was found in the LAMA3 gene in American Saddlebred foals born with the skin-blistering condition epitheliogenesis imperfecta. The deletion confirms that this autosomal recessive condition in the American Saddlebred Horse can indeed be classified as JEB and corresponds to Herlitz JEB in humans. A diagnostic test was developed and nine of 175 randomly selected American Saddlebred foals from the 2007 foal crop were found to be carriers of the mutation (frequency of 0.026).

Sustained phenotypic reversion of junctional epidermolysis bullosa dog keratinocytes: Establishment of an immunocompetent animal model for cutaneous gene therapy

Gene transfer represents the unique therapeutic issue for a number of inherited skin disorders including junctional epidermolysis bullosa (JEB), an untreatable genodermatose caused by mutations in the adhesion ligand laminin 5 (alpha3beta3gamma2) that is secreted in the extracellular matrix by the epidermal basal keratinocytes. Because gene therapy protocols require validation in animal models, we have phenotypically reverted by oncoretroviral transfer of the curative gene the keratinocytes isolated from dogs with a spontaneous form of JEB associated with a genetic mutation in the alpha3 chain of laminin 5. We show that the transduced dog JEB keratinocytes: (1) display a sustained secretion of laminin 5 in the extracellular matrix; (2) recover the adhesion, proliferation, and clonogenic capacity of wild-type keratinocytes; (3) generate fully differentiated stratified epithelia that after grafting on immunocompromised mice produce phenotypically normal skin and sustain permanent expression of the transgene. We validate an animal model that appears particularly suitable to demonstrate feasibility, efficacy, and safety of genetic therapeutic strategies for cutaneous disorders before undertaking human clinical trials.