Junctional Epidermolysis Bullosa Patients Research Articles

Clinical and molecular features in a cohort of Middle Eastern patients with epidermolysis bullosa.

Epidermolysis bullosa (EB) features skin and mucosal fragility due to pathogenic variants in genes encoding components of the cutaneous basement membrane. Based on the level of separation within the dermal-epidermal junction, EB is sub-classified into four major types including EB simplex (EBS), junctional EB (JEB), dystrophic EB (DEB), and Kindler EB (KEB) with 16 EB-associated genes reported to date. We ascertained a cohort of 151 EB patients of various Middle Eastern ethnic backgrounds. The cohort was comprised of EBS (64%, 97/151), DEB (21%, 31/151), JEB (12%, 18/151), and KEB (3%, 5/151). KRT14 and KRT5 variants were most common among EBS patients with 43% (42/97) and 46% (45/97) of EBS patients carrying mutations in either of these two genes, respectively. Truncal involvement was more common in KRT14-associated EBS as compared to EBS due to KRT5 mutations (p < .05). Mutations in COL17A1 and laminin 332-encoding genes were identified in 55% (10/18) and 45% (8/18) of JEB patients. Scarring alopecia, caries, and EB nevi were most common among JEB patients carrying COL17A1 mutations as compared to laminin 332-associated JEB (p < .05). Abnormal nails were evident in most DEB and JEB patients while poikiloderma was exclusively observed in KEB (p < .001). EB patients of Middle Eastern origin were found to feature specific phenotype-genotype correlations of relevance to the diagnosis and genetic counseling of patients in this region.

849 Optimization of intravenous gentamicin to restore functional laminin 332 in junctional epidermolysis bullosa patients harboring nonsense mutations

Junctional epidermolysis bullosa (JEB) is an incurable and fatal inherited blistering skin disease most commonly caused by nonsense mutations in LAMA3, LAMB3, or LAMC2 genes. These mutations impair the ability to produce functional laminin 332, needed for epidermal-dermal adherence. Previously, we demonstrated that intravenous (IV) gentamicin daily at 7.5 mg/kg for two weeks promoted readthrough of nonsense mutations and produced functional laminin 332. Here, we determined if treating the patients with higher gentamicin doses and more prolonged treatment would induce more functional laminin 332, and provide more long-term clinical improvement.

Hologene 5: A Phase II/III Clinical Trial of Combined Cell and Gene Therapy of Junctional Epidermolysis Bullosa.

Epidermolysis bullosa (EB) is a group of devastating genetic diseases characterized by skin and mucosal fragility and formation of blisters, which develop either spontaneously or in response to minor mechanical trauma. There is no definitive therapy for any form of EB. Intermediate junctional EB (JEB) caused by mutations in the gene LAMB3 has been the first genetic skin disease successfully tackled by ex vivo gene therapy. Here, we present a multicenter, open-label, uncontrolled phase II/III study that aims at confirming the efficacy of Hologene 5, a graft consisting of cultured transgenic keratinocytes and epidermal stem cells and meant to combine cell and gene therapy for the treatment of LAMB3-related JEB. Autologous clonogenic keratinocytes will be isolated from patients’ skin biopsies, genetically corrected with a gamma-retroviral vector (γRV) carrying the full-length human LAMB3 cDNA and plated onto a fibrin support (144cm2). The transgenic epidermis will be transplanted onto surgically prepared selected skin areas of at least six JEB patients (four pediatric and two adults). Evaluation of clinical efficacy will include, as primary endpoint, a combination of clinical parameters, such as percentage of re-epithelialization, cellular, molecular, and functional parameters, mechanical stress tests, and patient-reported outcome (PRO), up to 12months after transplantation. Safety and further efficacy endpoints will also be assessed during the clinical trial and for additional 15years in an interventional non-pharmacological follow-up study. If successful, this clinical trial would provide a therapeutic option for skin lesions of JEB patients with LAMB3 mutations and pave the way to a combined cell and gene therapy platform tackling other forms of EB and different genodermatoses.Clinical Trial Registration: EudraCT Number: 2018-000261-36.

Next-generation sequencing through multigene panel testing for the diagnosis of hereditary epidermolysis bullosa in Chinese population.

Epidermolysis bullosa (EB) is a heritable blistering disorder. We performed a next-generation sequencing-based multigene panel test and successfully predicted 100% of the EB types, including, 36 EB simplex (EBS), 13 junctional EB (JEB), 86 dystrophic EB (DEB), and 3 Kindler EB. Chinese JEB and recessive DEB (RDEB) patients have relatively mild phenotypes; for severe type separately accounts for 45.5% and 23.8%, respectively. We identified 96 novel and 49 recurrent pathogenic variants in 11 genes, although we failed to detect the second mutation in one JEB and five RDEB patients. We identified one novel p.E475K mosaic mutation in the clinically normal mother of one out of 13 EBS patients with KRT5 mutations, one recurrent p.G2034R mosaic mutation, and one novel p.G2043R mosaic mutation in the clinically normal relatives of two out of 19 dominant DEB patients. This study shows that next-generation technology could be an effective tool in diagnosing EB.

594 Gentamicin therapy induces functional laminin 332 and improves wound healing in junctional epidermolysis bullosa patients harboring nonsense mutations

Herlitz Junctional Epidermolysis Bullosa (H-JEB) is an incurable and fatal inherited blistering skin disease most commonly caused by nonsense mutations in the LAMA3, LAMB3, or LAMC2 genes. These mutations impair production of functional laminin 332, which is needed for epidermal-dermal adherence. Previously, we demonstrated in vitro that gentamicin induced readthrough of premature stop codons (PTC) in H-JEB cultured keratinocytes harboring nonsense mutations and restored functional laminin 332. Herein, we examined if topical gentamicin could induce PTC readthrough and create new laminin 332 in H-JEB patients. H-JEB patients with nonsense mutations in LAMA3 and LAMB3 applied 0.5% gentamicin ointment topically to open wound Test sites daily for 14 days. Patient skin biopsies were examined before and at one and three months after treatment for the expression of laminin 332 and α6β4 integrin. Wounds were evaluated using photographs taken at zero, one and three months after treatment and Test Sites were assessed for new blister formation based on patient diaries and weekly questionnaires. Gentamicin treated sites exhibited newly created, correctly localized laminin 332 at the dermal-epidermal junction of their skin. The restoration of laminin 332 at these sites varied between 40% and 60% of the laminin 332 expression found in normal human skin and was durable for at least three months. Moreover, restored laminin 332 resulted in significantly increased expression and polarization of β4 integrin (from baseline 30% to 100% at 1 month and 3 months). Topical gentamicin corrected dermal-epidermal separation, improved wound closure and reduced new blister formation. No adverse events were observed. In summary, topical gentamicin reads through nonsense mutations in H-JEB patients and creates new laminin 332. Gentamicin therapy may provide a novel, low cost, non-invasive, and readily available therapy for JEB patients with nonsense mutations.

Carriers with functional null mutations in LAMA3 have localized enamel abnormalities due to haploinsufficiency.

The hereditary blistering disease junctional epidermolysis bullosa (JEB) is always accompanied by structural enamel abnormalities of primary and secondary dentition, characterized as amelogenesis imperfecta. Autosomal recessive mutations in LAMA3, LAMB3 and LAMC2 encoding the heterotrimer laminin 332 (LM-332) are among the genes causing JEB. While examining pedigrees of JEB patients with LAMA3 mutations, we observed that heterozygous carriers of functional null mutations displayed subtle enamel pitting in the absence of skin fragility or other JEB symptoms. Here, we report two new LAMA3 functional null mutations: nonsense c.2377C>T p.(Arg793Ter) and splice-site c.4684+1G>A mutation in heterozygous carriers exhibiting enamel pitting. Both parents had offspring affected with JEB and displayed subtle enamel pitting of secondary dentition without any sign of skin blistering. The reported enamel abnormality in LAMA3 mutation carriers could be attributed to a half dose effect of the laminin α3 chain (haploinsufficiency).

125. Engineered Nucleases-Mediated In Situ Correction of a Genetic Defect By Homologous Recombination Into the Native Locus

Engineered nucleases specific for genomic targets are extensively used to generate DSBs that increase the rate and efficiency of homologous recombination (HR). We seek to determine the efficacy of nucleases in a clinical relevant genetic defect.The genetic defect we are addressing as model to test the nucleases-mediated genome editing technology is the junctional epidermolysis bullosa (JEB), a family of severe skin adhesion disorders due to autosomal recessive mutations in the LAMB3 gene coding for the laminin-332 heterotrimer, a key component of the dermal-epidermaljunction. Recently, we provided proof of principle that ZFN-mediated, AAVS1-targeted GFP addition can be achieved in human keratinocytes and in long-term repopulating epithelial stem cells in a validated preclinical model of xenotransplantation of human skin equivalents on immunodeficient mice.This project aims at the demonstration of a successful in situ correction of the LAMB3 gene in primary keratinocytes from Herlitz JEB patients. Recently TALEN-based gene correction for dystrophic EB has been reported. Similarly, we have developed a genome editing approach for JEB. In particular we have designed TALENs specific for the second intron of LAMB3 gene and a HR cassette including a splicible LAMB3 cDNA (from exon 3 to the end of the gene). In particular immortalized JEB keratinocytes were transfected with TALEN mRNAs and infected with an IDLV vector carrying the HR cassette. The in situ gene correction has been evaluated by site-specific PCR and knock-in expression of the corrected LAMB3 gene on bulk population. We then assessed targeting efficiency and specificity by extensive molecular analyses of single-cell clones isolated by limiting dilution from the TALENs/IDLV-treated immortalized JEB population. We isolated 256 clones and expanded 69 of them. Sixteen out of 69 clones showed an in vitro adhesion advantage, hosted the HR cassette correctly integrated into the predetermined locus, expressed the corrected LAMB3 gene and produced the laminin-332 protein. In parallel, CRISPR-Cas9 nuclease has been designed on the same locus to compare the transduction efficiency and cleavage activity and to translate the knock-in targeting platform to primary JEB keratinocytes.

Immunogenicity of decidual stromal cells in an epidermolysis bullosa patient and in allogeneic hematopoietic stem cell transplantation patients.

Allogeneic mesenchymal stromal cells (MSCs) are widely used in regenerative medicine, but little is known about their immunogenicity. In this study, we monitored the therapeutic and immunogenic effects of decidual stromal cells (DSCs) from term placentas when used as a therapy for generalized severe junctional epidermolysis bullosa (JEB) (previously termed Herlitz JEB), a lethal condition caused by the lack of functional laminin-332. An 11-month-old JEB patient was treated with five infusions of allogeneic DSCs within a 3-month period. Amniotic membranes (AMs) were applied to severe wounds. After the treatment, wounds started to heal in the middle of the blisters, but the improvements were transient. After two infusions of DSCs, the JEB patient had developed multispecific anti-HLA class-I antibodies. No antibodies to laminin-332 were detected, but the patient had high levels of anti-bovine serum albumin antibodies, which could bind to DSCs. Peripheral blood mononuclear cells (PBMCs) from the patient had a higher proliferative response to DSCs than to third-party PBMCs, which contrasts with the pattern observed in healthy donors. Human DSCs and MSCs induced similar xenoreactivity in mice. Two of 16 allogeneic stem cell-transplanted patients, treated with DSCs for graft-versus-host disease or hemorrhagic cystitis, showed a positive flow cytometric crossmatch test. One patient had anti-HLA antibodies before DSC infusion, whereas the other had no anti-HLA antibodies at any time. AM and DSC infusions may have improved the healing process in the JEB patient, but DSCs appeared to induce anti-HLA antibodies. The risk of alloimmunization by DSCs seems to be low in immunocompromised patients.

Advances in Gene/Cell Therapy in Epidermolysis Bullosa

In the past few years, substantial preclinical and experimental advances have been made in the treatment of the severe monogenic skin blistering disease epidermolysis bullosa (EB). Promising approaches have been developed in the fields of protein and cell therapies, including allogeneic stem cell transplantation; in addition, the application of gene therapy approaches has become reality. The first ex vivo gene therapy for a junctional EB (JEB) patient was performed in Italy more than 8 years ago and was shown to be effective. We have now continued this approach for an Austrian JEB patient. Further, clinical trials for a gene therapy treatment of recessive dystrophic EB are currently under way in the United States and in Europe. In this review, we aim to point out that sustainable correction of autologous keratinocytes by stable genomic integration of a therapeutic gene represents a realistic option for patients with EB.

Increased levels of matrix metalloproteinase‐9 and interleukin‐8 in blister fluids of dystrophic and junctional epidermolysis bullosa patients

Increased levels of matrix metalloproteinase‐9 and interleukin‐8 in blister fluids of dystrophic and junctional epidermolysis bullosa patients

Collagen XVII (BP180) modulates keratinocyte expression of the proinflammatory chemokine, IL‐8

Collagen XVII (COL17), a transmembrane protein expressed in epidermal keratinocytes (EK), is targeted by pathogenic autoantibodies in bullous pemphigoid. Treatment of EK with anti-COL17 autoantibodies triggers the production of proinflammatory cytokines. In this study, we test the hypothesis that COL17 is involved in the regulation of the EK proinflammatory response, using IL-8 expression as the primary readout. The absence of COL17 in EK derived from a junctional epidermolysis bullosa patient or shRNA-mediated knockdown of COL17 in normal EK resulted in a dysregulation of IL-8 responses under various conditions. The COL17-deficient cells showed an abnormally high IL-8 response after treatment with lipopolysaccharide (LPS), ultraviolet-B radiation or tumor necrosis factor, but exhibited a blunted IL-8 response to phorbol 12-myristate 13-acetate exposure. Induction of COL17 expression in COL17-negative EK led to a normalization of the LPS-induced proinflammatory response. Although α6β4 integrin was found to be up-regulated in COL17-deficient EK, siRNA-mediated knockdown of the α6 and β4 subunits revealed that COL17's effects on the LPS IL-8 response are not dependent on this integrin. In LPS-treated cells, inhibition of NF-kappa B activity in COL17-negative EK resulted in a normalization of their IL-8 response, and expression of an NF-kappa B-driven reporter was shown to be higher in COL17-deficient, compared with normal EK. These findings support the hypothesis that COL17 plays an important regulatory role in the EK proinflammatory response, acting largely via NF-kappa B. Future investigations will focus on further defining the molecular basis of this novel control network.

Risk of squamous cell carcinoma in junctional epidermolysis bullosa, non-Herlitz type: Report of 7 cases and a review of the literature

Squamous cell carcinoma (SCC) is the most severe complication and most common cause of death in patients with recessive dystrophic epidermolysis bullosa. The risk of developing SCC among patients with junctional epidermolysis bullosa (JEB) is unclear from the literature; however, in our center we noticed an unexpected number of SCCs among adult patients with JEB. To review all documented patients with JEB in whom an SCC developed, both from our epidermolysis bullosa (EB) center and those reported in the literature. A search in our EB registry documenting all JEB patients visiting our EB referral center from 1990 through 2010 revealed 7 JEB patients who developed 1 or more SCCs. A systematic literature search revealed 8 relevant articles documenting a total of 7 patients who developed an SCC. In our EB registry we found 7 patients with JEB who developed an SCC; these were all adults classified with non-Herlitz type JEB. The frequency of developing an SCC among adult JEB patients (n = 28) in our center was therefore 25%. In the literature, we found 7 case reports of JEB complicated by SCC (also classified as JEB, non-Herlitz type), bringing the total number of documented cases to 14. The first SCC in JEB patients developed at an average age of 50 years (median, 52 years; range, 28-70 years). In 9 of 14 cases, multiple primary SCCs occurred, with a total of 45 SCCs. The SCCs are most often located on the lower extremities, in areas of chronic blistering, long-standing erosions, or atrophic scarring. Three patients (21%) developed metastases and died on average 8.9 years after diagnosis of the initial SCC. This study was retrospective and the statistical analyses were based on a small number of patients. From their third decade, adult patients with JEB have an increased risk (1:4) of developing SCC on their lower extremities. The SCCs have a high recurrence rate and follow an aggressive course that results in death in 1 of 5 patients. We recommend annual checks of all JEB patients for SCC starting at 25 years of age.

Correction of Laminin-5 Deficiency in Human Epidermal Stem Cells by Transcriptionally Targeted Lentiviral Vectors

Deficiency of the basement membrane component laminin-5 (LAM5) causes junctional epidermolysis bullosa (JEB), a severe and often fatal skin adhesion defect. Autologous transplantation of epidermal stem cells genetically corrected with a Moloney leukemia virus (MLV)-derived retroviral vector reconstitutes LAM5 synthesis, and corrects the adhesion defect in JEB patients. However, MLV-derived vectors have genotoxic characteristics, and are unable to reproduce the physiological, basal layer-restricted expression of LAM5 chains. We have developed an alternative gene transfer strategy based on self-inactivating (SIN) or long terminal repeat (LTR)-modified lentiviral vectors, in which transgene expression is under the control of different combinations of promoter-enhancer elements derived from the keratin-14 (K14) gene. Analysis in human keratinocyte cultures and in fully differentiated skin regenerated onto immunodeficient mice showed that gene expression directed by K14 enhancers is tissue-specific and restricted to the basal layer of the epidermis. Transcriptionally targeted lentiviral vectors efficiently transduced clonogenic stem/progenitor cells derived from a skin biopsy of a JEB patient, restored normal synthesis of LAM5 in cultured keratinocytes, and reconstituted normal adhesion properties in human skin equivalents transplanted onto immunodeficient mice. These vectors are therefore an effective, and potentially more safe, alternative to MLV-based retroviral vectors in gene therapy of JEB.Molecular Therapy (2008) 16 12, 1977-1985 doi:10.1038/mt.2008.204.

Cloning of Genes for Basement Membrane Proteins and Discovery of Mutations in Epidermolysis Bullosa

In the 1980s, the specialized basement membrane zone proteins collagen VII and laminin 5 were discovered as components of the anchoring fibrils and anchoring filaments, respectively. The next milestones were reached with cloning of the cDNAs for these proteins. In 1991, Parente et al. (1991) reported the cloning of a partial cDNA for collagen VII. Logically, this cDNA was used to determine the size of the mRNA of collagen VII, 8.5 kb, and to determine the chromosomal localization of the COL7A1 gene in the locus 3p21. However, the cloning also had an unexpected impact: the cDNA sequence demonstrated that the Nto C-terminal orientation of the collagen VII molecule was the opposite of what had previously been assumed. Protein chemical analysis yielded a collagen with a large non-collagenous NC1 and a small non-collagenous NC2 domain. In analogy to procollagens, it was assumed that the large globulus was the propeptide, located in the C-terminus. The cDNA sequence clearly showed that this assumption was not correct: the NC-1 domain was the N-terminal globulus and the small NC-2 domain represented the C-terminal propeptide. This finding was immensely important for understanding the aggregation and polymerization of collagen VII to the anchoring fibrils. It also had an impact on the understanding of genotype–phenotype correlations in dystrophic epidermolysis bullosa (EB), because soon after the paper by Parente and co-workers, the full-length cDNA was cloned, and the first COL7A1 mutations were reported in dystrophic epidermolysis bullosa (Figure 1). Moreover, the cDNA cloning allowed recombinant expression of the N-terminal NC-1 domain of collagen VII and its use in enzyme-linked immunosorbent assay type assays for detection of autoantibodies in epidermolysis bullosa acquisita. In 1994, two important studies appeared back-to-back in Nature Genetics. Pulkkinen et al. (1994) and Aberdam et al. (1994) reported the first laminin 5 mutations in junctional EB (JEB). Both used the candidate gene approach, based on the knowledge that antibodies to laminin 5 (at that time known as kalinin or nicein) produced reduced/negative staining patterns in Herlitz JEB skin, indicating that this protein is abnormal in this disease. Aberdam et al. (1994) employed linkage analysis in four large families using microsatellites associated with the LAMC2 gene, which encodes the laminin g2 chain; they found linkage of Herlitz JEB to LAMC2, with a high logarithm of ODDS (LOD) score of 5.3. Subsequent mutation screening revealed a homozygous LAMC2 point mutation leading to a premature stop codon in one of the families. Pulkkinen et al. (1994) proceeded by reverse transcriptase PCR of mRNA isolated from JEB patients’ keratinocytes, followed by mutation detection using heteroduplex analysis. The heteroduplexes, which indicated mutations, were sequenced. In one patient, a homozygous point mutation was found and predicted to cause aberrant splicing. In another patient, a heterozygous deletion–insertion mutation led to a premature termination codon. While the molecular consequences of the mutations remained elusive in part, these two papers established laminin 5 as the Herlitz JEB gene. Consequently, mutations in the LAMA3 and LAMB3 genes encoding the other chains of laminin 5, a3 and b3 were disclosed soon thereafter. These studies opened the avenue for mutation detection in at least 11 different genes encoding proteins of the dermal–epidermal junction. To date, many hundreds of mutations have been disclosed in different EB subtypes, certain genotype–phenotype correlations have emerged and we are starting to understand the molecular rationales for novel, biologically valid therapeutic strategies.

811. Correction of Laminin-5 β3 Chain Deficiency in Human Epidermal Stem Cells by Transcriptionally Targeted Lentiviral Vectors

Mutations in any of the genes encoding the laminin 5 heterotrimer (|[alpha]|3, |[beta]|3 and |[gamma]|2) cause junctional epidermolysis bullosa (JEB), a severe and often fatal skin adhesion defect. We and others have shown that expression of a retrovirally transferred |[beta]|3-chain cDNA in keratinocytes from affected patients reconstitutes normal synthesis, assembly and secretion of laminin 5, and corrects the adhesion defect in vitro and in vivo. We have recently started a phase-I clinical trial of gene therapy of JEB based on transplantation of cultured skin derived from autologous epidermal stem cells transduced with a MLV-derived retroviral vector. Since gamma- retroviral vectors have raised safety concerns for the genotoxic risk associated with the insertion of LTR elements into the human genome, we developed an alternative gene transfer strategy based on LTR- modified, HIV-derived lentiviral vectors. Two self-inactivating (SIN) lentiviral vectors were built, in which expression of either GFP or a LAMB3 cDNA is under the control of either a constitutive promoter (PGK) or the keratinocyte-specific, 2.2-kb promoter-enhancer of keratin 14 (K14). In a third construct, expression of the transgene is under the control of the viral LTR, modified by replacing the U3 region with two K14 enhancer elements. Analysis in human keratinocyte cultures and in full-thickness human skin equivalents reconstituted onto immunodeficient mice showed that GFP expression directed by the K14 elements is tissue-specific and restricted to the basal layer of the epidermis. Expression of laminin5 from the three alternative vectors was evaluated in keratinocyte cultures derived from skin biopsies of JEB patients. Biochemical and cell kinetics assays demonstrated transduction of epidermal clonogenic stem/progenitor cells and full phenotypic correction of JEB keratinocytes with all vectors. Southern blot analysis of individual cell clones showed that LTR-modified lentiviral vectors are genetically stable and integrate in multiple copies in the human genome. This study shows that the use of lentiviral vectors transcriptionally targeted to the basal keratinocytes by the insertion of restricted enhancer elements is an effective, and potentially safer, alternative for gene therapy of JEB.

Proteolytic Processing of the Laminin α3 G Domain Mediates Assembly of Hemidesmosomes but Has No Role on Keratinocyte Migration

Laminin-5 (Lm5), the major adhesion ligand of basal epithelial cells, undergoes complex extracellular proteolytic processing that influences cell adhesion and migration. In tumor cell lines, the proteolytic truncation of the C-terminal G domain of the Lm alpha3 chain induces assembly of hemidesmosomes and downregulates cell migration. To define the biological functions of the alpha3 G domain processing in physiological conditions, we have expressed a series of mutant alpha3 complementary DNA in human primary alpha3-null keratinocytes immortalized by human papillomavirus E6E7 (HKalpha3 cells). Using monolayer and organotypic cell cultures we show that: (1) the hinge region between subdomains G3 and G4 carries the proteolytic cleavage sites; (2) nucleation of the hemidesmosomal proteins is independent of the proteolytic maturation of the alpha3 G domain, whereas formation of mature hemidesmosomes relies on proteolytic cleavage of alpha3; and (3) the proteolytic processing plays no role in cell migration, which suggests that nucleation of hemidesmosomal structures in culture does not reflect the migratory potential of the epithelial cells. Our results also demonstrate that HKalpha3 cells are a unique model system, which will be useful to dissect the functions and molecular interactions of Lm5.

Inherited Junctional Epidermolysis Bullosa in the German Pointer: Establishment of a Large Animal Model

Junctional epidermolysis bullosa (JEB) is a genodermatosis suitable for gene therapy because conventional treatments are ineffective. Here, we elucidate the genetic basis of mild JEB in a breed of dogs that display all the clinical traits observed in JEB patients. The condition is associated with reduced expression of laminin 5 caused by a homozygous insertion (4818+207ins6.5 kb) of repetitive satellite DNA within intron 35 of the gene (lama3) for the laminin alpha3 chain. The intronic mutation interferes with maturation of the alpha3 pre-messenger RNA resulting in the coexpression of a transcript with a 227 nucleotide insertion and a wild-type mRNA that encodes scant amounts of the alpha3 polypeptide. Our results show that the amino acid sequence and structure of the canine and human alpha3 chain are highly conserved and that the reduced expression of laminin 5 affects the adhesion and clonogenic potential of the JEB keratinocytes. These JEB dogs provide the opportunity to perform gene delivery in a naturally occurring genodermatosis and to evaluate host tolerance to recombinant laminin 5.

Laminin-5 Mutational Analysis in an Italian Cohort of Patients with Junctional Epidermolysis Bullosa

Junctional epidermolysis bullosa (JEB) is a rare genodermatosis characterized by dermal-epidermal separation that is caused by mutations in the genes encoding hemidesmosomal components and laminin-5, the major epithelial adhesion ligand. Here, we report on the mutational analysis of LAMA3, LAMB3, and LAMC2 genes encoding laminin-5 chains in 19 Italian patients, 11 affected with the severe Herlitz (H JEB) and eight with the mild non-Herlitz variant of JEB (non-H JEB). Eighteen mutations, seven of which were novel, were identified and their consequences analyzed at the mRNA and protein level. Premature termination codon mutations in both alleles of LAMB3 or LAMC2 genes were found in nine of the 11 H JEB patients, with a prevalence of mutations in LAMC2. In one case, a homozygous frameshift mutation in LAMB3 was associated to illegitimate splicing leading to non-H JEB. One H JEB patient showed a large intragenic duplication within LAMC2, a genetic defect so far uncovered in laminin-5 genes. Splicing or missense mutations, were prevalent in non-H JEB patients. Collectively, five mutations appeared to be frequent in laminin-5 JEB patients: R635X, 29insC, E210K, W143X in LAMB3 and R95X in LAMC2. These recurrent mutations account for approximately 44% of laminin-5 JEB alleles in Italian patients.

Analysis of the LAMB3 gene in a junctional epidermolysis bullosa patient reveals exonic splicing and allele-specific nonsense-mediated mRNA decay

How splicing, the process of intron removal in pre-messenger RNA (mRNA), is carried out with such fidelity in human cells is still not understood, although some general rules are being proposed mainly by in vitro experiments. These rules are currently being redefined by analysis of splicing mechanisms in patients presenting splicing defects. We analysed material of a patient suffering from junctional epidermolysis bullosa, a heritable blistering skin disease. Absence of laminin-5 protein together with hypoplastic hemidesmosomes at the dermo-epidermal junction in the patient's skin was shown by immunohistochemical analysis and immunoelectron microscopy. Subsequent DNA analysis revealed heterozygosity for the mutations R635X and 3009C → T in the LAMB3 gene. The latter did not alter codon translation, but introduced an exonic splice site in exon 20. Interestingly, this exonic splice site, which presented a splice score of only 68.6, was preferentially used by the spliceosome over the wild-type splice site at the exon 20–intron 20 border, which showed a splice score of 92.2. LAMB3 mRNA was still detectable in RT-PCR analysis although the aberrantly spliced mRNA leads to a stop codon in exon 21, 5′ of the commonly assumed 3′ border for nonsense-mediated mRNA decay. These results describe an exception to the proposed rules of pre-mRNA splicing and RNA degradation.

P‐35 Nonlethal junctional epidermolysis bullosa in a dog

Junctional epidermolysis bullosa (JEB) is a rare hereditary or autoimmune bullous skin disease of humans, horses and dogs. It has been reported that JEB patients have blisters, erosions or ulcers affecting the face, digits and tail predominantly. Histopathologically, separation of the epidermis and dermis occurs within the lamina lucida of the basement membrane zone (BMZ) and, biochemically, there is a deficiency of laminin 5, integrin α6β4, or BPAG2. Mutations in the alpha‐chain of laminin 5 in nonlethal JEB in dogs has been reported. Our patient was an 8‐month‐old female mixed‐breed dog that presented with hair loss, blisters and scar formation on the face, trunk and feet that were present since 2 months of age. Histopathology of the skin revealed atrophy of the hair follicles and liquefactive degeneration of the dermo‐epidermal junction with minimal cell infiltration. Electron microscopy revealed that blister formation was located within the lamina lucida. These findings corresponded with canine JEB. The immunofluorescence test (IIF) revealed that the expression of BMZ proteins, including laminin 5, BPAG2, integrin α6β4 and type XVII collagen, were not decreased compared with normal skin. The IIF using the patient's serum showed a negative reaction. Although the disease has progressed, the patient is still alive one year after the onset of lesions. Moreover, although we could not determine the genetic background or the causative proteins, this is likely a case of hereditary JEB because of the young age at onset and autoantibodies against the BMZ were not detected. Funding: Self‐funded.